1. The game of squash has recently been associated with a high incidence of ventricular arrhythmias and sudden death. To investigate this further, plasma catecholamines and potassium (K+) were monitored during a game of squash in six normal volunteers.
2. No cardiac arrhythmias were seen in this study despite the subjects reaching maximum heart rates of 181 ± 5 beats/min (mean ± sem).
3. During exercise, plasma K+ rose from 3.82 ± 0.16 to 4.29 ± 0.2 mmol/l, but after 90 s rest this fell to 3.68 ± 0.28 mmol/l and after 180 s to 3.44 ± 0.17 mmol/l. This rapid K+ shift could not be accounted for by generalized changes in venous acid-base status or by changes in venous plasma catecholamines. Although pre-treatment with a β2-antagonist caused the overall plasma K+ levels to be higher, it had no significant effect on the fall in plasma K+ after exercise.
4. Such rapid K+ shifts after exercise might contribute to arrhythmogenesis in susceptible individuals. The precise mechanism of the fall in K+ after exercise remains undetermined, but it seems not to involve catecholamines stimulating β2-adrenoceptors and is more likely to be due to increased skeletal muscle blood flow and/or intracellular acidosis.