[Radionuclide ventriculographic assessment of cardiac function based on the analysis of cardiac reserve during...

To evaluate the contribution of myocardial contractility and preload to increase cardiac output during supine bicycle exercise, quantitative radionuclide ventriculography was performed at rest (R) and during peak exercise (Ex) in 43 patients with coronary artery disease (CAD) and 13 normal subjects. Myocardial contractility was estimated from the ratio of peak systolic pressure to end-systolic volume index (P/V index). During Ex in normal subjects, P/V index invariably increased and its percent change from R to Ex averaged 98 +/- 46 percent. Stroke index (SI) in normal subjects increased from 48 +/- 9 to 57 +/- 7 ml/m2 during Ex (p less than 0.001) without an increase in end-diastolic volume index (EDVI) (76 +/- 11 vs 78 +/- 11 ml/m2, NS). Ten of 43 patients with CAD, whose percent increase in P/V index was more than 40 percent, showed a significant increase in SI during Ex (44 +/- 5 vs 51 +/- 12 ml/m2, p +/- 0.05) without an increase in EDVI (86 +/- 14 vs 87 +/- 15 ml/m2, NS). In 16 of 43 patients with CAD whose percent increase in P/V index was less than 40 percent, SI increased from 44 +/- 10 to 51 +/- 15 ml/m2 (p less than 0.01) during Ex with an increase in EDVI (102 +/- 24 vs 117 +/- 29 ml/m2, p less than 0.001). In the remaining 17 patients with CAD whose P/V index decreased during Ex, SI did not increase during Ex (48 +/- 14 vs 44 +/- 12 ml/m2, NS) despite an increase in EDVI (80 +/- 19 vs 94 +/- 18 ml/m2, p less than 0.01). These results indicate that the Frank-Starling mechanism operates under limited augmentation in myocardial contractility, and that its compensatory function may have limitations under the severely depressed reserve of myocardial contractility.