PubMed · 5800307
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T F Sanders. 1969. Left bundle branch block benign?. https://pubmed.ncbi.nlm.nih.gov/5800307/
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BACKGROUND: Analysis of the surface ECG can predict the locations of pacing foci but is of limited value for locating arrhythmogenic substrates causing ventricular tachycardia because of the effects of myocardial infarction, ischaemia, and bundle branch block on ventricular activation. AIM: To determine whether analysis of the initial 60 ms segment of the surface QRS improves the accuracy of the ECG for predicting ventricular tachycardia origin we correlated the locations of 37 arrhythmogenic areas present in 20 patients with the 3D vectors of the ventricular tachycardias generated by each respective area. METHODS: The 3D vector of each ventricular tachycardia morphology was calculated from the integrals of the initial 60 ms of the surface vectorcardiogram and from the entire QRS recorded in each lead of the Frank orthogonal lead vectorcardiogram. Sixty eight-morphologies of ventricular tachycardia were mapped using simultaneous recordings from 60 catheter electrodes. RESULTS: Ventricular tachycardias with 3D vectors directed inferiorly and posteriorly or superiorly and anteriorly were more likely to originate from the septum, P = 0.04, whereas tachycardias directed superiorly and to the right were more likely to originate from the inferior wall and the cardiac apex, P = 0.001. However, the same arrhythmogenic area could generate multiple ventricular tachycardias with different 3D vectors. In addition, ventricular tachycardias with similar 3D vectors were generated by arrhythmogenic areas in the septal, apical and inferior walls. The variances of the mean 3D vectors of ventricular tachycardias originating from each of 12 different cardiac regions were no different when based on the initial 60 ms of the surface QRS than on the entire surface QRS. CONCLUSION: Analysis of the surface ECG provides only an approximate guide to the locations of arrhythmogenic areas generating ventricular tachycardia even when analysis is restricted to the initial forces in the surface QRS. Therefore, detailed mapping is needed to accurately determine the number and location of arrhythmogenic areas.
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A 52-year-old female with no structural heart disease presented with a right bundle branch block (RBBB)/right axis deviation tachycardia with a cycle length of 300 msec. P waves were not discernible on the surface ECG. Baseline electrophysiology study in the drug-free state revealed no evidence for anterograde or retrograde conducting accessory pathways (APs) or for dual AV node physiology. Retrograde VA block with AV dissociation was present at a ventricular paced cycle length of 600 msec (sinus cycle length of 635-700 msec). AV nodal Wenckebach occurred during decremental atrial pacing at a cycle length of 300 msec. During isoproterenol administration, a left lateral AP with retrograde only conduction became manifest with 1:1 VA conduction to 380 msec. No anterograde AP conduction was present. Orthodromic reciprocating tachycardia with a cycle length of 285-315 msec was easily induced. We conclude that total functional conduction block can exist in APs, and unmasking of total conduction block can be accomplished with isoproterenol. All patients with undiagnosed tachycardias should have full repeat stimulation studies during adrenergic stimulation if the initial baseline evaluation is nondiagnostic.