Case 68

A 62-year-old woman was admitted to the intensive care unit with acute pulmonary oedema requiring intubation. She had a past medical history of myocardial infarction with LVEF of 25%, NYHA class III heart failure, and LBBB for which an Abbott CRT-D had been implanted. The doctors on the intensive care unit were concerned as they saw intermittent loss of pacing spikes on telemetry. Her 12-lead ECG and device interrogation are shown in Figure 68.1.

In selected CRT recipients, well-timed negative AV hysteresis with fusion pacing with intrinsic AV conduction can reduce QRS duration compared to standard biventricular pacing.¹ Furthermore, in LBBB, RV activation may be normal, and LV-only pacing may be delivered to avoid inducing RV dyssynchrony. All devices which offer this feature have to periodically determine what the current PR interval is. This can be as frequently as every minute and can be measured over as little as one AV delay. In the current example, the Abbott SyncAV algorithm measures the AVI over three cycles to check for stability, and to avoid undue shortening of the adjusted AVI due to ventricular premature beats falling after an atrial event (see Volume 1, Case 63). The device will allow intrinsic AV activation to occur at the programmed long AVI and then shorten the AVI by the programmable offset. This allows tailoring of CRT programming to shorten QRS duration and increase CRT delivery in case the intrinsic AVI shortens over time (e.g. in case of reduction in beta-blocker dose).