**11. Cardiac catheterisation and interventions**

Catheterisation used to be the main diagnostic modality available when it was first introduced in 1946. The era of angiographic anatomic delineation is fading. Echocardiography is now preferred for evaluation of valvar and congenital cardiac defects with 3D echo promising real time surgical images of the valves for repair. MRI and CT angiography is fast replacing angiogram for delineation of complex relationship, volume estimation of chamber, extra cardiac vessels, aortic arches and venous anomalies. The field of MR imaging, has the potential to completely replace diagnostic angiography. The routine use of catheterization before single ventricle surgeries is being questioned, as the same information can be made available through non-invasive means

Angiogram still has a role in

**a.** M- Mode – uses a narrow ultrasound beam to provide a 'ice pick' image of the structure. It has good axial resolution. Used to measure the degree of movement of leaflets. Chamber

**b.** 2-D mode –uses *phased array transducers* which are multiple piezoelectric crystals that both transmits and receives ultrasound simultaneously; used to provide an image of the

**c.** 3-D mode *uses matrix array transducers* and sophisticated parallel array processing to provide real time image. With progressive miniaturization, real-time 3D Transesophageal

**d.** Doppler imaging – can be used to estimate the velocity and direction of blood flow to estimate the pressure gradient cross sectional flow area and prediction of intracardiac

**e.** Contrast Echocardiography – is based on the fact that any intravascular injection produces a contrast which can be detected by echocardiography. Used for intracardiac and great artery level shunts in patients with poor windows, for detecting pulmonary venous

**f.** Fetal echocardiography – using trans abdominal screening majority of the cardiovascular malformations can be detected by 17- 20 weeks of life; by transvaginal window, heart and

It is a imaging modality which uses magnetic fields and radiofrequency energy to stimulate hydrogen nuclei which emits radiofrequency waves that are used to construct images. Over the 1990's the field has evolved from a procedure which takes a long time to produce a series of static images to one in which real time 3-D visualization is possible. MRI uses magnetic field of strength 0.5 Tesla to 3 Tesla (1 Tesla is 10,000 Gauss; earth magnetic field is 0.5 G). MRI uses

*Synchronisation or respiratory motion compensation* is required as the heart is a moving object and 'gating' or ' synchronization' is required to return to the same point in the cardiac cycle in order to freeze the cardiac motion. Pulse oximetry, ECG signal or MRI navigator echoes can be used for gating. Advances in *gradient coil and parallel acquisition* methods can obviate the

**a.** Spin Echo – uses a radiofrequency pulse that tilts the hydrogen protons by 90 degrees followed by a second 180 degree pulse, which are used to generate images. Produces images in which the flowing 'blood is black'. This provides static anatomic information, with excellent blood myocardium contrast. Used for assessing cardiac tumours, pericar‐

malformation and for detecting baffle leak following atrial switch procedures.

great vessels can be visualized at the end of 1st trimester. [16]

fields which are 5000 to 60000 more powerful than the earth's magnetic field.

dial disease and thoracic masses. Takes a relatively longer time

**10. Magnetic Resonance Imaging**

need for synchronization.

Two main modalities of MRI are:

images provide excellent images intraoperatively for planning valve repairs.

thickness is measured using 2-D directed M-mode imaging.

'section' of the heart.

238 Principles and Practice of Cardiothoracic Surgery

pressures.


**c.** Measurement of flow, pressure, reactivity and resistance of pulmonary vasculature to various drugs in patients with elevated pulmonary artery pressure.

restriction at the interatrial septum, tricuspid atresia, pulmonary atresia, mitral atresia. Septostomy with a blade would be required if the infant is > 6-8 weeks as the septum

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**2.** Widen things that are narrow – involving the blood vessels and heart valves, done using balloon catheters and stents to prevent recoil in case of vessels. The stent gets incorporated into the vessel wall. There can be neointimal proliferation causing restenosis, usually in the first 2 years The procedure uses special plastic polymer balloons which will not inflate beyond predetermined size even under high pressure. This needs a guide wire to be placed across the narrow area with balloon placed across so as to place the waist (middle of the

**a.** Pulmonary valvar stenosis- for gradients > 40 mmHg, has almost replaced surgery, except

**b.** Peripheral and branch pulmonary artery stenosis in the setting of postoperative tetralogy of Fallot, pulmonary atresia,- are surgical challenges and balloon dilatation with stenting

**c.** Aortic valve stenosis – used when gradient > 50-60 mm Hg in the absence of AR can be life-saving in small infants, can also be used for discrete subvalvar aortic stenosis but not

**d.** Coarctation of aorta – preferred for re-coarctation or for coarctation in grown up children where it can be combined with stenting. Not for coarctation in infancy which has high

**e.** Mitral valves – works well for rheumatic heart disease, not very successful with congenital MS. Heart block, tearing of leaflet and occurrence of MR are possible complications.

**g.** Systemic vein stenosis in the setting of post- operative Mustard or Senning's procedure,

**h.** Close things that are open – this uses devices mounted on catheters that are passed

ASD, VSD and PDA's – ASD's upto 32 mm diameter can be closed, the defect needs a rim of 4 mm for the device to be centred and placed. Amplatzer devices are FDA approved and have

Closure of VSD requires careful assessment to ensure that the device would not interfere with tricuspid or aortic valvar mechanisms. Arrhythmias, stroke, perforation, device embolization,

Large PDA's > 5mm are closed with Amplatzer I device which has a single aortic rim and is

sausage) in the narrow region which is dilated with dilute contrast.

has emerged as preferred alternatives with 60-80% success rate.

when the valve is very dysplastic or associated infundibular obstruction

becomes thicker.

Used commonly for

for tunnel like subaortic stenosis.

**f.** Prosthetic valves and conduits

incomplete closures are the risks involved.

the longest track record.

mushroom shaped.

rate of recurrence and surgery is better option.

does not work in the presence of pulmonary vein stenosis.

through long and large sheaths after crossing the area to be closed.

**d.** Estimation of cardiac output, Qp/Qs calculation for assessment of operability.

The cardiac output can be calculated by the thermodilution technique or the Fick's principle.

Fick's principle is based on the fact that

'The uptake or release of substance by an organ is equivalent to the blood flow to the organ multiplied by the arteriovenous difference of the substance'

O2 is used as the indicator and all the systemic organs or lungs are considered as one organ to estimate the systemic or pulmonary output respectively.

We use the 02 consumption in ml/min/m2 and this divided by the arteriovenous difference would give the systemic or pulmonary flows. The consumption is made available through estimates based on age, sex and heart rate.

Systemic output would be the difference between the arterial oxygen content and mixed venous oxygen content (ideally measured in the middle of right atrium to average for the superior vena caval, inferior vena caval or coronary sinus venous blood whose oxygen content may be different)

Pulmonary output would be the difference between the pulmonary venous and pulmonary artery oxygen content.

Qp/Qs can be easily calculated even if we do not have the values of oxygen consumption. We need the systemic arterial, mixed venous and pulmonary arterial and pulmonary venous oxygen content (which is assumed to be 100% in the absence of pulmonary pathology).

Pressure measurements are based on fluid filled catheters, or large bore catheters with multiple side holes which would yield accurate description of intracardiac waveforms. The resistance is calculated using the Ohm's law, which is the difference in the pressure across the organ divided by the amount of blood flowing through it. PVR (Pulmonary vascular resistance) would be transpulmonary gradient (difference between the mean PA and LA pressures) divided by the pulmonary flow. Measured in mmHg/ L/min/m2 or Wood units [18]
