Abstract
Historically, left ventricular (LV) performance has been quantified by measuring indices of global performance, such as stroke work, developed pressure and the LV end-systolic pressure-volume relation (ESPVR) [1]. Suga and Sagawa [1] extended their initial pioneering studies on contractility-defining end-systolic pressure-volume relationships (ESPVR) by incorporating the graphic area inside the LV pressure-volume loop (stroke work or SW) plus the ESPVR-defined left-sided triangle of potential work (Fig. 1), called the LV pressure-volume area (PVA) [2]. Measuring myocardial oxygen consumption (MVO2) as the product of arterio-coronary sinus oxygen content difference and coronary sinus blood flow, they demonstrated that changes in the LV PVA induced proportional changes in MVO2. Thus, increasing either LV volume or ejection pressure increases MVO2 in a predictable fashion. Similarly, any process that reduces this PVA also reduces MVO2. This simple and elegant construct allows physicians to predict with great accuracy the impact of specific drugs and surgical interventions on LV ejection efficiency, defined as the ratio of SW to MVO2. This construct assumes that myocardial contraction occurs in a uniform fashion from initiation of systole to end-ejection, such that all components of the contractile apparatus shorten to a minimal volume at the same instant.
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