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

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• The stroke work (SW)-pulmonary capillary wedge pressure (PCWP) relationship is often negative in congestive heart failure (CHF).
• This negative slope is traditionally interpreted as decreased left ventricular (LV) contractility.
• This interpretation assumes PCWP directly reflects LV end-diastolic volume.

Purpose of the Study:

• To test the hypothesis that a negative SW-PCWP slope in CHF is due to decreased transmural LV end-diastolic pressure (LVEDP), not altered contractility.
• To investigate the role of pericardial pressure in modulating LV filling and SW.
• To accurately assess LV contractility in a canine model of CHF.

Main Methods:

• Congestive heart failure (CHF) was induced in six dogs via rapid pacing.
• Hemodynamic parameters and LV dimensions were measured during anesthesia and volume manipulation.
• Transmural LVEDP was calculated by subtracting pericardial pressure from LVEDP.

Main Results:

• Volume loading increased LVEDP and pericardial pressure but decreased transmural LVEDP and SW.
• The SW-LVEDP relationship exhibited a negative slope, consistent with previous findings.
• However, the SW-transmural LVEDP and SW-segment length relationships remained positive, indicating unchanged contractility.

Conclusions:

• The negative SW-PCWP slope in CHF does not necessarily indicate decreased contractility.
• Accurate assessment of transmural LVEDP, by accounting for surrounding pressures, is crucial.
• LV contractility remains preserved in this model of CHF despite altered filling pressures.