**Role of Transthoracic Echocardiography in Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve**

Yasser Baghdady, Hussein Hishmat and Heba Farook *Cairo University Egypt* 

#### **1. Introduction**

112 Echocardiography – New Techniques

We can precisely assess the change of geometry of the submitral apparatus after operation by using 2-D transthoracic echocardiography. It would be useful for the comparison

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Kubota K, Otsuji Y, Ueno T, et al. (2010) J Thorac Cardiovasc Surg. *Functional mitral stenosis* 

Langer F, Schäfers HJ. (2007) J Thorac Cardiovasc Surg. *RING plus STRING: papillary muscle* 

Magne J, Sénéchal M, Mathieu P, et al. (2008) J Am Coll Cardiol. *Restrictive annuloplasty for ischemic mitral regurgitation may induce functional mitral stenosis.* 51:1692-1701. Matsui Y, Suto Y, Shimura S, et al. (2005) Ann Thorac Cardiovasc Surg. *Impact of papillary* 

Matsunaga A, Tahta SA & Duran CM. (2004) J Heart Valve Dis. *Failure of reduction* 

Messas E, Guerrero JL, Handschumacher MD, et al. (2001) Circulation. *Chordal cutting: a new* 

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Nordblom P, Bech-Hanssen O. (2007) Echocardiography. *Reference values describing the* 

Rodriguez F, Langer F, Harrington KB, et al. (2004) Circulation. *Cutting second-order chords* 

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*normal mitral valve and the position of the papillary muscles.*24:665-672.

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*repositioning as an adjunctive repair technique for ischemic mitral regurgitation.* 133:247-

*muscles approximation on the adequacy of mitral coaptation in functional mitral* 

**5. Conclusion** 

**6. References**

249.

between different surgical procedures.

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Visualization of the epicardial coronary arteries by echocardiography is technically challenging. The physical nature of ultrasound waves prevents them from delineating the coronary tree because of multiple factors. The resolution of tansthoracic echo using a 2.5- 3.5MHz probe is only 2mm while the diameter of the epicardial coronary arteries ranges from 1.5 to 4mm. The epicardial coronaries are relatively superficial in the chest, so the lie in near field of the ultrasound waves. The translational and rotational motion of the coronary arteries in the AV grooves poses a challenge in obtaining stable Doppler signals. The relatively low velocity of coronary flow compared to the flow velocity in the ventricles makes color signals hard to discern. Finally, the tomographic nature of the echocardiographic study makes differentiation between adjacent vessels e.g. the LAD and the diagonal branches extremely difficult. Despite these difficulties, the need for a noninvasive bedside tool that could allow inference of the coronary arteries pushed towards more efforts in using echo for that aspect. Using dedicated high-frequency probes made assessment of the left main coronary, the LAD and even the posterior descending branch of the RCA feasible in a large proportion of patients (Hozumi et al., 1998). Transthoracic and transesophageal echo can provide data regarding coronary patency, the presence of coronary stenosis or coronary ectasia (Iliceto S, et al., 1991, Kozakova M, et al., 1997, Lambertz et al., 2000).

#### **2. Coronary flow and Doppler analysis**

Normal antegrade coronary flow is predominant diastolic with a small systolic component (Heinz Lambertz et al., 2004). Systolic flow is less important and is a less stable measure as it can be eve retrograde. It may be difficult to record both diastolic and systolic flow in the same cardiac cycle in all patients, because of cardiac motion that displaces the coronary artery from the ultrasound beam in systole. Diastolic flow is antegrade in both epicardial and intramural vessels, whereas systolic flow is antegrade in epicardial but retrograde in intramural vessels, because blood is squeezed backwards by myocardial contraction (Vernon Anderson H et al., 2000). As a result of the two opposite forces, the magnitude of systolic flow velocity may change along the coronary tree and close to the origin of a

Role of Transthoracic Echocardiography in

LCX branches (Heinz Lambertz et al., 2004).

visualize the left main trunk as seen in the figure below.

Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve 115

the aortic valve. Then make slight clockwise rotation and anterior tilt of the transducer to

Fig. 1. Parasternal short axis view showing left main stem and its bifurcation into LAD and

Color Doppler imaging of the coronary flow in the proximal portion of the left coronary artery is technically difficult for two reasons: First, the almost orthogonal alignment of coronary flow to the ultrasound beam and second, the interposition of the right ventricular outflow tract and pulmonary artery. The left main coronary artery can also be imaged from an apical transducer position. From the classical five chamber view, the transducer is carefully angled more anteriorly until the ascending aorta is visualized. With slight tilting and rotation of the transducer, the left and the right coronary arteries can be recorded in one imaging plane: The orifice of the left coronary artery is located approximately three O'clock.

The orifice of the RCA can be detected at approximately ten O'clock.

Fig. 2. Modified apical five-chamber view illustrating the origin of the left and right

coronary artery from the aortic bulbus (Heinz Lambertz et al., 2004).

perforator there might be a watershed area with stagnation of systolic flow. Therefore, the epicardial anterograde systolic flow is mainly a capacitance, rather than a nutrient flow, and may not reflect myocardial perfusion.

