Abnormal Right Atrial Electrograms Predict the Transition to Chronic Atrial Fibrillation in Paced Patients with Sick Sinus Syndrome

Sinus bradycardia and sinus pauses immediately after electrical cardioversion of persistent atrial fibrillation--what do they mean?

BACKGROUND

To determine the role of sinus bradyarrhythmia (SB) immediately after electrical cardioversion of persistent atrial fibrillation (AF) on the short-term recurrence rate and long-term pacemaker need and all-cause mortality.

METHODS

SB defined as sinus bradycardia (sinus rate <40 bpm for ≥2 consecutive cycles) and/or sinus pauses (>2 s), were recorded during 5 minutes immediately after successful DC cardioversion in 140 consecutive patients with persistent AF.

RESULTS

SB was observed during the first minute of SR in 31 patients (22%). Sinus bradycardia was present in 27 patients, sinus pauses in 16 (>3 s in 10) patients, and both in 12 patients. Compared to patients without SB, the mean heart rate during the first minute after cardioversion was lower, 57 ± 13 versus 63 ± 11 bpm; P < 0.05, while the mean heart rates during the subsequent 4 minutes were not statistically significantly different. The AF recurrence rates were not significantly different at 1 week (45% vs. 40%), or at 3 months (68% vs. 53%) in patients with or without SB. After a mean follow-up of 86 ± 6 months the pacemaker implantation rate was 10% versus 11% (NS) and an all-cause mortality of 26 versus 18% (NS).

CONCLUSIONS

SB immediately after electrical cardioversion of persistent AF had no significant impact on the 3-month AF recurrence rate, the long-term need for pacemaker or all-cause mortality.

Sinus node revisited

PURPOSE OF REVIEW

Sinus node disease (SND) is a common clinical condition and is the most common indication for permanent pacemaker implantation. This review aims to revisit the complex sinus node anatomy, the evolving understanding of its pacemaking mechanisms, the atrial myopathy in SND and sinus node remodeling.

RECENT FINDINGS

Recent high-density noncontact mapping of the human sinus node showed multiple origins of sinus activation and exit sites with preferential pathways of conduction. Perhaps, a newly described discrete paranodal area containing a molecular mixture of nodal and atrial cells may account for this long recognized discrepancy between the anatomical and functional sinus node. The funny current (I(f)) driven 'membrane clock' is not solely responsible for sinus node automaticity, following recent recognition of the importance of the 'calcium clock'. Several molecular links to sinus node remodeling have recently been identified: loss of connexin-43 expression and down-regulation of I(ca,L) in aging; reduced I(f) and down-regulation of I(f) encoding HCN4 and HCN2 subunits in heart failure; and calcium clock malfunction with down-regulated HCN4, HCN2 and minK in atrial fibrillation.

SUMMARY

Ongoing research with improved technology and techniques continues to unravel new understandings and challenges to the century old discovery of the anatomical sinus node.

Effects of acute autonomic modulation on atrial conduction delay and local electrograms duration in paroxysmal atrial fibrillation

Slowed atrial conduction may contribute to reentry circuits and vulnerability for atrial fibrillation (AF). The autonomic nervous system (ANS) has modulating effects on electrophysiological properties. However, complex interactions of the ANS with the arrhythmogenic substrate make it difficult to understand the mechanisms underlying induction and maintenance of AF.

AIM

To determine the effect of acute ANS modulation in atrial activation times in patients (P) with paroxysmal AF (PAF).

METHODS AND RESULTS

16P (9 men; 59±14years) with PAF, who underwent electrophysiological study before AF ablation, and 15P (7 men; 58±11years) with atrioventricular nodal reentry tachycardia, without documentation or induction of AF (control group). Each group included 7P with arterial hypertension but without underlying structural heart disease. The study was performed while off drugs. Multipolar catheters were placed at the high right atrium (HRA), right atrial appendage (RAA), coronary sinus (CS) and His bundle area (His). At baseline and with HRA pacing (600ms, shortest propagated S2) we measured: i) intra-atrial conduction time (IACT, between RAA and atrial deflection in the distal His), ii) inter-atrial conduction time (interACT, between RAA and distal CS), iii) left atrial activation time (LAAT, between atrial deflection in the distal His and distal CS), iv) bipolar electrogram duration at four atrial sites (RAA, His, proximal and distal CS). In the PAF group, measurements were also determined during handgrip and carotid sinus massage (CSM), and after pharmacological blockade of the ANS (ANSB). AF was induced by HRA programmed stimulation in 56% (self-limited - 6; sustained - 3), 68.8% (self-limited - 6; sustained - 5), and 50% (self-limited - 5; sustained - 3) of the P, in basal, during ANS maneuvers, and after ANSB, respectively (p=NS). IACT, interACT and LAAT significantly lengthened during HRA pacing in both groups (600ms, S2). P with PAF have longer IACT (p<0.05), a higher increase in both IACT, interACT (p<0.01) and electrograms duration (p<0.05) with S2, and more fragmented activity, compared with the control group. Atrial conduction times and electrograms duration were not significantly changed during ANS stimulation. Nevertheless, ANS maneuvers increased heterogeneity of the local electrograms duration. Also, P with sustained AF showed longer interACT and LAAT during CSM.

