Pacemaker-mediated tachycardia initiated by coincident P-wave undersensing and ventricular blanking period

Accuracy of the pacemaker-mediated tachycardia algorithm in Boston Scientific devices

INTRODUCTION

The incidence of pacemaker-mediated tachycardia (PMT) varies as a function of patient characteristics, device programming and algorithm specificities. We investigated the efficacy of the Boston Scientific algorithm by reviewing PMT episodes in a large device population.

METHODS

In this multicenter study, we included 328 patients implanted with a Boston Scientific device: 157 non-dependent patients with RYTHMIQ™ activated (RYTHMIQ group), 76 patients with permanent AV-conduction disorder (AV-block group) and 95 Cardiac Resynchronization Therapy patients (CRT group). For each patient, we reviewed the last 10 remote monitoring-transmitted EGMs diagnosed as PMT.

RESULTS

We analyzed 784 PMT episodes across 118 patients. In the RYTHMIQ group, the diagnosis of PMT was correct in most episodes (80%) of which 69% was directly related to the prolongation of the AV-delay associated with the RYTHMIQ algorithm. The usual triggers for PMT were also observed (PVC 16%, PAC 9%). The remainder of the episodes (20%) in RYTHMIQ patients and most episodes of AV-block (66%) and CRT patients (74%) were incorrectly diagnosed as PMT during sinus tachycardia at the maximal tracking rate. The inappropriate intervention of the algorithm during exercise causes non-conducted P-waves, loss of CRT (sustained in six patients) and may have been pro-arrhythmogenic in one patient (induction of ventricular tachycardia).

CONCLUSION

Algorithms to minimize ventricular pacing can occasionally have unintended consequences such as PMT. The PMT algorithm in Boston Scientific devices is associated with a high rate of incorrect PMT diagnosis during exercise resulting in inappropriate therapy with non-conducted P-waves, loss of CRT and limited risk of pro-arrhythmic events.

Diagnosis of atrial undersensing in dual chamber pacemakers: impact of autodiagnostic features

Atrial undersensing occurs in a considerable number of patients, both with single lead VDD pacemakers and with DDD devices. The aim of this study was to investigate the diagnostic efficacy of electrocardiographic methods and autodiagnostic pacemaker features to detect atrial sensing dysfunction. Two hundred and thirty-one patients with AV block received single lead VDD pacemakers or DDD devices. Atrial sensitivity was programmed to 0.1 or 0.18 in VDD devices and to 0.5 mV in DDD devices; the rate limits were set to 40 and 160 beats/min. Twelve-lead ECG recording for 1 minute during deep respiration and change of body position, 24-hour Holter ECG recording, and treadmill exercise were performed 2 weeks and 15 months after pacemaker implantation. AV synchrony and, if available, P wave amplitude histogram were sampled by autodiagnostic pacemaker features and compared to electrocardiographic findings. Atrial undersensing was assumed, if AV synchrony was below 100% or if minimal P wave amplitude (PWA) was equal to the programmed atrial sensitivity. Intermittent atrial undersensing occurred in 20.7% of patients. The diagnostic sensitivities of the various methods used to detect atrial sensing failures were: 24-hour Holter monitoring 97.5%, P wave amplitude histogram 90.0%, stored AV synchrony 68.0% without significant difference between the various devices, treadmill exercise testing 58.8%, and 12-lead ECG recording 21.3%. In one patient, atrial undersensing was exclusively detected by exercise testing. In conclusion, autodiagnostic pacemaker features facilitate the evaluation of atrial sensing performance. However, to exclude intermittent atrial malesensing, routine Holter monitoring and treadmill exercise are still needed.

Should unipolar leads be implanted in the atrium? A Holter electrocardiographic comparison of threshold adapted unipolar and high sensitive bipolar sensing

The accuracy of atrial sensing plays a central role in dual chamber pacing. Recent Holter electrocardiographic studies showed a high incidence of atrial malsensing. We investigated the efficacy of bipolar atrial sensing at high sensitivity compared to threshold adapted unipolar sensing. One hundred consecutive patients with identical dual chamber pacemakers and bipolar atrial leads were investigated. Mean and individual range of 40 unipolar and bipolar telemetered atrial potentials were calculated; sensing threshold was determined by a semiautomatic sensing test. Oversensing was investigated with the help of a muscle provocation test. Twenty-four-hour Holter monitoring was performed at the highest bipolar sensitivity as well as at a unipolar sensitivity of half the measured sensing threshold. Mean atrial potential was significantly lower during bipolar mode compared to the unipolar sensing configuration, 3.66 +/- 1.75 versus 3.85 +/- 1.62 mV, P = 0.02. The bipolar atrial potentials showed a higher individual range than the unipolar signals, 2.44 +/- 2.62 versus 1.79 +/- 0.92 mV, P < 0.01. Sensing threshold did not differ significantly, 2.76 +/- 1.33 versus 2.67 +/- 1.29 mV. Mean oversensing threshold was 1.21 mV at unipolar configuration, whereas oversensing could not be provoked at a bipolar sensitivity of 0.5 mV. The incidence of atrial undersensing was significantly higher at threshold adapted unipolar sensing compared to bipolar sensing at highest atrial sensitivity, 35% versus 22%, P = 0.04. Oversensing did not occur at bipolar sensing, but was observed in 56% of patients at unipolar mode. Thirty-two percent of patients showed both atrial undersensing and oversensing at the unipolar sensing configuration. The muscle provocation test reached a sensitivity of 89% and a specificity of 95% in prediction of atrial oversensing during daily life. In conclusion, unipolar atrial potentials are more stable than bipolar ones. On the other hand, bipolar atrial sensing is less prone to the perception of myopotentials. Programming a high bipolar sensitivity significantly improves atrial sensing. Thus, bipolar leads should generally be implanted in the atrium.

Programming a long paced atrioventricular interval may be risky in DDDR pacing

In patients with intermittent AV block and dual chamber pacemakers, a long paced AV interval of 200 msec or more can be selected to prolong pulse generator life (by avoiding the ventricular pace output) and to enable a more physiological and hemodynamically superior activation sequence. This case report describes the potential risks of programming a long paced AV interval in a patient with a DDDR pacemaker. T wave pacing, as described here, can occur if the conducted QRS complex is not sensed because it occurs during the ventricular blanking period (delivery of the atrial stimulus). This can be initiated by the mechanisms that induce apparent and actual P wave undersensing of the conducted QRS complex. In this case report apparent P wave undersensing and subsequent T wave pacing with ventricular capture (in a patient with intermittent AV block) occurred frequently during an exercise test done in the DDDR mode with a paced AV interval of 200 msec, according to the clinical evaluation protocol.

The superfast atrial recharge pulse: a cause of pectoral muscle stimulation in patients equipped with a unipolar DDD pacemaker

Pectoral muscle stimulation may cause serious discomfort to patients equipped with a pulse generator. Insulation defects of the lead, connector problems and defective coating of the pacemaker can are common causes of local muscle contractions. This report describes pectoral muscle stimulation caused by the atrial superfast recharge pulse incorporated into the atrial channel of a commercially available unipolar DDD pacemaker. As pectoral muscle stimulation could not be eliminated by reprogramming the pacemaker to a lower atrial output in some patients a redesign of the pacemaker is highly required.