Empirical correlation of triggered activity and spatial and temporal re-entrant substrates with arrhythmogenicity in a murine model for Jervell and Lange-Nielsen syndrome

Abstract

KCNE1 encodes the beta-subunit of the slow component of the delayed rectifier K(+) current. The Jervell and Lange-Nielsen syndrome is characterized by sensorineural deafness, prolonged QT intervals, and ventricular arrhythmogenicity. Loss-of-function mutations in KCNE1 are implicated in the JLN2 subtype. We recorded left ventricular epicardial and endocardial monophasic action potentials (MAPs) in intact, Langendorff-perfused mouse hearts. KCNE1 (-/-) but not wild-type (WT) hearts showed not only triggered activity and spontaneous ventricular tachycardia (VT), but also VT provoked by programmed electrical stimulation. The presence or absence of VT was related to the following set of criteria for re-entrant excitation for the first time in KCNE1 (-/-) hearts: Quantification of APD(90), the MAP duration at 90% repolarization, demonstrated alterations in (1) the difference, APD(90), between endocardial and epicardial APD(90) and (2) critical intervals for local re-excitation, given by differences between APD(90) and ventricular effective refractory period, reflecting spatial re-entrant substrate. Temporal re-entrant substrate was reflected in (3) increased APD(90) alternans, through a range of pacing rates, and (4) steeper epicardial and endocardial APD(90) restitution curves determined with a dynamic pacing protocol. (5) Nicorandil (20 microM) rescued spontaneous and provoked arrhythmogenic phenomena in KCNE1 (-/-) hearts. WTs remained nonarrhythmogenic. Nicorandil correspondingly restored parameters representing re-entrant criteria in KCNE1 (-/-) hearts toward values found in untreated WTs. It shifted such values in WT hearts in similar directions. Together, these findings directly implicate triggered electrical activity and spatial and temporal re-entrant mechanisms in the arrhythmogenesis observed in KCNE1 (-/-) hearts.

Fig. 1

Representative MAP recordings from intrinsically beating KCNE1^−/− hearts Langendorff-perfused with control Krebs–Henseleit solution demonstrating typical spontaneous triggered activity occurring as ectopic MAP waveforms (asterisk) in association with the onset of spontaneous VT (a) in contrast to their absence in similarly perfused intrinsically beating WT hearts (b). Treatment with 20 µM nicorandil reduced both triggered activity and VT in KCNE1^−/− hearts (c). WT hearts treated with nicorandil did not show triggered activity or VT (d)

Fig. 2

MAP recordings obtained during a PES protocol used to assess for provoked arrhythmogenic tendencies. They demonstrate the typical initiation of VT in untreated KCNE1^−/− hearts observed in five out of five hearts (a) and the prevention of such VT by treatment with nicorandil (20 µM) in four out of five hearts (P < 0.05) (c). WT hearts were refractory to PES provocation whether untreated (b) or treated with nicorandil (d)

Fig. 3

Representative MAP waveforms during steady-state 8-Hz pacing recorded from the left ventricular epicardia and endocardia of KCNE1^−/− (a and c) and WT (b and d) hearts perfused with control solution (a and b) or 20 µM nicorandil (c and d). KCNE1^−/− hearts had longer epicardial MAP waveforms (a) than WTs similarly perfused with control solution (b), and both were shortened by nicorandil (c and d) while endocardial MAPs were conserved in both (c and d)

Fig. 4

APD at 30%, 50%, 70%, and 90% repolarization quantified from MAP recordings made from the epicardium of KCNE1^−/− (a) and WT (b) hearts during 8-Hz extrinsic pacing demonstrated a concentration-dependent reduction in APD₉₀ and APD₇₀ with nicorandil. In contrast, similarly obtained MAP recordings from the endocardium of KCNE1^−/− (c) and WT (d) hearts demonstrated conserved APD values during perfusion with nicorandil (*P < 0.05; **P < 0.01; ***P < 0.001)

Fig. 5

The transmural gradient of repolarization, ∆APD₉₀, determined from endocardial and epicardial MAP recordings during 8-Hz extrinsic pacing through a range of nicorandil concentrations in KCNE1^−/− (a) and WT hearts (b) (*P < 0.05; ***P < 0.001)

Fig. 6

Comparison of epicardial APD₉₀, VERP, and local critical intervals for re-excitation measured during steady 8-Hz extrinsic pacing over a range of nicorandil concentrations in the epicardium of KCNE1^−/− (a) and WT (b) hearts (*P < 0.05; **P < 0.01; ***P < 0.001). APD₉₀ data set from Fig. 5

Fig. 7

APD₉₀ alternans recorded over a range of BCLs from the epicardium (a and c) and endocardium (b and d) of untreated (a and b) and nicorandil-treated (20 µM) (c and d) KCNE1^−/− (a and c) and WT (b and d) hearts

Fig. 8

Epicardial restitution curves recorded from the epicardium of KCNE1^−/− (a and c) and WT (b and d) hearts perfused with control solution (a and b) or 20 µM nicorandil (c and d)

Fig. 9

Endocardial restitution curves recorded from the endocardium of KCNE1^−/− (a and c) and WT (b and d) hearts perfused with control solution (a and b) or 20 µM nicorandil (c and d)

Fig. 10

CDI (a and b) and maximum gradients (c and d) derived from restitution curves from the epicardium and endocardium of KCNE1^−/− (a and c) and WT (b and d) hearts perfused with control solution or 20 µM nicorandil (*P < 0.05; **P < 0.01, ***P < 0.001)