Left ventricular volume in aortic stenosis measured by an angiocardiographic and a thermodilution method.

Abstract

The action of the left ventricle is impaired in aortic stenosis to a variable degree, and since the extent of myocardial damage will influence the management and prognosis in the individual patient, some way of determining myocardial function is required. For a full assessment of left ventricular performance it is necessary to measure the changes in both volume and pressure throughout the cardiac cycle. Pressure measurements are easily obtained by left heart catheterization, but provide an incomplete picture if the left ventricular volume is not known. The heart size on the chest radiograph is often used in the estimation of left ventricular volume in aortic stenosis, but a more precise measurement is desirable. The two presently available methods of volume determination involve measurement of the angiocardiogram taken in two planes, or the injection of cold saline into the left ventricle and the recording of the beat by beat temperature change in the ascending aorta. These methods are subject to different technical difficulties, and, as neither has received wide acceptance as providing an accurate estimate of left ventricular volume, we have included both in our routine preoperative assessment of patients with aortic stenosis. In this report we give the results of volume measurements in aortic stenosis, compare the angiocardiographic with the thermodilution technique, and show the poor relation between these measurements and the size of the heart in the conventional radiograph. PATIENTS AND METHODSLeft ventricular volume measurements were made during the course of pre-operative left heart catheterizaReceived October 12, 1967. tion in 23 patients with aortic stenosis, aged from 9 to 62 years, the obstruction being at valve level in all but one, where the stenosis was a subvalvar fibrous ring (Table I). All patients were in sinus rhythm and, despite the frequent finding of an early diastolic murmur, none of the patients was judged on clinical or haemodynamic grounds to have significant aortic regurgitation. Volume measurements were not made when there was any mitral valve regurgitation.A postero-anterior chest radiograph was available, taken at a tube to film distance of six feet for each patient, and from this the heart size was expressed as the cardiothoracic ratio.In early studies promethazine (phenergan) 50 mg. was given intramuscularly before the procedure, but later investigations were carried out without premedication. Catheterization of the right heart from the right long saphenous vein using local skin anaesthesia was followed in each case by transseptal puncture, placing a Brockenbrough catheter in the left ventricle. A No. 6 Gensini catheter was placed in the femoral artery by the percutaneous method and advanced to the ascending aorta. The cardiac output was measured by the injection of indocyanine green into the left ventricle and the withdrawal of blood from the aorta through a Gilford cuvette, calibration being carried out by the dynamic method (Emanuel et al., 1966; Shineboume, Fleming, and Hamer...

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“…Systematic analysis of thermodilution curves suggests that the technique gives a satisfactory estimate of left ventricular volume under the conditions of the present study. The close agreement between left ventricular diastolic volumes measured by this technique and by angiocardiography (Fleming and Hamer, 1968) gives further confidence in the validity of the method. Though there is considerable variation in the thermodilution ratio, the ability to carry out repeated estimates allows the demonstration of a consistent difference before and after the drugs, which in three cases reaches statistical significance.…”

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“…Patients in group II tend to have bigger hearts on the chest x-ray examination than those in group I. This finding suggests an increase in left ventricular volume in group II, though we have shown a poor correlation between heart size on chest x-ray examination and direct measurements of left ventricular volume in aortic stenosis (Fleming and Hamer, 1968). The slightly faster ejection rate of group II subjects could be accounted for on this basis, as an identical velocity of contraction in a larger ventricle will result in a faster rate of ejection.…”