Dispersion of atrial refractoriness in patients with sinus node dysfunction

Clinical review of sick sinus syndrome and atrial fibrillation

Sick sinus syndrome (SSS) is a set of diseases with abnormal cardiac pacing, which manifests as diverse cardiac arrhythmias, especially bradycardia. The clinical presentation is inconspicuous in the early stage, but with the progression of this disease, patients may present with symptoms and signs of end-organ hypoperfusion. As a common result in the natural history of the disease, SSS coexisting with atrial fibrillation (AF) forms the basis of bradycardia-tachycardia syndrome. Age-related interstitial fibrosis is considered to be the common pathophysiological mechanism between SSS and AF. The combination of these diseases will adversely affect the condition of patients and the efficiency of subsequent treatment. Although the exact mechanism is not clear to date, the extensive structural and electrical remodeling of the atrium are considered to be the important mechanism for the occurrence of AF in patients with SSS. Pacemaker implantation is the first-line treatment for symptomatic patients with SSS and documented bradycardia history. In view of the adverse effects of AF on the treatment of SSS, researchers have focused on evaluating different pacing modes and algorithms to reduce the risk of AF during pacing. Catheter ablation may also be used as an alternative second-line therapy for some patients with SSS and AF.

Long-term clinical outcomes of catheter ablation in patients with atrial fibrillation predisposing to tachycardia-bradycardia syndrome: a long pause predicts implantation of a permanent pacemaker

Background

There is a controversy as to whether catheter ablation should be the first-line therapy for tachycardia-bradycardia syndrome (TBS) in patients with atrial fibrillation (AF).

Methods

We aimed to investigate long-term clinical outcomes of catheter ablation in patients with TBS and AF. Among 145 consecutive patients who underwent catheter ablation of AF with TBS, 121 patients were studied.

Results

Among 121 patients, 11 (9.1%) received implantation of a permanent pacemaker during a mean 21 months after ablation. Length of pause on termination of AF was significantly greater in patients who received pacemaker implantation after ablation than those who underwent ablation only (7.9 ± 3.5 vs. 5.1 ± 2.1 s, p < 0.001). Using a multivariate model, a long pause of 6.3 s or longer after termination of AF was associated with the requirement to implant a permanent pacemaker after ablation (HR 1.332, 95% CI 1.115-1.591, p = 0.002).

Conclusion

This study suggests that, in patients with AF predisposing to TBS, long pause on termination of AF predicts the need to implant a permanent pacemaker after catheter ablation.

Electronic supplementary material

The online version of this article (10.1186/s12872-018-0834-0) contains supplementary material, which is available to authorized users.

Mutation of the Na+/K+-ATPase Atp1a1a.1 causes QT interval prolongation and bradycardia in zebrafish

The genetic underpinnings that orchestrate the vertebrate heart rate are not fully understood yet, but of high clinical importance, since diseases of cardiac impulse formation and propagation are common and severe human arrhythmias. To identify novel regulators of the vertebrate heart rate, we deciphered the pathogenesis of the bradycardia in the homozygous zebrafish mutant hiphop (hip) and identified a missense-mutation (N851K) in Na⁺/K⁺-ATPase α1-subunit (atp1a1a.1). N851K affects zebrafish Na⁺/K⁺-ATPase ion transport capacity, as revealed by in vitro pump current measurements. Inhibition of the Na⁺/K⁺-ATPase in vivo indicates that hip rather acts as a hypomorph than being a null allele. Consequently, reduced Na⁺/K⁺-ATPase function leads to prolonged QT interval and refractoriness in the hip mutant heart, as shown by electrocardiogram and in vivo electrical stimulation experiments. We here demonstrate for the first time that Na⁺/K⁺-ATPase plays an essential role in heart rate regulation by prolonging myocardial repolarization.

Mechanisms of atrial fibrillation in athletes: what we know and what we do not know

Exercise is an emerging cause of atrial fibrillation (AF) in young individuals without coexisting cardiovascular risk factors. The causes of exercise-induced atrial fibrillation remain largely unknown, and conclusions are jeopardised by apparently conflicting data. Some components of the athlete's heart are known to be arrhythmogenic in other settings. Bradycardia, atrial dilatation and, possibly, atrial premature beats are therefore biologically plausible contributors to exercise-induced AF. Challenging findings in an animal model suggest that exercise might also prompt the development of atrial fibrosis, possibly due to cumulative minor structural damage after each exercise bout. However, there is very limited, indirect data supporting this hypothesis in athletes. Age, sex, the presence of comorbidities and cardiovascular risk factors, and genetic individual variability might serve to flag those athletes who are at the higher risk of exercise-induced AF. In this review, we will critically address current knowledge on the mechanisms of exercise-induced AF.

Mitochondrial dysfunction on sinoatrial node and pulmonary vein electrophysiological activities

Atrial fibrillation (AF) is associated with mitochondrial dysfunction. Sinoatrial node (SAN) dysfunction increases arrhythmogenesis of pulmonary veins (PVs), which is the most important trigger of AF; however, it is not clear whether mitochondrial dysfunction differentially regulates electrical activity of SANs and PVs. In the present study, conventional microelectrodes were used to record the action potentials (APs) in isolated rabbit PVs, SANs, left atrium (LA) and right atrium (RA) before and after application of trifluorocarbonylcyanide phenylhydrazone (FCCP; a mitochondrial uncoupling agent) at 10, 100 and 300 nM. FCCP application at 100 and 300 nM decreased spontaneous rates in PVs and in SANs at 10, 100 and 300 nM. FCCP shortened the 20, 50 and 90% AP durations in the LA, and shortened only the 20% AP duration in the RA. FCCP caused a greater rate reduction in SANs than in PVs; however, in the presence of coenzyme-Q₁₀ (10 µM), FCCP reduced the beating rate in PVs and SANs to a similar extent. In SAN-PV preparations with intact electrical connections, FCCP (100 nM) application shifted the SAN-PV electrical conduction into PV-SAN conduction in 5 (62.5%) of 8 preparations. In conclusion, mitochondrial dysfunction modulates PV and SAN electrical activities, which may contribute to atrial arrhythmogenesis.

Catheter ablation of atrial fibrillation in patients with concomitant sinus bradycardia-Insights from the German Ablation Registry

AIMS

This investigation addresses procedural characteristics of catheter ablation in patients with atrial fibrillation (AF) and sinus bradycardia.

METHODS

From the prospective, multi-center German Ablation Registry 1073 patients with sinus rhythm at the time of AF ablation were divided into two groups according to heart rate at start of procedure (A, <60 beats per minute (bpm), n=197; B, 60-99bpm, n=876).

RESULTS

Acute procedural success was high (≥98%) and similar between groups. Procedure duration and energy application time were increased in group A (180min vs. 155min and 2561s vs. 1879s, respectively). Major complications were more frequent in group A (2.2% vs. 0.5%), and a greater proportion of these patients was discharged under antiarrhythmic medication (64% vs. 52%).

CONCLUSION

Catheter ablation of AF with concomitant sinus bradycardia is associated with high procedural efficacy, longer procedure- and energy application durations, and a slightly elevated complication rate.

Atrial remodelling in atrial fibrillation: CaMKII as a nodal proarrhythmic signal

CaMKII is a serine-threonine protein kinase that is abundant in myocardium. Emergent evidence suggests that CaMKII may play an important role in promoting atrial fibrillation (AF) by targeting a diverse array of proteins involved in membrane excitability, cell survival, calcium homeostasis, matrix remodelling, inflammation, and metabolism. Furthermore, CaMKII inhibition appears to protect against AF in animal models and correct proarrhythmic, defective intracellular Ca(2+) homeostasis in fibrillating human atrial cells. This review considers current concepts and evidence from animal and human studies on the role of CaMKII in AF.

Electrolyte disturbances differentially regulate sinoatrial node and pulmonary vein electrical activity: A contribution to hypokalemia- or hyponatremia-induced atrial fibrillation

BACKGROUND

Hypokalemia and hyponatremia increase the occurrence of atrial fibrillation. Sinoatrial nodes (SANs) and pulmonary veins (PVs) play a critical role in the pathophysiology of atrial fibrillation.

OBJECTIVE

The purpose of this study was to evaluate whether electrolyte disturbances with low concentrations of potassium ([K(+)]) or sodium ([Na(+)]) modulate SAN and PV electrical activity and arrhythmogenesis, and to investigate potential underlying mechanisms.

