Key result
Arrhythmias induced by extrasystolic action potentials in murine long QT models occur under conditions of higher conduction velocity and greater sensitivity to extrastimuli than in controls.
In murine models of long QT syndrome, arrhythmias induced by extrasystolic action potentials occur under conditions of higher conduction velocity and greater sensitivity to extrastimuli compared to controls.
Cautions against extrapolating murine LQT mechanisms to patients; leaves open conduction velocity's role in clinical arrhythmia risk.
AIM: QT interval prolongation reflecting delayed action potential (AP) repolarization is associated with polymorphic ventricular tachycardia and early after depolarizations potentially initiating extrasystolic APs if of sufficient amplitude. The current experiments explored contributions of altered re-excitation thresholds for, and conduction of, such extrasystolic APs to arrhythmogenesis in Langendorff-perfused, normokalaemic, control wild-type hearts and two experimental groups modelling long QT (LQT). The two LQT groups consisted of genetically modified, Scn5a(+/ΔKPQ) and hypokalaemic wild-type murine hearts. METHODS: Hearts were paced from their right ventricles and monophasic AP electrode recordings obtained from their left ventricular epicardia, with recording and pacing electrodes separated by 1 cm. An adaptive programmed electrical stimulation protocol applied pacing (S1) stimulus trains followed by premature (S2) extrastimuli whose amplitudes were progressively increased with progressive decrements in S1S2 interval to maintain stimulus capture. Such protocols culminated in either arrhythmic or refractory endpoints. RESULTS: Arrhythmic outcomes were associated with (1) lower conduction velocities in their initiating extrasystolic APs than refractory outcomes and (2) higher conduction velocities in the LQT groups than in controls. Furthermore, (3) the endpoints were reached at longer S1S2 coupling intervals and with smaller stimulus amplitudes in the LQT groups compared with controls. This was despite (4) similar relationships between conduction velocity and S1S2 coupling interval and between re-excitation thresholds and S1S2 coupling interval in all three experimental groups. CONCLUSIONS: Arrhythmias induced by extrasystolic APs in the LQT groups thus occur under conditions of higher conduction velocity and greater sensitivity to extrastimuli than in controls.
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Duehmke et al. (2012) studied Long QT syndrome (murine models). Genetically modified Scn5a(+/ΔKPQ) and hypokalaemic wild-type murine hearts vs. Normokalaemic control wild-type hearts was evaluated on Arrhythmic outcomes, conduction velocities, and re-excitation thresholds. Arrhythmias induced by extrasystolic action potentials in murine long QT models occur under conditions of higher conduction velocity and greater sensitivity to extrastimuli than in controls.
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