Heart failure enhanced pulmonary vein arrhythmogenesis and dysregulated sodium and calcium homeostasis with increased calcium sparks

Introduction: Late sodium currents and intracellular Ca²⁺ (Ca²⁺_i) dynamics play an important role in arrhythmogenesis of pulmonary vein (PV) and heart failure (HF). It is not clear whether HF enhances PV arrhythmogenesis through modulation of Ca²⁺ homeostasis and increased late sodium currents. The aim of this study was to investigate the sodium and calcium homeostasis in PV cardiomyocytes with HF. Methods and Results: Whole-cell patch clamp was used to investigate the action potentials and ionic currents in isolated rabbit single PV cardiomyocytes with and without rapid pacing induced HF. The Ca²⁺_i dynamics were evaluated through fluorescence and confocal microscopy. As compared to control PV cardiomyocytes (n = 18), HF PV cardiomyocytes (n = 13) had a higher incidence of delayed afterdepolarization (45% vs 13%, P < 0.05) and faster spontaneous activity (3.0 ± 0.2 vs 2.1 ± 0.2 Hz, P < 0.05). HF PV cardiomyocytes had increased late Na⁺ currents, Na ⁺/Ca²⁺ exchanger currents, and transient inward currents, but had decreased Na⁺ currents or L-type calcium currents. HF PV cardiomyocytes with pacemaker activity had larger Ca²⁺_i transients (R410/485, 0.18 ± 0.04 vs 0.11 ± 0.02, P < 0.05), and sarcoplasmic reticulum Ca²⁺ stores. Moreover, HF PV cardiomyocytes with pacemaker activity (n = 18) had higher incidence (95% vs 70%, P < 0.05), frequency (7.8 ± 3.1 vs 2.3 ± 1.2 spark/mm/s, P < 0.05), amplitude (F/F₀, 3.2 ± 0.8 vs 1.9 ± 0.5, P < 0.05), and longer decay time (65 ± 3 vs 48 ± 4 ms, P < 0.05) of Ca²⁺ sparks than control PV cardiomyocytes with pacemaker activity (n = 18). Conclusions: Dysregulated sodium and calcium homeostasis, and enhanced calcium sparks promote arrhythmogenesis of PV cardiomyocytes in HF, which may play an important role in the development of atrial fibrillation.