Electrophysiologic Substrate in Congenital Long QT Syndrome: Noninvasive Mapping with Electrocardiographic Imaging (ECGI)
Background—Congenital Long QT syndrome (LQTS) is an arrhythmogenic disorder that causes syncope and sudden death. While its genetic basis has become well-understood, the mechanisms whereby mutations translate to arrhythmia susceptibility in the in situ human heart have not been fully defined. We used noninvasive ECG imaging (ECGI) to map the cardiac electrophysiologic substrate and examine whether LQTS patients display regional heterogeneities in repolarization, a substrate which promotes arrhythmogenesis.
Methods and Results—25 subjects (9 LQT1, 9 LQT2, 5 LQT3 and 2 LQT5) with genotype and phenotype positive LQTS underwent ECGI. Seven normal subjects provided control. Epicardial maps of activation, recovery times (RT), Activation-recovery intervals (ARI) and repolarization dispersion were constructed. Activation was normal in all patients. However, RT and ARI were prolonged relative to control, indicating delayed repolarization and abnormally long APD (312 ± 30 ms vs. 235 ± 21 ms in control). ARI prolongation was spatially heterogeneous, with repolarization gradients much steeper than control (119 ± 19 ms/cm vs. 2.0 ± 2.0 ms/cm). There was variability in steepness and distribution of repolarization gradients between and within LQTS types. Repolarization gradients were steeper in symptomatic patients (130 ± 27 ms/cm in 12 symptomatic patients vs. 98 ± 19 ms/cm in 13 asymptomatic patients; P < 0.05).
Conclusions—LQTS patients display regions with steep repolarization dispersion caused by localized APD prolongation. This defines a substrate for reentrant arrhythmias, not detectable by surface ECG. Steeper dispersion in symptomatic patients suggests a possible role for ECGI in risk stratification.
- Received May 27, 2014.
- Revision received August 21, 2014.
- Accepted September 9, 2014.