INTRODUCTION
Interatrial blocks (IAB) were initially described as partial, when the P-wave duration was ≥120 ms and advanced when the P-wave duration was ≥120 ms and presented a biphasic morphology in the inferior leads (II, III, aVF) 1. These general concepts were then summarized in a consensus document 2, and several studies have since demonstrated the relation between IAB and new or recurrent episodes of atrial fibrillation (AF)3, 4, stroke recurrence 5, and progression from persistent to permanent AF 6.
IAB is also a relatively frequent common finding in patients referred for cardiac implantable electronic device (CIED) implantation, especially those with sick sinus syndrome, perhaps reflecting the existence of extensive atrial cardiomyopathy 7. Some authors have demonstrated the relationship between a pre-existing IAB and the development of new atrial high-rate episodes (AHRE) during routine CIED interrogations 8-10. On the other hand, atrial stimulation may also aggravate or even unmask an IAB, especially in patients with preexisting atrial cardiomyopathy, further evidencing the conduction delay within the atria and hence the duration of the P-wave 11, 12. This is particularly frequent when the atrial lead is positioned in the right atrial appendage (considered the “preferred placement location”). In such cases, the traditional definition of IAB may not apply, because the duration of the paced P-wave may be unusually long and with different morphology patterns. Our study aimed to evaluate whether both sinus and paced P-wave duration before and after implantation of a CIED could predict future development of AHRE and to define the best paced P-wave duration cut-off to predict new AHRE episodes.
METHODS
Patients in sinus rhythm with no previous paroxysmal or persistent AF and with dual-chamber pacemakers (PMs), implantable cardioverter-defibrillators (ICDs), and devices for cardiac resynchronization therapy (CRT) capable of atrial activity monitoring were included in the study. Standard rate-adaptive chamber devices were used (Abbott, St Paul, MN, USA; Medtronic, Inc., Minneapolis, MN, USA). All atrial leads were bipolar and actively placed in the high right atrium (right atrial appendage), and ventricular leads were bipolar and passively placed at the right ventricular apex. By unit protocols, we set out to avoid right ventricular pacing in all dual-chamber PMs by prolonging the AV interval and/or using other dedicated algorithms when deemed necessary. ICDs were set to backup pacing mode (VDI 40 bpm) maintaining atrial sensing. Cardiac resynchronization therapy was programmed with an adequate AV interval to achieve ≥95% of biventricular pacing. Patients with sinus node dysfunction and clinical symptoms due to bradycardia were programmed in AAI/DDDR mode with a minimum frequency of 60 bpm, also using available algorithms to prevent ventricular pacing.
The following clinical and demographic data were obtained for each patient: sex, age, indication for CIED implantation, presence of cardiovascular risk factors (diabetes mellitus [DM], hypertension, and smoking), CHA2DS2-VASc score, presence of chronic obstructive pulmonary disease (COPD), and drugs used. A baseline echocardiographic study, including left ventricular ejection fraction (LVEF), was performed in all patients. Left atrium (LA) size (mm) measurements were obtained in four-chamber view.
All devices were first interrogated 3 months after CIED implantation and every 6 months thereafter. All scheduled PM check-ups were reviewed. Pacemaker atrial stimulation/sense parameters, atrial lead impedance, percentages of atrial and ventricular pacing, AHRE, automatic mode switch episodes, and noise episodes were recorded. AHRE was defined as an episode of atrial rate ≥225 bpm with a minimum duration of 5 min, and the duration of the episodes was divided into four groups (5 min-1 h; 1-12 h; 12-24 h; >24 h).