Unusual cause of desynchronization in a cardiac resynchronization device.

This report describes a new cause of desynchronization encountered in a cardiac resynchronization device functioning in the VVIR mode. Left ventricular stimulation was inhibited when the sensor-driven rate exceeded the programmed left ventricular (LV) maximum trigger rate. With these devices, it is important to program the LV maximum trigger interval (essentially equivalent to a LV upper interval) to a value equal or faster than the sensor-driven upper rate.

Pacemaker repetitive nonreentrant ventriculoatrial synchrony. Why did automatic mode switching occur?

Repetitive nonreentrant ventriculoatrial synchrony during dual-chamber pacing is characterized by long intervals alternating with short intervals. This arrangement activated automatic mode switching in a St Jude dual-chamber pacemaker in which the algorithm requires an atrial sensed event for automatic mode switching initiation. Automatic mode switching activation by an atrial sensed event (retrograde P wave) was puzzling because the programmed postventricular atrial period was longer than the retrograde ventriculoatrial conduction time.

P-wave locking in the postventricular atrial refractory period of cardiac resynchronization devices. Management with the Biotronik system.

Electrical desynchronization in cardiac resynchronization therapy (CRT) occurs when sinus P waves are continually locked in the postventricular atrial refractory period (PVARP). This process is characterized by sequences of a P wave as an atrial event in the PVARP followed by a conducted and sensed ventricular event. Such sequences are more common in patients with a prolonged PR interval, often initiated by premature ventricular complexes (PVC) and terminated by PVCs or slowing of the sinus rate.

Conventional and biventricular pacing in patients with first-degree atrioventricular block.

Recent reports suggest that first-degree atrioventricular block is not benign. However, there is no evidence that shortening of the PR interval can improve outcome except for symptomatic patients with a very long PR interval ≥0.3 s.

Sensing of 2 atrial rhythms by a pacemaker in a transplanted heart.

A patient who had undergone orthotopic heart transplantation received a VDD pacemaker for AV block. The pacemaker sensed both the recipient and donor atrial rhythms. The atrial lead must be implanted in the donor atrium: a double atrial electrogram requires a different atrial site unless programmable atrial sensitivity can establish preferential sensing of donor P waves.

Paradoxical atrial undersensing by a dual chamber pacemaker during atrial fibrillation.

This report describes paradoxical atrial undersensing by a dual chamber pacemaker in a patient with paroxysmal atrial fibrillation. Atrial undersensing was present only when the device was programmed to a high sensitivity but sensing normalized when a lower sensitivity was programmed. This unusual response should be differentiated from the recently documented lock-in behavior of pacemakers delivering managed ventricular pacing.

Using devices with a variable postventricular atrial refractory period for cardiac resynchronization.

Automatic postventricular atrial refractory period (Auto-PVARP) is a dynamic interval designed to provide a longer PVARP at slower rates to enhance protection against pacemaker tachycardia (PMT) and a shorter PVARP to enhance atrial sensing at high rates. Auto-PVARP is often programmed in Medtronic devices for cardiac resynchronization therapy (CRT) with little knowledge of its intricate manifestations and disadvantages. The use of Auto-PVARP is contradictory to the universal teaching that CRT devices should be programmed with a short PVARP.

Significance of missing telemetered markers in implanted cardioverter-defibrillators.

Background: We report three patients with St Jude ICDs (St. Jude Medical, Sylmar, CA, USA) where some aspect of the marker channel was missing.

Methods And Results: Two cases were caused by the simultaneous occurrence of two distinct cardiac or device events that affected the proper delivery of markers by the telemetry system.

Atrial lead malfunction presenting as new onset pacemaker-mediated tachycardia.

This report describes the de novo occurrence of pacemaker-mediated tachycardia (PMT) in a patient with a dual-chamber implantable cardioverter-defibrillator and stable retrograde ventriculoatrial conduction time. The same rate-adaptive post-ventricular atrial refractory period (PVARP) duration had previously prevented PMT. Oversensing of atrial false signals from a defective lead shortened the PVARP with consequent sensing of retrograde conduction.

