Define myocardial contractility and briefly describe dP/dT, the end systolic pressure volume (ESPV) relationship and the ejection fraction (EF).

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College Answer

Contractility represents the performance of the heart at a given preload and afterload. It is 
the change in peak isometric force (isovolumic pressure) at a given initial fibre length (end 
diastolic volume). All indices of myocardial contractility are dependent on preload or 
afterload to a varying degree. The dP/dT is the maximum rate of change in left ventricular 
pressure during isovolumetric contraction, after mitral valve closes and before the aortic 
valve opens. It is preload dependant and afterload independent. A diagram of a pressurevolume loop is very helpful when describing the ESPV. Absence of a diagram (correctly 
labelled and scaled) was a weakness in many answers. Candidates were then expected to at 
least explain that, as preload is increased a new pressure volume loop is generated. Each 
new PV loop has a new end systolic point that is at a slightly higher pressure and volume 
than the previous end systolic point. The line connecting the end-systolic points is called the 
linear ESPVR. The slope of the ESPVR or Emax is used as an index of myocardial contractility. 
Ejection fraction is the percentage of the ventricular end diastolic volume (EDV) which is 
ejected with each stroke volume (SV). Ejection fraction = stroke volume/end diastolic 
volume X 100 (Normal range 55 to 70%). Only a minority of candidates achieved the depth 
of knowledge required for a Level 1 topic