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

Long-term outcome of transvenous bipolar atrial leads implanted in children and young adults with congenital heart disease

AIMS

Atrial leads are often implanted in paediatric patients needing a pacemaker (PM). The aim of this study is the evaluation of their outcome in young patients.

METHODS AND RESULTS

We evaluated transvenous atrial leads outcome in children and young adults from a single centre, with a retrospective analysis. A P< 0.05 was considered significant. Between 1992 and 2008, 110 patients, 75 with congenital heart defects (d-transposition of great arteries status/post, s/p, Mustard 41%, atrioventricular septal defect 11%, tetralogy 9%, ventricular septal defect 8%), aged 13.3 ± 5.3 years, underwent PM implantation with bipolar atrial transvenous leads for sinus node dysfunction (50%), atrioventricular block (38%), cardiomyopathies, and primary ventricular arrhythmias (12%). Leads are steroid-eluting (98%), tined (59%), screw-in (41%), polyurethane-insulated (72%), silicone-insulated (28%), and have been positioned by transcutaneous puncture of subclavian vein into right atrial appendage/remnant (RAA, 50%), right atrial free wall/septum (25%), left atrium (s/p Mustard, 25%). Follow-up duration is 6.4 ± 4.8 (range 0.1-18) years. At multivariate analysis, younger age at implant was a risk factor for lead failure (4 leads, 3.5%) (P= 0.03); 16 leads (14%) dislodged post-implantation and 12 were successfully repositioned, the others extracted or abandoned. Dislocation occurred more frequently with screw-in leads (P= 0.03) positioned outside RAA (P= 0.02). Atrial threshold showed a small but significant increase, 0.002 V/month (P< 0.001), impedance showed a decrease (0.6 Ω/month, P< 0.001), P-wave showed no significant difference.

CONCLUSIONS

Transvenous bipolar atrial leads have good long-term results in young patients, with a very low rate of lead failure. Older age at implant can further reduce this rate. Lead dislodgement is frequent in the post-operative period.

Efficacy and safety of bipolar sensing with high atrial sensitivity in dual chamber pacemakers

In dual chamber pacemakers, atrial sensing performance is decisive for maintenance of AV synchrony. Particularly, the efficacy of mode switching algorithms during intermittent atrial tachyarrhythmias depends on the sensitive detection of low potential amplitudes. Therefore, a high atrial sensitivity of 0.18 mV, commonly used in single lead VDD pacemakers, was investigated for its efficacy and safety in DDD pacing. Thirty patients received dual chamber pacemakers and bipolar atrial screw-in leads for sinus node syndrome or AV block; 15 patients suffered from intermittent atrial fibrillation. Pace makers were programmed to an atrial sensitivity of 0.18 mV. Two weeks, 3, 9, and 15 months after implantation, P wave sensing threshold and T wave oversensing thresholds for the native and paced T wave were determined. The myopotential oversensing thresholds were evaluated by isometric contraction of the pectoral muscles. Automatic mode switch to DDIR pacing was activated when the mean atrial rate exceeded 180 beats/min. The patients were followed by 24-hour Holter monitoring. Two weeks after implantation, mean atrial sensing threshold was 1.81 +/- 0.85 mV (range 0.25-2.8 mV) without significant differences during further follow-up. Native T wave sensing threshold was < 0.18 mV in all patients. In 13% of patients, paced T waves were perceived in the atrial channel at the highest sensitivity. This T wave sensing could easily be avoided by programming a postventricular atrial refractory period exceeding 300 ms. Myopotential oversensing could not be provoked and Holter records showed no signs of sensing dysfunction. During a 15-month follow-up, 1,191 mode switch events were counted by autodiagnostic pacemaker function. Forty-two of these events occurred during Holter monitoring. Unjustified mode switch was not observed. In DDD pacemakers, bipolar atrial sensing with a very high sensitivity is efficient and safe. Using these sensitivity settings, activation of the mode switch algorithm almost completely avoids fast transmission of atrial rate to the ventricle during atrial fibrillation.