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Although rarely life-threatening on short term, atrial fibrillation leads to increased mortality and decreased quality of life through its complications, including heart failure and stroke. Recent studies highlight the benefits of maintaining sinus rhythm. However, pharmacological long-term rhythm control strategies may be shadowed by associated proarrhythmic effects. At the same time, electrical cardioversion is limited to hospitals, while catheter ablation therapy, although effective, is invasive and is dedicated to specific patients, usually with low amounts of atrial fibrosis (preferably Utah I-II). Cardiac optogenetics allows influencing the heart’s electrical activity by applying specific wavelength light pulses to previously engineered cardiomyocytes into expressing microbial derived light-sensitive proteins called opsins. The resulting ion influx may give rise to either hyperpolarizing or depolarizing currents, thus offering a therapeutic potential in cardiac electrophysiology, including pacing, resynchronization, and arrhythmia termination. Optogenetic atrial fibrillation cardioversion might be achieved by inducing a conduction block or filling of the excitable gap. The authors agree that transmural opsin expression and appropriate illumination with an exposure time longer than the arrhythmia cycle length are necessary to achieve successful arrhythmia termination. However, the efficiency and safety of biological cardioversion in humans remain to be seen, as well as side effects such as immune reactions and loss of opsin expression. The possibility of delivering pain-free shocks with out-of-hospital biological cardioversion is tempting; however, there are several issues that need to be addressed first: applicability and safety in humans, long-term behaviour, anticoagulation requirements, and fibrosis interactions.

Aims Tachycardia‐induced cardiomyopathy (TCM) represents a partially reversible type of cardiomyopathy (CM) that is often underdiagnosed and cardiac chamber remodelling in TCM remains incompletely understood. We aim to explore differences in the dimensions of the left ventricle and functional recovery in patients with TCM compared with patients with other forms of CM. Methods and results We identified patients with reduced ejection fraction (≤50%) and/or atrial fibrillation or flutter with a left ventricular ejection fraction that improved from baseline (≥15% in left ventricular ejection fraction at follow‐up or normalization of cardiac function with at least 10% improvement). Patients were then divided into two groups: (A) TCM patients and (B) patients with other forms of CM (controls). Two hundred thirty‐eight patients were included (31% female, 70 years median age), 127 patients had TCM, and 111 had other forms of CM. Patients with TCM did not significantly improve indexed left ventricular volume (LVEDVI) after treatment (60 [45, 84] mL/m2 versus 56 [45, 70] mL/m2, P = ns) compared with controls (67 [54, 81] mL/m2 versus 52 [42, 69] mL/m2, P < 0.001). Patients with TCM patients had significantly worse fractional shortening at baseline than controls (15.5 [12, 23] vs. 20 [13, 30], P = 0.01) and higher indexed left atrial volume (LAVI) at baseline than controls (48 [37, 58] vs. 41 [33, 51], P = 0.01) that remained dilated at follow‐up (follow‐up LAVI 41 [33, 52] mL/m2). Good predictors of TCM were: normal LVEDVI (LVEDVI < 58 mL/m2 (M) and < 52 mL/m2 (F)) (odds ratio [OR] 5.2; 95% confidence interval [CI] 2.2–13.3, P < 0.001), fractional shortening < 30% (OR 3.5; 95% CI 1.4–9.2, P = 0.009), LAVI >40 mL/m2 (OR 3.4; 95% CI 1.6–7.3, P = 0.001) and normal wall thickness left ventricle (OR 3.2; 95% CI 1.4–7.8, P = 0.008). 54% of patients with TCM demonstrated diastolic dysfunction at follow‐up, without differences from controls (54% vs. 43%, P = ns). 21% of patients with TCM showed persistent heart failure symptoms at follow‐up compared with 4.5% of controls, P = 0.004. Conclusions TCM patients have a specific pattern of functional recovery with persistent remodelling of the left atria and left ventricle. Several echocardiographic parameters might help identify TCM before treatment.

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