Electrocardiography of cardiac resynchronization therapy: Pitfalls and practical tips

Abstract

Cardiac resynchronization therapy (CRT) has been established as an effective mode of therapy in patients with heart failure and concurrent cardiac dyssynchrony, principally in the form of left bundle branch block (LBBB). The widespread use of CRT has ushered in a new landscape in 12-lead electrocardiography (ECG). ECG readings in these patients are most important to guide troubleshooting and also appropriate device programming, as well as discerning and managing nonresponders. A set of four ECG recordings need to accompany each patient with a CRT device, including a baseline ECG and recordings from monochamber (right and left ventricular) and biventricular pacing, which can be compared against a new recording to facilitate the evaluation of proper versus problematic biventricular pacing. Precordial ECG leads V1/2 acquired at the fourth intercostal space and limb leads, I and III, together with a quick assessment of perpendicular leads I and aVF to determine the quadrant of the QRS axis in the hexaxial diagram, may provide the framework for proper ECG interpretation in these patients. This important issue of 12lead ECG in CRT patients is herein reviewed, pitfalls are pointed out and practical tips are provided for ECG reading to help recognize and manage problems with CRT device function. Furthermore, several pertinent ECG recordings and tabulated data are provided, and an algorithm is suggested that integrates prior algorithms and relevant information from current literature.

High-pass filter settings and the role and mechanism of discrete ventricular electrograms in left bundle branch pacing

“…The isoelectric interval is often observed between the pacing artifact and the paced discrete ventricular component. This phenomenon includes the true isoelectric interval (time required for immediate peri-electrode tissue excitation or a local response) and local conduction time (time required for propagated excitation to recruit sufficient local myocardial tissue to produce the ventricular EGM) ( 14 ). Typically, the isoelectric interval is short (<30 ms) ( 4 ).…”

“…Typically, the isoelectric interval is short (<30 ms) ( 4 ). An increased isoelectric interval may result from nonhomogeneous excitation propagation from the stimulation site and conduction delay in the His–Purkinje system ( 14 ). A previous study positioned a linear multielectrode catheter along the left ventricular septum to record intracardiac signals from the base to the apex to assess left ventricular activation sequences ( 15 ).…”

High-pass filter settings and possible mechanism of discrete electrograms in left bundle branch pacing

“…This phenomenon includes the true isoelectric interval (time required for immediate peri-electrode tissue excitation or a local response) and local conduction time (time required for propagated excitation to recruit sufficient local myocardial tissue to produce the ventricular EGM). [12] Typically, the isoelectric interval is short (<30 ms). [5] An increased isoelectric interval may result from nonhomogeneous excitation propagation from the stimulation site and conduction delay in the His-Purkinje system.…”

“…The copyright holder for this preprint this version posted September 2, 2022. ; https://doi.org/10.1101/2022.09.01.22279483 doi: medRxiv preprint from nonhomogeneous excitation propagation from the stimulation site and conduction delay in the His-Purkinje system. [12] A previous study positioned a linear multielectrode catheter along the left ventricular septum to record intracardiac signals from the base to the apex to assess left ventricular activation sequences. [13] According to the "V"-shaped conduction pattern observed in this study, the mechanism underlying the formation of the isoelectric interval may be associated with the propagation of impulse or pacing stimulus through the conduction system, reaching the distal part of the His-Purkinje system to excite the apical myocardium, and subsequent propagation to the basal myocardium in the interventricular septum by the electrode sensing (Figure 2).…”