#### **2.1 The parameters that can be assessed by coronary Doppler imaging include**


The baseline coronary flow velocity may change from one beat to the other of even 5–10 cm/s. Elevated resting flow velocities may occur in tachycardia, anaemia, hyperthyroidism, severe left ventricular hypertrophy etc ( Czernin J er al, 1993, Voci P et al., 2004). Coronary vasodilators increase the diameter of the epicardial artery and reduce baseline flow velocity. Analysis of the coronary Doppler waveform can provide useful information about vessel patency and the presence of severe stenosis or moderate stenosis. Noninvasive Doppler has some alleged advantages over IVUS/FFR. Echocardiography avoids contact with the coronary artery, which may be reactive during myocardial infarction. Echo also measuring velocities in regions inaccessible to IVUS such as the septal perforators. The most important limitation of transthoracic Doppler measurement is the difficulty of obtaining accurate adjustment of the Doppler beam parallel to the coronary flow. If the angle between the Doppler beam and the coronary artery is >60°, diastolic flow velocity could be underestimated.

#### **3. Visualization of different coronary artery segments by Echo-Doppler**

#### **3.1 Transthoracic echocardiography**

In general, assessment of coronary blood flow differs in different coronary arteries. The LAD blood flow can be assessed by using high frequency transducers due to the proximity of this vessel to the chest wall. However, this technique is not suitable for imaging peripheral RCA flow because of the distance between the transducer and the basal inferior cardiac wall (7- 10cm). Therefore a lower frequency transducer is required to overcome the problem of inadequate penetration depth of a high frequency transducer. Individual coronary anatomy shows considerable patient to patient variability. Therefore it is not possible to visualize a segment of the right coronary artery in the posterior interventricular grove in every patient (Lethen H et al., 2003, Meimoun P et al., 2004, 2005, Tokai K et al., 2003, Ueno Y et al., 2002, 2003). Recording an accurate systolic-diastolic pulsed wave Doppler signal is often hampered by respiratory movements and lateral as well as vertical motion of the basal inferior cardiac wall during the cardiac cycle. This problem can partially be resolved by obtaining Doppler signals in apnea.

#### **3.2 LMT and proximal segments of the left and right coronary arteries**

The proximal portion of the left coronary artery can be visualized from a modified high parasternal short axis view. First obtain the classic parasternal short axis view at the level of

perforator there might be a watershed area with stagnation of systolic flow. Therefore, the epicardial anterograde systolic flow is mainly a capacitance, rather than a nutrient flow, and

The baseline coronary flow velocity may change from one beat to the other of even 5–10 cm/s. Elevated resting flow velocities may occur in tachycardia, anaemia, hyperthyroidism, severe left ventricular hypertrophy etc ( Czernin J er al, 1993, Voci P et al., 2004). Coronary vasodilators increase the diameter of the epicardial artery and reduce baseline flow velocity. Analysis of the coronary Doppler waveform can provide useful information about vessel patency and the presence of severe stenosis or moderate stenosis. Noninvasive Doppler has some alleged advantages over IVUS/FFR. Echocardiography avoids contact with the coronary artery, which may be reactive during myocardial infarction. Echo also measuring velocities in regions inaccessible to IVUS such as the septal perforators. The most important limitation of transthoracic Doppler measurement is the difficulty of obtaining accurate adjustment of the Doppler beam parallel to the coronary flow. If the angle between the Doppler beam and the coronary artery is >60°, diastolic flow velocity could be

**2.1 The parameters that can be assessed by coronary Doppler imaging include** 

**3. Visualization of different coronary artery segments by Echo-Doppler** 

**3.2 LMT and proximal segments of the left and right coronary arteries** 

In general, assessment of coronary blood flow differs in different coronary arteries. The LAD blood flow can be assessed by using high frequency transducers due to the proximity of this vessel to the chest wall. However, this technique is not suitable for imaging peripheral RCA flow because of the distance between the transducer and the basal inferior cardiac wall (7- 10cm). Therefore a lower frequency transducer is required to overcome the problem of inadequate penetration depth of a high frequency transducer. Individual coronary anatomy shows considerable patient to patient variability. Therefore it is not possible to visualize a segment of the right coronary artery in the posterior interventricular grove in every patient (Lethen H et al., 2003, Meimoun P et al., 2004, 2005, Tokai K et al., 2003, Ueno Y et al., 2002, 2003). Recording an accurate systolic-diastolic pulsed wave Doppler signal is often hampered by respiratory movements and lateral as well as vertical motion of the basal inferior cardiac wall during the cardiac cycle. This problem can partially be resolved by

The proximal portion of the left coronary artery can be visualized from a modified high parasternal short axis view. First obtain the classic parasternal short axis view at the level of

may not reflect myocardial perfusion.

 Diastolic flow velocity Systolic flow velocity Diastolic Deceleration time Coronary flow reserve

underestimated.

**3.1 Transthoracic echocardiography** 

obtaining Doppler signals in apnea.

the aortic valve. Then make slight clockwise rotation and anterior tilt of the transducer to visualize the left main trunk as seen in the figure below.

Fig. 1. Parasternal short axis view showing left main stem and its bifurcation into LAD and LCX branches (Heinz Lambertz et al., 2004).

Color Doppler imaging of the coronary flow in the proximal portion of the left coronary artery is technically difficult for two reasons: First, the almost orthogonal alignment of coronary flow to the ultrasound beam and second, the interposition of the right ventricular outflow tract and pulmonary artery. The left main coronary artery can also be imaged from an apical transducer position. From the classical five chamber view, the transducer is carefully angled more anteriorly until the ascending aorta is visualized. With slight tilting and rotation of the transducer, the left and the right coronary arteries can be recorded in one imaging plane: The orifice of the left coronary artery is located approximately three O'clock. The orifice of the RCA can be detected at approximately ten O'clock.

Fig. 2. Modified apical five-chamber view illustrating the origin of the left and right coronary artery from the aortic bulbus (Heinz Lambertz et al., 2004).

