Holter monitoring in the evaluation of congenital long QT syndrome

Background: Long QT syndrome (LQTS) is a potentially lethal cardiac channelopathy that affects one in 2,000 persons; causes syncope, seizures, and sudden death; and is both under- and overdiagnosed. LQTS diagnostic miscues have stemmed from assessment of ambulatory electrocardiographic monitoring (Holter) results. Objective: We sought to determine the prevalence of positive Holter monitor tests and its diagnostic significance in evaluating LQTS. Methods: We performed an institutional review board-approved review of patients evaluated in our LQTS clinic from 2000 to 2009 who had Holter testing during their evaluation. Included patients (N = 473) were diagnosed with LQTS or dismissed as otherwise normal. Holters classified as positive had an episode of nonsustained ventricular tachycardia, supraventricular tachycardia, ≥4 couplets/day, ≥10 premature ventricular contractions/hour, or >5-second sinus pause. Results: Among 209 patients dismissed as normal (128 females, average age 21 ± 15 years, average QTc 424 ± 39 ms), 27 (12.9%) had a positive Holter, while among 264 patients with LQTS (149 females, average age 22 ± 16 years, average QTc 472 ± 41 ms), 30 (11.3%) had a positive Holter (P = NS). Patients with LQT3 (5/23, 21%) and genotype-negative LQTS (5/19, 26%) had a higher rate of positive Holter testing compared to LQT1 patients (7/124, 6%, P < 0.03). Among the 473 Holters, only one (0.2%) impacted clinical decision making. Conclusion: Routine Holter monitoring appears to be of minimal clinical utility from a diagnostic and prognostic perspective in evaluating LQTS, and may not be cost effective. Whether Holter monitoring aids in therapeutic decisions such as dosing or whether ambulatory QTc measurements, provided by some newer devices, might help in the diagnostic evaluation warrants further scrutiny.