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Altered re‐excitation thresholds and conduction of extrasystolic action potentials contribute to arrhythmogenicity in murine models of long QT syndrome
Author(s) -
Duehmke R. M.,
Pearcey S.,
Stefaniak J. D.,
Guzadhur L.,
Jeevaratnam K.,
Costopoulos C.,
Pedersen T. H.,
Grace A. A.,
Huang C. L.H.
Publication year - 2012
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2012.02443.x
Subject(s) - refractory period , repolarization , nerve conduction velocity , medicine , cardiology , electrophysiology , long qt syndrome , qt interval , optical mapping , stimulus (psychology) , anesthesia , psychology , psychotherapist
Aim QT interval prolongation reflecting delayed action potential ( AP ) repolarization is associated with polymorphic ventricular tachycardia and early after depolarizations potentially initiating extrasystolic AP s if of sufficient amplitude. The current experiments explored contributions of altered re‐excitation thresholds for, and conduction of, such extrasystolic AP s to arrhythmogenesis in L angendorff‐perfused, normokalaemic, control wild‐type hearts and two experimental groups modelling long QT ( LQT ). The two LQT groups consisted of genetically modified, Scn5a +/Δ KPQ 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 ( S 1) stimulus trains followed by premature ( S 2) extrastimuli whose amplitudes were progressively increased with progressive decrements in S 1 S 2 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 AP s 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 AP s in the LQT groups thus occur under conditions of higher conduction velocity and greater sensitivity to extrastimuli than in controls.