Utility of Cardiopulmonary Exercise Testing in Assessing Beta-Blocker Efficacy in LQTS: Moving Away From...

Currently, there is no specific standard to assess beta blocker efficacy in long QT syndrome (LQTS).

To describe our institutional experience with utilizing cardiopulmonary exercise testing (CPET) to assess for chronotropic suppression and to compare frequency of life-threatening events (LTEs) on intentional "submaximal" treatment to those on maximal treatment.

We queried our Inherited Arrhythmia Registry and identified patients with LQTS who were on "submaximal" beta blocker doses (nadolol < 0.75-mg/kg/day & propranolol < 2 mg/kg/day) with at least 6 months follow up. Adequate beta blockade effect was defined as at least 15% decrease from maximal HR.

The study included 127 LQTS patients: 47% on maximal therapy, 43% on submaximal therapy, and 10% not receiving treatment. Thirty three percent of patients were on submaximal therapy due to side effects, none in patients less than 10 years of age. Baseline characteristics were similar between the groups. There was no significant difference in LTEs between maximal and submaximal therapy (8% vs. 5.4%, p = 0.72). During CPET, patients on maximal therapy were more likely to exhibit adequate chronotropic suppression (60% vs. 40%, p = 0.01). None of the patients on submaximal therapy with adequate chronotropic effect experienced LTEs during follow-up.

Adequate chronotropic suppression was achieved with "submaximal" beta blocker dose in 40%. Despite similar baseline risk profiles, LTEs were not significantly different in patients with submaximal versus maximal therapy. CPET may be a useful modality to devise an individualized treatment plan, especially in those who cannot tolerate the recommended guideline directed dose.