Role of Transthoracic Echocardiography in

2010).

**3.5 Visualization of the RCA** 

Lambertz et al., 2004).

Doppler analysis of coronary blood flow.

Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve 117

Fig. 4. Modified apical view showing the distal segment of the LAD (H. Farouk, et al.,

To visualize the posterior descending branch of the RCA, the left ventricle is first imaged in a conventional apical two-chamber view. From this position, the transducer is slightly rotated anti-clockwise and carefully tilted anteriorly. Using color Doppler, coronary blood

Fig. 5. Modified apical two-chamber view. Color Doppler flow map showing the proximal part of the posterior interventricular branch in the posterior interventricular groove (Heinz

After detection of the characteristic predominant diastolic blood flow in the basal part of the posterior interventricular groove, the sample volume (2.0-3.5mm) is positioned for spectral

flow in the posterior interventricular groove can be identified.

#### **3.3 Visualization of the middle segment of the LAD**

The middle and distal portion of the left anterior descending artery lies in the anterior ventricular groove close to the anterior chest wall. Due to the proximity of the middle and distal left anterior descending artery to a precordially located transducer, these coronary segments are ideal for transthoracic echocardiographic examination. From the classic parasternal short axis view at the level of the papillary muscles, a lateral displacement of the transducer by 2-3cm allows the visualization of the anterior interventricular groove. With caudal displacement of the transducer of 1-2 intercostal spaces, Color Doppler is used to identify the coronary flow in the anterior groove. Once a predominant diastolic flow signal is detected from a vessel within the anterior interventricular groove, activate the zoom mode while keeping the Doppler box small with adjustment of the velocity range at 12-24cm/s. From the previous view, the transducer is rotated 70 to 90º to obtain the best LAD long axis view. For measurement of the coronary flow velocity, pulsed wave Doppler is used with a sample size of 3mm and care should be taken to avoid an angle exceeding 35 to 45º.

Fig. 3. Modified PLAX view allowing color Doppler assessment of coronary blood flow in the mid segment of the LAD (Heinz Lambertz et al., 2004).

#### **3.4 Visualization of the distal segment of the LAD**

The distal part of the left anterior descending artery can be recorded in a modified foreshortened three-chamber view from an apical window. From the conventional apical 2 chamber view the transducer is rotated anti-clockwise to obtain an apical long axis view, showing the left ventricle and left ventricular outflow tract. Using the color Doppler, the distal segment of the LAD, located in the apical part of the interventricular groove can be detected close to the apex of the left ventricle. From this view, the transducer is shifted 1 to 2 intercostal spaces cranially with anterior tilt to visualize the peripheral epicardial segments of the LAD.

Fig. 4. Modified apical view showing the distal segment of the LAD (H. Farouk, et al., 2010).

#### **3.5 Visualization of the RCA**

116 Echocardiography – New Techniques

The middle and distal portion of the left anterior descending artery lies in the anterior ventricular groove close to the anterior chest wall. Due to the proximity of the middle and distal left anterior descending artery to a precordially located transducer, these coronary segments are ideal for transthoracic echocardiographic examination. From the classic parasternal short axis view at the level of the papillary muscles, a lateral displacement of the transducer by 2-3cm allows the visualization of the anterior interventricular groove. With caudal displacement of the transducer of 1-2 intercostal spaces, Color Doppler is used to identify the coronary flow in the anterior groove. Once a predominant diastolic flow signal is detected from a vessel within the anterior interventricular groove, activate the zoom mode while keeping the Doppler box small with adjustment of the velocity range at 12-24cm/s. From the previous view, the transducer is rotated 70 to 90º to obtain the best LAD long axis view. For measurement of the coronary flow velocity, pulsed wave Doppler is used with a

sample size of 3mm and care should be taken to avoid an angle exceeding 35 to 45º.

Fig. 3. Modified PLAX view allowing color Doppler assessment of coronary blood flow in

The distal part of the left anterior descending artery can be recorded in a modified foreshortened three-chamber view from an apical window. From the conventional apical 2 chamber view the transducer is rotated anti-clockwise to obtain an apical long axis view, showing the left ventricle and left ventricular outflow tract. Using the color Doppler, the distal segment of the LAD, located in the apical part of the interventricular groove can be detected close to the apex of the left ventricle. From this view, the transducer is shifted 1 to 2 intercostal spaces cranially with anterior tilt to visualize the peripheral epicardial

the mid segment of the LAD (Heinz Lambertz et al., 2004).

**3.4 Visualization of the distal segment of the LAD** 

segments of the LAD.

**3.3 Visualization of the middle segment of the LAD** 

To visualize the posterior descending branch of the RCA, the left ventricle is first imaged in a conventional apical two-chamber view. From this position, the transducer is slightly rotated anti-clockwise and carefully tilted anteriorly. Using color Doppler, coronary blood flow in the posterior interventricular groove can be identified.

Fig. 5. Modified apical two-chamber view. Color Doppler flow map showing the proximal part of the posterior interventricular branch in the posterior interventricular groove (Heinz Lambertz et al., 2004).

After detection of the characteristic predominant diastolic blood flow in the basal part of the posterior interventricular groove, the sample volume (2.0-3.5mm) is positioned for spectral Doppler analysis of coronary blood flow.

