ECG Identification of Scar-Related Ventricular Tachycardia With a Left Bundle Branch Block Configuration
What electrocardiographic findings distinguish idiopathic from scar-related ventricular arrhythmias (VAs) with a left bundle branch block (LBBB) morphology?
The electrocardiograms (ECGs) of 81 patients (mean age 53 years) with 118 LBBB VAs were analyzed retrospectively to develop an algorithm for distinguishing idiopathic from scar-related VAs. The algorithm was validated prospectively in 132 patients (mean age 53 years) with 179 LBBB VAs. Myocardial scar was identified by pathological Q waves, wall motion abnormalities, delayed enhancement on magnetic resonance imaging, or voltage mapping. Twenty-three VAs in the retrospective group and 59 VAs in the validation group were not scar-related.
In the retrospective analysis, the independent predictors of scar-related LBBB VA were precordial transition after V4, notched S-wave downstroke in V1-V2, and an interval >90 ms in V1 between the QRS and nadir of the S-wave. In the validation group, the presence of any of these criteria indicated scar-related VA, and their absence indicated idiopathic VAs. This algorithm had a sensitivity of 96% and a specificity of 83% for identifying scar-related LBBB VA.
The authors concluded that the ECG pattern during an LBBB VA is helpful in identifying VAs that are scar-related.
Sometimes patients with structural heart diseases such as cardiac sarcoidosis present with an LBBB-pattern ventricular tachycardia (VT) and little or no overt clinical evidence of heart disease. These patients can be mistakenly diagnosed as having idiopathic VT. The ECG findings described in this study will be helpful in avoiding this type of misdiagnosis.
Keywords: Sarcoidosis, Tachycardia, Ventricular, Heart Conduction System, Bundle-Branch Block, Electrocardiography, Magnetic Resonance Imaging
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