CONCLUSION

Atrial conduction times, electrograms duration and fractionated activity are increased in PAF, suggesting a role for conduction delays in the arrhythmogenic substrate. Acute vagal stimulation is associated with prolonged interACT and LAAT in P with inducible sustained AF and ANS modulation may influence the heterogeneity of atrial electrograms duration.

Left atrial remodeling in patients with atrial septal defects

BACKGROUND

Information regarding left atrial (LA) substrate in conditions predisposing to atrial fibrillation (AF) is limited.

OBJECTIVE

This study sought to characterize the left atrial remodeling that results from chronic atrial stretch caused by atrial septal defect (ASD).

METHODS

Eleven patients with hemodynamically significant ASDs and 12 control subjects were studied. The following were evaluated using multipolar catheters: effective refractory period (ERP) at 7 sites, P-wave duration (PWD), conduction time, and inducibility of AF. LA electroanatomic maps were created to determine atrial activation, and regional conduction and voltage abnormalities.

RESULTS

Patients with ASDs showed significant LA enlargement (P <0.001), unchanged or prolonged atrial ERPs, increase in LA conduction times (P = 0.03), prolonged PWD (P <0.001), regional conduction slowing (P <0.001), greater number of double potentials or fractionated electrograms (P <0.0001), reduced atrial voltage (P <0.001), and more frequent electrical scar (P = 0.005) compared with control subjects. In addition, patients with ASDs showed a greater propensity for sustained AF with single extrastimuli (4 of 11 vs. 0 of 12, P = 0.04).

CONCLUSION

ASDs are associated with chronic left atrial stretch, which results in remodeling characterized by LA enlargement, loss of myocardium, and electrical scar that results in widespread conduction abnormalities but with no change or an increase in ERP. These abnormalities were associated with a greater propensity for sustained AF.

Sinus Node Disease: An Idiopathic Right Atrial Myopathy

Sinus node disease was previously thought to be a disease limited to the sinus node and its atrial connections. However, recent reports have demonstrated sinus node disease as a disease of the entire right atrial myocardium. These patients have widespread electrophysiological abnormalities of their atria, including prolonged refractory periods and slowed conduction. In addition to these electrical changes, there are significant structural changes, such as fibrosis and fatty infiltration, which can be detected endocardially as regions of fractionated signals, low-voltage electrograms, and electrically silent areas. In most cases, the etiology of these changes is unknown. These changes may contribute to the high prevalence of atrial fibrillation seen in patients with sinus node disease.

Angiotensin-Converting Enzyme Inhibitor Suppresses the Incidence of Prolonged and Fractionated Right Atrial Electrograms

INTRODUCTION

Although prolonged and fractionated right atrial electrograms have been reported as predictors of the development of chronic atrial fibrillation in patients with paroxysmal atrial fibrillation (PAF), the effects of angiotensin-converting enzyme inhibitor (ACEI) on these electrophysiologic abnormalities remain unknown. The purpose of this study was to evaluate whether ACEI influences these electrophysiologic abnormalities of atrial muscle in patients with PAF.

METHODS

While taking oral ACEI for hypertension, 12 patients (ACEI group) with PAF underwent electrophysiologic study (EPS). Catheter mapping of 12 right atrial sites and right atrial extrastimulation were performed during sinus rhythm. Twenty-four age-matched patients with PAF but not taking oral ACEI were included as a control group.

RESULTS

The longest duration of the right atrial electrogram was significantly shorter and the maximum number of fragmented deflections per patient was significantly lower in the ACEI group than in the control group (79 +/- 15 ms vs 100 +/- 15 ms, P < 0.005; 5.5 +/- 1.9 vs 7.9 +/- 2.4, P < 0.001, respectively). The number of abnormal atrial electrograms per patient was significantly lower in the ACEI group than in the control group (0.5 +/- 1.4 vs 2.1 +/- 1.8, P < 0.05). The percentage of patients with at least one abnormal atrial electrogram was significantly lower in the ACEI group than in the control group (16.7% vs 79.2%, P < 0.0005).

CONCLUSIONS

ACEI use is associated with a decrease in the incidence of prolonged and fractionated right atrial electrograms in patients with PAF. In addition, we suggest that ACEI may help prevent PAF from becoming chronic.