Role of Transthoracic Echocardiography in

Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve 119

Fig. 7. Pulsed wave Doppler profile of mammary artery. The systolic flow velocity is

In immediate proximity of the mid and distal portion of the left anterior descending artery, septal side branches with varying caliber can be seen by color Doppler analysis. Frequently, the vessel course can be followed over a longer distance within the ventricular septum. Diagonal branches or a dominant intermediate branch can't always be clearly differentiated from the left anterior descending artery, as they may have approximately the same diameter

Fig. 8. Parasternal short axis view illustrating a perforator branch in the mid septum (Heinz

typically higher than the diastolic (Heinz Lambertz et al., 2004).

**3.8 Detection of the septal branches of the LAD by TTE** 

and an almost parallel course.

Lambertz et al., 2004).

Fig. 6. Characteristic biphasic spectral Doppler recording of coronary blood flow velocity in the distal RCA (Heinz Lambertz et al., 2004).

The modified apical two-chamber view used for assessment of the right coronary artery blood flow allows alignment of the ultrasound beam roughly parallel to the course of the posterior descending artery, thus, unlike assessment of the flow of the left anterior descending artery, provide an adequate registration of the coronary flow velocity.

#### **3.6 Detection of the left circumflex artery by TTE**

The proximal third of the LCX can be examined using an apical or parasternal short axis view approach. To assess the distal left circumflex artery, we use the apical 5 chamber view with the transducer is rotated clockwise to direct the imaging plane posteriorly and inferiorly. The direction of the CBF of the circumflex artery is not parallel to the ultrasound beam. Because the success rate in visualizing the flow in the mid and distal circumflex is limited, assessment of the coronary flow reserve is of limited clinical significance in cases of suspected left circumflex artery disease (Heinz Lambertz et al., 2004)

#### **3.7 Detection of the left internal mammary artery**

The proximal mammary artery is best visualized from a supraclavicular view using high frequency transducer (8 MHz linear transducer). A patent mammary artery graft is recognized by its typical baseline spectral Doppler flow profile, showing considerably higher diastolic blood flow velocity compared to the other vessels originating in close proximity to the subclavian artery.

Fig. 6. Characteristic biphasic spectral Doppler recording of coronary blood flow velocity in

The modified apical two-chamber view used for assessment of the right coronary artery blood flow allows alignment of the ultrasound beam roughly parallel to the course of the posterior descending artery, thus, unlike assessment of the flow of the left anterior

The proximal third of the LCX can be examined using an apical or parasternal short axis view approach. To assess the distal left circumflex artery, we use the apical 5 chamber view with the transducer is rotated clockwise to direct the imaging plane posteriorly and inferiorly. The direction of the CBF of the circumflex artery is not parallel to the ultrasound beam. Because the success rate in visualizing the flow in the mid and distal circumflex is limited, assessment of the coronary flow reserve is of limited clinical significance in cases of

The proximal mammary artery is best visualized from a supraclavicular view using high frequency transducer (8 MHz linear transducer). A patent mammary artery graft is recognized by its typical baseline spectral Doppler flow profile, showing considerably higher diastolic blood flow velocity compared to the other vessels originating in close

descending artery, provide an adequate registration of the coronary flow velocity.

suspected left circumflex artery disease (Heinz Lambertz et al., 2004)

the distal RCA (Heinz Lambertz et al., 2004).

**3.6 Detection of the left circumflex artery by TTE** 

**3.7 Detection of the left internal mammary artery** 

proximity to the subclavian artery.

Fig. 7. Pulsed wave Doppler profile of mammary artery. The systolic flow velocity is typically higher than the diastolic (Heinz Lambertz et al., 2004).

#### **3.8 Detection of the septal branches of the LAD by TTE**

In immediate proximity of the mid and distal portion of the left anterior descending artery, septal side branches with varying caliber can be seen by color Doppler analysis. Frequently, the vessel course can be followed over a longer distance within the ventricular septum. Diagonal branches or a dominant intermediate branch can't always be clearly differentiated from the left anterior descending artery, as they may have approximately the same diameter and an almost parallel course.

Fig. 8. Parasternal short axis view illustrating a perforator branch in the mid septum (Heinz Lambertz et al., 2004).

Role of Transthoracic Echocardiography in

Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve 121

In contrast to the transthoracic approach, TEE imaging allows a reliable Doppler flow analysis in the proximal left anterior descending artery, because the ultrasound beam can be aligned almost parallel to the anatomical course of the vessel. However, due to motion artifacts caused by respiratory excursions and ventricular contraction, adequate recording of

the coronary blood flow can be obtained more easily during a short period of apnea.

Fig. 11. Color Doppler illustrating normal coronary blood flow within the left main artery

Fig. 12. Orifice of the right coronary artery. The TEE scanning plane is aligned roughly

Transesophageal echocardiography, with or without contrast, is a low cost method and easily repeatable, which can be used to evaluate coronary circulation in selected patients. However, this approach has less clinical importance in evaluating the hemodynamic relevance of a left anterior descending artery stenosis. This is based on the fact that most of the left anterior descending artery stenoses are located distal to those left anterior descending artery segments that can be visualized by Transesophageal echocardiography.

parallel to a long axis of the ascending aorta ((Heinz Lambertz et al., 2004)

and its bifurcation into LAD and LCX (Heinz Lambertz et al., 2004).

#### **3.9 Transesophageal echocardiography**

The best way to image the proximal segment of the coronary artery is a transesophageal short axis view at the level of the aortic bulb with a slight anteflexion of the probe. From this view the left main stem and the proximal LAD can be visualized in about 70 to 90% of patients. The success rate in imaging the proximal segment of the left circumflex is even higher (75 to 90%). The best way to visualize the ostuim of the right coronary artery is a sagittal scanning plane showing the ascending aorta in a long axis (Lambertz H et al., 2000). With a slight clockwise rotation of the probe, a short segment of the right coronary artery originating from the aortic bulb can be imaged from the majority of patients.

