Stroke volume paradox in heart failure: mathematical validation

Abstract

Background In some patients with ischemic cardiomyopathy, despite large increases in ventricular size with decreased cardiac output, the paradox of preserved stroke volume has been observed. Following surgical ventricular restoration, despite marked improvements clinically and in ventricular volumes and ejection fraction, a decrease in stroke volume was observed. Methods 101 consecutive patients with postinfarction left ventricular aneurysms were studied by 2-dimensional echocardiography and contrast ventriculography at baseline, and 57 of these patients at 1.7 to 2.2 years (mean 1.95 ± 0.44 years) after surgical ventricular restoration. Results Surgical ventricular restoration resulted in a decrease in end-diastolic volume index of 40.2 mL (95% confidence interval: 33.6–46.7) and stroke volume index of 10.0 mL (95% confidence interval: 6.6–13.5), and an increase in ejection fraction of 6.7% (95% confidence interval: 5.5–7.9). The stroke volume index had a significant linear relationship with the end-diastolic volume index at rest in patients with end-diastolic volume index <150 mL ( r = 0.64, p < 0.001). In patients with end-diastolic volume index >150 mL, this linear relationship was not seen. The change in end-diastolic volume index and stroke volume index had a significant linear relationship ( r = 0.72, p < 0.001) that persisted at 1.95 years after surgery. Conclusions In ischemic cardiomyopathy, stroke volume increases linearly with increases in end-diastolic volume up to a certain magnitude of end-diastolic volume, beyond which it decreases. Hence, following surgical ventricular restoration, decreases in stroke volume are not a reflection of impaired cardiac function.