METHODS

Conventional microelectrodes were used to record electrical activity in rabbit SAN and PV tissue preparations before and after perfusion with different low [K(+)] or [Na(+)], interacting with the Na(+)-Ca(2+) exchanger inhibitor KB-R7943 (10 μΜ).

RESULTS

Low [K(+)] (3.5, 3, 2.5, and 2 mM) decreased beating rates in PV cardiomyocytes with genesis of delayed afterdepolarizations (DADs), burst firing, and increased diastolic tension. Low [K(+)] (3.5, 3, 2.5, and 2 mM) also decreased SAN beating rates, with genesis of DADs. Low [Na(+)] increased PV diastolic tension, DADs, and burst firing, which was attenuated in the co-superfusion with low [K(+)] (2 mM). In contrast, low [Na(+)] had little effect on SAN electrical activities. KB-R7943 (10 μΜ) reduced the occurrences of low [K(+)] (2 mM)- or low [Na(+)] (110 mM)-induced DAD and burst firing in both PVs and SANs.

CONCLUSION

Low [K(+)] and low [Na(+)] differentially modulate SAN and PV electrical properties. Low [K(+)]- or low [Na(+)]-induced slowing of SAN beating rate and genesis of PV burst firing may contribute to the high occurrence of atrial fibrillation during hypokalemia or hyponatremia.

Slow sinus heart rate as a potential predictive factor of paroxysmal atrial fibrillation in stroke patients

BACKGROUND

Paroxysmal atrial fibrillation (PAF) is a strong independent risk factor for ischemic stroke and is also associated with stroke severity and mortality. However, the detection rate of PAF in patients with ischemic stroke is limited because they are often asymptomatic or present with sinus rhythm on electrocardiograms (ECGs). In the present study, we aimed to identify predictors of PAF in stroke patients by continuous ECG monitoring of the heart rate in sinus rhythm.

METHODS

We enrolled 741 consecutive patients with acute symptomatic ischemic stroke who were admitted to our hospital. Exclusion criteria were the following: (1) patients with persistent AF, (2) cardiac pacemaker users and (3) incomplete clinical investigations. Each patient was subject to 24-hour Holter ECG, cardiac monitoring by inpatient telemetry and routine transthoracic echocardiography. The minimum and mean sinus heart rates (SHRs) on 24-hour Holter ECGs were recorded. The presence of PAF was judged on the basis of previous history and cardiac studies during hospitalization. Clinical characteristics of the patients with and without PAF were compared, and multiple logistic regression analysis was performed to identify the predictors of PAF.

RESULTS

Of all enrolled patients, 606 (mean age 68.2 years, 63.4% male) were eligible for analysis, and the presence of PAF was confirmed in 116 subjects (19.1%). In the univariate analysis, the patients with and without PAF showed significant differences in age (74.3 vs. 66.7 years, p < 0.001), dyslipidemia (32.8 vs. 50.4%, p = 0.001), chronic heart failure (16.4 vs. 4.7%, p < 0.001), admission National Institute of Health Stroke Scale score (8.5 vs. 6, p < 0.001) and absence of vascular etiology (80.2 vs. 54.1%, p < 0.001). Furthermore, the minimum and mean SHRs were slower in the patients with than in those without PAF (46.5 vs. 54.0 bpm, p < 0.001 and 70.7 vs. 73.8 bpm, p = 0.009, respectively). In 501 (82.7%) out of 606 patients, minimum SHRs were detected at night (from 9:00 p.m. to 7:00 a.m.). A minimum SHR was an independent predictive factor of PAF in the multivariate analysis (odds ratio 1.08, 95% confidence interval 1.05 - 1.12, p < 0.001).

CONCLUSIONS

A slow SHR on monitoring ECG is a potential predictive factor of PAF in patients with ischemic stroke.

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 dysfunction in atrial fibrillation patients: the evidence of regional atrial substrate remodelling

AIMS

It remains unclear as to whether regional atrial substrates of certain areas of the atrium in patients with atrial fibrillation (AF) can be related to sinoatrial node dysfunction. We investigated the relationship between the biatrial substrate characteristics and sinus node function in these patients.

METHODS AND RESULTS

The study enrolled 34 patients (aged 57 ± 11 years old; 20 males) who underwent catheter ablation for symptomatic paroxysmal AF. Sinus node dysfunction was defined as having corrected sinus node recovery time longer than 550 ms. Atrial substrate analyses of both atria and atrial conductive properties were investigated in patients with (Group 1) and without sinus node dysfunction (Group 2). The mean global bipolar voltage of both atria and the atrial refractory period were similar between the two groups. Regional analysis showed that the mean bipolar voltage for patients in Group 1 was lower than in Group 2 (1.0 ± 0.3 vs. 2.1 ± 0.7 mV, P < 0.001) only in the sinus node region, while the electrophysiological properties were similar for both groups in other anatomic regions of both atria. The right atrial total activation time was significantly longer (97 ± 9 vs. 89 ± 10 ms, P = 0.023) and the conduction velocity along the crista terminalis was significantly slower (1.0 ± 0.2 vs. 1.2 ± 0.3 m/s, P = 0.019) in Group 1 patients than in Group 2 patients.

CONCLUSION

In patients with AF, regional atrial remodelling near the sinus node area was associated with sinus node dysfunction.

Prevalence of atrial fibrillation and stroke in paced patients without prior atrial fibrillation: a prospective study

BACKGROUND

Several reports suggest that the incidence of stroke and atrial fibrillation is reduced in patients receiving physiologic pacemakers, compared with patients receiving a ventricular pacemaker.

HYPOTHESIS

The study was undertaken to address the impact of different pacing modalities on the incidence of stroke and atrial fibrillation.

METHODS

We prospectively analyzed 210 consecutive patients. Those with previous episodes of cerebral ischemia and/or atrial fibrillation were excluded from the study. The study population included 100 patients paced for total atrioventricular (AV) block or second-degree AV block (type II Mobitz) and 110 patients paced for sick sinus syndrome (SSS). The pacing mode was randomized. All patients underwent a brain computed tomography (CT) scan at the date of enrollment and after 1 and 2 years. Patients were followed for 2 years, and the incidence of atrial fibrillation and stroke was evaluated.

RESULTS

The incidence of atrial fibrillation was 10% at 1 year and 11% at 2 years. Comparing the different pacing modalities, we reported an increase in the incidence of atrial fibrillation in patients receiving ventricular pacing (p < 0.05). On the other hand, no difference was found between patients paced for AV block and those paced for SSS. At the end of follow-up, we reported 29 cases of cerebral ischemia: 9 patients had AV block while 20 had SSS (p < 0.05). Comparing the different pacing modalities, there was an increase in the incidence of stroke in patients receiving ventricular pacing (p < 0.05).

CONCLUSION

There was an increase in the incidence of stroke and atrial fibrillation in patients with ventricular pacing.

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.

Increased P wave dispersion after the radiofrequency catheter ablation in overt pre-excitation patients: the role of atrial vulnerability

The pathogenesis of paroxysmal atrial fibrillation (PAF) in patients with overt pre-excitation and effect of elimination of accessory pathways on the appearance of AF are still controversial. We demonstrated the increased P max and P wave dispersion (PWD) reflecting more inhomogeneous and prolonged atrial conduction in patients with Wolff-Parkinson-White (WPW) syndrome and PAF attacks. One-hundred and fifty-one patients who underwent radiofrequency (RF) catheter ablation due to paroxysmal tachycardia medicated by accessory pathway were enrolled in this study. The patients were classified into two groups according to the presence of previous PAF attacks. We compared the clinical characteristics, echocardiograhic findings, P max and PWD values measured after normalization of PR intervals and disappearance of pre-excitation after ablation in overt pre-excitation patients. Although the differences in age, left atrial diameter and left ventricular ejection fraction (LVEF) were not significant in both groups, P maximum (130.0+/-8.4 vs. 122.3+/-8.7 ms, p=0.002) and P wave dispersion values measured after ablation (50.3+/-7.2 vs. 35.7+/-6.1 ms, p=0.001) were significantly higher in patients with previous PAF attacks. Accessory pathway (AP) antegrade and retrograde effective refractory period (ERP) values were shorter (276+/-27.3 vs. 321.0+/-48.7, p=0.001; 263.4+/-41.3 vs. 299.7+/-38.2, p=0.002, respectively) in patients with PAF attack when compared to those without PAF attacks. Higher P wave dispersion values in patients with previous PAF attacks suggest the important role of inhomogenous and discontinuous propagation of sinus impulses. Therefore, we concluded that not only the accessory pathway but also inhomogenous propagation of sinus impulses may play an important role in occurrence of AF in patients with pre-excitation.

