A 68-year-old man with symptomatic sinus node dysfunction and intact AV conduction undergoes permanent pacemaker implantation. The ECG shows atrial pacing spikes followed by intrinsic AV conduction, with maintained **D** (AV synchrony in DDD mode). Which of the following is the PRIMARY advantage of this pacemaker mode over VVI pacing in this patient?

Explanation

## Why Preservation of atrial contribution to ventricular filling and prevention of pacemaker syndrome is right DDD mode (dual-chamber pacing and sensing with mode switch) maintains AV synchrony by allowing atrial contraction to precede ventricular pacing, preserving the atrial "kick" that contributes 15–20% to ventricular filling. This is the defining advantage over VVI (single-chamber ventricular pacing), which loses AV synchrony and can cause "pacemaker syndrome"—a constellation of symptoms including reduced cardiac output, dyspnea, fatigue, and syncope due to loss of coordinated atrial-ventricular contraction. In patients with sinus node dysfunction and intact AV conduction (as in this case), DDD is the preferred mode per ACC/AHA guidelines because it restores normal hemodynamics and symptom relief. (Harrison 21e Ch 247; ACC/AHA Pacemaker Guidelines) ## Why each distractor is wrong - **Reduced risk of lead dislodgement from the right atrium**: Lead dislodgement is a mechanical complication related to implantation technique and lead design, not the pacing mode itself. Both DDD and VVI can experience dislodgement; DDD actually requires an additional atrial lead, which theoretically increases dislodgement risk. - **Elimination of the need for rate-responsive programming in chronotropic incompetence**: DDD mode does not inherently provide rate responsiveness; if the patient has chronotropic incompetence (inability to increase heart rate with activity), a rate-responsive suffix (DDDR) would be needed. VVI can also be rate-responsive (VVIR). The mode choice does not eliminate the need for rate-response assessment. - **Decreased incidence of tricuspid regurgitation from atrial lead placement**: Tricuspid regurgitation is a known complication of RV lead placement (not atrial lead placement), due to mechanical trauma to the tricuspid valve. The presence of an atrial lead in DDD does not reduce TR risk; in fact, the additional atrial lead adds a second lead in the right heart. **High-Yield:** DDD is the gold-standard mode for sinus node dysfunction with intact AV conduction because it preserves AV synchrony and prevents pacemaker syndrome; VVI is reserved for chronic atrial fibrillation where atrial contribution is lost anyway. [cite: Harrison 21e Ch 247; ACC/AHA Pacemaker Guidelines]