Pacing systems tachycardias

Fig. 19.19 Pacemaker output settings for lowest current drain and maximum longevity induction of an endless loop tachycardia during an atrial capture threshold test in a patient with a Pacesetter Affinity DR pacing system. The automatic PMT detection and termination algorithm recognized the tachycardia and promptly terminated it. Meanwhile, the recording provided details as to the tachycardia interval and the retrograde conduction interval providing guidance as to programming the PVARP.

The essential parts to the baseline ICD interrogation include evaluation of the detection and therapy measurements, real-time measurements, pacing system function, and if present, review of any tachycardia episodes (Table 20.2). 

Pacemaker-mediated tachycardia arises from retrograde conduction via the normal conduction system of the heart of a paced or intrinsic ventricniar event to the atrium. The tracking of the retrogradely conducted atrial complex must occur for PMT to occur. The successive ventricular-paced event that tracks this atrial complex also results in retrograde conduction to the atrinm. 

Permanent pacing is recommended as a class I indication in symptomatic or asymptomatic patients with exercise-induced AV block (absent at rest) because the vast majority are due to tachycardia-dependent block in the His-Purkinje system and carry a poor prognosis (20-22) (Fig. 10.13). This... 

Undersensing. Inappropriate delivery of pacing stimuli when the pacemaker system fails to sense P-waves or QRS complexes defines undersensing. Delivery of stimuli can be harmful if they occur during the atrial and ventricular relative refractory periods that are predisposed to tachyarrhythmia induction. Of particular concern is the induction of ventricular tachycardia or fibrillation when ventricular pacing occurs on the terminal portion of the T-wave ( R-on-T ), especially in the critical care setting where concomitant ischemia, metabolic and electrolyte abnormalities are frequently present. 

Fig. 19.12 Event histogram from a patient implanted with a Trilogy DR+. The indication for pacing was the bradycardia-tachycardia syndrome. Over the past 42 days, the majority of the complexes were in the base rate or sleep rate bins. Rate modulation had not yet been enabled and there were relatively few native atrial rates above 75 bpm. The system functioned in a nontracking mode approximately 3% of the time (AMS bin) with 1,776 mode switch episodes. Based on this event histogram demonstrating the presence of chronotropic incompetence, rate-modulation was enabled.

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