**9. Coronary circulation and anatomy**

The myocardium is perfused during diastole through the coronary system (fig 6).

The major vessels of the coronary circulation are the left main coronary that divides into left anterior descending and circumflex branches, and the right main coronary artery. The left and right coronary arteries originate at the base of the aorta from openings called the coronary ostia located just distal to the aortic valve leaflets.

Intra-Aortic Balloon Counterpulsation Therapy

Fig. 7. Stage 1 Vasoconstriction

Fig. 8. Stage 2 - Hypervolemia

and Its Role in Optimizing Outcomes in Cardiac Surgery 49

ischemia has been found to be silent (Hensley 1995). Silent ischemia can translate into perioperative infarct or ischemia both of which could cause heart failure. Left Ventricular failure can be divided into three stages. Stage 1 (fig 7) is manifested as vasoconstriction leading to decreased pumping efficiency, increased LV volume and pressure. These physiological events activate baroreceptors leading to increased heart rate, increased afterload (SVR), increased

Stage two (Fig 8) leads to hypervolemia as the heart tries to compensate with the additional afterload. There is a decrease in cardiac output and glomerular filtration pressure, further activating the Renin-Angiotensisn system. There is an increase in sodium and water reabsorption leading to an increase in preload and afterload. There is a decrease in cardiac

myocardial oxygen demand and ultimately an increase in preload (LVEDP).

Fig. 6. The Coronary System

The left and right coronary arteries and their branches lie on the surface of the heart, and therefore are sometimes referred to as the epicardial coronary vessels. These vessels distribute blood flow to different regions of the heart muscle. When the vessels are not diseased, they have a low vascular resistance relative to their more distal and smaller branches that comprise the microvascular network. As in all vascular beds, it is the small arteries and arterioles in the microcirculation that are the primary sites of vascular resistance, and therefore the primary site for regulation of blood flow. The arterioles branch into numerous capillaries that lie adjacent to the cardiac myocytes. A high capillary-to-cardiomyocyte ratio and short diffusion distances ensure adequate oxygen delivery to the myocytes and removal of metabolic waste products from the cells (e.g., CO2 and H+). Capillary blood flow enters venules that join together to form cardiac veins that drain into the coronary sinus located on the posterior side of the heart, which in turn drain into the right atrium. There are also anterior cardiac veins and thebesian veins that drain directly into the cardiac chambers. The LAD supplies blood to the front (anterior-septal) portion of the heart and the LCX supplies the side (anterio-lateral) and back (posterior) of the left ventricle. The right coronary artery supplies blood to the ventricles, the right atrium (RA), the inferior portion of the myocardium and the sino-atrial node. The LAD give rise to various branches called the diagonals and marginal's while the RCA bifurcates into the posterior descending artery (PDA) and the acute marginal artery. The RCA supplies blood to the inferior portion of the myocardium.

### **10. Heart failure**

Forward heart failure or congestive heart failure is defined as the inability of the heart to keep up with its demand. Forward heart failure can lead to backward heart failure. Heart failure can be caused by structural heart disease, coronary artery disease, Cardiomyopathy or conduction disorders, more often than not requiring surgical correction. Conduction disorder can impair C.O by causing a too slow/fast heart rate, loss of atrial kick or loss of conduction. Left ventricular failure is directly related to the need for an IAB. Heart failure can be manifested as angina, crescendo or unstable angina or exercise induced angina. Heart failure causes ischemia and myocardial ischemia can be silent. Ninety seven percent of peri-operative

The left and right coronary arteries and their branches lie on the surface of the heart, and therefore are sometimes referred to as the epicardial coronary vessels. These vessels distribute blood flow to different regions of the heart muscle. When the vessels are not diseased, they have a low vascular resistance relative to their more distal and smaller branches that comprise the microvascular network. As in all vascular beds, it is the small arteries and arterioles in the microcirculation that are the primary sites of vascular resistance, and therefore the primary site for regulation of blood flow. The arterioles branch into numerous capillaries that lie adjacent to the cardiac myocytes. A high capillary-to-cardiomyocyte ratio and short diffusion distances ensure adequate oxygen delivery to the myocytes and removal of metabolic waste products from the cells (e.g., CO2 and H+). Capillary blood flow enters venules that join together to form cardiac veins that drain into the coronary sinus located on the posterior side of the heart, which in turn drain into the right atrium. There are also anterior cardiac veins and thebesian veins that drain directly into the cardiac chambers. The LAD supplies blood to the front (anterior-septal) portion of the heart and the LCX supplies the side (anterio-lateral) and back (posterior) of the left ventricle. The right coronary artery supplies blood to the ventricles, the right atrium (RA), the inferior portion of the myocardium and the sino-atrial node. The LAD give rise to various branches called the diagonals and marginal's while the RCA bifurcates into the posterior descending artery (PDA) and the acute marginal artery. The RCA supplies

Forward heart failure or congestive heart failure is defined as the inability of the heart to keep up with its demand. Forward heart failure can lead to backward heart failure. Heart failure can be caused by structural heart disease, coronary artery disease, Cardiomyopathy or conduction disorders, more often than not requiring surgical correction. Conduction disorder can impair C.O by causing a too slow/fast heart rate, loss of atrial kick or loss of conduction. Left ventricular failure is directly related to the need for an IAB. Heart failure can be manifested as angina, crescendo or unstable angina or exercise induced angina. Heart failure causes ischemia and myocardial ischemia can be silent. Ninety seven percent of peri-operative

Fig. 6. The Coronary System

blood to the inferior portion of the myocardium.

