Cardiac Catheterization

Diagnostic coronary angiography is the standard of reference for determining the severity of stenosis resulting from atherosclerosis in the coronary arteries. Visualization of the lumen of the coronary artery to assess for the need for vascularization is performed by injection of iodinated contrast directly into the coronary arteries. Since the contrast resolution is limited with fluoroscopy (the imaging method used during angiography), direct enhancement of the blood pool in the artery of interest is required. Conventional coronary angiography (CCA) further requires direct arterial puncture and selective cannulation of the ostia of the left

and right coronary arteries and, if present, each saphenous vein graft or internal mammary graft to obtain optimal selective contrast enhancement. Most commonly the catheter is threaded through the femoral or radial arteries, then retrograde up the aorta, and the coronary arteries are cannulated. Dye is injected and images are taken in several standard positions (Fig. 2.1a-b). The catheter also is passed retrograde past the aortic valve and into the left ventricular cavity to measure pressures as well as perform contrast ventriculography to assess wall motion, ejection fraction and the presence and severity of mitral regurgitation. The left ventricular silhouette on the RAO angiogram has five segments: anterobasal, anterolateral, apical, diaphragmatic and posterobasal (Fig. 2.2). Both akinesis and hypokinesis can be identified, as well as aneurysmal segments.

Coronary angiography identifies and assesses the severity of coronary artery atherosclerotic lesions. Generally the angiographic assessment of arterial stenosis can be divided into three major categories. The first group includes vessels with less than 50% luminal diameter narrowing, the second group includes vessels with 50-70% decrease in luminal diameter and the third group includes vessels with greater than 70% decrease. Reduction of the coronary artery diameter by 50% or more is generally considered significant since it represents a 75% reduction in

Fig. 2.2. Right anterior oblique left ventriculogram.

RAO LEFT VENTRICULOGRAM

cross-sectional area. A 75% decrease in luminal diameter results in 95% reduction in cross-sectional area.

By selective catheterization of the right coronary artery and the left coronary artery and by using multiple views and projections, all the coronary arteries and their branches should be visualized. Lesions in these vessels can be identified and their severity can be assessed.

Angiography is done also to evaluate valvular heart disease. Exact ejection fraction is measured on ventriculography at cardiac catheterization by measuring the end diastolic volume minus the end systolic volume divided by the end diastolic volume. Normal ejection fraction is greater than 55%. The valve area can be measured according to the Gorlin formula by the mean gradients measured at cardiac catheterization. The valve area equals flow divided by 44 times the square root of the mean gradient across the valve. If both aortic insufficiency and mitral regurgitation are present, neither the aortic nor mitral valve area can be measured accurately at catheterization because the flow across a single valve cannot be assessed. The normal mitral valve orifice area in adults is 4 to 5 cm2, and the normal aortic valve area is 2.6 to 3.5 cm2.

The following valve gradients are considered severe stenosis:

1) aortic 50 mmHg;

2) mitral 15 mmHg;

3) tricuspid 5 mmHg;

4) pulmonary 15 mmHg.

When grading regurgitation of the mitral or tricuspid valve, 1+ indicates wisps of regurgitation going back into the left atrium or right atrium; 2+ regurgitation goes back more than half the diameter of the atrium; 3+ regurgitation hits the back wall of the left or right atrium; and 4+ regurgitation actually extends retrograde into the pulmonary vein or cavae. Generally, 1+ is mild regurgitation, 2-3+ is moderate regurgitation, and 4+ is severe regurgitation.

At cardiac catheterization, pressure time measurements can be performed with the catheter in the left ventricle and in the aorta to measure different conditions of aortic stenosis or aortic insufficiency.

Some therapeutic valvular interventions can be performed at the time of cardiac catheterization. Valvuloplasty can be performed in some instances, for example pulmonary valvuloplasty has proven to be effective for pulmonary stenosis. For mitral stenosis, valvuloplasty is considered in certain situations. Patients who have severe left ventricular dysfunction may undergo valvuloplasty as a bridge to later mitral valve replacement. Also patients of an extremely advanced age may be considered candidates for valvuloplasty, if their condition requires it. The results and chance of a stroke after valvuloplasty are similar to a closed commissurotomy (i.e. a commissurotomy which is done off cardiopulmonary bypass simply by opening the left atrium and placing the gloved finger through the mitral valve). One needs to keep the patient on coumadin for 6 weeks prior to valvuloplasty to prevent thrombus from forming in the atrium in the region of the valve. Valvuloplasty in aortic stenosis is less effective because of the chance of severe aortic insufficiency after the valvuloplasty.

In 1993, 1.8 million cardiac catheterization procedures were performed. Given the trend of increased utilization, it is possible by 2010 that annual use will exceed 3.0 million cardiac catherizations.

Coronary angiography is the only method currently available for defining the details of the entire coronary endoluminal vascular anatomy, and it provides the reference standard against which other tests are compared. Although coronary lesions that reduce luminal diameter <50% are considered hemodynamically insignificant, they are not clinically benign. These lesions can progress, either acutely or chronically, and patients with nonsignificant obstructions have significantly more cardiovascular events during follow-up than those with truly normal coronary angiograms.

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