title: Prevalence and clinical correlates of QT prolongation in patients with hypertrophic cardiomyopathy.
abstract: OBJECTIVE
  Congenital or acquired QT prolongation is a risk factor for life-threatening arrhythmias. In patients with hypertrophic cardiomyopathy (HCM), the QT interval may be intrinsically prolonged. However, the prevalence, cause, and significance of QT prolongation among patients with HCM are unknown.
  
  
  RESULTS
  After exclusion of patients on QT-prolonging drugs, a blinded, retrospective analysis of electrocardiograms, echocardiograms, and genotype status in 479 unrelated patients with HCM [201 females, age at diagnosis 41 ± 18 years, maximal left ventricular wall thickness (MLVWT) 22 ± 6 mm] from two independent centres was performed. The mean QTc was 440 ± 28 ms. The QTc exceeded 480 ms in 13% of patients. Age, gender, family history of HCM or sudden cardiac arrest, and genotype status had no association with QTc. Patients with a QTc over 480 ms were more symptomatic at diagnosis (P < 0.001), had a higher MLVWT (P = 0.03), were more obstructive (P < 0.001), and were more likely to have undergone septal reduction therapy (P = 0.02). There was a weak but significant direct linear relationship between QTc and peak outflow gradient (r(2) = 0.05, P < 0.0001).
  
  
  CONCLUSIONS
  Compared with <1 in 200 otherwise healthy adults, QT prolongation (QTc > 480 ms) was present in 1 out of 8 patients with HCM. The QTc was partly reflective of the degree of cardiac hypertrophy and left ventricular outflow tract obstruction. Because of its pro-arrhythmic potential and its potential relevance to management and risk stratification, routine QTc assessment should be performed in patients with HCM, particularly when concomitant use of QT-prolonging medications is considered.
authors.affiliation: Department of Pediatrics/Division of Pediatric Cardiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Johnson
authors.forename: Camilla
authors.initials: C
authors.lastname: Grifoni
authors.forename: J Martijn
authors.initials: JM
authors.lastname: Bos
authors.forename: Maha
authors.initials: M
authors.lastname: Saber-Ayad
authors.forename: Steve R
authors.initials: SR
authors.lastname: Ommen
authors.forename: Stefano
authors.initials: S
authors.lastname: Nistri
authors.forename: Franco
authors.initials: F
authors.lastname: Cecchi
authors.forename: Iacopo
authors.initials: I
authors.lastname: Olivotto
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
mesh_terms: D000328:Adult; D002312:Cardiomyopathy, Hypertrophic / Q000150:complications* / Q000628:therapy; D016757:Death, Sudden, Cardiac / Q000209:etiology; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation; D005260:Female; D005838:Genotype; D006801:Humans; D008133:Long QT Syndrome / Q000209:etiology* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D014694:Ventricular Outflow Obstruction / Q000209:etiology; D055815:Young Adult