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

Although pacing therapy for sick sinus syndrome (SSS) is established, the risk of developing chronic atrial fibrillation (CAF) makes pacing therapy infeasible in some patients. We evaluated whether electrophysiological characteristics of atrial muscle can serve as predictors of the transition to CAF after pacemaker implantation in patients with SSS. Eighty-nine patients with SSS underwent electrophysiological study before pacing therapy. Catheter mapping of 12 right atrial sites was performed during sinus rhythm during electrophysiological. An abnormal atrial electrogram was defined as having a duration of 100 ms or longer, or eight or more fragmented deflections, or both. Right atrial extrastimulation was also performed for atrial vulnerability. After electrophysiological study, all patients underwent pacemaker implantation and were followed up. During the follow-up period of 85 +/- 50 months, development of CAF was observed in 12 patients (group A). The remaining 77 patients remained in sinus rhythm (group B). There were significantly more abnormal atrial electrograms in group A than group B (2.7 +/- 2.3 vs 0.8 +/- 1.2; P < 0.001). The distribution of abnormal atrial electrograms was also greater in group A; patients in group A had more abnormal atrial electrograms than patients in group B in both the high and middle right atrium (P < 0.005 and P < 0.01, respectively). Kaplan-Meier analysis showed that almost 50% of the paced patients with abnormal atrial electrograms (n = 42) developed CAF (P < 0.005). Our data suggest that the existence of abnormal atrial electrograms is predictive of the transition to CAF in paced patients with SSS.

Monophasic action potentials of the right atrium in patients with paroxysmal atrial fibrillation

To investigate the mechanism of atrial fibrillation (AF), monophasic action potentials (MAPs) from the atrial myocardium were studied in 7 patients with paroxysmal AF (PAF) and in 7 control individuals. The MAPs were recorded using a contact catheter during sinus rhythm and continuous pacing at the high right atrium (HRA) with pacing cycle lengths of 600, 500 and 400 ms. MAPs were obtained from 6 sites in each participant. The MAPD90 was measured from onset to 90% of MAP repolarization. Average, maximal and minimal MAPD90 (avMAPD90, maxMAPD90 and minMAPD90) were obtained from all participants. The dispersion of MAPD90 (dispMAPD90) was defined as the difference between maxMAPD90 and minMAPD90. The width of each atrial potential (WAP) and the wavelength index (WLI=MAPD90/WAP) were determined. Average, maximal and minimal WLI (avWLI, maxWLI and minWLI) were obtained from all participants. The avMAPD90 and maxMAPD90 did not significantly differ between the 2 groups. The minMAPD90 in the PAF group was significantly smaller than that in the control group at HRA pacing with cycle lengths of 500 and 400 ms (210+/-18ms vs 245+/-14 ms, p<0.05; 207+/-23 ms vs 238+/-20 ms, p<0.05; respectively). The dispMAPD90 was significantly longer in the PAF group than in the control group during sinus and HRA pacing. The WAP value did not differ between the 2 groups. The minWLI in the PAF group was significantly smaller than that in the control group at HRA pacing with cycle lengths of 500 and 400 ms (3.3+/-0.5 vs 3.8+/-0.3, p<0.05; 3.2+/-0.4 vs 3.7+/-0.3, p<0.02). A shortened and widened dispersion of atrial refractoriness may play an important role in the genesis of AF. Furthermore, smaller wavelengths may form in the atrium of patients with PAF.

Different patterns of atrial activation in idiopathic atrial fibrillation: simultaneous multisite atrial mapping in patients with paroxysmal and chronic atrial fibrillation

OBJECTIVES

We aimed to evaluate: 1) the behavior of electrical activity simultaneously in different atrial regions during atrial fibrillation (AF); 2) the difference of atrial activation between paroxysmal and chronic AF; 3) the atrial refractoriness dispersion; and 4) the correlation between the effective refractory periods (ERPs) and the FF intervals.

BACKGROUND

Little data exist on the electrophysiologic characteristics of the different atrial regions in patients with AF. A more detailed knowledge of the electrical activity during AF may provide further insights to improve treatment of AF.

METHODS

Right and left atria were extensively mapped in 30 patients with idiopathic AF (18 paroxysmal and 12 chronic). In different atrial locations, we analyzed 1) the FF interval duration; and 2) the grade of organization and, in case of organized electrical activity, the direction of atrial activation. Furthermore, in patients with paroxysmal AF, we determined the atrial ERP, evaluated the ERP dispersion and assessed the presence of a correlation between the ERPs and the FF intervals.

RESULTS

In patients with chronic AF, we observed a shortening of the FF intervals and a greater prevalence of disorganized activity in all the atrial sites examined. In patients with paroxysmal AF, a significant dispersion of refractoriness was observed. The right lateral wall showed longer FF intervals and more organized atrial activity and, unexpectedly, the shortest mean ERPs. In contrast, the septal area showed shorter FF intervals, greater disorganization and the longest mean ERPs.

CONCLUSIONS

Electrical activity during AF showed a significant spatial inhomogeneity, which was more evident in patients with paroxysmal AF. The mean FF intervals did not correlate with the mean ERPs.

Clinical study to investigate the predictive parameters for the onset of atrial fibrillation in patients with essential hypertension

BACKGROUND

The risk factors involved in the onset of atrial fibrillation (AF) are well known, but the predictive clinical and paraclinical parameters for the onset of AF in hypertensive patients have not been investigated specifically.

METHODS AND RESULTS

We retrospectively analyzed 97 consecutive patients with hypertension and no known history of AF or cardiovascular events who attended the cardiology outpatient clinic. The analysis was based on clinical data, the noninvasive ambulatory 24-hour measurement of blood pressure (AMBP), a standard 12-lead electrocardiogram, and a Doppler echocardiogram. After a mean follow-up of 25 +/- 3 months, 19 (19. 5%) patients had AF, 3 (15.8%) of whom had a cerebrovascular accident. The patients with AF were older than the others and their AMBP showed higher mean systolic diurnal and nocturnal blood pressures, though no differences in the clinical blood pressure readings were present. On the electrocardiogram, the maximum duration of the P wave and its dispersion were more prolonged in the patients with AF. On the Doppler echocardiogram, left ventricular mass and left atrial dimension were higher in the patients with AF, and the A-wave velocity of diastolic mitral flow was reduced in these patients. In the multivariate analysis, age (odds ratio 3.28, P <.001), diurnal systolic blood pressure (odds ratio 1.35, P <.01) and nocturnal systolic blood pressure (odds ratio 1.16, P <.01), maximum duration of the P wave (odds ratio 2.09, P <.01), dispersion of the P wave (odds ratio 2.52, P <.001), echocardiographic left ventricular mass (odds ratio 1.43, P <.01), left atrial dimension (odds ratio 2.81, P <.001), and velocity of the A wave (odds ratio 2. 24, P <.01) were independent predictors for the onset of AF. After correction for age, maximum duration of the P wave (odds ratio 1.34, P <.01), dispersion of the P wave (odds ratio 1.63, P <.001), and the velocity of the A wave (odds ratio 1.42, P <.01) remained independent predictors for the onset of AF.

CONCLUSIONS

In patients with hypertension, age and the level of diurnal and nocturnal systolic blood pressures measured by 24-hour AMBP are important independent predictors for the onset of AF. Independent of age, increases in left atrial dimension and left ventricular mass, prolongation of the maximum duration and dispersion of the P wave and reduced A-wave velocity are also predictors for the onset of AF.

Atrial pacing for the prevention of atrial fibrillation after cardiovascular surgery

OBJECTIVE

The purpose of this study was to determine the efficacy of atrial pacing in the prevention of atrial fibrillation following cardiovascular surgery.

BACKGROUND

Although pharmacologic therapy has been used to help prevent postoperative atrial fibrillation, it suffers from limited efficacy and adverse effects. In the nonoperative setting, novel pacing strategies have been shown to reduce recurrences of atrial fibrillation and prolong arrhythmia-free periods in patients with paroxysmal atrial arrhythmias.

