2/1 block during exercise
A 28-year-old woman surgically implanted with a triple-chamber pacemaker (1 atrial lead, 2 left ventricular leads) for congenital complete atrioventricular block; programming in DDD mode (single left ventricular lead) 60-120 beats/minute; sensation of blockpnea on exertion; exercise test (bending of the legs) with the telemetry head positioned over the pulse generator; EGM tracing recorded during vigorous effort with, from one beat to the next, sensation of blockpnea (exercise was halted at this precise moment to obtain a high quality tracing).
Tracing 27a: vigorous exertion;
- AS-VP interval with programmed AV delay;
- P wave blocked since falling within the PVARP (AR);
- new AS-VP interval with programmed AV delay;
- new P wave blocked since falling within the PVARP (AR); 2/1 block;
- the sudden drop in rate favors the emergence of a junctional escape rhythm (narrow QRS); atrioventricular dissociation;
- repetition of 2/1 intervals alternating with junctional escape;
Tracing 27b: tracing recorded during recovery;
- 2/1 block with a followed P wave (AS) and a P wave in the blocked refractory period (AR);
- slowing of the heart rate during recovery and return of AS-VP intervals with 1/1 conduction.
This tracing allows emphasizing certain programming specificities in young patients with preserved activity and contractile function implanted with a pacemaker:
- the pacing site is essential since these young patients with complete atrioventricular block will be paced permanently for many years. A left ventricular pacing may have a less deleterious effect than right ventricular pacing in terms of remodeling and ventricular function;
- similarly, it is essential to adjust the programming parameters to the specific characteristics of these patients. In this patient, the 2/1 point is set much too low; this setting is responsible for the observed symptoms. Indeed, the sensed AV delay was programmed at 160 ms without programming of an adjustable AV delay. The PVARP was programmed at 350 ms without automatic reduction during a rate acceleration. The sum of these two atrial refractory periods establishes a 2/1 point below 120 beats per minute, well below the actual capacities of the patient. The total atrial refractory period that defines the 2/1 point corresponds to the sum of AV delay + PVARP.
This patient presents a congenital complete atrioventricular block without anterograde or retrograde conduction at rest or during exertion. The risk of PMT is therefore zero. This allows programming a PVARP as short as possible with an adjustable AV delay. The 2/1 point should be pushed beyond the maximum capacities of the patient.