69-year-old man implanted with a Medtronic dual-chamber pacemaker following repeated syncopes due to sinus node dysfunction; the 2 pacing leads are well positioned with normal pacing impedances, correct sensing and satisfactory pacing thresholds; 3 days after implantation, pacemaker evaluation; programming of various pacing modes and recording of tracings; for this first tracing, device programmed to DDD mode 70 bpm.
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DDD mode
ECG 4A: Atrial unipolar pacing (high-amplitude stimulus) and ventricular unipolar pacing after a fixed atrioventricular delay;
ECG 4B: Repeated AP-VP cycles (atrial and ventricular pacing) at 70 bpm;
Comments: The DDD mode is the standard programming mode of dual-chamber pacemakers or resynchronization devices. It ensures atrioventricular synchronization at rest as well as during exercise during sensed or paced atrial activity. The basic principle of DDD mode is to synchronize ventricular pacing on atrial sensing or pacing (triggered operation). Spontaneous atrial or ventricular activity sensed outside the refractory period respectively inhibits atrial or ventricular pacing (inhibited function). This mode hence allows the preservation of atrioventricular synchrony for low sinus rates up to the highest rate limit (maximal tracking rate). Each sensed atrial event outside the refractory period between the lower rate and the synchronous upper rate or atrial pacing initiates an AV delay with ventricular pacing in the absence of spontaneous ventricular sensing. AV delays that follow sensed and paced atrial events are independently programmable; a shortening of the AV delays can be programmed when the rates increase (rate-adaptive AV delay) or can be modified according to the spontaneous conduction intervals. In DDDR mode, the pacemaker follows the fastest rate, whether spontaneous or sensor-driven. The synchronous upper rate and the maximum response rate are independently programmable.
The programming of the DDD mode thus appears satisfactory in this patient. However, follow-up would probably reveal a ventricular pacing percentage close to 100%. This would thus correspond to a functioning deemed normal and appropriate. However, ODO analysis revealed that this patient has a preserved AV conduction. One of the priorities of programming a pacemaker is to avoid unnecessary right ventricular pacing. This reduces battery consumption and prolongs the life of the device and, above all, avoids right ventricular pacing that is associated with short, medium and long-term adverse effects on hemodynamics, ventricular remodeling and the occurrence of atrial arrhythmias. Indeed, right ventricular pacing induces an asynchronous interventricular and intraventricular activation and relaxation sequence. A high percentage of ventricular pacing in a patient with preserved AV conduction should question the physician at the time of the pacemaker interrogation and discuss the use of specific algorithms favoring spontaneous conduction.
Take-home message: DDD mode is designed to respond to the characteristics presented by all implanted patients as a whole but may be associated with a high percentage of deleterious ventricular pacing in patients with preserved atrioventricular conduction.
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Regarding this ECG, which answer(s) is(are) true?
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