Cardiac electrical and functional activity following an outdoor cold-water swimming event

Abstract

Aims: Participation in outdoor cold-water swimming (OCWS) events combines endurance exercise and cold exposure. Concerns have emerged about the potential risk of acute adverse cardiac events during OCWS, particularly during endurance events. We analysed the effect of prolonged OCWS on cardiac function in trained athletes.

Methods: The swimming event consisted of laps over a 1000-m course, for up to 6 h, in water at 15 °C. Twenty participants (11 males, 47.3 ± 8.6 years old) were included. Core temperature (T_core) was monitored using an ingestible temperature sensor during and up to 1 h after the swim. Body composition, blood pressure, electrocardiogram (ECG), and transthoracic echocardiography were assessed 1 day before the event and within the first hour upon completion of the swim.

Results: Mean body mass index was 27.1 ± 5.1 kg/m² and fat mass was 25.2 ± 9.1 %. Mean duration of swimming was 214 ± 115 min. Minimum Tcore was 35.6 ± 1.3 °C. A significant lengthening of the QT interval corrected (QTc) for heart rate was observed post-exercise (437.7 ± 27.7 vs. 457.2 ± 35.9 ms, p = 0.012), with 5 participants exhibiting post-exercise QTc >500ms. OCWS did not alter the biventricular systolic function and left ventricular relaxation. No correlation was observed between ΔQTc and ΔTcore.

Conclusion: OCWS seemed to acutely delay post-exercise cardiac repolarization without alteration of cardiac function in a healthy trained population. Additional investigations would be warranted to explore the clinical implications of QT lengthening and its relationship with autonomic nervous system regulation during OCWS.

Keywords: Body temperature; Cardiac function; Cold-water immersion; Echocardiography; QT interval lengthening; Water sports.