Management of Atrial Fibrillation Suppression in AF-HF COmorbidity Therapy - MASCOT


The goal of the trial was to evaluate overdrive atrial pacing (AOP) in patients with heart failure implanted with a cardiac resynchronization therapy (CRT) device.

Study Design

Patients Enrolled: 409
Mean Follow Up: One year
Mean Patient Age: Mean age 68 years
Female: 21

Patient Populations:

Heart failure in New York Heart Association (NYHA) class III or IV; spontaneous QRS ≥130 ms and/or mechanical interventricular delay >50 ms; LVEF ≤35%; left ventricular end diastolic diameter ≥55 mm; optimized medical regimen.


Unstable angina or acute MI within 3 months; CABG or PCI within 3 months; life expectancy < 6 months; permanent atrial fibrillation.

Primary Endpoints:

Permanent atrial fibrillation at 1 year

Secondary Endpoints:

Incidence of new-onset AF; changes in LVEF, LVESD, LVEDD; changes in NYHA functional class; changes in quality of life; mortality.

Drug/Procedures Used:

After successful CRT implantation but before hospital discharge, patients were randomized to AOP ON (n=197) or AOP OFF (n=197).

Principal Findings:

At study entry, mean LVEF was 25%, and 86% of patients had NYHA class III heart failure. Average QRS duration was 163 ms. A history of paroxysmal AF was present in 19% of the cohort and 50% had ischemic heart disease. Concomitant medications included diuretics (95%), ACE/ARBs (87%), and beta-blockers (71%).

Atrial pacing was more frequent in the AOP ON group than the AOP OFF group (80% vs. 30%, p < 0.0001). There was no difference in ventricular pacing (95% in each group) but heart rate was higher in the AOP ON group (72 bpm vs. 67 bmp, p = 0.05). Measures of heart failure severity were improved in both groups at 1 year relative to baseline, without a difference between groups, including improvement of ≥1 NYHA class (67% with AOP ON vs. 70% with AOP OFF), LVEF (mean 33.1% vs. 32.7%, respectively), and LVESD (57 mm vs. 53 mm, respectively). There was no difference in the primary endpoint of permanent AF between groups (3.3%, n = 7 patients in the AOP ON group vs. n = 6 patients in the AOP OFF group). Mortality at 1 year had occurred in 7.6% of the AOP ON group and 11.7% of the AOP OFF group (p = NS).


Among patients with heart failure implanted with a CRT device, atrial overdrive pacing was not associated with a difference in the rate of permanent atrial fibrillation at 1 year compared to without use of atrial overdrive pacing.

While no difference was observed between the treatment groups in permanent atrial fibrillation, it should be noted that the event rate was very low (3.3%), making the trial highly underpowered. Although there was no efficacy benefit on permanent atrial fibrillation, there was no evidence of an adverse impact of having the atrial overdrive pacing on or off. Similar improvements were observed from baseline in several measures of heart failure severity, including NYHA class, LVEF, and LVESD. The presenter suggested that AOP should be switched off to save battery energy and could then be turned on as needed based on device diagnostics and patient symptoms in the case of atrial tachyarrhythmias.


Padeletti L, Musilli N, Porciani MC, et al. Atrial fibrillation and cardiac resynchronization therapy: the MASCOT study. Europace. 2004 Sep;5 Suppl 1:S49-54.

Presented by Dr. Luigi Padeletti at the American Heart Association Annual Scientific Session, Orlando, FL, November 2007.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Myocardial Ischemia, Cardiac Pacing, Artificial, Diuretics, Heart Failure, Pacemaker, Artificial, Heart Rate, Cardiac Resynchronization Therapy, Tachycardia

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