Ventricular interaction and external constraint account for decreased stroke work during volume loading in CHF

The slope of the stroke work (SW)-pulmonary capillary wedge pressure (PCWP) relation may be negative in congestive heart failure (CHF), implying decre ased contractility based on the premise that PCWP is simply related to left ventricular (LV) end-diastolic volume. We hypothesized that the negative s lope is explained by decreased transmural LV end-diastolic pressure (LVEDP) , despite the increased LVEDP, and that contractility remains unchanged. Ra pid pacing produced CHF in six dogs. Hemodynamic and dimension changes were then measured under anesthesia during volume manipulation. Volume loading increased pericardial pressure and LVEDP but decreased transmural LVEDP and SW. Right ventricular diameter increased and septum-to-LV free wall diamet er decreased. Although the slopes of the SW-LVEDP relations were negative, the SW-transmural LVEDP relations remained positive, indicating unchanged c ontractility. Similarly, the SW-segment length relations suggested unchange d contractility. Pressure surrounding the LV must be subtracted from LVEDP to calculate transmural LVEDP accurately. When this was done in this model, the apparent decrease in contractility was no longer evident. Despite the increased LVEDP during volume loading, transmural LVEDP and therefore SW de creased and contractility remained unchanged.