Fig. 9. Transesophageal echocardiography illustrating the left main stem and its bifurcation into LAD and LCX ((Heinz Lambertz et al., 2004).

With a pulsed wave Doppler, sample volume positioned in the proximal portion of the left anterior descending coronary artery, systolic as well as diastolic flow can be recorded (Iliceto S, et al. , 1991)

Fig. 10. TEE recording from a normal LAD.CBF occurs systolic-diastolic with the highest velocity during diastole (Heinz Lambertz et al., 2004).

The best way to image the proximal segment of the coronary artery is a transesophageal short axis view at the level of the aortic bulb with a slight anteflexion of the probe. From this view the left main stem and the proximal LAD can be visualized in about 70 to 90% of patients. The success rate in imaging the proximal segment of the left circumflex is even higher (75 to 90%). The best way to visualize the ostuim of the right coronary artery is a sagittal scanning plane showing the ascending aorta in a long axis (Lambertz H et al., 2000). With a slight clockwise rotation of the probe, a short segment of the right coronary artery

Fig. 9. Transesophageal echocardiography illustrating the left main stem and its bifurcation

With a pulsed wave Doppler, sample volume positioned in the proximal portion of the left anterior descending coronary artery, systolic as well as diastolic flow can be recorded

Fig. 10. TEE recording from a normal LAD.CBF occurs systolic-diastolic with the highest

originating from the aortic bulb can be imaged from the majority of patients.

**3.9 Transesophageal echocardiography** 

into LAD and LCX ((Heinz Lambertz et al., 2004).

velocity during diastole (Heinz Lambertz et al., 2004).

(Iliceto S, et al. , 1991)

In contrast to the transthoracic approach, TEE imaging allows a reliable Doppler flow analysis in the proximal left anterior descending artery, because the ultrasound beam can be aligned almost parallel to the anatomical course of the vessel. However, due to motion artifacts caused by respiratory excursions and ventricular contraction, adequate recording of the coronary blood flow can be obtained more easily during a short period of apnea.

Fig. 11. Color Doppler illustrating normal coronary blood flow within the left main artery and its bifurcation into LAD and LCX (Heinz Lambertz et al., 2004).

Fig. 12. Orifice of the right coronary artery. The TEE scanning plane is aligned roughly parallel to a long axis of the ascending aorta ((Heinz Lambertz et al., 2004)

Transesophageal echocardiography, with or without contrast, is a low cost method and easily repeatable, which can be used to evaluate coronary circulation in selected patients. However, this approach has less clinical importance in evaluating the hemodynamic relevance of a left anterior descending artery stenosis. This is based on the fact that most of the left anterior descending artery stenoses are located distal to those left anterior descending artery segments that can be visualized by Transesophageal echocardiography.

Role of Transthoracic Echocardiography in

**4.2 Coronary artery occlusion** 

retrogradely or anterogradely.

**4.3 Severe coronary stenosis** 

**4.4 Moderate coronary stenosis** 

**4.5 Coronary flow reserve** 

Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve 123

Diastolic deceleration time was markedly longer in patients with viable myocardium than partially viable or non-viable myocardium. A DDT <190ms is always associated with nonviable myocardium. However, this finding was not consistent among different studies.

Coronary flow can be measured by transthoracic coronary Doppler ultrasound in occluded coronary arteries receiving collateral flow. Reverse diastolic flow at rest, reflecting retrograde filling of the artery by collaterals, is a very specific marker of coronary occlusion but it unfortunately has a low sensitivity, since collaterals may perfuse the vessel either

Coronary artery stenosis could be identified with color Doppler as local spot of turbulence. An abnormal maximal-to-prestenotic blood flow velocity ratio greater than 2.0 would signify a critical stenosis. These findings have an overall sensitivity of 82% and specificity of 92%. The sensitivity and specificity were, respectively, 73% and 92% for left anterior descending coronary artery, 63% and 96% for right coronary artery, and 38% and 99% for left circumflex coronary artery stenoses. For left main coronary stenosis, echo showed a 92% sensitivity and 62% specificity to identify IVUS significant (MLA < 6 mm2) left main stenosis if taking a peak diastolic velocity cut off of 112 cm/sec (Gerkens U, et al. , 1989, Samdarshi TE et al.,1990)

The assessment of moderate-severity coronary stenosis by angiography has limitations related to the "lumenographic "nature of angiography (Topol EJ, et al., 1995). The concept of coronary flow reserve performed by Doppler intracoronary wire during coronary angiography can be also performed by echocardiography. The major advantages of coronary flow assessment by TTDE are that it is completely non-invasive, relatively inexpensive, and gives objective and accurate information on the physiological significance both in epicardial native coronary stenosis as well as in detecting coronary restenosis following coronary percutaneous interventions (Caiati C et al., 1999, 1999, Hozumi T et al., 1998). Another important value of

Coronary flow reserve is defined as the maximal increase in coronary blood flow (by using a strong coronary vasodilator) above its basal level for a given perfusion pressure. So, it is a ratio of maximal (stimulated) to baseline (resting) coronary blood flow. The best sampling site of the coronary flow, for assessing the functional significance of a stenosis, is the distal tract of the vessel which could be easily obtained with TDE. Proximal to the stenosis CFR may be normal as there are side branches between the sampling site and the stenosis, which reflects perfusion in normal territories (Voci P et al., 2004). The angle correction is redundant given that CFR is the ratio between hyperemic and baseline flow velocity, and it is not affected by the actual flow velocity. However, the angle has to be kept as small as possible. Blood flow velocity measurements are performed offline by contouring the spectral Doppler signals, using the integrated software package of the ultrasound system. Final values of flow velocity represent

TTDE study of CFVR is the assessment of microvascular coronary circulation.

