Exercise clue to long QT syndrome prognosis

By Eleanor McDermid, Senior medwireNews Reporter

The size of reduction in heart rate immediately after exercise is associated with the presence of arrhythmias in patients with long QT syndrome (LQTS) type 1 (LQT1), report researchers.

Symptomatic patients had significantly larger reductions in the first minute after exercise than nonsymptomatic patients, indicating reduced vagal reflexes, show the findings in the Journal of the American College of Cardiology.

By putting LQTS patients through an exercise test, physicians can "know whether the patient is at high or low risk for life-threatening arrhythmias and will tailor therapy accordingly, more or less aggressively," say Peter Schwartz (University of Pavia, Italy) and team.

But in an accompanying commentary, Koonlawee Nademanee (Pacific Rim Electrophysiology Research Institute, Los Angeles, California, USA) says: "One has to recognize that the current guideline recommends that all LQT1 patients should be treated with β-blockers, so how is the information from exercise test going to alter one's treatment plan for LQT1 patient?"

He calls for more research "so that a clear-cut protocol, key parameters, and treatment plan can be developed as a guideline to general practitioners who care for LQT1 patients."

Nademanee also cautions that the study population was very select, so the results may not be widely applicable. The patients were drawn from a related South African LQT1 cohort with identical mutations (n=47) and from an Italian LQTS cohort (n=122; 66 with LQT1) that included a large proportion of patients at high risk for symptoms.

All patients undertook an exercise stress test on a bicycle ergometer, to a similar maximal heart rate and workload. During the first minute after ceasing exercise, South African LQT1 patients with symptoms had an average heart rate reduction of 19 beats per minute (bpm), compared with 13 bpm in those without symptoms. The reductions in Italian patients with and without symptoms were 27 versus 20 bpm, respectively. The differences between the symptomatic and symptom-free groups were statistically significant.

In the two groups combined, patients in the top tertile of heart rate reduction had a 3.3-fold increased odds for being symptomatic, while those in the bottom tertile had a 76% reduced odds. The association between heart rate reduction and symptoms existed whether patients exercised off or on beta blockers.

Patients with LQTS type 2 and 3 had similar heart rate reductions after exercise regardless of whether they had symptoms.

Schwartz et al say that LQT1 patients should avoid any regular and serious physical activity, and if they do participate in intense activity, "they should avoid stopping suddenly, and should instead decelerate slowly to prevent a vagal rebound."

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