![]() The current case, which we have described as “escape-noncapture bigeminy,” is an apparent bigeminal rhythm based on essentially the same mechanism as typical escape-capture bigeminy. J = junctional focus JCL = junctional cycle length S = sinus node SCL = sinus cycle length. The slower mechanism (the slow sinus rate) resets the faster mechanism (the junctional focus) because the junctional focus does not conduct retrograde to the sinus node. Ladder diagram drawing, illustrating the mechanism of common escape-capture bigeminy due to sinus node dysfunction and junctional escape focus without retrograde conduction. The sinus node, while having a slower intrinsic rate, always resets the junction. This is a persistent and stable rhythm because, while the junction has a faster intrinsic rate, it never resets the sinus node owing to lack of VA conduction from the junctional focus. One observes a bigeminal rhythm in which there are alternating long and short R-R intervals, the shorter R-R interval containing a sinus P wave ( Figure 2). 2 This is most commonly seen in patients with sinus node dysfunction and a junctional escape rhythm in which the junctional escape rate is faster than the underlying sinus rate. The third and most interesting mechanism is a so-called escape-capture bigeminy. The second beat will occasionally be aberrated owing to the Ashman phenomenon, and this can be misconstrued as ventricular bigeminy. For example, with 3:2 Wenckebach conduction through the atrioventricular node, one gets a bigeminal rhythm because the 2 conducted beats are followed by a pause owing to every third atrial beat being blocked. The second category is bigeminy due to 3:2 conduction. Atrial bigeminy can also manifest as blocked atrial bigeminy. 1 First, and most commonly, bigeminal rhythms are a result of premature ectopic beats, which can arise from the ventricle but may also arise from the atrium or the atrioventricular node, and produce ventricular bigeminy, atrial bigeminy, or junctional bigeminy, respectively. They are common and can occur owing to 3 principal broad mechanisms. Once it became apparent that there was a complete fracture, the fixed interval of noncapturing pacemaker spikes in relation to the underlying rhythm was initially mysterious.īigeminal rhythms are simply rhythms in which heartbeats occur persistently in groups of 2. ![]() In addition, the measured lead impedance of 2904 ohms was not typical for complete lead fracture. This case is interesting because on presentation, pacemaker failure was obvious but the presenting ECG suggested not fracture, but exit block because the device was clearly continuing to sense the underlying rhythm. A preprocedure transthoracic echocardiogram showed a structurally normal heart with normal ventricular function. A chest radiograph demonstrated probable lead fracture. Pacing continued with pacemaker spikes occurring at a fixed interval following each native QRS. The lead impedance was 2904 ohms, but the device failed to capture at maximum output. Upon interrogation of her device, the pacemaker was at the elective replacement indicator and the mode had been automatically reset from VVIR at a lower rate limit of 75 to VVI at a rate of 65. Her initial electrocardiogram (ECG) showed complete heart block with a junctional or ventricular escape rhythm of 45 beats per minute (bpm) with noncapturing ventricular pacing stimulus artifacts ( Figure 1). Owing to our concerns for possible lead failure, we brought the patient in for evaluation and interrogation of her device. The device was not interrogated at that time. ![]() The patient had largely been asymptomatic aside from a 1-time complaint of shortness of breath with exertion, for which she was evaluated in a local emergency room. There had been a sudden rise in lead impedance from an average lead impedance of 303 to 1891 ohms 2 months previously, and the current transmission reported an impedance of 3827 ohms. She was followed but moved out of state for several years, and on moving back to our area, her first CareLink transmission noted a ventricular lead programmed output 5.00 V at 1.00 ms in unipolar mode, with the generator at the recommended replacement time. ![]() She underwent 2 generator changes with retention of the original lead, the last 5 years prior (Medtronic Adapta ADSR01). A 12-year-old girl with a history of congenital complete atrioventricular block had implantation of a single-chamber epicardial pacemaker in infancy using a unipolar lead (Medtronic 4965-25).
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