Pacemaker crosstalk in a dual-chamber pacemaker refers to the detection of a paced signal in one chamber by the lead in another chamber, and to the misrepresentation of the paced signal as a cardiac depolarization signal. Ventricular safety pacing (SP) prevents ventricular asystole due to crosstalk. The following paragraphs cover some of the typical clinical situations presenting as pseudomalfunctions. Rate changes in the presence of normal pacemaker function can occur because of magnet operation, timing variations (A-A vs V-V), upper-rate behavior (Wenckebach or 2:1 block), pacemaker-mediated tachycardia (PMT), or rate response. Most common are the rate-related pseudomalfunctions. Pseudomalfunctions are classified under 3 categories: 1) rate-related, 2) atrioventricular (AV) interval/refractory period-related, and 3) model-related. Pseudomalfunctions are unusual and unexpected ECG findings that appear to be pacemaker malfunctions but actually are normal pacemaker behavior. Some resemble intrinsic QRS and represent pseudofusion, whereas others show a morphology between intrinsic beats and paced beats and thereby represent true fusion between conducted impulses and paced beats.Pseudomalfunction The patient is being treated with cardiac resynchronization therapy, and the tracing shows QRS complexes of various morphologies and durations. Intracardiac atrial and right ventricular (RV) electrograms (EGMs), along with a surface electrocardiogram (ECG), in a patient with atrial fibrillation and congestive heart failure. The main causes of undersensing are pacemaker programming problems (improper sensing threshold), insufficient myocardial voltage signal, lead or pacer failure (fibrosis, fracture, etc.), or an electrolyte abnormality. This typically results in the appearance of too many pacing spikes, as seen on ECG ( Fig. Atrial or ventricular pacing spikes arise regardless of P waves or QRS complex. Undersensing occurs when the pacemaker fails to detect spontaneous myocardial depolarization, which results in asynchronous pacing.
Multiple factors-including antiarrhythmic drug use, physical activity level, posture, time of day, and comorbidity-could all affect the pacing threshold. The pacing threshold is the minimum required energy that consistently triggers a depolarization of the paced chamber. Pacing spikes are visible at a rate of 65 beats/min and are marching through without capture, even though the ventricular myocardium is not expected to be refractory at those times.What Affects the Pacing Threshold? Surface electrocardiogram from a patient with a single-chamber pacemaker shows sinus rhythm with first-degree atrioventricular block.
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