Title of Trial
Mode Selection Trial in Sinus Node Dysfunction (MOST)

Date and Citation of Primary Publication(s) or References
Lamas GA, Lee KL, Sweeney MO et al. Ventricular pacing or dual chamber pacing for sinus node dysfunction, N Engl J Med 2002; 346: 1854-62.

Purpose of the Trial
Evaluate the effects of pacing mode choice in patients with symptomatic sinus node dysfunction.

Study Category
Pacing

Patient Population
Inclusion Criteria
Sinus node dysfunction requiring implantation of a permanent pacemaker. For the quality of life analysis, a score of 17 or higher on the Mini-mental state examination.

Exclusion Criteria
Serious concomitant illness.

Study Design
Single blind randomized trial. Patients received dual chamber pacemakers and were randomized to the DDD or VVI pacing modes.

Primary Endpoint
Death and nonfatal stroke

Secondary Endpoints
Composite of death, stroke, and hospitalization for heart failure, atrial fibrillation, heart-failure score, pacemaker syndrome, and quality of life.

Baseline Characteristics
Patient number: 2010 patients
Mean Age: 74 years
Gender: 48% female
Other characteristics: Over 50% with a history of supraventricular tachycardia including atrial fibrillation within the past three weeks. Twenty-one percent of patients had atrioventricular block. Over 80% of patients were NYHA class I or II at baseline.

Time to Follow-up
Median follow-up was 33 months.

Results
No difference was detected in the primary endpoint of combined death and nonfatal stroke (Dual chamber: 21.5% vs. ventricular: 23.0%; p = 0.48). In patients assigned to dual chamber pacing, the risk of atrial fibrillation was lower (hazard ratio: 0.79; 95% CI: 0.66-0.95, p = 0.008). Heart failure hospitalizations were not different between the two pacing modes. However, patients in the dual chamber pacing group had better heart failure scores compared to the ventricular pacing group (p < 0.001). At three months both pacing modes were associated with an improved quality-of-life. Dual chamber pacing was associated with small improvements in quality-of-life when compared to ventricular pacing. The physical role and emotional role categories of the SF-36 scale demonstrated the largest improvements with dual chamber pacing. At last follow-up, 31% of patients assigned to ventricular pacing had been reprogrammed to dual chamber pacing; 49% of patients were crossed over due to the development of pacemaker syndrome. The overall complication rate for pacemaker implantation was 4.8% at 30 days.

Endpoint	Dual chamber pacing (n= 1014)	Ventricular pacing (n= 996)	P
All cause mortality and nonfatal stroke	21.5%	23.0%	0.48
Chronic atrial fibrillation	15.2%	26.7%	<0.001
Heart failure hospitalizations	10.3%	12.3%	0.13

Sponsor
National Heart, Lung, and Blood Institute, Medtronic, Guidant, and St. Jude Medical.

Trial Status:  Completed