![]() This patient had intermittent 3:2 AV Wenckebach at other times, and then resumed 1:1 conduction on subsequent ECGs, consistent with AV node disease ![]() Intracardiac His bundle electrogram would definitively identify the site of block. Pacemaker placement is indicated for symptomatic 2:1 block without reversible cause (e.g., drug effect) and generally for asymptomatic 2:1 block due to infranodal disease. A resumption of 1:1 conduction favors AV node block while worsening of block strongly favors infranodal disease. A possibly useful bedside diagnostic test for chronic 2:1 block (in the absence of active ischemia) would be to increase the sinus rate (mild exercise). Block (infranodal) in the His-Purkinje system would be favored by a concomitant bundle branch block and/or with a PR interval of 160 ms or less. In general, with 2:1 block, involvement of the AV node is favored by a narrow QRS complex and a prolonged PR interval, or by the presence of intermittent AV Wenckebach. The site of block could be proximal (in the AV node) or more distal, in the His-Purkinje system. There is no evidence of acute inferior ischemia, either. infranodal) from this single ECG with 2:1 conduction. It is not possible to reliably identify the point of block (nodal vs. The ECG shows a bradyarrhythmia with non-conducted sinus P waves alternating with normally conducted P waves. The QRS area and T area and some of the QRS and T area have been shown to be strong predictors of volumetric response and survival after CRT, but they are not commercially available for clinical practice. The area under the three-dimensional QRS complex and three-dimensional T-wave reflect unopposed electrical forces during ventricular depolarization and repolarization, respectively. Vectorcardiography is a method for recording three-dimensional information about the direction of the electrical forces.Time to peak dyssynchrony measures on echo are not specific to the electrical substrate responsive to CRT, and therefore, they are unlikely to be effective for selecting patients that may benefit from CRT. Strain-based speckle tracking echocardiography–derived dyssynchrony (systolic stretch index) and the visual assessment of dyssynchrony (septal flash and apical rocking) are potential emerging echocardiographic parameters for CRT consideration. ![]()
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