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Mechanically induced arrhythmias in hypertrophic heart

D.A. Saint and D.Y. Kim, School of Medical Sciences, University of Adelaide, Adelaide, SA 5000, Australia.

Introduction. We have previously shown that rapid stretch of the ventricle or rapid release of tension can induce arrhythmias (Saint, Kelly & Mackenzie, 2010). Hypertrophic hearts show increased sensitivity to stretch induced arrhythmias (Evans, Dalton & Lev, 2000), but how these mechanisms may be altered in hypertrophic hearts is not well understood. Here we investigate mechanically induced arrhythmias in isolated hearts from Wistar-Kyoto (control) and age-matched Spontaneously Hypertensive Rats (SHR).

Methods. Langendorff perfused hearts had a fluid filled balloon placed in the left ventricle, connected to a servo-driven syringe injector. Epicardial monophasic action potentials and intraventricular pressure were monitored to detect ectopic beats. Left Ventricular End Diastolic Pressure (LVEDP) was set at 5 to 10 mm Hg and the minimum step pressure increase which just triggered an ectopic beat was taken as threshold for stretch-induced arrhythmias (St-Ar).

Results. SHR had pronounced cardiac hypertrophy (cardiac index 0.48 ± 0.02%, n=15 in SHR vs 0.41 ± 0.02%, n=11 in Wistar-Kyoto; P <<0.01). Hearts from SHR had a lower threshold for St-Ar (21.2 ± 3.6 mm.Hg (n=5) compared to 49.4 ± 4.7 mm.Hg for control (n=5), p << 0.01). Perfusion of the hearts with 100 μM streptomycin increased the threshold in both groups (39.7 ± 9.0 mm.Hg in SHR (n=5); p = 0.07 and 69.4 ± 6.9 mm.Hg in control (n=5); p = 0.04).

Discussion. Hypertrophic hearts (SHR) are more sensitive to mechanically induced arrhythmias. Streptomycin (a blocker of stretch-activated channels) decreased the sensitivity in both SHR and control.

Evans SJ, Dalton GR & Levi AJ. (2000) Journal of Cardiovascular Risk, 7(3): 163-75.

Saint DA, Kelly D & Mackenzie L. (2010) in Mechanosensitivity of the Heart, pp 275-300 Eds Kamkin and Kiseleva, Springer.