Pacemaker-mediated tachycardia initiated by an atrioventricular search algorithm to minimize right ventricular pacing.

We report the initiation of pacemaker-mediated tachycardia by a St Jude implantable cardioverter-defibrillator with a programmed Ventricular Intrinsic Preference algorithm used for minimizing or inhibiting right ventricular pacing. This feature prolongs the atrioventricular (AV) delay periodically to determine if ventricular sensed events follow atrial events. Retrograde ventriculoatrial conduction and pacemaker-mediated tachycardia were initiated by long extended AV delays of 300 and 400 milliseconds.

Reappraisal of the traditional Wenckebach phenomenon with a modified ladder diagram.

Understanding of the traditional Wenckebach phenomenon is enhanced by using a modified ladder diagram where AV conduction in any cycle is represented by a slanted line in the AV bar together with similar AV conduction lines of all the preceding cycles. The diagram facilitates calculation of the duration of RR intervals (equal to the basic PP or sinus interval minus the PR or AV increment applied to this particular cycle) and the duration of the pause (equal to 2 × PP or sinus interval minus the sum of all the increments applied to the AV delay). The modified Wenckebach diagram should help students understand the mysterious clustering of QRS complexes or "paradoxical" increase of the ventricular rate that occurs during a Wenckebach sequence.

Escape-echo bigeminy.

Escape-capture bigeminy is a well-known arrhythmia characterized by group beating of a junctional beat followed by a conducted sinus beat. We report a variant of this arrangement where a junctional beat gives rise to a retrograde P wave, which is then conducted back to the ventricles producing a hitherto undescribed combination (escape-echo bigeminy) resembling escape-capture bigeminy. The clinical significance of escape-echo bigeminy appears similar to that of classic escape-capture bigeminy.

Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part II.

The interval from the pacemaker stimulus to the onset of the earliest paced QRS complex (latency) may be prolonged during left ventricular (LV) pacing. Marked latency is more common with LV than right ventricular (RV) pacing because of indirect stimulation through a coronary vein and higher incidence of LV pathology including scars. During simultaneous biventricular (BiV) pacing a prolonged latency interval may give rise to an ECG dominated by the pattern of RV pacing with a left bundle branch block configuration and commonly a QS complex in lead V1.

Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part I.

Cardiac resynchronization therapy (CRT) has added a new dimension to the electrocardiographic evaluation of pacemaker function. During left ventricular (LV) pacing from the posterior or posterolateral coronary vein, a correctly positioned lead V1 registers a tall R wave and there is right axis deviation in the frontal plane with few exceptions. During simultaneous biventricular stimulation from the right ventricular (RV) apex and LV site in the coronary venous system, the QRS complex is often positive (dominant) in lead V1 and the frontal plane QRS axis usually points to the right superior quadrant and occasionally the left superior quadrant.

Ablation of left ventricular tachycardia via transeptal approach and crossing of a mechanical mitral valve prosthesis.

This report describes the clinical course of a patient with left ventricular assist device (LVAD) and refractory ventricular tachycardia (VT) who underwent successful left ventricular (LV) mapping and ablation complicated by the presence of a bioprosthetic aortic and a mechanical mitral valve. LV catheterization was achieved by crossing the mechanical valve. The patient remained hemodynamically stable during the procedure most likely as a result of LVAD support.

Abolition of diaphragmatic pacing by nonsurgical retraction of a left ventricular lead.

This report describes the nonsurgical elimination of intractable diaphragmatic stimulation by partial withdrawal of a left ventricular (LV) pacing lead (in the coronary venous system) with resultant preservation of LV pacing. The procedure entailed the use of a deflectable catheter in the right atrium for ensnaring the LV lead. At the 3-month follow-up, the absence of diaphragmatic stimulation was associated with a satisfactory LV pacing threshold and dramatic clinical improvement from effectual biventricular pacing.