Plasma potassium concentration and cardiac repolarisation markers, T-T and T-T/QT, during and after exercise in healthy participants and in end-stage renal disease.

Purpose: The cardiac T-wave peak-to-end interval (T) is thought to reflect dispersion in ventricular repolarisation, with abnormalities in T associated with increased risk of arrhythmia. Extracellular K modulates cardiac repolarisation, and since arterial plasma K concentration ([K]) rapidly increases during and declines following exercise, we investigated the relationship between [K] and T with exercise.

Methods: Serial ECGs (T, T/QT ratio) and [K] were obtained from 8 healthy, normokalaemic volunteers and 22 patients with end-stage renal disease (ESRD), at rest, during, and after exhaustive exercise.

Results: Post-exercise [K] nadir was 3.1 ± 0.1, 5.0 ± 0.2 and 4.0 ± 0.1 mmol.L (mean ± SEM) for healthy participants and ESRD patients before and after haemodialysis, respectively. In healthy participants, compared to pre-exercise, recovery-induced low [K] was associated with a prolongation of T (110 ± 8 vs. 87 ± 5 ms, respectively, p = 0.03) and an increase in T/QT ratio (0.28 ± 0.01 vs. 0.23 ± 0.01, respectively, p = 0.01). Analyses of serial data revealed [K] as a predictor of T in healthy participants (β = -0.54 ±0.05, p < 0.0001), in ESRD patients (β = -0.75 ± 0.06, p < 0.0001) and for all data pooled (β = -0.61 ± 0.04, p < 0.0001). The [K] was also a predictor of T/QT ratio in healthy participants and ESRD patients.

Conclusions: T and T/QT ratio are predicted by [K] during exercise. Low [K] during recovery from exercise was associated with increased T and T/QT, indicating accentuated dispersion of ventricular repolarisation. The findings suggest that variations in [K] with physical exertion may unmask electrophysiological vulnerabilities to arrhythmia.