The evolutionary pace in implantable cardioverter-defibrillator (ICD) therapy has slowed. After rapid developments in the 1990s, during which we saw the advent of transvenous ICDs, biphasic waveforms, tiered therapy, active cans, dual-chamber pacing and cardiac resynchronization therapy, the pace has slowed. With the exception of the totally subcutaneous ICD, the past ten years have seen few major advances in ICD therapy. There are several reasons for this plateau, including the higher regulatory and financial hurdles associated with bringing revolutionary changes in the device industry to market. Some increase in the height of the hurdles, unfortunately, appears to be justified based on the recent experiences with the Fidelis and Riata ICD lead recalls. However, many opportunities to further optimize ICD therapy remain.
An example of a concept that could address some of the current limitations to ICD therapy is that of the VDD ICD lead. Although VDD leads have been less well adopted in the United States compared to other places such as Europe for pacing, there may be more widespread acceptance of the VDD concept for defibrillators.
There are many advantages to a dual-chamber ICD system compared to a single-chamber right ventricular (RV) ICD system. The added benefits include the ability to provide physiological pacing in patients with AV block (AVB), atrial-based pacing for patients with sinus node dysfunction (SND), and a platform on which cardiac resynchronization (CRT) can be delivered by adding a single left ventricular (LV) lead. An atrial lead also provides atrial electrograms to permit detection of atrial fibrillation (AF) by the device, discrimination between ventricular and supraventricular tachycardias (SVT), and improved interpretation of stored intracardiac electrograms (EGMs). With the exception of the ability to pace the atrium, a VDD lead system provides all of the benefits that come with a dual-chamber system, without the downsides to implantation of a separate atrial lead (Table).
What are the risks of implanting an atrial lead at the time of defibrillator implantation? In addition to the increased costs and procedure times associated with dual-chamber compared to single-chamber ICDs, the tradeoffs also include higher complication rates and possibly an increase in the death rate. Data from the ACC-NCDR ICD Registry database from 2011 showed that not only is the implant-related adverse event rate higher when a patient receives a dual-chamber ICD (3.2% compared to 2.1% for a single-chamber ICD; p < 0.001), but the in-hospital mortality rate is also higher — 45% higher after adjusting for comorbidities and ICD indications.1
What is the experience with atrial sensing in VDD ICD leads systems? In the ADRIA study published in 2010, Sticherling and colleagues compared the outcomes in patients who received a VDD ICD lead compared to patients who received a conventional dual-chamber device.2 For the BIOTRONIK VDD systems, the implant time was shorter (67±30 vs. 79±30 min, P=0.003), the P-waves were similar (3.5±0.8 vs. 3.2±0.6 mV), atrial sensing was stable over 12 months, and the surgical revision rate was the same. Furthermore, the sensitivity and specificity of SVT discrimination were similar. Studies of VDD ICD systems have also shown that when patients are properly selected, the number of patients who subsequently require addition of an atrial lead for atrial pacing is very low. The experience with the totally subcutaneous ICD, which also cannot deliver atrial pacing, also suggests that we are able to predict which patients who have an indication for a defibrillator are going to need atrial pacing.
Given the higher rate of complications and death related to placement of an atrial lead at the time of ICD implantation, and the evidence that a VDD ICD system can reliably offer most of the advantages of a dual-chamber ICD system, there is great potential for a VDD ICD system in the United States.
- Dewland TA, Pellegrini CN, Wang Y, et al. 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;58:1007-1013.
- Sticherling C, Zabel M, Spencker S, et al. Comparison of a novel, single-lead atrial sensing system with a dual-chamber implantable cardioverter-defibrillator system in patients without antibradycardia pacing indications: Results of a Randomized Study. Circ Arrhythm Electrophysiol 2010;4:56-63.