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

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.