METHODS

A total of 154 patients (115 men; mean age, 65 +/- 10 years; ejection fraction, 53 +/- 10%) undergoing cardiac surgery (coronary artery bypass surgery, 88.3%; aortic valve replacement, 4.5%; coronary bypass + aortic valve replacement, 7.1%) had right and left atrial epicardial pacing electrodes placed at the time of surgery. Patients were randomized to either no pacing, right atrial (RAP), left atrial (LAP) or biatrial pacing (BAP) for 72 h after surgery. Beta-adrenergic blocking agents were administered concurrently to all patients following surgery.

RESULTS

There was a reduction in the incidence of postoperative atrial fibrillation from 37.5% in patients receiving no postoperative pacing to 17% (p < 0.005) in patients assigned to one of the three pacing strategies. The length of hospital stay was reduced by 22% from 7.8 +/- 3.7 days to 6.1 +/- 2.3 days (p = 0.003) in patients assigned to postoperative atrial pacing. The incidence of atrial fibrillation was lower in each of the paced groups (RAP, 8%; LAP, 20%; BAP, 26%) compared with patients who did not receive postoperative pacing (37.5%).

CONCLUSION

Postoperative atrial pacing, in conjunction with beta-blockade, significantly reduced both the incidence of atrial fibrillation and the length of hospital stay following cardiovascular surgery. Additional studies are needed to determine the most effective anatomic pacing site.

Electrophysiologic characteristics of the atrium in sinus node dysfunction: atrial refractoriness and conduction

INTRODUCTION

Clinical electrophysiology (EP) has focused attention on the EP properties of atrial muscle in patients with atrial fibrillation (AF). Patients with sinus node dysfunction (SND) sometimes are included in these studies, but the characteristics of these patients with SND alone appear less well investigated.

METHODS AND RESULTS

We reviewed EP data of 46 patients (mean age 70 +/- 8 years) with SND, who underwent EP study for evaluation of the atrial substrate. In 16 patients, a history of paroxysmal AF was documented, but not in the remaining 30 patients who had SND alone. We considered as control a group of 25 subjects (mean age 63 +/- 14 years), who were referred to our EP laboratory for unexplained syncope or AV conduction disturbances. Following pharmacologic washout and at a drive cycle of 600 msec, effective (ERP) and functional refractory periods (FRP), S1-A1 and S2-A2 latency, A1 and A2 width, latent vulnerability index (ERP/A2), and P wave duration on the surface ECG were measured. Intra-atrial conduction times were measured from the stimulus artifact by pacing the high right atrium (HRA), to the corresponding atriograms at the AV node (HRA-AVN), low lateral atrium (HRA-LLA), and low interatrial septum close to the coronary sinus ostium (HRA-CSO). Compared with the control group, SND patients did not show differences in ERP (238 +/- 26 msec vs 250 +/- 29 msec), FRP (274 +/- 25 msec vs 280 +/- 32 msec), S1-A1 (38 +/- 15 msec vs 33 +/- 11 msec) and S2-A2 latency (67 +/- 24 msec vs 63 +/- 25 msec), or HRA-AVN (81 +/- 24 msec vs 65 +/- 19 msec), HRA-LLA (36 +/- 30 msec vs 40 +/- 27 msec), and HRA-CSO (77 +/- 17 msec vs 80 +/- 15 msec) conduction times. In contrast, we observed strong differences in atriogram durations A1 (59 +/- 19 msec vs 39 +/- 13 msec; P < 0.001) and A2 (92 +/- 28 msec vs 57 +/- 18 msec; P < 0.001), as well as in the latent vulnerability index ERP/A2 (2.8 +/- 1.2 msec vs 4.8 +/- 1.7; P < 0.001). Also, the P wave was slightly longer (104 +/- 18 msec vs 94 +/- 45 msec; P < 0.05). No significant statistical difference in EP parameters was found between SND patients with or without documented AF.

CONCLUSION

In patients with SND, atrial refractoriness appears similar to that of control subjects. The most important EP abnormality appears to be local conduction slowing disturbances, with prolonged basal and postextrastimuli atriograms, responsible for a lower vulnerability index. This could explain, at least in part, the tendency of patients with SND to develop AF during their natural history. Normality of atrial refractoriness, in contrast to atrial conduction disorders, might explain why atrial pacing shows a preventative effect on the development of AF and why antiarrhythmic drugs often are ineffective.

Catheter mapping of spontaneous and induced atrial fibrillation in man

The clinical electrophysiologic study of atrial fibrillation [AF] has recently progressed from static characterization of the substrate to the dynamic investigation of both induced and spontaneous AF in man. Prior studies have demonstrated inhomogeneity and greater dispersion of atrial refractoriness in patients with AF, but recently atrial electrical remodeling with consequent abbreviation of atrial refractory periods has also been reported. Yet further experimental observations have suggested the existence of additional arrhythmogenic mechanisms for certain AF subsets. These include studies that have demonstrated a stable atrial flutter circuit in one atrium with fibrillatory conduction or a focal atrial tachyarrhythmia arising commonly in the left atrium. Efforts at catheter mapping of AF are now in progress. New mapping techniques and novel devices are currently being employed. We have performed catheter mapping simultaneously in right and left atrial sites at onset and during sustained pacing-induced and spontaneous AF in patients with ischemic and/or hypertensive heart disease. Atrial premature complexes that initiated spontaneous AF typically had coupling intervals ranging from 260 to 400 ms and most frequently arose in the crista terminalis, right atrioventricular junction or superior left atrium. AF at onset showed discrete electrograms at virtually all right and left atrial regions mapped and the region of earliest atrial activation during AF was in close proximity to the premature complexes in over 90% of patients. The regional atrial activation sequence for the first 10 AF beats demonstrated stable or unstable patterns in individual patients. In contrast to spontaneous AF, the initial arrhythmia of induced AF was seen to have a significantly different site of earliest atrial activation but similar discrete electrograms in different atrial regions. However, as with spontaneous AF, the site of extrastimulus delivery was in close proximity to the first induced beat. We conclude that regional catheter mapping of AF is feasible and safe in man and organized electrical activity is frequently observed at AF onset in patients with heart disease. Both right and left atrial regions can be the source of atrial premature complexes and at the onset of spontaneous AF. Induced AF may have differing activation patterns than spontaneous AF but both demonstrate earliest activation in proximity to the initiating atrial premature complex. These findings may help explain therapeutic benefits of right and left atrial interventions and pacing therapies in AF.

Regional endocardial mapping of spontaneous and induced atrial fibrillation in patients with heart disease and refractory atrial fibrillation

We performed simultaneous catheter mapping of right and left atrial regions at onset and during sustenance of spontaneous atrial fibrillation (AF) in patients with ischemic and/or hypertensive heart disease. Seventeen patients with structural heart disease had spontaneous and electrically induced AF episodes mapped from their onset simultaneously in multiple right and left atrial regions. Atrial premature complexes (APCs) that initiated spontaneous AF had coupling intervals ranging from 260 to 400 ms (mean 332 +/- 61), most commonly arising from the lateral right atrium (31%), right atrioventricular junction (13%), atrial septum (6%), superior left atrium (25%), or inferior left atrium (25%). APC morphology on surface electrocardiograms did not correlate with origin in specific atrial regions. The earliest regions of atrial activation for the first AF cycle were the lateral right atrium (n = 5), superior left atrium (n = 4), distal or mid coronary sinus (n = 4), atrial septum (n = 2), and right atrioventricular junction at the His bundle location (n = 2). Spontaneous AF at onset usually showed discrete but irregular electrograms at virtually all right and left atrial sites mapped, with a reproducible region of AF initiation in all 8 patients with multiple events. The region of earliest atrial activation at spontaneous AF onset was in close proximity to the APC origin in 15 of 16 patients (94%), and 39 of 40 episodes (97%) mapped. Stable patterns of right and left atrial activation were observed at AF onset in 14 patients. Induced AF elicited with right atrial stimulation demonstrated different sites of earliest regional atrial activation at onset compared with spontaneous AF events in 4 of 8 patients. However, discrete intracardiac electrograms were also present in induced AF in all of the mapped atrial regions. Furthermore, the site of extrastimulus delivery in induced AF was also found to be in close proximity to the earliest region of atrial activation for the first AF beat. We conclude that spontaneous AF is initiated by APCs arising in different right or left atrial regions in patients with structural heart disease and the initial region of atrial activation in AF is in proximity to the region of APC origin. Organized and repetitive electrical activation is frequently observed in both right and left atria at AF onset. Although electrically induced AF may have different activation patterns than spontaneous AF at onset in many patients, both types of AF demonstrate organization and earliest atrial activation in proximity to the initiating APC.

