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Mode switching failure during atrial flutter: the '2:1 lock-in' phenomenon
M Goethals1, W Timmermans, P Geelen
1Cardiovascular Centre Aalst, OLV Ziekenhuis, Moorselbaan 164, Aalst 9300, Belgium. marc.goethals@olvz-aalst.be
Summary
A specific pacemaker mode switching failure, termed "2:1 lock-in," affects patients with atrial flutter. This occurs when the pacemaker incorrectly tracks the flutter, leading to rapid ventricular pacing.
Area of Science:
- Cardiology
- Biomedical Engineering
- Electrophysiology
Background:
- Dual chamber pacemakers utilize automatic mode switching (MS) algorithms to optimize pacing.
- Atrial flutter can pose challenges to the proper functioning of these MS algorithms.
Observation:
- A retrospective review of 134 patients with pacemakers revealed seven (5.2%) experienced MS failure during atrial flutter.
- This failure, termed "2:1 lock-in," resulted in sustained rapid ventricular pacing.
Findings:
- The "2:1 lock-in" phenomenon occurs when the pacemaker's AV delay plus post-ventricular atrial blanking exceeds the atrial flutter cycle length.
- Additionally, tachycardia detection rate and maximum tracking rate must be greater than half the atrial flutter rate for this failure to manifest.
Implications:
- Understanding the mechanism of "2:1 lock-in" is crucial for preventing inappropriate pacing in patients with atrial flutter.
- Recommendations for pacemaker programming and flutter detection algorithms are proposed to mitigate this issue.