Adverse effects of first-degree AV-block in patients with sinus node dysfunction: data from the mode selection trial

Pacing Clin Electrophysiol. 2014 Sep;37(9):1111-9. doi: 10.1111/pace.12404. Epub 2014 May 4.


Background: Patients with a pacing indication and first-degree atrioventricular (AV)-block pose a clinical challenge. The prognostic impact of first-degree AV-block in patients with sinus node dysfunction and the impact of pacing in this setting are not known.

Methods: In the Mode Selection Trial (MOST), 2,010 patients with sinus node dysfunction were randomized to either dual-chamber (DDD-R) or ventricular (VVI-R) pacing and followed for a median of 33 months. We report on clinical outcomes in patients with first-degree AV-block (PR interval > 200 ms) compared with patients who had a normal PR interval at baseline.

Results: Patients with first-degree AV-block (n = 378) were older (median [Q1, Q3]; 76 [70, 82] years vs 73 [66, 79] years, P< 0.0001), more often male (57% vs 49%, P = 0.0049), and had more comorbidity, such as hypertension (66% vs 60%, P = 0.034) and heart failure (24% vs 17%, P = 0.0050) than patients with normal AV-conduction (n = 1,159). In multivariable analyses, patients with first-degree AV-block were at greater risk of death, stroke, or heart failure hospitalization (hazard ratio [HR] 1.31, 95% confidence interval [CI] 1.06-1.61, P = 0.013). A trend towards a higher incidence of atrial fibrillation was seen (HR 1.24, 95% CI 0.98-1.55, P = 0.069). No significant interactions between pacing arm and prolonged versus normal PR were found for any endpoint, and hazard ratios were consistent across subgroups.

Conclusions: First-degree AV-block is associated with more advanced disease but is still an independent predictor of poor clinical outcome. Neither DDD-R nor VVI-R pacing, as employed in MOST, eliminate the negative effects associated with first-degree AV-block.

Keywords: PR interval; first-degree AV-block; outcome assessment; pacemaker; randomized clinical trial; sinus node dysfunction.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Atrioventricular Block / complications*
  • Atrioventricular Block / therapy*
  • Cardiac Pacing, Artificial / methods*
  • Comorbidity
  • Electrocardiography*
  • Female
  • Humans
  • Male
  • Pacemaker, Artificial
  • Prognosis
  • Prospective Studies
  • Risk Factors
  • Sick Sinus Syndrome / complications*
  • Sick Sinus Syndrome / therapy*
  • Treatment Outcome