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1 Medicine, University Health Network, Toronto, ON, Canada; Medicine, Mount Sinai Hospital, Toronto, ON, Canada
2 Medicine, University Health Network, Toronto, ON, Canada
* To whom correspondence should be addressed. E-mail: vijay.chauhan{at}uhn.on.ca.
Increased repolarization heterogeneity can provide the substrate for reentrant ventricular arrhythmias in animal models of cardiomyopathy. We hypothesized that ventricular repolarization heterogeneity is also greater in patients with cardiomyopathy and ventricular arrhythmia vulnerability (inducible ventricular tachycardia or positive microvolt T wave alternans, VT/TWA) when compared to a similar patient population without ventricular arrhythmia vulnerability (no VT/TWA). Endocardial and epicardial repolarization heterogeneity were measured in VT/TWA (n=12) and no VT/TWA (n=10) using transvenous 26-electrode catheters placed along the anteroseptal RV endocardium and LV epicardium. Local activation times (AT), activation recovery intervals (ARI), and repolarization times (RT) were measured from unipolar electrograms. Endocardial RT dispersion along the apicobasal ventricle was greater in VT/TWA than no VT/TWA (12±2 vs. 2.5±0.4ms/mm, p<0.005) due to greater ARI dispersion (12±2 vs. 2.9±0.4ms/mm, p<0.005). AT dispersion was similar between the two groups (1.3±0.3 vs. 0.7±0.3 ms/mm, p=NS). Epicardial RT dispersion along the apicobasal ventricle was greater in VT/TWA than no VT/TWA (10±2 vs. 2.6±0.4ms/mm, p<0.05) due to greater ARI dispersion (10±2 vs. 1.9±0.2ms/mm, p<0.05). AT dispersion was similar between the two groups (1.2±0.4 vs. 0.8±0.2 ms/mm, p=NS). A plot of AT as a function of ARI revealed an inverse linear relationship for no VT/TWA such that progressively later activation was associated with progressively shorter ARI. The AT-ARI relationship was nonlinear in VT/TWA. In conclusion, patients with cardiomyopathy and VT/TWA have greater endocardial and epicardial repolarization heterogeneity than those without VT/TWA without associated conduction slowing. The steep repolarization gradients in VT/TWA may provide the substrate for functional conduction block and reentrant ventricular arrhythmias.
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