El Assaad I; Division of Cardiology & Cardiovascular Medicine, Cleveland, Ohio, USA.
Heilbronner AK; Zahka K; Hammond B; Patel A; Aziz PF

Journal of Cardiovascular Electrophysiology. 36(9):2287-2295, 2025 Sep. VI 1

OBJECTIVE: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.