Key result
In the normal canine in situ heart, left ventricular contractility (Emax) potentiated in the first postextrasystolic beat consistently decayed in alternans within 5 to 6 beats.
p-value: p=<0.05
The study demonstrates that postextrasystolic contractility normally decays in alternans rather than exponentially in the normal canine in situ heart, challenging the view that alternans decay indicates abnormal cardiac conditions.
Alternans decay of postextrasystolic potentiation occurs in normal hearts; leaves open whether the pattern distinguishes pathology in humans.
We have reported that the postextrasystolic (PES) potentiation of left ventricular (LV) contractility usually decays in alternans at heart rates above 80-100 beats/min in the canine excised, cross-circulated heart. We examined whether the PES contractility would also decay in alternans even in the canine in situ heart presumably more physiological than the excised heart. In anesthetized, ventilated, and open-chest mongrel dogs, we measured LV pressure and volume with a micromanometer and a conductance catheter cannulated into the LV and obtained LV end-systolic maximum elastance (E(max)) as the reasonably load-independent contractility index. We inserted an extrasystole followed by a compensatory pause into steady-state regular beats at heart rates above 90 beats/min and analyzed the PES decay pattern of E(max). We found that E(max) potentiated in the first PES beat decayed in alternans within 5-6 PES beats. This indicates that PES contractility also decays in alternans in the normal canine in situ heart.
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Shimizu et al. (2003) studied Normal cardiac physiology (n=7). Extrasystole with compensatory pause vs. Steady-state regular beats was evaluated on Decay pattern of left ventricular end-systolic maximum elastance (Emax) during postextrasystolic beats (p=<0.05). In the normal canine in situ heart, left ventricular contractility (Emax) potentiated in the first postextrasystolic beat consistently decayed in alternans within 5 to 6 beats.
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