OBJECTIVES: Our aim was to determine whether myocardial fibrosis, detected by 
cardiovascular magnetic resonance (CMR), represents an arrhythmogenic substrate 
in hypertrophic cardiomyopathy (HCM).
BACKGROUND: Myocardial fibrosis is identified frequently in HCM; however, the 
clinical significance of this finding is uncertain.
METHODS: We studied prevalence and frequency of tachyarrhythmias on 24-h 
ambulatory Holter electrocardiogram (ECG) with regard to delayed enhancement 
(DE) on contrast-enhanced CMR in 177 HCM patients (age 41 +/- 16 yrs; 95% 
asymptomatic or mildly symptomatic).
RESULTS: Premature ventricular contractions (PVCs), couplets, and nonsustained 
ventricular tachycardia (NSVT) were more common in patients with DE than those 
without DE (PVCs: 89% vs. 72%; couplets: 40% vs. 17%; NSVT: 28% vs. 4%; p < 
0.0001 to 0.007). Patients with DE also had greater numbers of PVCs (202 +/- 655 
vs. 116 +/- 435), couplets (1.9 +/- 5 vs. 1.2 +/- 10), and NSVT runs (0.4 +/- 
0.8 vs. 0.06 +/- 0.4) than non-DE patients (all p < 0.0001); DE was an 
independent predictor of NSVT (relative risk 7.3, 95% confidence interval 2.6 to 
20.4; p < 0.0001). However, extent (%) of DE was similar in patients with and 
without PVCs (8.2% vs. 9.1%; p = 0.93), couplets (8.5% vs. 8.4%; p = 0.99), or 
NSVT (8.3% vs. 8.5%; p = 0.35).
CONCLUSIONS: In this large HCM cohort with no or only mild symptoms, myocardial 
fibrosis detected by CMR was associated with greater likelihood and increased 
frequency of ventricular tachyarrhythmias (including NSVT) on ambulatory Holter 
ECG. Therefore, contrast-enhanced CMR identifies HCM patients with increased 
susceptibility to ventricular tachyarrhythmias.