Dual-Chamber ICD Selection Is Associated With Increased Complication Rates and Mortality Among Patients Enrolled in the NCDR ICD Registry

Editor’s Note:  This article is based on Dewland TA, Pellegrini CN, Wang Y, Marcus GM, Keung E, Varosy PD.Dual-chamber implantable cardioverter-defibrillator selection is associated with increased complication rates and mortality among patients enrolled in the NCDR implantable cardioverter-defibrillator registry. J Am Coll Cardiol 2011; 58:1007-13.

In the field of implantable cardiac defibrillators (ICDs), as in other areas of rapid technologic advance, upgraded systems and “device improvements” are often met with enthusiasm, with a desire to use new technology due to the perceived imperfections of past products. This is nowhere more evident than in the technologic changes that have occurred with ICDs, as offshoots of pacemaker technology, since their first clinical use twenty-six years ago.

Basic programming and telemetric capabilities clearly enhance the functional utility and ease of use of these systems. Beyond these, the introduction of various algorithmic and hardware “advancements,” often without comprehensive prior clinical validation, may also understandably be met with a desire on the part of implanters to use the newer systems to improve clinical outcomes of their patients. Yet the end result of such widespread utilization of new device technologies may not produce the anticipated clinical results. Then the question arises: “How do we incorporate new technologies sensibly and safely into clinical use to benefit, and not harm, our patients”?

The cardiac arrhythmia literature itself is filled with many studies in which the anticipated outcome of a major clinical trial has not produced expected results. Early termination of the CAST trial is a good example.1 Designed to prove that suppression of PVCs in patients with ischemic cardiomyopathy was a desired endpoint, increased mortality in the anti-arrhythmic arm of the study forced suspension of the trial.

More relevant to the manuscript by Dewland and co-authors is the DAVID study.2,3 Originally designed to demonstrate reductions in heart failure hospitalization and mortality in patients receiving dual chamber ICDs vs. single chamber ICDs, the study showed the opposite. The combined endpoint of heart failure hospitalization and mortality was increased to 22.6% in patients whose ICD systems were programmed to pace in a dual camber mode compared with 13.3% when only VVI backup pacing was used (p=0.03), with a trend toward an overall increase in mortality alone. A subsequent theoretical analysis resurrected data from the AVID secondary prevention ICD study, which had demonstrated a significant mortality reduction for patients receiving an ICD compared to the use of anti-arrhythmic medication alone (primarily amiodarone) for the prevention of a recurrence of cardiac arrest or hemodynamically intolerable VT.4 The patients in the AVID trial received single chamber ICDs; based on data from the DAVID trial, had they received dual chamber systems with programming similar to that in DAVID, the mortality benefit in the ICD group in the AVID study for secondary prevention would have been nonexistent.5

It is clear now that the primary clinical detriment in programming devices in the dual chamber mode in the DAVID trial stemmed from the frequency of right ventricular pacing. Even in patients with a pre-existing left bundle branch block, the detriment remained. DAVID II, comparing single chamber atrial pacing with back-up bradycardia ventricular pacing alone showed no detriment to the use of an atrial lead in the long-term combined endpoint of hospitalization for heart failure and mortality.6 Neither of the DAVID trials specifically addressed indications for the use of an atrial lead or its appropriate utilization.

Examination of “soft indications” (sinus bradycardia, first degree AV block, or IVCD) for pacing in ICD systems as a sub-study of the DAVID trial showed no long term benefit to the use of an atrial lead when it was expected that the patient “might” need pacing in the future.7 Such anticipated “soft indications” likely remain a reason that a large number of atrial leads were implanted as combined dual chamber ICD systems when examining the NCDR database. Dewland and co-authors note that only 40.4% of patients who received a dual chamber ICD system met specific accepted criteria recorded on the registry form for the placement of an atrial lead.2

The use of an atrial lead in ICD systems in the NCDR database appears to be related to an increase in pre-discharge morbidity and mortality. Some of the morbidity is understandable (though potentially preventable) with the use of more complex lead system, such as an increased incidence of coronary sinus damage (likely due to failed attempts at placement of a coronary sinus lead) and an increased incidence of pneumothorax (probably due to additional access attempts). Each of these potential morbidities might, however, be reduced with variations in technique; for example, using more retained guide wires for access rather than using multiple punctures for access.

The use of an atrial lead in ICD systems in the NCDR database appears to be related to an increase in pre-discharge morbidity and mortality. Some of the morbidity is understandable (though potentially preventable) with the use of more complex lead system, such as an increased incidence of coronary sinus damage (likely due to failed attempts at placement of a coronary sinus lead) and an increased incidence of pneumothorax (probably due to additional access attempts). Each of these potential morbidities might, however, be reduced with variations in technique; for example, using more retained guide wires for access rather than using multiple punctures for access.