Fig. 13. Visualization of the coronary blood flow in the proximal right coronary artery (Heinz Lambertz et al., 2004).

It has to be taken also into consideration that approximately 20% to 30% of the patients cannot be investigated by Doppler because of respiration, obesity, chest deformity and emphysema, acute changes in cardiac volume, or inadequately stable position of the Doppler signal. Flow in the branches could be erroneously interpreted as the flow in the main trunk. In particular, this could happen for LAD in the two-chamber or in the short axis view, where a long diagonal branch or the first septal perforator might also be visualized.

#### **4. Clinical utilization of echocardiographic coronary imaging**

#### **4.1 Coronary artery patency**

In the particular situation of acute myocardial infarction, a non-invasive way to visualize the LAD should be of great help to diagnose the success of reperfusion. In this setting, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the transthoracic echo Doppler in the noninvasive assessment of the LAD reperfusion with 2.5MHz transducer were 81.6%, 64%, 90.7%, 54% and 78% respectively (H. Farouk et al., 2010). Detection of the distal LAD flow by TTDE was significantly correlated with the reperfusion as assessed by coronary angiography.

Epicardial coronary flow is not always synonymous with cellular myocardial perfusion as seen in the no-reflow phenomenon. Visualization of septal perforator flow can be a more reliable marker of reperfusion. Voci et al (Voci P et al., 2004) considered a myocardial segment to be reperfused when at least two of the predicted four to five perforators could be visualized by transthoracic echo after acute MI. A recanalization score (RS) of 1 to 4 was used—where 1 = LAD closed, no perforators; 2 = LAD open, no perforators; 3 = LAD open, 1 to 2 segments with perforators; 4 = LAD open, 3 to 4 segments with perforators. RS discriminated recovery of ventricular function better than TIMI flow. The RS was the best single multivariate predictor (p < 0.0001) of percent changes in wall motion score index and the ejection fraction.

Antti Saraste et al, (Saraste M et al., 2005) found that diastolic deceleration time of the LAD flow velocity correlated with myocardial fluorodeoxyglucose uptake in the LAD territory. Diastolic deceleration time was markedly longer in patients with viable myocardium than partially viable or non-viable myocardium. A DDT <190ms is always associated with nonviable myocardium. However, this finding was not consistent among different studies.

#### **4.2 Coronary artery occlusion**

122 Echocardiography – New Techniques

Fig. 13. Visualization of the coronary blood flow in the proximal right coronary artery

**4. Clinical utilization of echocardiographic coronary imaging** 

It has to be taken also into consideration that approximately 20% to 30% of the patients cannot be investigated by Doppler because of respiration, obesity, chest deformity and emphysema, acute changes in cardiac volume, or inadequately stable position of the Doppler signal. Flow in the branches could be erroneously interpreted as the flow in the main trunk. In particular, this could happen for LAD in the two-chamber or in the short axis view, where a long diagonal branch or the first septal perforator might also be visualized.

In the particular situation of acute myocardial infarction, a non-invasive way to visualize the LAD should be of great help to diagnose the success of reperfusion. In this setting, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the transthoracic echo Doppler in the noninvasive assessment of the LAD reperfusion with 2.5MHz transducer were 81.6%, 64%, 90.7%, 54% and 78% respectively (H. Farouk et al., 2010). Detection of the distal LAD flow by TTDE was significantly correlated with the

Epicardial coronary flow is not always synonymous with cellular myocardial perfusion as seen in the no-reflow phenomenon. Visualization of septal perforator flow can be a more reliable marker of reperfusion. Voci et al (Voci P et al., 2004) considered a myocardial segment to be reperfused when at least two of the predicted four to five perforators could be visualized by transthoracic echo after acute MI. A recanalization score (RS) of 1 to 4 was used—where 1 = LAD closed, no perforators; 2 = LAD open, no perforators; 3 = LAD open, 1 to 2 segments with perforators; 4 = LAD open, 3 to 4 segments with perforators. RS discriminated recovery of ventricular function better than TIMI flow. The RS was the best single multivariate predictor (p

Antti Saraste et al, (Saraste M et al., 2005) found that diastolic deceleration time of the LAD flow velocity correlated with myocardial fluorodeoxyglucose uptake in the LAD territory.

< 0.0001) of percent changes in wall motion score index and the ejection fraction.

(Heinz Lambertz et al., 2004).

**4.1 Coronary artery patency** 

reperfusion as assessed by coronary angiography.

Coronary flow can be measured by transthoracic coronary Doppler ultrasound in occluded coronary arteries receiving collateral flow. Reverse diastolic flow at rest, reflecting retrograde filling of the artery by collaterals, is a very specific marker of coronary occlusion but it unfortunately has a low sensitivity, since collaterals may perfuse the vessel either retrogradely or anterogradely.

