E.S.Prakash, MBBS, MD Division of Basic Medical Sciences, Mercer University School of Medicine

1. Plotting the End-Systolic Pressure Volume Relationship (slope of the ESPVR) to assess Myocardial Contractility E.S.Prakash, MBBS, MD Division of Basic Medical Sciences, Mercer University School of Medicine http://medicine.mercer.edu prakash_es@mercer.edu http://esprakash.wordpress.com License (2011):

2. The intent is to briefly clarify how the End-Systolic Pressure Volume Relationship (ESPVR) is obtained. • In experimental situations, the slope of the ESPVR line provides an index of the the effect of an intervention of interest on myocardial contractility, when it may not be possible to control both afterload and preload.

3. P-V Loops showing the effect of an intervention on the slope of the “End-systolic Pressure Volume Relationship (ESPVR)”, an index of Myocardial ContractilityX-axis: Left ventricular volume (ml); Y-axis: left ventricular pressure (mm Hg)Forgive the simplicity in the ejecting limb of the P-V loops – they are simplified to straight lines here; you know LVP hits its high around mid-ejection. ESPVR generated by joining end-systolic points in 3 different P-V loops after an intervention whose effect on contractility is of interest ‘Control’ ESPVR Slope (contractility) generated by joining end-systolic points in 3 different P-V loops in variably loaded beats, and the experimenter does not change factors known to affect contractility considerably. Which ESPVR – blue or black - represents better myocardial contractility?

4. Assess contractility in the baseline (‘control’) state by joining the end-systolic points of P-V loops from multiple cycles. It is OK if these beats are variably loaded (differing EDV and ESV). This line called ESPVR may intercept the x-axis or the Y-axis or even zero. • Assess contractility after the intervention of interest (say, stimulating sympathetic nerves or administration of a drug or occlusion of coronary artery etc), by joining the end-systolic points of P-V loops from multiple cycles. • The ESPVR line that is steeper with respect to the x-axis represents better contractility. • Does contractility change under standard (control) conditions from beat to beat? • It may but it has been shown that such changes are of a much lesser magnitude than with interventions that are clinically significant (example, coronary artery occlusion, beta-adrenergic agonists etc) Kass DA and Maughan WL (1988) . From E-max to pressure volume relations: a broader view http://circ.ahajournals.org/content/77/6/1203.long accessed 1 Oct 2011

5. P-V Loops showing the effect of an intervention on the slope of the “End-systolic Pressure Volume Relationship (ESPVR)”, an index of Myocardial ContractilityX-axis: Left ventricular volume (ml); Y-axis: left ventricular pressure (mm Hg)Forgive the simplicity in the ejecting limb of the P-V loops – they are simplified to straight lines here; you know LVP hits its high around mid-ejection. ‘Control’ (Baseline) ESPVR Slope ESPVR after an intervention of interest When you have such a figure and the slopes are labeled ESPVR lines, then one can assume that the lines have been obtained following the procedure described in the previous 2 slides. Which ESPVR – blue or black - represents better myocardial contractility?

6. Contractility in GRAY better than BROWN better than BLUE All beats were identically preloaded (same end-diastolic volume). So is the afterload. Under such conditions, higher the stroke volume or ejection fraction, better the contractility. One does not need slopes of ESPVRs here to tell this. Figure below: Y-axis represents Left Ventricular Pressure. Compare myocardial contractility in the 3 P-V loops below. 0 60 120 Left ventricular volume (ml)

7. The slope of the ESPVR is one of the better indices of myocardial contractility. But there are caveats. The following 2 references provide detailed treatment of this concept: Sagawa K et al. End-Systolic Pressure/Volume Ratio: A new index of myocardial contractility. American Journal of Cardiology 1977; 40: 748-753 http://www.smjr.org/files/cards/sagawa%20-%20am%20j%20cardiol.pdf Kass DA and Maughan WL . From E-max to pressure volume relations: a broader view. Circulation 1988 http://circ.ahajournals.org/content/77/6/1203.long accessed 1 Oct 2011