Intracellular calcium dynamics and acetylcholine-induced triggered activity in the pulmonary veins of dogs with pacing-induced heart failure

doi:10.1016/j.hrthm.2008.04.009

Heart Rhythm

Volume 5, Issue 8, August 2008, Pages 1170-1177

https://doi.org/10.1016/j.hrthm.2008.04.009 Get rights and content

Background

Heart failure increases autonomic nerve activities and changes intracellular calcium (Ca_i) dynamics.

Objective

The purpose of this study was to investigate the hypothesis that abnormal Ca_i dynamics are responsible for triggered activity in the pulmonary veins (PVs) during acetylcholine infusion in a canine model of heart failure.

Methods

Simultaneous optical mapping of Ca_i and membrane potential was performed in isolated Langendorff-perfused PV–left atrial (LA) preparations from nine dogs with ventricular pacing-induced heart failure. Mapping was performed at baseline, during acetylcholine (1 μmol/L) infusion (N = 9), and during thapsigargin and ryanodine infusion (N = 6).

Results

Acetylcholine abbreviated the action potential. In four tissues, long pauses were followed by elevated diastolic Ca_i, late phase 3 early afterdepolarizations, and atrial fibrillation (AF). The incidence of PV focal discharges during AF was increased by acetylcholine from 2.4 ± 0.6 beats/s (N = 4) to 6.5 ± 2.2 beats/s (N = 8; P = .003). PV focal discharge and PV–LA microreentry coexisted in 6 of 9 preparations. The spatial distribution of dominant frequency demonstrated a focal source pattern, with the highest dominant frequency areas colocalized with PV focal discharge sites in 35 (95%) of 37 cholinergic AF episodes (N = 8). Thapsigargin and ryanodine infusion eliminated focal discharges in 6 of 6 preparations and suppressed the inducibility of AF in 4 of 6 preparations. PVs with focal discharge have higher densities of parasympathetic nerves than do PVs without focal discharges (P = .01), and periodic acid–Schiff (PAS)-positive cells were present at the focal discharge sites.

Conclusion

Ca_i dynamics are important in promoting triggered activity during acetylcholine infusion in PVs from pacing-induced heart failure. PV focal discharge sites have PAS-positive cells and high densities of parasympathetic nerves.

Introduction

Direct autonomic nerve recordings in a canine heart failure model show that not only sympathetic but also vagal nerves discharges are increased in heart failure, and simultaneous sympathovagal discharges are common triggers of atrial arrhythmias.¹ Vagal activation is thought to promote atrial fibrillation (AF) by shortening the refractory period, which accelerates and stabilizes reentrant excitation.² However, acetylcholine infusion also may induce late phase 3 early afterdepolarizations and triggered activity in normal canine atria³ if acetylcholine-induced action potential duration (APD) shortening is coupled with increased intracellular calcium (Ca_i) transient. The large and persistent Ca_i transient that occurs in late diastole activates the Na⁺/Ca²⁺ exchanger (NCX), leading to afterdepolarizations and triggered activity.⁴ Heart failure is associated with abnormal Ca_i handling and increased NCX activity.⁵ The purpose of this study was to perform high-density simultaneous membrane potential (Vm) and Ca_i mapping⁶ to determine if Ca_i dynamics are directly responsible for triggered activity in the pulmonary veins (PVs) during acetylcholine infusion in a canine model of pacing-induced heart failure. A second aim of the study was to perform immunohistochemical studies to test the hypothesis that autonomic innervation and specialized conducting cells are juxtaposed to the PV focal discharge sites.

Section snippets

Methods

The research protocol was approved by the Institutional Animal Care and Use Committees of Chang Gung Memorial Hospital. Nine mongrel dogs (weight 16–29 kg) were used in the study. Under isoflurane anesthesia, the chest was opened via right thoracotomy. A screw-in bipolar pacing lead was inserted into the right ventricle and connected to an Itrel III neurostimulator (Medtronic, Inc., Minneapolis, MN, USA) for chronic pacing at 240 bpm starting 2 days after implantation until heart failure was

Results

Left ventricular ejection fraction decreased from 54% ± 16% to 26% ± 8% (N = 9; P <.001) after 42 ± 7 days of rapid pacing. Compared with nonpaced normal dogs (137 ± 15 ms, N = 4), APD₈₀ was longer in heart failure dogs (214 ± 16 ms, N = 9; P <.001). Mean τ of Ca_i decline was larger in the heart failure group (26.0 ± 4.5 ms, N = 9) than in the nonpaced control group (18.6 ± 0.4 ms, N = 4). Acetylcholine significantly shortened APD₈₀ (80 ± 42 ms, N = 9; P <.001) but increased mean τ of Ca_i

Discussion

We found that isolated PVs from dogs with heart failure may develop ectopic rhythms that compete with sinus rhythm. After APD was shortened by acetylcholine, the same sites might serve as sources of rapid activations during AF. Histologic findings at these sites showed abundant PAS-positive cells and rich parasympathetic innervation. These findings imply that Ca_i dynamics are important in promoting triggered activity during acetylcholine infusion in PVs from pacing-induced heart failure.

Acknowledgments

We thank Avile McCullen, Lei Lin, and Elaine Lebowitz for assistance.

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Figure 1 shows 2 episodes of AT from patient 10. Similar to that found in ambulatory dogs,3,4 the onset of AT was preceded by increased SKNA (black arrows). In addition, there was a burst of SKNA and transient HR acceleration (by >10 beats/min in 31 episodes and by >5 beats/min in 1 episode) before AT termination (blue arrows).
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: This study was supported by CMRPG33016 to Dr. Chou, a Piansky Endowment to Dr. Fishbein, a Pauline and Harold Price Endowment and Medtronic-Zipes Endowment to Dr. Chen. This study was supported in part by an AHA Established Investigatorship Award and by NIH Grants P01-HL78931, R01-HL58533, 66389, 78932, and 71140.

: This manuscript was processed by a guest editor.

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Original-experimentalIntracellular calcium dynamics and acetylcholine-induced triggered activity in the pulmonary veins of dogs with pacing-induced heart failure

Background

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Methods

Results

Discussion

Acknowledgments

Left stellate ganglion and vagal nerve activity and cardiac arrhythmias in ambulatory dogs with pacing-induced congestive heart failure

J Am Coll Cardiol

Cholinergic atrial fibrillation in a computer model of a two-dimensional sheet of canine atrial cells with realistic ionic properties

Circ Res

Reinduction of atrial fibrillation immediately after termination of the arrhythmia is mediated by late phase 3 early afterdepolarization-induced triggered activity

Circulation

Sodium-calcium exchange initiated by the Ca2+ transient: an arrhythmia trigger within pulmonary veins

J Am Coll Cardiol

Effects of experimental heart failure on atrial cellular and ionic electrophysiology

Circulation

Intracellular calcium dynamics and anisotropic reentry in isolated canine pulmonary veins and left atrium

Circulation

Relationship between regional cardiac hyperinnervation and ventricular arrhythmia

Circulation

Intracellular calcium and vulnerability to fibrillation and defibrillation in Langendorff-perfused rabbit ventricles

Circulation

Triggered firing in pulmonary veins initiated by in vitro autonomic nerve stimulation

Heart Rhythm

Original-experimental
Intracellular calcium dynamics and acetylcholine-induced triggered activity in the pulmonary veins of dogs with pacing-induced heart failure

Sodium-calcium exchange initiated by the Ca²⁺ transient: an arrhythmia trigger within pulmonary veins