Cardiac Performance, Dr. D. Penney

Intervals within electromechanical systole, Q - S2

Q marks the beginning of depolarization of the ventricle

S1 is 1st heart sound (closing of AV valves)

S2 is 2nd heart sound (closing of semi-lunar valves).

PEP (pre-ejection period; period when ventricle is electrically activated & contracting isovolumetrically)

= (Q - S2) - (LVET)
= Q - aortic valve opening*

* obtained from carotid pulse with a superficial pulse transducer.
ICT (isovolumetric contraction time)
= (S1 - S2) - (LVET)

LVET (left ventricular ejection time)

= (S1 - S2) - ICT or
= (Q - S2) - PEP

Q to S1 is due to the delay between electrical and mechanical events

= (Q - S2) - (S1 - S2)

Note: In healthy subjects PEP/LVET = 0.35 +/- 0.04. An elevated ratio is an index of pathology (i.e. a negative inotropic or dromotropic action)

Last changed 03/18/98

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