#### **4.3 Severe coronary stenosis**

Coronary artery stenosis could be identified with color Doppler as local spot of turbulence. An abnormal maximal-to-prestenotic blood flow velocity ratio greater than 2.0 would signify a critical stenosis. These findings have an overall sensitivity of 82% and specificity of 92%. The sensitivity and specificity were, respectively, 73% and 92% for left anterior descending coronary artery, 63% and 96% for right coronary artery, and 38% and 99% for left circumflex coronary artery stenoses. For left main coronary stenosis, echo showed a 92% sensitivity and 62% specificity to identify IVUS significant (MLA < 6 mm2) left main stenosis if taking a peak diastolic velocity cut off of 112 cm/sec (Gerkens U, et al. , 1989, Samdarshi TE et al.,1990)

#### **4.4 Moderate coronary stenosis**

The assessment of moderate-severity coronary stenosis by angiography has limitations related to the "lumenographic "nature of angiography (Topol EJ, et al., 1995). The concept of coronary flow reserve performed by Doppler intracoronary wire during coronary angiography can be also performed by echocardiography. The major advantages of coronary flow assessment by TTDE are that it is completely non-invasive, relatively inexpensive, and gives objective and accurate information on the physiological significance both in epicardial native coronary stenosis as well as in detecting coronary restenosis following coronary percutaneous interventions (Caiati C et al., 1999, 1999, Hozumi T et al., 1998). Another important value of TTDE study of CFVR is the assessment of microvascular coronary circulation.

#### **4.5 Coronary flow reserve**

Coronary flow reserve is defined as the maximal increase in coronary blood flow (by using a strong coronary vasodilator) above its basal level for a given perfusion pressure. So, it is a ratio of maximal (stimulated) to baseline (resting) coronary blood flow. The best sampling site of the coronary flow, for assessing the functional significance of a stenosis, is the distal tract of the vessel which could be easily obtained with TDE. Proximal to the stenosis CFR may be normal as there are side branches between the sampling site and the stenosis, which reflects perfusion in normal territories (Voci P et al., 2004). The angle correction is redundant given that CFR is the ratio between hyperemic and baseline flow velocity, and it is not affected by the actual flow velocity. However, the angle has to be kept as small as possible. Blood flow velocity measurements are performed offline by contouring the spectral Doppler signals, using the integrated software package of the ultrasound system. Final values of flow velocity represent

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value of coronary flow velocity reserve by transthoracic Doppler echocardiography for diagnosis of significant left anterior descending artery stenosis in patients with

an average of three cardiac cycles. TDE-CFR is defined as hyperemic diastolic mean (or peak) flow velocity divided by baseline flow velocity. It is important to underscore that during administration of the vasodilating agent, the transducer probe is in the same position as baseline, and machine settings including size of sample volume and velocity scale are not changed. The mean time required to complete a CFR test is around 10–15 min.

Adenosine is the most commonly used vasodilator to assess TDE-CFR. It is a potent vasodilator producing maximal coronary vasodilatation within 40-50 seconds. Given its short half life (10s) and rapid onset of action, it allows CFR measurements more rapidly than other vasodilators. Furthermore, Adenosine acts mainly at the level of the microcirculation and does not alter significantly the diameter of the coronary artery. Adenosine is administered intravenously (0.140 mg/kg/min) for 5 minutes (Lapeyre AC III et al., 2004, Sudhir K et al., 1993, Verani MS, 1991, Wilson R et al., 1990). The normal range of CFVR for both men and women is ≥ 2.7. The cut-off value of 2 of CFR for detecting significant epicardial coronary stenosis or to predict ischemia in the underlying territory has been demonstrated in various studies (Kern MJ et al., 1996, Matsumara Y et al., 2003).

The feasibility of TDE-CFR for LAD artery is very high, with more than 90% in experienced hands, and nearly 100% with the use of intravenous contrast agents (Caiati C et al., 1999). The feasibility is less in the PDA artery, between 54 and 86% due to technical limitations (Hozumi T et al., 1998, Lethen H et al., 2003, Ueno Y et al., 2002). The measurements of TDE-CFR, in the LAD as in the PDA arteries, are closely correlated with invasive measurements using a Doppler flow wire. The feasibility of TDE-CFR in the circumflex artery is more challenging given the particular anatomy of this artery and the poor resolution of the lateral wall.

#### **4.6 Kawasaki disease and congenital coronary anomalies**

In the pediatric population, visualization of the proximal portions of the left and the right coronaries by transthoracic echo is achievable in almost all cases. Therefore, it is routine to comment on the origin and the course of the proximal left and right coronary arteries in all pediatric studies. The aneurysms of the proximal RCA and proximal LAD in Kawasaki disease provide the diagnosis in infants with febrile illness and the classic rash and can be useful in follow up of this condition (Satomi G et al., 1984, Yoshikawa J et al., 1979). Also, failure of visualization of one of the coronary arteries in children with cardiomyopathy should prompt excluding the diagnosis of anomalous origin of the coronary from the pulmonary artery. Also anomalous origin of the right coronary from the left sinus of valsalva which poses a threat of sudden cardiac death can be readily diagnosed in children by transthoracic echo.

#### **5. Conclusion**

Echocardiography can be used to visualize the epicardial coronary arteries directly in a large proportion of patients. The success is greatest in children, ostia of the left and right coronary arteries and in the LAD. However, it is unlikely, at least in the near future, that echo can provide complete anatomical assessment of the coronary tree. X-ray bases modalities, namely angiography and CT are still superior in providing anatomical details. Nevertheless, in some clinical situations, echo can provide very useful data regarding coronary patency, severe stenosis, moderate coronary lesions, the state of the microcirculation and congenital coronary anomalies.

