Atrial pacing, the forgotten pacing mode

Abstract

In patients with sick sinus syndrome and normal atrioventricular conduction, physiological pacing can be accomplished with either a single chamber atrial pacemaker AAI/R or a dual chamber pacemaker DDD/R. The single chamber device has the advantages of simpler implantation and lower initial costs, while the dual chamber device offers protection in case atrioventricular conduction disturbances develop in the future. When rigorous attention is paid to the pre-implantation selection criteria, the incidence of reported second- or third-degree atrioventricular block varied between 0.4 and 1.8% per annum. Medical practice, however, has shifted to predominant implantation of DDD/R pacemakers in more than 95% of patients with sick sinus syndrome. Recent publications have reported an increase in left atrial diameter, decrease in left ventricular fractional shortening and increased incidence of atrial fibrillation in patients with DDD/R pacing as compared with patients with single chamber atrial devices. These changes were proportional to the percentage of ventricular paced beats.

New algorithms in dual chamber devices have been developed in order to minimise ventricular stimulation. These are being evaluated at present. In my opinion there is still a place for atrial pacing in selected patients with sick sinus syndrome with a minimum risk of developing complete atrioventricular block. (Neth Heart J 2008;16(Suppl1):S25-S27.)

This year (2008) is the 50th anniversary of the first implantation of a ventricular pulse generator. In the early years, ventricular pacing was the only modality available to treat symptomatic patients with atrioventricular (AV) block as well as the sick sinus syndrome (SSS). The idea to pace the atrium in patients with SSS and intact AV conduction was first realised in 1966 by implantation of electrodes in the wall of either atrium by thoracotomy,¹ and subsequently by the transvenous route. In 1969, Kastor et al. reported on long-term pervenous atrial pacing in five patients with intact AV conduction; this was for the treatment of refractory ventricular arrhythmias in two patients and marked sinus bradycardia in three, two of whom also had paroxysmal supraventricular arrhythmias.² The pervenous method was used to avoid a thoracotomy, and atrial pacing was chosen over ventricular pacing to preserve the normal AV contraction sequence.

The difficulty in the early years of atrial pacing was in positioning the tip of the electrode securely in contact with the right atrial musculature. In 1977, Moss et al. reported their ten-year experience with atrial pacing from the coronary vein in 50 patients with implanted pervenous pacemakers.³ The indications for atrial pacing were symptomatic sinus bradycardia (72%), atrial bradycardia-tachycardia (brady-tachy) syndrome (20%) and recurrent tachyarrhythmias (8%). Follow-up averaged 31 months per patient, with a median of 26 months, range 3 to 9 months. Eleven patients died in the series during the ten years, but pacemaker malfunction could not be implicated as the cause of death in any of these patients. In each case effective pacing was documented during the terminal episode.

The first transvenous implantation of atrial leads in the Netherlands took place in the Catharina Hospital, Eindhoven, in December 1977.⁴ We initially used helicoidal electrodes (Helifix Vitatron Medical B.V., Dieren, the Netherlands) fixed near the base of the right atrial appendage by two or three clockwise turns (figures 1 and 2). Our indications for atrial pacing are shown in table 1, and our pre-implantation requirements in table 2. The His-ventricular (H-V) interval was measured in patients in whom infra Hisian conduction delay could not be excluded. Only patients with a normal H-V interval (35-55 msec) were accepted for atrial pacing.

Figure 1 .

Photograph of the Helifix lead, showing the helicoidal shape of the electrode. The helicoidal shape was constructed from a closed loop, which enables atraumatic fixation around trabeculae in the right ventricle as well as in the atrial appendage.

Figure 2 .

Diagram showing the dimensions and materials of the Helifix lead. The electrode is constructed from platinum-iridium (90-10%) and the surface area was 11mm ². The insulation material of the lead is silicone rubber.

Table 1.

Indications for atrial pacing.