Heterogeneous changes in electrophysiologic properties in the paroxysmal and chronically fibrillating human atrium

INTRODUCTION

The regional changes in atrial electrophysiologic properties related to atrial fibrillation (AF) in patients with paroxysmal AF (PAF) and chronic AF (CAF) remain unclear. The purpose of this study was to investigate the regional changes in atrial electrophysiology in patients with AF.

METHODS AND RESULTS

We evaluated the atrial electrophysiology at different sites (high right atrium, low right atrium [LRA], and distal coronary sinus [DCS]) in 11 patients with CAF, 8 patients with PAF, and 10 controls. Patients with CAF had significantly prolonged interatrial conduction and corrected sinus node recovery time, and shortened atrial effective refractory period (ERP) with loss of rate-related adaptation in the DCS, but had paradoxic prolongation of atrial ERP in the LRA, as compared with patients with PAF and the controls. As a result, the spatial distribution of atrial ERP that was observed in the controls and in patients with PAF was reversed in patients with CAF, without an increase in the dispersion of atrial refractoriness. Patients with PAF showed intermediate changes in atrial conduction times and atrial refractoriness as compared with patients with CAF and controls.

CONCLUSION

There was a regional heterogeneity on the changes of atrial electrophysiology in different parts of the atrium, and the "normal" spatial distribution of atrial refractoriness was reversed in patients with CAF. The electrophysiologic changes observed in patients with PAF appear to behave as if in transition from the control state to CAF, suggesting progressive changes in atrial electrophysiologic properties.

Regional right and left atrial activation patterns during single- and dual-site atrial pacing in patients with atrial fibrillation

We examined the activation of the right atrium and left atrium by pacing from different atrial sites using several single- and dual-site atrial pacing modes in patients with atrial fibrillation or flutter. We also analyzed the effect of these pacing modes on fixed coupled extrastimuli in this population. Patients underwent detailed mapping of regional right atrial (RA) and left atrial (LA) sites. Bipolar pacing was performed individually from the high right atrium, coronary sinus ostium, and the distal coronary sinus, and simultaneously from the high right atrium and coronary sinus ostium (dual-site RA pacing) or high right atrium and distal coronary sinus (biatrial pacing). Extrastimuli were delivered from the high right atrium at fixed coupling intervals of 350 and 250 ms. Twenty patients with atrial fibrillation were studied. P-wave duration during pacing was significantly abbreviated by both dual-site RA and biatrial pacing (p <0.001 vs high RA pacing, respectively) but not by any other single-site atrial pacing method. Both dual-site atrial pacing modes also significantly abbreviated P wave durations for closely coupled high RA premature beats (p <0.001) in contrast to high RA pacing. During the basic pacing drive and for high RA extrastimuli, RA activation at the crista terminalis and atrial septum was comparable in sinus rhythm, high RA pacing, and in both dual-site atrial pacing methods, but was significantly delayed by coronary sinus ostial and distal coronary sinus pacing. In contrast, proximal coronary sinus activation was delayed with high RA pacing compared with all other pacing modes, and high RA extrastimuli encountered reduced conduction delay at this location with dual-site atrial pacing modes. LA activation was advanced superiorly by both single-site coronary sinus pacing methods and both dual-site atrial pacing techniques. Inferior and lateral LA activation was advanced by all pacing modes using a coronary sinus pacing site. However, earlier activation of LA sites occurred for high RA premature beats after both dual-site pacing methods (p <0.05) compared with single-site pacing modes. Incremental conduction delay at different atrial regions for closely coupled high RA extrastimuli ranged from 33% to 120% during high RA pacing and was significantly attenuated at multiple RA and LA sites by dual-site RA and biatrial pacing. Distinct global, as well as regional electrophysiologic effects, may mediate the variable antiarrhythmic effects of different and novel atrial pacing methods.

Atrial vulnerability in patients with paroxysmal "lone" atrial fibrillation

Little is known about the electrophysiological properties of the atrium predisposing to paroxysmal atrial fibrillation (AF), especially in patients without structural heart disease. This study was conducted to analyze intraatrial conduction, atrial refractoriness, and arrhythmia inducibility in patients with lone paroxysmal AF. An electrophysiological study was performed in 24 patients with a documented history of lone paroxysmal AF but in sinus rhythm at the time of the electrophysiological study. Twelve patients without any history of atrial arrhythmias served as controls. The patients with lone paroxysmal AF showed a significant prolonged local conduction time S1A1 (70 +/- 21 ms vs 36 +/- 12 ms, P < 0.0001), a lack of rate adaptation of the functional refractory period (FRP changes/cycle length changes < 10% in 15 of 24 patients with lone paroxysmal AF vs 1/12 controls, P = 0.002) and a higher incidence of inducible AF with only one extrastimulus (13/24 vs 0/12, P = 0.0014). The total P wave duration in the surface ECG (89 +/- 14 ms vs 83 +/- 8 ms, P = 0.15), the intraatrial conduction time (36 +/- 14 ms vs 28 +/- 8 ms, P = 0.07), the presence of a fragmented atrial electrogram (16/24 vs 7/12, P = 0.62), the absolute value of the effective refractory period (204 +/- 28 ms vs 212 +/- 23 ms, P = 0.42), and the vulnerability index (3.0 +/- 1.5 vs 3.6 +/- 1.5, P = 0.26) were not statistically different between the two groups. The presence of a prolonged (> 50 ms) S1A1 and/or the presence of a lack of rate adaptation of the FRP and/or the presence of inducible AF identified patients with spontaneous lone paroxysmal AF with a sensitivity of 96%, a specificity of 67%, a positive predictive value of 85%, and a negative predictive value of 89%. In patients with lone paroxysmal AF, the electrophysiological study using conventional techniques allows not only to detect AF inducibility using a nonaggressive protocol, but also to reveal several electrophysiological abnormalities related to the atrial substrate itself. This atrial vulnerability may explain the high incidence of recurrences in patients with lone paroxysmal AF.

Power spectral analysis of heart period variability of preceding sinus rhythm before initiation of paroxysmal atrial fibrillation

Time domain analysis of heart period variability in patients without structural heart disease demonstrated increased parasympathetic modulation before paroxysmal atrial fibrillation (AF) occurring predominantly at night. However, diurnal differences in autonomic activity preceding AF episodes in a diverse patient population have not been assessed. Accordingly, we performed spectral analysis of heart period variability on Holter recordings during sinus rhythm preceding AF in 29 patients, 17 with night and 12 with day episodes. Samples taken 5, 10, and 20 minutes before AF onset were compared. Normalized high-frequency (HF) spectral power change was greater when comparing the interval 10 to 5 minutes with 20 to 10 minutes preceding AF in 26 of 29 patients (0.09 +/- 0.07 vs 0.03 +/- 0.02; p < 0.0001). HF spectral power increased before 3 of 12 AF episodes during the day compared with 15 of 17 AF episodes during the night (p = 0.001). Nocturnal AF episodes were preceded by increased HF spectral power in the 5- versus the 20-minute sample expressed as natural logarithm-transformed values (5.6 +/- 4.8 vs 4.2 +/- 4.0; p < 0.005) and normalized values (0.19 +/- 0.09 vs 0.10 +/- 0.07; p < 0.02), a decrease in low-frequency/HF ratio (1.05 +/- 0.61 vs 2.21 +/- 1.75; p < 0.05) and heart rate (60 +/- 13 vs 71 +/- 13 beats/min; p = 0.06). Structural heart disease was more common with daytime than nocturnal AF episodes (58% vs 18%, p < 0.05). In conclusion, HF spectral power change was increased preceding most AF episodes. However, diurnal differences were demonstrated. Contrary to daytime AF, increased parasympathetic activity preceded predominantly nocturnal AF, mostly in younger patients with structurally normal hearts.

