Dual-chamber Implantable Cardioverter Research Articles

Do atrial tachyarrhythmias beget ventricular tachyarrhythmias in defibrillator recipients?

This study was designed to analyze the incidence of "dual tachycardia"-ventricular tachycardia (VT) or ventricular fibrillation (VF) preceded by paroxysmal atrial tachycardia (AT) or atrial fibrillation (AF)-in patients receiving dual-chamber implantable cardioverter defibrillators (ICDs). Paroxysmal AT/AF occurs commonly in patients who receive ICDs for the treatment of life-threatening VT/VF. Although AF is associated with an adverse prognosis in the setting of structural heart disease, the relationship between AT/AF and VT/VF is unclear. We followed 537 patients undergoing implantation of the Jewel AF ICD (Model 7250, Medtronic, Minneapolis, Minnesota) for 11.4 +/- 8.2 months. These included 398 patients with a history of at least two episodes of AT or AF during the preceding year as well as 139 patients enrolled because of VT/VF alone. There were 233 dual tachycardia episodes in 45 patients during follow-up. Overall, 8.9% of episodes detected as VT/VF were dual tachycardias, and 20.3% of patients with VT/VF had at least one dual tachycardia episode. The median duration of AT/AF preceding the first VT/VF detection was 1.09 h (25% to 75% quartile 0.24 to 33.4 h). When AT/AF continued between two consecutive VT/VF detections, the median interdetection interval was 11 min. When AT/AF terminated either because of a ventricular therapy or spontaneously, the median interdetection interval was prolonged to 71 h (p < 0.001). Dual tachycardia is common in ICD recipients with a history of AT/AF. The duration of AT/AF preceding the first VT/VF detection is < or =1 h about 50% of the time. Termination of the AT/AF significantly delays the time to the next VT/VF detection.

High incidence of device-related and lead-related complications in the dual-chamber implantable cardioverter defibrillator compared with the single-chamber version.

Recently, the routine use of dual-chamber implantable cardioverter defibrillators (DC-ICD) has been advocated over the single-chamber version (SC-ICD), but there are few reports of the frequency of complications between the 2 types of ICDs. Between July 1997 and April 1999, 178 consecutive patients underwent implantation of either a transvenous SC-ICDs (n=104) or a DC-ICDs (n=74). Twelve (16%) of the 74 patients with a DC-ICD had a total of 16 major complications compared with 6 (6%) of the 104 patients with a SC-ICD (p=0.01). The 16 DC-ICD complications included atrial lead dislodgment (4), ventricular lead malfunction (4), and pocket infection/hematoma (3), and the 6 SC-ICD complications included ventricular lead dislodgment (2) and pocket hematoma (3). Patients with a DC-ICD had less left ventricular function (29% vs 35%, p=0.035) and a higher prevalence of non-ischemic cardiomyopathies (48% vs 28%, p=0.0076). In conclusion, the DC-ICD may have a higher frequency of device- and lead-related major complications.

Should all implantable cardioverter defibrillators for ventricular arrhythmias be dual-chamber devices?

The advantages of a dual-chamber implantable cardioverter defibrillator (ICD) over a single-chamber ICD include physiologic pacing capability, atrial electrogram storage, enhanced arrhythmia discrimination algorithms, and a potential to treat atrial arrhythmia by pacing or defibrillation. Current evidence supports the supposition that dual-chamber ICDs are definitely indicated in patients who have a concomitant indication for physiologic pacing, such as bradycardia or bradycardia-dependent ventricular tachyarrhythmias. Refined dual-chamber arrhythmia discrimination algorithms and enhanced atrial therapies are probably required for patients with frequent supraventricular arrhythmias. Furthermore, in patients with systolic heart failure, low ejection fraction, and intraventricular conduction delay, triple-chamber ICDs with biventricular pacing may improve their functional status and prevent sudden arrhythmic death. Careful patient selection is required to optimize the cost-effectiveness of these sophisticated technologies.

Worldwide clinical experience with a new dual-chamber implantable cardioverter defibrillator system.