1	Symptomatic bradycardia
2	Brady-tachy syndrome
3	Uncontrollable SV arrhythmias in patients who initially received a Wl pacemaker for brady-tachy syndrome
4	Pacemaker syndrome with Wl pacing in patients with SSS; this group also included patients with ventriculo-atrial conduction and disabling symptoms due to haemodynamic impairment of cardiac performance
5	Selected patients with drug refractory ventricular arrhythmias who responded to overdrive atrial stimulation

Table 2.

Pre-implantation requirements.

1	ECG
	- PR interval ≤0.22 seconds
	- No bundle branch block
2	Atrial pacing up to 140 ppm; atropine 0.5 to 1.0 mg was injected IV if Wenkebach block occurred at a heart rate <140 ppm.

ppm=pulses per minute, IV= intravenously.

Atrial pacing (AAI/R) versus dual chamber pacing (DDD/R)

In patients with SSS and normal AV conduction, physiological pacing can be accomplished with either a single chamber atrial pacemaker AAI/R or a dual chamber pacemaker DDD/R. The single chamber device has the advantages of simpler implantation and lower initial costs, while the dual chamber device offers protection in case AV conduction disturbances develop in the future.

The reported incidence of second- or third-degree AV block in patients with AAI/R pacemakers varied between 0.6%⁵ and 1.8% per annum^6,7 and its incidence was much higher in patients with complete left bundle branch block or bifascicular block.⁷ Elshot reported the incidence of AV block in the first 41 consecutive patients who received AAI pacemakers in Catharina Hospital Eindhoven before October 1980 with a mean follow-up of 12.3 years (range 11-14 years).⁴ The annual incidence of clinically significant AV block was 0.4%. A single patient with brady-tachy syndrome developed permanent grade III AV block during follow-up (2.5%). There were no pacemaker-related deaths.

In all published reports AV conduction disturbances occurred more frequently in patients with brady-tachy syndrome. The antiarrhythmic drug therapy that was prescribed to these patients probably contributed to this.

Should we implant DDD/R pacemakers in all patients with SSS?

Advantage

If complete AV block suddenly develops without an escape rhythm, this pacing modality will promptly stimulate the right ventricle and prevent the occurrence of syncope.

Disadvantages

In a randomised trial to compare AAI/Rand DDD/R pacing in 177 consecutive patients with SSS, Nielsen et al. found during a mean follow-up of 2.9±1.1 years that DDD/R pacing with a fixed long AV delay caused increased left atrial (LA) diameter as measured by M-mode echocardiography while DDD/R pacing with a short AV delay caused both increased LA diameter and decreased left ventricular fractional shortening (LVFS).⁸ No changes occurred in LA or LV diameters or LVFS during AAI/R pacing. Atrial fibrillation was significantly less common during AAI/R pacing. These findings are directly related to the percentage of RV pacing in the programmed DDD/R mode.

Pacemaker manufacturers have developed new algorithms in dual chamber devices that will minimise ventricular pacing.⁹ Clinical studies are in progress in order to evaluate this promising pacing modality.

Are single chamber atrial pacemaker (AAI/R) still implanted?

In Denmark in 2006, an AAI/R system was used in 8.1% of first implants (the Danish Pacemaker and ICD Register). In the Netherlands an AAI/R system was used in 2.8% of all implants in 2004, 2.9% in 2005, and 3% in 2006. A small number of AAI/R pacemakers are still implanted in other countries (including Australia and New Zealand) but not in the United States.

Conclusion

In my opinion there is still a place for the implantation of atrial pacemakers in patients with SSS.

Rigorous attention, however, should be paid to the pre-implantation selection criteria as stated above. The occurrence of complete AV block is seldom reported, and without disastrous consequences. It is advisable to insert two leads at the initial implant with the ventricular lead capped and the atrial lead connected to an atrial demand pacemaker AAI/R. This policy will facilitate eventual upgrading of the system to dual chamber pacing should high grade AV block occur in the future.