Single-lead VDD pacing--a serious alternative for atrioventricular synchronous pacing in patients with atrioventricular block?

This editorial refers to ‘Long-term follow-up of DDD and VDD pacing: a prospective non-randomized single-centre comparison of patients with symptomatic atrioventricular block’ by S. Marchandise et al., on page 496 For >20 years, single-lead VDD pacemakers have been implanted in patients with atrioventricular (AV) block and normal sinus node function.1 A single tripolar or quadripolar passive fixation lead is placed in the apex of the right ventricle for unipolar or bipolar ventricular sensing and pacing. Two sensing rings floating in the right atrium are used for bipolar sensing of the atrial potential. Due to lacking wall contact of the atrial dipole in most patients, atrial potential amplitudes are lower than those of fixed atrial electrodes. Thus, a high atrial sensitivity allowed by a differential sensing amplifier is usually needed for AV synchronous pacing in single-lead VDD devices. Since atrial pacing is not possible, a sinus node disease is a contraindication for VDD pacing and has to be ruled out before implantation. Several registries and randomized trials have shown an equivalent therapeutic efficacy of single-lead VDD pacing2–4 compared with DDD pacemakers. Long-term complications5 and costs of AV synchronous pacing therapy may be reduced by single-lead VDD pacemaker implantation.6,7 Despite these encouraging results, single-lead VDD pacing did not get beyond a ‘niche’ therapy for AV synchronous pacing.8 The concern about the unpredictable loss of AV synchrony due to low and varying atrial amplitudes may be the most likely reason for the infrequent use of single-lead VDD pacemakers. In addition, many investigators may not find worthwhile excluding the sinus node disease appropriately prior to VDD pacemaker implantation. Marchandise et al.9 report the results of a single centre prospective registry in 420 patients with AV block who either received a single-lead VDD or a DDD pacemaker during the last decade. As known from the previous studies, the increased incidence of atrial undersensing was a major drawback of single-lead VDD pacing. Authors state that AV synchronous pacing mode with good atrial sensing was not maintained in one-third of VDD pacemaker recipients after a mean follow-up of ∼2 years. At first sight, this result supports the concerns against single-lead VDD pacing. However, most of the patients reaching this endpoint were characterized by atrial potential amplitudes <0.5 mV only. When programming a sufficiently high atrial sensitivity, AV synchrony at >95% was maintained in the vast majority of these patients. Nevertheless, a complete loss of AV synchrony was observed more frequently than in the previous studies. VVIR mode was programmed for atrial undersensing in 7.1% of VDD pacemakers, while another 1.8% of patients received an additional atrial lead for the same reason. Adding the patients who were programmed to VVIR mode for permanent atrial fibrillation, ∼17% of patients lost the AV synchronous pacing mode in the single-lead VDD group during a follow-up of 2 years. Compared with former trials, which reported the maintenance of AV synchronous pacing mode in up to 94% of patients with single-lead VDD pacemakers,2 this rate appears high. A substantially older patient age in the study by Marchandise et al.9 may be one reason for this difference. A mean patient age of 77 years is surely responsible for a higher incidence of persistent atrial fibrillation compared with the previous observations. It is known that atrial sensing performance of single-lead VDD pacemakers worsens with age;10 this might be another reason for a greater loss of AV synchrony. Furthermore, the authors did not report in detail, how sinus node disease, which might be another reason for the loss of AV synchrony in single-lead VDD pacing, was excluded prior to pacemaker implantation. What can we learn from this trial? A high atrial sensitivity (e.g. 0.1–0.2 mV) should be primarily programmed in single-lead VDD pacemakers to achieve better initial AV synchrony than reported in this registry. However, it has been clearly shown in the registry that even a relatively high incidence of atrial undersensing does not impact on clinical endpoints in patients with single-lead VDD pacemakers. Frequent atrial undersensing was well tolerated by the majority of patients, documented by a low incidence of upgrades to a DDD pacemaker. Atrial fibrillation, cardiovascular endpoints, and worsening of left ventricular function have not been observed more frequently than in DDD pacemaker recipients. After correction for differences in patient age, all-cause mortality was not significantly higher in patients with single-lead VDD pacemakers. These results correspond to the previous findings. Surprisingly, the complication rate was not significantly lower in single-lead VDD pacemaker therapy, an experience we accumulated during long-term follow-up of pacemaker recipients.5 This difference may be caused by distinct implantation strategies such as venous access as well as by a smaller sample size of this study. Adding the results of this registry to the present literature, I share the conclusion made by Marchandise et al.9 that single-lead VDD pacing is still worth considering in patients with AV block. For which patients should we consider single-lead VDD pacing in the year 2011? The answer of this question mainly depends on the individual experience in this particular pacing mode. If one implants single-lead VDD pacemakers only in a few patients which were ‘too old or too sick to receive a regular DDD device’, the results will be presumably bad. A high patient age or the presence of an enlarged right atrium or ventricle surely elevates the risk for atrial undersensing. In these patients, single-lead VDD pacing should not be considered primarily. Single-lead VDD pacing will achieve good results in centres with (i) a continuous experience in this pacing therapy, and (ii) a structured evaluation of patients including a thoroughful rule-out of a sinus node dysfunction. If one of these requirements is not fulfilled and single-lead VDD pacemakers were mainly used as ‘better VVI devices’ VDD pacemaker therapy should be avoided. Same applies to patients with urgent need for pacemaker implantation. Despite of almost 15 years of encouraging data, including the present study, and recent guideline recommendations, I expect that single-lead VDD pacing will remain a niche therapy frequently used only by a number of enthusiasts. A new application may increase the interest in single-lead VDD devices. A floating atrial dipole integrated in a high-voltage right ventricular lead is used for dual-chamber detection algorithms of an implantable cardioverter defibrillator (ICD) system. First studies showed a higher stability of the atrial potential as compared with pacemaker therapy and a highly reliable discrimination between ventricular and supraventricular arrhythmias.11 However, larger and randomized trials are needed to clearly determine the value of the single-lead VDD design compared with single-chamber as well as dual-chamber ICD therapy. Conflict of interest: none declared.