Electrophysiological properties of the fibrillating atrium: implications for therapy

1. Atrial fibrillation (AF) is the most commonly occurring cardiac dysrhythmia and remains a challenge to medical therapy. Although the disorder has been recognized for over 100 years, surprisingly very little is understood about its pathophysiology. Over the past decade, a variety of experimental and animal models of AF have been developed and these have provided insights into the mechanism of AF. 2. The pathophysiology of AF is complex. Atrial fibrillation can be caused either by a single source of very rapid impulses or, in the majority of cases, by multiple random re-entering wavelets. The notion that AF may be initiated by a single rapid firing focus and the perpetuation of AF may be partly dependent on macro re-entry around the natural atrial orifices provides a new potential curative therapy for AF by radiofrequency ablation. 3. Shortening of atrial wavelength, either by slow atrial conduction velocities, short atrial refractory periods or both, seems to predispose to development of intra-atrial re-entry and, thus, AF. The functional mechanism by which anti-arrhythmic drugs terminate AF appears to be by prolonging the wavelength and decreasing the number of re-entry wavelets. These understandings are important for the future development of effective anti-arrhythmic agents against AF. 4. The presence of a short and variable excitable gap during AF may be potentially important for termination of AF by pacing. 5. New insights are being gained into the potential role and mechanism of electrical remodelling of the atrium due to AF. Repeated induction of AF by rapid atrial pacing leads to a shortening of atrial refractoriness with loss of rate adaptation, which favours the induction and maintenance of AF. These electrophysiological changes were assumed to occur during repeated AF and to facilitate the generation of multiple re-entrant wavelets. These data suggest that prompt restoration of sinus rhythm and new novel therapy that prevents or diminishes electrical remodelling may promote maintenance of sinus rhythm after successful cardioversion.

Correlation between initial potentials on a signal-averaged P-wave and indice of electrophysiologic measurements in the right atrium

The aim of this study was to determine whether initial potentials of the P-wave on a signal-averaged electrocardiogram (SAE) during sinus rhythm reflect indices of electrophysiologic measurements in the high lateral right atrium. A total of 67 patients underwent P-wave signal averaging during electrophysiologic testing. The correlation between root mean square voltages for the initial 10 and 20 msec of the P-wave on the SAE and indices of electrophysiologic measurements, sinus node recovery time (SRT) and sinoatrial conduction time (SACT), obtained from programmed stimuli, was evaluated. It was found that the initial potentials of the P-wave on the SAE correlated negatively with SRT and SACT (-0.37 < or = r < or = -0.30). It was concluded that the initial potentials correlated with indices of electrophysiologic measurements, although the statistical significance was weak.

Dependency on atrial electrophysiological properties of appearance of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome: evidence from atrial vulnerability before and after radiofrequency catheter ablation and surgical cryoablation

The pathogenesis of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome and the effects of elimination of accessory pathways on the appearance of atrial fibrillation are still controversial. Fifty-four patients with Wolff-Parkinson-White syndrome were classified into three groups: a No AF group (n = 24), patients without paroxysmal atrial fibrillation; an RF-AF Group (n = 12), patients with paroxysmal atrial fibrillation whose accessory pathways were eliminated using radiofrequency catheter ablation; and a Cryo-AF Group (n = 18), patients with paroxysmal atrial fibrillation whose accessory pathways were eliminated with surgical cryoablation. The electrophysiological characteristics of each group were evaluated prior to and following the elimination of their accessory pathways. As indices of atrial vulnerability, the presence of fragmented atrial activity and repetitive atrial firing zones were assessed. Inducibility of atrial fibrillation was significantly reduced following ablation of accessory pathways in the Cryo-AF group (83.3%-5.6%, P < 0.0001), while it was unchanged in the RF-AF group (83.3%-75%). In preablation studies, the effective refractory periods of the atrium in the RF-AF group and the Cryo-AF group were significantly shorter compared with the No AF group (204 +/- 18 ms, 197 +/- 16 ms vs 246 +/- 44 ms, respectively, P < 0.0001). Following ablation, the effective refractory period for patients in the Cryo-AF group was significantly prolonged compared with before ablation (197 +/- 16 ms to 232 +/- 24 ms, P < 0.0001). As a result of this prolongation of the effective refractory period of the atrium, the fragmented atrial activity and repetitive atrial response zones narrowed following ablation in the Cryo-AF group, but not in the RF-AF group. Therefore, the pathogenesis of atrial fibrillation in patients with Wolff-Parkinson-White syndrome may depend on the refractory period of the atrium rather than on the presence of accessory pathways.

Wavelength and atrial vulnerability: an endocavitary approach in humans

If atrial vulnerability parameters are well defined, wavelength (WL) measurement (conduction velocity x refractory period), has never been assessed through an endocavitary electrophysiological exam. We investigated 30 patients (14 female, mean age 63.4 +/- 13 y.o.), 10 with paroxysmal atrial fibrillation (PAF group), 10 with ischemic cerebral injury (ICI group) by comparison with 10 controls (C group). The upper to lower right atrium conduction time and velocity were measured in the right atrium with a decapolar electrode catheter applied along the free wall. Others parameters correlated to atrial excitability were also taken into account: effective (ERP) and functional refractory periods (FRP); spontaneous or paced atrial electrogram (A1) or extrastimulated atrial electrogram (A2) widths, ERP/A2 ratio, provocative atrial testing. Measurements were taken in sinus rhythm and in 600-460 ms paced cycle lengths. If ERP, FRP, A1 widths are the same in the 3 groups, PAF and ICI groups have a significant increased conduction time and lower conduction velocity, leading to a shorter A1 WL during 600 and 460 ms paced rhythms (p < 0.05) and A2 WL during 460 ms paced rhythm. The provocative testing was positive in 60% of PAF and ICI groups, and there is a significant correlation between arrhythmia induction and 600 ms A1 WL or 460 ms A2 WL. This electrophysiological study suggests the possibility of an approach in humans of wavelength concept and proves the presence of correlation between a short wavelength and atrial spontaneous or induced arrhythmias. A no-arrhythmia band (A1 WL > 17 cm during 600 ms paced rhythm, A1 WL > 16 cm or A2 WL > 12 cm during 460 ms paced rhythm) and a fibrillation-band (A1 WL < 12 cm during 600 and 460 ms pacing, A2 WL < 7 cm during 460 ms pacing) can be defined. Therefore, the ICI group has the same atrial pattern as the AF group.

Atrial electrophysiological features in patients with Wolff-Parkinson-White and atrial fibrillation: absence of rate adaptation of intraatrial conduction time parameters

Clinical electrophysiology has not yet clearly defined atrial features that can predict spontaneous occurrence of atrial fibrillation (AF). The aim of this work was to identify atrial electrophysiological features that can distinguish Wolff-Parkinson-White patients with spontaneous AF from those without this arrhythmia. Sixty-nine patients with Wolff-Parkinson-White were divided into three groups: group I (16 patients) with spontaneous AF; group II (35 patients) with reciprocating tachycardia but not AF; and group III (18 patients) asymptomatic without documented arrhythmias. Atrial effective refractory periods (ERPs) and intraatrial conduction times in response to premature extrastimuli were analyzed. The latter were evaluated as the A1A2 interval minus the correspondent S1S2 interval (A1A2-S1S2), S1A2 and the interval A1A2 following the shortest S1S2 producing atrial activation (FRP'). All the parameters have been evaluated in two atrial sites and at two atrial pacing cycle lengths (600 and 400 ms). For all the parameters, the difference ("gradient") was calculated between the values of the same parameter measured at the atrial pacing cycle length of 600 ms and that found at the atrial pacing cycle length of 400 ms in the same recording site in each patient was calculated. Atrial ERP did not differ significantly in the three groups. Intraatrial conduction parameters, evaluated in the high right atrium (HRA), were longer when measured at an atrial pacing of 400 ms and showed a lack of rate adaptation in patients with spontaneous AF. In group I patients in particular, FRP' became longer with the increase of atrial rate, while in groups 2 and 3, it usually shortened. The mean gradient of HRA FRP' was -15.0 +/- 19 ms in group I as compared to 5.7 +/- 13 ms in group II and 6.4 +/- 13 ms in group III (P < 0.001); sensitivity, specificity, and negative predictive value of a negative gradient in the identification of patients with spontaneous AF, were, respectively, 83%, 75%, and 93%. Patients from groups 2 and 3 did not differ in any of the analyzed parameters. Patients with Wolff-Parkinson-White and spontaneous AF showed prolonged intraatrial conduction times and a different behavior in response to modification of heart rate.

