Ann Thorac Surg 2003;75:1208
© 2003 The Society of Thoracic Surgeons
Invited commentary
Arthur Wallace, MD, PhD,
Mark Ratcliffe, MD
VAMC Surgery 112D, San Francisco Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA
e-mail: mark.ratcliffe{at}med.va.gov
In their manuscript, Tanoue and colleagues attempted to calculate arterial elastance (EA), ventricular elastance at end-systole (EES), stroke work (SW), and the pressure volume area (PVA) in patients before and after the Dor procedure. They found that EA was not changed but EES improved, the EA/EES ratio fell from 2.9 to 1.6, and left ventricular (LV) efficiency (SW/PVA) increased.
An improvement in LV efficiency (output work/total energy consumption) is desirable in patients with heart failure. Efficiency can be either measured directly or calculated, but if calculated, LV efficiency and function are determined by EES, diastolic compliance, and EA. End systole and diastolic compliance have fairly obvious effects. However, efficiency and function can be improved even when EES and diastolic compliance are unchanged. For instance, LV efficiency and function of patients with heart failure improve with afterload reduction, an effect that becomes optimum when the EA/EES ratio is close to 1. In addition, surgical operations that reduce ventricular volume directly effect EES and diastolic compliance but, as Tanoue and colleagues have shown, do not effect EA. The key question is what really happens to the EES and diastolic compliance since failure to measure the true end-systolic and diastolic pressure-volume relationships makes calculations of ventricular function and efficiency impossible.
The main problem is that Tanoue and colleagues did not correctly measure EES prior to their analysis. They approximated it with the formula EES = mean arterial pressure/minimum left ventricular volume, which is probably inappropriate when LV volume is surgically reduced. Specifically, their EES approximation assumes that Vo is fixed at the origin. This approximation may be used when comparing different LV contractile states in which the primary effect is on EES itself (slope). Unfortunately, the operation performed on these patients changed the Vo, making the assumption invalid. For instance, Vo is significantly reduced after Batista’s operation and is probably reduced after the Dor procedure as well.
We applaud the efforts of Tanoue and colleagues but believe that actual measurement of EES, diastolic compliance, EA, and efficiency after the Dor procedure are necessary before this issue is concluded.
