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The number of patients with pacemaker/implantable cardioverter (PMK/ICD) is increasing and frequently cardiologists are called to decide about some arrhythmic events happened in this subgroup of subjects. We have also to consider that often, previous arrhythmias justified the implant of these devices so we can expect a lot of electrocardiograms (ECG) to interpret with accuracy.
ECG analysis in pacemaker patients:
Regarding bradyarrhythmias the diagnosis of these and therapies of the device are not so difficult to analyze (sino-atrial blocks, atrioventricular (AV) blocks, etc.). Of major interest for the clinician appears the ability to understand some modalities to treat arrhythmic events by the PMK/ICD that could make someone thinking to a malfunction (1-4). For example there are PMKs that can activate some algorithms for the treatment of neuromediated car-dioinhibitory syncope (for example the function RDR - Rate Drop Response) or to look for the spontaneous AV conduction in order to decrease the percentage of right ventricular pacing (Medtronic - MVP Minimal Ventricular Pacing). In the former example (Fig. 1) the integrated diagnostic system of PMKs is able to recognize a rapid decrease of heart rate during a vasovagal reflex. A specific planning allows to detect a drop in heart rate so that the device will start to stimulate at 110-120 bpm to avoid the syncopal phenomenon. In the latter the PMK stimulate in AAI/R (AAI/R +) until 1:1 AV conduction persists. After a blocked atrial beat the PMK supplies ventricular back up pacing to avoid symptomatic pauses and if the AV conduction is not restored the PMK switches in DDD/R modality. Periodically conduction tests are performed to verify if AV conduction is restored and in this case the PMK automatically turns back to AAI/R modality. During this mode switching we could see on the ECG some phases of AV block, and so we could think of a malfunction. The analysis of the beat following the blocked atrial beat, that is stimulated with a short AV interval, allows us to give a correct interpretation of the phenomenon. Search AV is another algorithm to minimize right ventricular pacing. It automatically analyzes conduction sequences and gradually increases the paced and sensed AV delays until intrinsic ventricular activation is uncovered. A programmable maximum offset allows the titration of search limits.