Pacing strategies to prevent atrial fibrillation

The role of cardiac pacing in preventing atrial fibrillation in patients at risk for this arrhythmia is a relatively new concept. This article discusses the influence of the pacing mode, rate, atrial pacing site, and novel pacing algorithms on the prevention of atrial fibrillation.

Electrophysiologic aspects of human atrial fibrillation

This article reviews the important developments that have led to current understanding of atrial fibrillation, the data that support its mechanistic dependence on various forms of reentrant excitation, and the resultant electrophysiologic and clinical implications of clinicians' evolving understanding.

Wavelength index at three atrial sites in patients with paroxysmal atrial fibrillation

The purpose of this study was to evaluate the wavelength index (WLI) at three atrial sites in a group of 23 patients with recurrent episodes of lone paroxysmal atrial fibrillation (LPAF) and a control group (n = 20). All patients underwent programmed atrial stimulation (paced cycle length = 600 ms) at high, medium, and low lateral right atrial wall. P wave duration, sinus cycle length, and corrected sinus node recovery time were not significantly different between the two study groups. WLI was calculated according to the following formulas: atrial effective refractory period (AERP)/duration of atrial extrastimulus electrogram (A2) or AERP/A2 + atrial latency; and atrial functional refractory period (AFRP)/A2. WLI was significantly shorter in LPAF than in the control group at each of the paced atrial sites independently of the formula used. Duration of premature atrial electrogram appeared to play the major role in determining the difference in WLI between patients with paroxysmal atrial fibrillation and the control group.

Atrial late potentials in patients with paroxysmal atrial fibrillation detected using a high gain, signal-averaged esophageal lead

High gain, signal-averaged ECGs using conventional surface lead technique and a transesophageal lead technique were performed in 45 idiopathic paroxysmal atrial fibrillation patients and in 33 normal controls. Both techniques showed increased P wave duration in patients compared with the controls (P < 0.001), but higher P wave amplitudes were obtained using the transesophageal technique compared with surface leads (patients: 169.8 +/- 81.7 microV vs 15.8 +/- 7.3 microV; P < 0.0005; controls: 163.5 +/- 22.1 microV vs 18.5 +/- 5.2 microV; P < 0.0005). The signal-averaged transesophageal lead, but not the surface recordings, identified the presence of atrial late potentials evidenced by lower root mean square voltages in the terminal portion of the P wave: in last 10 seconds, 4.4 +/- 1.3 microV versus 8.5 +/- 3.0 microV; P < 0.001; in last 20 seconds, 7.0 +/- 2.3 microV versus 16.0 +/- 7.9 microV; P < 0.001; in last 30 seconds, 12.5 +/- 5.3 microV versus 23.8 +/- 12.8 microV; P < 0.001, in patients with respect to controls. The criterion P wave duration > or = 110 msec had 85% sensitivity, 100% specificity, and 100% positive predictive value in identifying the patients; the combined criteria P wave duration > or = 110 msec and root mean square for the last 10 msec < or = 6.5 showed 80% sensitivity, 100% specificity, and 100% predictive value. The signal-averaged transesophageal lead produces a higher amplitude signal, which reveals fractionation of atrial activation in atrial fibrillation and allows identification of individuals predisposed to this arrhythmia.

Repetitive atrial firing and fragmented atrial activity elicited by extrastimuli in the sick sinus syndrome with and without abnormal atrial electrograms

Endocardial catheter mapping of the right atrium during sinus rhythm and programmed atrial stimulation were performed in 50 patients with sick sinus syndrome to investigate the relationship between abnormal atrial electrograms recorded during sinus rhythm and some determinants of the atrial vulnerability such as repetitive atrial firing and fragmented atrial activity elicited by single extrastimulus. The patients were divided into 2 groups on the basis of the presence (Group I) or absence (Group II) of abnormal atrial electrograms recorded during sinus rhythm. In Group I (N = 32), repetitive atrial firing was induced in 23 (72%) patients, and in Group II (N = 18) in 6 (33%) patients; p less than 0.01. The repetitive atrial firing zone was 41 +/- 37 ms in Group I and 12 +/- 18 ms in Group II; p less than 0.001. Fragmented atrial activity was induced in 30 (94%) patients from Group I, and in 8 (44%) patients from Group II; p less than 0.0001. The fragmented atrial activity zone was 47 +/- 42 ms in Group I and 14 +/- 19 ms in Group II; p less than 0.0001. The atrial electrogram width at the premature beat (A2; p < 0.02) and the maximum A2/A1 ratio (p < 0.002) were 178 +/- 53 ms and 196% +/- 40%, respectively in Group I, and 141 +/- 36 ms and 159% +/- 30%, respectively in Group II. Atrial fibrillation was induced in 13 (41%) patients from Group I, and in 1 (6%) patient from Group II (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Normal AV node function in patients with sinus node dysfunction after cardiac transplantation

Postoperative atrioventricular nodal (AVN) function was compared in 55 patients with normal and 50 patients with impaired sinus node (SN) function after cardiac transplantation (corrected SN recovery time > 520 msec or sinus arrest +/- escape rhythm). Fifty-two patients had fixed atrial pacing at cycle lengths between 600 and 430 msec, and 53 patients at cycle lengths from 600 to 300 msec between postoperative weeks 1 to 3. Relative (stimulus-R interval; AVNRRP) and effective AVN refractory period (AVNERP) were determined in 53 patients at a cycle length of 500 msec. Only one of 105 recipients had high degree AVN conduction disturbance characterized by a Wenckebach phenomenon at cycle length < 630 msec in the first postoperative week. Three patients with normal and two patients with impaired SN function had Wenckebach cycle lengths > 430 msec while the Wenckebach cycle lengths were < or = 430 msec in the remainder (p = NS). Resting PQ interval (146 +/- 18 vs 162 +/- 32; p = 0.09), Wenckebach cycle length (350 +/- 53 vs 362 +/- 50 msec), AVNRRP (356 +/- 38 vs 367 +/- 37 msec), and AVNERP (217 +/- 48 vs 244 +/- 49 msec) did not differ significantly between patients with normal and impaired SN function. AVN conduction did not deteriorate during 318 +/- 130 days of follow-up (PQ at follow-up 154 +/- 17 and 158 +/- 22 msec, patients with normal and impaired SN function, respectively). One DDD pacemaker was placed for AVN conduction disturbance while 22 pacemakers were implanted for SN deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative relationship between atrial refractoriness and the dispersion of refractoriness in atrial vulnerability

We investigated the quantitative relationship between the atrial refractory period and the dispersion of refractoriness with respect to atrial vulnerability in 19 adult mongrel dogs. The atrial effective refractory period (AERP) was measured at the sinus node area (SNA), the low posterior right atrium (LRA), and the distal coronary sinus. The study was performed under the following conditions: (1) control status; (2) hypothermia (30 degrees C); (3) vagus nerve stimulation; and (4) a combination of (2) and (3). The subjects were separated into two groups: atrial fibrillation (AF) (+) group (n = 23), which developed AF by atrial extrastimulus due to increased vulnerability, and AF (-) group (n = 39), which did not develop AF. The mean AERP was 97 +/- 21 msec (mean +/- SD) in the AF (+) group and 124 +/- 23 msec in the AF (-) group, with a significantly shorter refractory period seen in the former (P less than 0.001). The dispersion of refractoriness was 59 +/- 24 msec in the AF (+) group and 29 +/- 18 msec in the AF (-) group, with a significant increase noted in the former (P less than 0.001). On X-Y coordinates (where X denotes the AERP, and Y denotes the dispersion of refractoriness) the data from the AF (+) group were clustered in the upper left region of the graph while the data from the AF (-) group were clustered in the lower right region. These two groups were separated by a linear equation of Y = 0.86X - 57 with a predictability of 90.3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial vulnerability

The electrophysiologic substrates of atrial flutter and fibrillation (AFF) have been studied in patients with paroxysmal arrhythmias. Atrial repetitive responses to extrastimuli are a nonspecific response, even though they can precipitate AFF. AFF inducibility is rather sensitive, but not very specific, in separating patients from controls. There is no established protocol to explore vulnerability in this fashion. Atrial refractoriness is abnormal in some patients. Some authors have found a tendency toward short effective refractory periods (AERP) and others have found a poor adaptation of AERP to decreases in cycle length. Unfortunately, these abnormalities are neither sensitive nor specific enough. Atrial conduction may be abnormal basally, but subtler abnormalities are shown by premature stimulation. Early extrastimuli are conducted with increased conduction delays in patients with paroxysmal AFF in relation to controls. Again, there is not enough sensitivity and specificity in the findings to make them of diagnostic value. Electrophysiologic abnormalities are detectable in patients with AFF, but larger studies, including reproducibility and the effect of drugs on the abnormal parameters, will be necessary to develop clinical applications.