Management of atrial tachyarrhythmias represents a significant challenge in patients with implantable cardioverter defibrillators (ICDs). Drug therapy of these arrhythmias is limited by moderate efficacy, ventricular proarrhythmia, and drug-device interactions. This study tested the safety and efficacy of a new dual-chamber ICD to detect and treat atrial as well as ventricular tachyarrhythmias. A dual-chamber ICD (Medtronic 7250 Jewel AF) was implanted in 293 of 303 patients at 49 centers in Europe, Canada, and North America. Specific data were collected at implant and during a mean follow-up period of 7.9+/-4.7 months. There were no clinically evident failures to detect and treat ventricular arrhythmias. In patients with at least one of the dual-chamber detection criteria activated, 1,056 of 1,192 episodes of ventricular tachycardia or fibrillation detected were judged to be appropriate (89% positive predictive accuracy). Therapy efficacy was 100% in the ventricular fibrillation zone and 98% in the ventricular tachycardia zone. Positive predictive accuracy for detection of atrial episodes was 95% (1,052/1,107). For episodes classified as atrial tachycardia by the device, the efficacy of atrial antitachycardia pacing and high-frequency (50-Hz) burst pacing was 55% and 17%, respectively. High-frequency burst pacing terminated 16.8% of episodes classified as atrial fibrillation, and atrial defibrillation had an estimated efficacy of 76%. The actuarial estimates of 6-month complication-free survival and total survival were 88% and 94%, respectively. This novel dual-chamber ICD is capable of safely and effectively discriminating atrial from ventricular tachyarrhythmias and of treating atrial tachyarrhythmias without compromising detection and treatment of ventricular tachyarrhythmias.

2:1 Tracking of Sinus Rhythm in a Patient with a Dual‐Chamber Implantable Cardioverter Defibrillator: What is the Mechanism?

A 49-year-old woman with hypertrophic obstructive cardiomyopathy received a dual-chamber pacemaker in 1995. It resulted in signiŽ cant reduction in the intraventricular pressure gradient and signiŽ cant improvement in symptoms. She developed ventricular tachycardia, and the pacemaker was replaced with a dual-chamber implantable cardioverter deŽ brillator (ICD). The ventricular pacing lead was extracted, and the preexistent atrial lead (P wave: 3 mV) and a new active-Ž xation, “integrated” bipolar deŽ brillation lead (Sprint SVC 6945; Medtronic Inc., Minneapolis, MN, USA) were connected to a GEM DR 7271 (Medtronic) generator. Programming was as follows: pacing mode DDD, lower rate 60 beats/min, upper rate 120 beats/min, sensed AV delay 100 msec, ventricular output 4 V at 0.4 msec, maximum atrial sensing 0.3 mV, maximum ventricular sensitivity 0.3 mV, postventricular atrial refractory period (PVARP) 310 msec, postpace ventricular blanking 240 msec, premature ventricular complex (PVC) response ON. Immediately after lead connection, an unusual pattern of pacemaker alternans was seen (Fig. 1). Only every other sinus beat was tracked as expected. The other beats presented intrinsic conduction with a PR interval longer than the programmed AV delay. What is the mechanism for the alternans?

Single-chamber versus dual-chamber implantable cardioverter defibrillators: indications and clinical results

The clinical benefit of standard (single-chamber) implantable cardioverter defibrillator (ICD) therapy in elderly patients or in subjects with moderate or severe heart failure who had ventricular tachyarrhythmias has been debated. We studied the follow-up of 450 patients who underwent standard ICD implantation at our institution in relation to the functional status of heart failure (New York Heart Association Class) or patient’s age. During a mean follow-up of 24±28 months (range, <1–114 months), 90 patients (23%) died: 9 patients (2%) from sudden arrhythmic death and 5 patients (1%) suddenly, but probably not from arrhythmic causes; 55 patients (14%) died from congestive heart failure and/or myocardial reinfarction and 21 patients (5%) from noncardiac causes. We could clearly demonstrate that ICD therapy was able to prevent sudden cardiac death, both in patients with severely depressed left ventricular function and in patients aged ≥65 years. An important step forward in ICD technology was the introduction of dual-chamber pacing possibilities to improve left ventricular dysfunction and to allow a more individualized ICD therapy. At our institution, we have implanted a dual-chamber ICD in 15 patients. Preliminary results showed that heart failure improved in 5 patients (33%) and remained unchanged in 10 patients (67%, p = not significant). There were no patients who had a lesser degree of heart failure after implant. Based on our experience so far, in addition to the hemodynamic benefits of dual-chamber ICDs, dual-chamber sensing and waveform storage capabilities are very helpful and promising diagnostic tools for the detection and handling of inappropriate ICD therapies.