Determinants of left ventricular preload-adjusted maximal power

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• Maximal left ventricular (LV) hydraulic power output (PWR(max)) is a key index of LV contractility.
• Preload-adjusted maximal power (PAMP) is typically calculated using a constant exponent (beta=2), but the optimal beta value varies with LV end-diastolic volume (V(ed)).

Purpose of the Study:

• To investigate the factors determining the optimal beta-factor for preload adjustment of LV power.
• To evaluate an alternative PAMP formulation incorporating V(0) for improved correlation with LV contractility.

Main Methods:

• Utilized 245 recordings from an ischemic heart pig model under steady-state and vena cava occlusion conditions.
• Determined end-systolic pressure-volume relation parameters (E(es) and V(0)) and optimal beta-factor by fitting curves.
• Calculated PAMP using standard and V(0)-incorporated formulations.

Main Results:

• The optimal beta-factor showed a weak correlation with V(ed) but an excellent exponential relation with V(0) (r=0.70).
• Standard PAMP calculation poorly correlated with E(es) (r=0.30).
• An alternative PAMP formulation incorporating V(0) demonstrated a strong correlation with E(es) (r=0.89).

Conclusions:

• Accurate preload adjustment of maximal LV power necessitates the incorporation of V(0).
• This requires measurements under altered loading conditions to determine V(0).
• The V(0)-incorporated PAMP formulation offers a more reliable index of LV contractility.