**10. Heart failure** 

ischemia has been found to be silent (Hensley 1995). Silent ischemia can translate into perioperative infarct or ischemia both of which could cause heart failure. Left Ventricular failure can be divided into three stages. Stage 1 (fig 7) is manifested as vasoconstriction leading to decreased pumping efficiency, increased LV volume and pressure. These physiological events activate baroreceptors leading to increased heart rate, increased afterload (SVR), increased myocardial oxygen demand and ultimately an increase in preload (LVEDP).

Fig. 7. Stage 1 Vasoconstriction

Stage two (Fig 8) leads to hypervolemia as the heart tries to compensate with the additional afterload. There is a decrease in cardiac output and glomerular filtration pressure, further activating the Renin-Angiotensisn system. There is an increase in sodium and water reabsorption leading to an increase in preload and afterload. There is a decrease in cardiac

Fig. 8. Stage 2 - Hypervolemia

Intra-Aortic Balloon Counterpulsation Therapy

**12. Indications for IAB insertion**

A. Pre-op predictors:

*al.,1996*)

B. Intra/post-op predictors: 1. Pre/post CPB ischemia 2. Incomplete repair or bypass 3. Prolonged CPB time

IAB use)

exact opposite, decreases the workload of the heart.

not including aortic regurgitation 3. Anticipated prolonged CPB time

6. Coronary obstruction via clot or otherwise

5. Particulate or air embolus in coronary arteries.

3. Unstable angina with or without ST segment elevation

systolic blood pressure, especially at an augmentation of 1:1

concomitant LV dysfunction

6. Persistent ST changes post CPB.

threatening extension of MI.

recommended

7. Congestive heart failure

9. Ventricular irritability

10. Bridge to transplant or destination therapy

(Percutaneous Transluminal Coronary Angioplasty)

In cardiac surgery the IAB is indicated for the following situations:

and Its Role in Optimizing Outcomes in Cardiac Surgery 51

inotrope infusion will only tend to increase the workload of the ventricle. The IABP does the

1. Grade 3 to 4 LV dysfunction or ejection fraction (EF) of less than 0.30 (*Dietl CA et* 

2. Severe and/or multiple valvular disease with end stage myocardial impairment

4. Coronary artery disease (CAD) only partially correctible by grafting with

5. Persistent ST Changes before, during or after induction of general anesthesia

Clinical indications for the IAB are listed below (fig 10 showcases benchmarks in 2005 for

1. Ventricular failure after myocardial infarction (MI) – (*Barron et al., 2001*) or acute myocardial infarction (AMI). As in all other cases the IAB will would decrease afterload and increase coronary perfusion. Early insertion is recommended to ameliorate the

2. Angina- chest pain is usually the initial stages of an MI and here again early insertion is

4. Cardiomyopathy- In the majority of cases when cardiomyopathy occurs the patient suffers from dilated cardiomyopathy and the IAB assist in raising mean blood pressure and reducing afterload. In a very few cases of initial stages of hypertrophic cardiomyopathy, where the ventricle tends to be a small volume ventricle (extremely thick myocardial wall), a sudden decrease in AEDP would result in insufficient volume left to fill the increased capacitance . This would actually result in a drop in MAP and

5. Acute mitral valve regurgitation (*Abid et al.,2002*) and/or stenosis with LV rupture 6. Aortic stenosis without aortic insufficiency (AI) or accompanied by mild AI

8. Intractable ventricular arrhythmias secondary to ischemia or otherwise. In these cases IAB's with fibre optic technology can be used to track rapid or irregular heart rhythms

11. Support in the catheterization laboratory (*Stone GW et al.,1997*) for stenting or PTCA

4. Large ventriculotomy or LV resection for LV aneurysm repair.

output, decrease in oxygen supply, increase in heart rate and increase in oxygen demand. There is an increase in pulmonary artery wedge pressures.

The final stage of LV failure (Fig 9) is the manifestation of tissue hypoxia. Decreased cardiac output, decreased MAP, decreased oxygenation coupled with pulmonary edema causes acceleration of anaerobic metabolism, lactic acid production, Tissue anoxia and finally tissue death. Its ideal to insert the IAB in stage one or by stage two, so that we prevent the final stage of heart failure.

Fig. 9. Stage 3 - Tissue Hypoxia and Apoptosis
