Sturm, Ralph E.

Multiple measurements of left ventricular volumes, ejection fractions, and circulatory pressures were made under conditions of varied outflow resistance in five intact anesthetized dogs by using a biplane videoangiographic recording system which displays simultaneously two roentgen images on the same television screen, records the images on video tape, and requires low radiation levels and small amounts of contrast medium. Aortic pressure was controlled by intra-aortic infusion of angiotensin or acetylcholine. With spontaneous sinus rhythm and normal aortic pressure, end-diastolic volume averaged 35 ml (2.3 ml/kg), and ejection fraction averaged 47% of end-diastolic volume. When aortic pressure was increased, average end-diastolic volumes increased to 53 ml and ejection fractions decreased to 29%. Conversely, when aortic pressure was decreased, average ejection fraction increased to 73%, although changes in stroke volume were usually not large under these conditions. Concomitant large changes in the shape of the left ventricular cavity were also observed. Similar changes were observed when heart rate was maintained constant by electrical pacing of the atria and ventricles with a constant atrial-ventricular stimulus interval. The variability in left ventricular volume and ejection fraction observed in the same animal during different circulatory states may account in part for the differences in values for these variables reported by different investigators.

Cardiac and aortic pressures were recorded after stellate ganglionectomy and vagotomy. Acute heart block was produced by injecting the atrioventricular node, and atrial and ventricular systoles were controlled electronically to occur independently or in any desired relationship. Angiocardiograms recorded on video tape after injections of 4 ml 69% Renovist into the left ventricle were analyzed with a videodensitometer able to detect small refluxes of contrast medium into the left atrium and correlate them with phases of the cardiac cycle. When ventricular driving was temporarily suspended but atrial driving continued, pressure records indicated mitral valve closure after each atrial systole, but reflux of contrast medium into the atrium occurred after each systole not followed by a normally sequenced ventricular systole. Driving with a 2: 1 atrioventricular stimulation resulted in reflux, with the alternate atrial contraction dissociated from ventricular systole. Thus, the mitral valve was not effectively closed by atrial systoles that were not followed by normally sequenced ventricular systoles.

Mitral valve function was assessed by roentgen videodensitometry. Mitral reflux was rare when single ventricular ectopic systoles were produced by electronic stimulation of the right or left ventricle at various times in the cardiac cycle. It was also rare during the compensatory pause after the ectopic systole or with the following postectopic systole. Recurrent ventricular ectopic systoles interposed once per cycle were associated with minor reflux when introduced in mid-cycle. Such extrasystoles occurred late enough in the cardiac cycle for the ventricle to relax after the primary systole and for the mitral valve to open before the extrasystole. The extrasystolic contractions were, however, weak and incapable of opening the aortic valve. When interposed early in the cardiac cycle, extrasystolic potentiation of the primary ventricular contraction occurred, and no or minimal mitral reflux was observed.