#### **6. References**

124 Echocardiography – New Techniques

an average of three cardiac cycles. TDE-CFR is defined as hyperemic diastolic mean (or peak) flow velocity divided by baseline flow velocity. It is important to underscore that during administration of the vasodilating agent, the transducer probe is in the same position as baseline, and machine settings including size of sample volume and velocity scale are not

Adenosine is the most commonly used vasodilator to assess TDE-CFR. It is a potent vasodilator producing maximal coronary vasodilatation within 40-50 seconds. Given its short half life (10s) and rapid onset of action, it allows CFR measurements more rapidly than other vasodilators. Furthermore, Adenosine acts mainly at the level of the microcirculation and does not alter significantly the diameter of the coronary artery. Adenosine is administered intravenously (0.140 mg/kg/min) for 5 minutes (Lapeyre AC III et al., 2004, Sudhir K et al., 1993, Verani MS, 1991, Wilson R et al., 1990). The normal range of CFVR for both men and women is ≥ 2.7. The cut-off value of 2 of CFR for detecting significant epicardial coronary stenosis or to predict ischemia in the underlying territory has been

The feasibility of TDE-CFR for LAD artery is very high, with more than 90% in experienced hands, and nearly 100% with the use of intravenous contrast agents (Caiati C et al., 1999). The feasibility is less in the PDA artery, between 54 and 86% due to technical limitations (Hozumi T et al., 1998, Lethen H et al., 2003, Ueno Y et al., 2002). The measurements of TDE-CFR, in the LAD as in the PDA arteries, are closely correlated with invasive measurements using a Doppler flow wire. The feasibility of TDE-CFR in the circumflex artery is more challenging

In the pediatric population, visualization of the proximal portions of the left and the right coronaries by transthoracic echo is achievable in almost all cases. Therefore, it is routine to comment on the origin and the course of the proximal left and right coronary arteries in all pediatric studies. The aneurysms of the proximal RCA and proximal LAD in Kawasaki disease provide the diagnosis in infants with febrile illness and the classic rash and can be useful in follow up of this condition (Satomi G et al., 1984, Yoshikawa J et al., 1979). Also, failure of visualization of one of the coronary arteries in children with cardiomyopathy should prompt excluding the diagnosis of anomalous origin of the coronary from the pulmonary artery. Also anomalous origin of the right coronary from the left sinus of valsalva which poses a threat of

Echocardiography can be used to visualize the epicardial coronary arteries directly in a large proportion of patients. The success is greatest in children, ostia of the left and right coronary arteries and in the LAD. However, it is unlikely, at least in the near future, that echo can provide complete anatomical assessment of the coronary tree. X-ray bases modalities, namely angiography and CT are still superior in providing anatomical details. Nevertheless, in some clinical situations, echo can provide very useful data regarding coronary patency, severe stenosis, moderate coronary lesions, the state of the microcirculation and congenital

changed. The mean time required to complete a CFR test is around 10–15 min.

demonstrated in various studies (Kern MJ et al., 1996, Matsumara Y et al., 2003).

given the particular anatomy of this artery and the poor resolution of the lateral wall.

sudden cardiac death can be readily diagnosed in children by transthoracic echo.

**4.6 Kawasaki disease and congenital coronary anomalies** 

**5. Conclusion** 

coronary anomalies.


**8** 

*Japan* 

Katsuomi Iwakura

**3D Myocardial Contrast Echocardiography** 

Early restoration of coronary perfusion is the most important objective in the management of ST-segment elevation myocardial infarction (STEMI), and primary percutaneous coronary intervention (PCI) is established as the most effective strategy for it. Advances in interventional techniques and pharmacological therapy have made it possible to achieve Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow in as many as 95% of patients undergoing primary PCI. Nevertheless, optimal myocardial perfusion is not achieved in approximately 15% of patients despite of successful opening of infarct-related artery. The inadequate myocardial perfusion, or "no-reflow" phenomenon, may be caused by microvascular damage after myocardial ischemia, distal coronary emboli resulting from thrombus, platelets and atheroma, in situ thrombosis, vasospasm, or cell necrosis and regional inflammatory responses induced by reperfusion. The no-reflow phenomenon is associated with worse functional and clinical outcomes after STEMI. It was linked to larger infarction size, lower ejection fraction, ventricular arrhythmias(Aiello *et al.*,1995), early congestive heart failure(Ito *et al.*,1996), and even cardiac rupture(Morishima *et al.*,1995). It may have an adverse effect on left ventricular (LV) remodeling(Gerber *et al.*,2000). Therefore, detection of no-reflow early after primary `PCI is important for the risk stratification of patients with STEMI. Several invasive and non-invasive imaging modalities have been developed to detect no-reflow. We had focused on one of these modalities, myocardial contrast echocardiography (MCE), and used it in several clinical studies to investigate the pathogenesis of the no-reflow. In this article, we investigated the ability of newly developed,

real-time 3D MCE to assess the microvascular dysfunction in patients with AMI.

**2. Imaging modalities for assessment of the no-reflow phenomenon** 

enhanced cardiac magnetic resonance (CMR).

**2.1 CMR and contrast-enhanced CT** 

No-reflow can be assessed during PCI with Thrombolysis In Myocardial Infarction (TIMI) flow grade(TIMI Study Group,1985), with TIMI-myocardial perfusion grade(van 't Hof *et al.*,1998) (TMPG), or with coronary flow velocity pattern assessed by Doppler guidewire(Iwakura *et al.*,1996). It can be better quantified by noninvasive imaging techniques, such as myocardial contrast echocardiography (MCE), cardiac CT, and contrast-

CMR using gadolinium can diagnose the no-reflow as: 1) lack of gadolinium enhancement during first pass (microvascular obstruction); and 2) lack of gadolinium enhancement within a

**1. Introduction** 

*Division of Cardiology, Sakurabashi Watanabe Hospital* 