Nevertheless, even correcting for clinical co-morbidities (precisely how statistically is unclear), the authors found an increased in-hospital morbidity and associated mortality with the placement of a dual chamber vs. a single chamber ICD. With the population receiving dual chamber systems being somewhat more elderly, perhaps implanters felt that the incidence of progressive sinus node dysfunction would be greater; however, similar soft indications in the DAVID trial did not appear to confer a benefit to dual chamber pacing.7

We do know that the incidence of atrial fibrillation increases with age.8 Is this enough to justify placing a second lead? Some data suggest that atrial pacing may reduce the incidence of atrial fibrillation and potentially its consequences, with some potential long term benefits of dual chamber pacing for this indication; however, the mode of pacing is also important. Neilsen and co-authors demonstrated adverse effects of increased left atrial diameter and decreased left ventricular fractional shortening with dual chamber DDDR pacing, especially with a shortened AV delay, compared with single chamber atrial AAIR pacing.9There was a concomitant increase in atrial fibrillation frequency in the DDDR pacing group. Right ventricular pacing uniformly has no beneficial effect on maintaining sinus rhythm.

According to the NCDR database, such benefits of atrial pacing may be outweighed by short term complications. A recent meta-analysis suggests that either ventricular or atrial pacing may increase the incidence of atrial fibrillation.10

Undoubtedly, the presence of an atrial lead makes discrimination of atrial vs. ventricular arrhythmias quite straightforward, though discrimination algorithms in single chamber ICDs can validate the majority of rhythm disorders. Moreover, the frequency of atrial fibrillation in patients who receive dual chamber devices is greater than that previously realized. Unrecognized events appear to have the same prognostic influence on cerebral thromboembolism as do manifest episodes of atrial fibrillation, and they likely have the same implications for anticoagulation.11,12 The MOST trial specifically showed a progressive increase in the incidence of atrial fibrillation in a linear fashion with respect to the percentage of ventricular pacing, as well as an increase in heart failure hospitalization with pacing frequencies over 40%, presumably due to a greater degree of ventricular desynchronization; this occurred with either VVIR or DDDR pacing modes.11 Various atrial pacing algorithms that are applicable to ICDs may reduce the incidence of atrial fibrillation, but the mortality benefits of such algorithms are not proven.13,14 The ability to document previously unrecognized atrial fibrillation with an atrial lead may, however, justify its use in patients at high risk for developing the arrhythmia. Although possible to do so, especially with the remote monitoring capabilities inherent in newer devices, silent atrial fibrillation can be identified, though its relationship to clinical events is unclear.

Undoubtedly, the presence of an atrial lead makes discrimination of atrial vs. ventricular arrhythmias quite straightforward, though discrimination algorithms in single chamber ICDs can validate the majority of rhythm disorders. Moreover, the frequency of atrial fibrillation in patients who receive dual chamber devices is greater than that previously realized. Unrecognized events appear to have the same prognostic influence on cerebral thromboembolism as do manifest episodes of atrial fibrillation, and they likely have the same implications for anticoagulation. The MOST trial specifically showed a progressive increase in the incidence of atrial fibrillation in a linear fashion with respect to the percentage of ventricular pacing, as well as an increase in heart failure hospitalization with pacing frequencies over 40%, presumably due to a greater degree of ventricular desynchronization; this occurred with either VVIR or DDDR pacing modes. Various atrial pacing algorithms that are applicable to ICDs may reduce the incidence of atrial fibrillation, but the mortality benefits of such algorithms are not proven.The ability to document previously unrecognized atrial fibrillation with an atrial lead may, however, justify its use in patients at high risk for developing the arrhythmia. Although possible to do so, especially with the remote monitoring capabilities inherent in newer devices, silent atrial fibrillation can be identified, though its relationship to clinical events is unclear.

The true cost-benefit of early placement of an atrial lead as opposed to device upgrade when required is also still not clear. Based on data from the current study of the NCDR database, any long term savings gained by avoiding reoperation to place an atrial lead later in the patient’s life would be offset by the costs of complications of dual chamber device implantation. Upgrades need to be considered in the context of data from the REPLACE registry, since each reoperation carries substantial risk that may outweigh the risk of initial device implantation.15 These data are also clear from the lead extraction literature, in which it is evident that device reoperation carries a substantially higher risk of infection than does initial device implantation.16 Preventing subsequent device infection or malfunction begins at the initial implantation or reoperation, with attention to strict sterility, minimization of procedure time, and selection of the appropriate device and lead(s) for the patient. The possibility that patients could be harmed with reoperation required to add an atrial lead is real, although based on the current study the potential risk of adding that lead early with the anticipation that it may eventually be required appears to carry a substantial complication rate as well.2,17,18

References

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