Define myocardial contractility and briefly describe dP/dT, the end systolic pressure volume (ESPV) relationship and the ejection fraction (EF).
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
As the "absence of a diagram (correctly labelled and scaled) was a weakness in many answers", a suggested diagram is produced here, which the author attempted to reconstruct as best he could from what the examiners wrote.
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