Provocation of supraventricular tachycardias by an intravenous class I antiarrhythmic drug

Antiarrhythmic drugs may aggravate or induce ventricular arrhythmia. The induction of a supraventricular tachycardia or its facilitation has rarely been reported. The purpose of the study was to know whether the potential for supraventricular proarrhythmic effect of a class Ia intravenous antiarrhythmic drug can be exposed during electrophysiologic study. Ajmaline was chosen because of its short duration of action. The protocol of the study consisted of an electrophysiological study and programmed atrial stimulation using 1 and 2 extrastimuli on driven rhythm and atrial pacing up to second-degree atrioventricular block. Then 1 mg/kg of ajmaline was injected and atrial pacing was performed 3 minutes after its injection. Supraventricular proarrhythmic effect of ajmaline was defined as the spontaneous occurrence of a supraventricular tachycardia or the facilitation of its induction. Seventy patients among 1955 presented a proarrhythmic effect: 63 developed a supraventricular tachyarrhythmia (atrial flutter, fibrillation, tachycardia) and 7 an atrioventricular reentrant tachycardia, either spontaneously (n = 23) or during atrial pacing (n = 47). Risk factors were identified in most patients: old age, underlying heart disease, history of spontaneous supraventricular tachycardia and/or induction of a supraventricular tachycardia by 2 extrastimuli on driven rhythm in the control state (34 patients), sinus node dysfunction (22 patients). Compared with patients without proarrhythmic supraventricular effect only the history of spontaneous supraventricular tachycardia and the existence of a sinus node dysfunction were significantly more frequent (P less than 0.05) in patients with proarrhythmic effect of ajmaline. In conclusion, the supraventricular proarrhythmic effect of intravenous ajmaline exists and is related both to the electrophysiologic characteristics of the drug and to the arrhythmia substrate. The results indicate that a supraventricular tachyarrhythmia may be induced by a class I antiarrhythmic drug.

Atrial Vulnerability and Electrophysiology Determined in Patients With and Without Paroxysmal Atrial Fibrillation

For elucidation of atrial electrophysiology and vulnerability an electrophysiological study was performed in 45 patients with documented paroxysmal atrial fibrillation and a control group (n = 46). Atrial vulnerability was assessed by programmed atrial stimulation with up to two extrastimuli during sinus rhythm and paced cycle lengths of 600 msec, 430 msec and 330 msec. Sustained atrial fibrillation or flutter was induced in 37/45 patients with paroxysmal atrial fibrillation in contrast to 9/46 patients in the control group (P less than 0.001). Left atrial diameter (M-mode echocardiogram), P wave duration, sinus cycle length, sinus node recovery time, and the effective refractory period of the right atrium were not significantly different between the two study groups. Intraatrial conduction time from the high right atrium (HRA) to the basal right atrium (A) and the functional refractory period of the right atrium were significantly longer in patients with paroxysmal atrial fibrillation.

Prolonged and fractionated right atrial electrograms during sinus rhythm in patients with paroxysmal atrial fibrillation and sick sinus node syndrome

Intraatrial catheter mapping of the right atrium was performed during sinus rhythm in 92 patients: Group I = 43 control patients without paroxysmal atrial fibrillation or sick sinus node syndrome; Group II = 31 patients with paroxysmal atrial fibrillation but without sick sinus node syndrome; and Group III = 18 patients with both paroxysmal atrial fibrillation and sick sinus node syndrome. Atrial electrograms were recorded at 12 sites in the right atrium. The duration and number of fragmented deflections of the atrial electrograms were quantitatively measured. The mean duration and number of fragmented deflections of the 516 atrial electrograms in Group I were 74 +/- 11 ms and 3.9 +/- 1.3, respectively. The criteria for an abnormal atrial electrogram were defined as a duration of greater than or equal to 100 ms or eight or more fragmented deflections, or both. Abnormal atrial electrograms were observed in 10 patients (23.3%) in Group I, 21 patients (67.7%) in Group II and 15 patients (83.3%) in Group III (Group II versus Group I, p less than 0.001; Group III versus Group I, p less than 0.001). The mean number of abnormal electrograms per patient with an abnormal electrogram was 1.3 +/- 0.7 in Group I, 2.5 +/- 1.9 in Group II and 3.5 +/- 2.5 in Group III (Group I versus Group II, p less than 0.01; Group II versus Group III, p less than 0.05). A prolonged and fractionated atrial electrogram characteristic of paroxysmal atrial fibrillation can be closely related to the vulnerability of the atrial muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Fragmented atrial activity in patients with transient atrial fibrillation

Prediction of atrial fibrillation (AF) is very important in patients with Wolff-Parkinson-White syndrome or in the selection of pacemaker therapeutic modality. In 25 patients with transient AF, the response of the atrial activity width to extrastimuli was examined in comparison with 25 patients without AF to see if the results could be used as an index of subsequent occurrence of AF. Programmed electrical stimulation using eight basic stimuli followed by single or double extrastimuli (P1P2 or P1P2P3) were delivered to the high right atrium, and the atrial activities were examined. The prolongation of the atrial activity caused by extrastimuli was termed fragmentation (Frg), and it was defined as the prolongation of more than 150% of the basic stimuli. Frg zone was defined as the zone of coupling intervals of the extrastimuli (P1P2 or P2P3) that caused Frg, and delta max Frg was defined as the difference between the widest Frg and the atrial wave width during basic stimuli. Fragmentation was reproducibly induced by extrastimuli, and there was an inverse relationship between Frg duration and the coupling interval of the extrastimuli (P1P2 or P2P3). Frg zone and delta max Frg were wider and longer in patients with transient AF in comparison with the control group for both single and double extrastimuli (p less than 0.001). AF inducibility using double extrastimuli was significantly high in patients with AF.(ABSTRACT TRUNCATED AT 250 WORDS)

Facioscapulohumeral muscular dystrophy: evidence for selective, genetic electrophysiologic cardiac involvement

Facioscapulohumeral muscular dystrophy is an autosomal dominant disorder with an incidence of 3 to 10 cases per million. The only type of cardiac involvement ascribed to this neuromuscular disorder is a unique form of heart disease--permanent atrial paralysis. However, reported cases of facioscapulohumeral muscular dystrophy probably represented instead what is now recognized as phenotypically similar Emery-Dreifuss dystrophy. Cardiac involvement, therefore, has not been convincingly reported in facioscapulohumeral muscular dystrophy, but because of the clinical similarity of that disorder to Emery-Dreifuss dystrophy and its genetic variants, a prospective investigation of the electrophysiologic properties of the atria and atrioventricular (AV) node and infranodal conduction was undertaken in 30 rigorously documented cases of facioscapulohumeral muscular dystrophy. All patients had a 12 lead surface electrocardiogram (ECG), 22 had a 24 h ambulatory ECG, 15 patients had two-dimensional echocardiographic/Doppler studies and 10 patients underwent 12 intracardiac electrophysiologic investigations. Left atrial, right atrial or biatrial P wave abnormalities were present in 60% of the surface ECGs. Evidence of abnormal AV node or infranodal conduction was present on intracardiac electrophysiologic study or surface ECG in 27% of patients. Atrial flutter or fibrillation was induced by single atrial extra stimuli in 10 of the 12 intracardiac electrophysiologic studies. Sinus node function was abnormal in three patients. This investigation provides the first secure evidence of cardiac involvement in facioscapulohumeral muscular dystrophy. The involvement is represented by relatively high susceptibility to induced atrial flutter or fibrillation during electrophysiologic study, together with less frequent evidence of abnormal sinus node function and abnormal AV node or infranodal conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial refractory periods after atrial premature beats in patients with paroxysmal atrial fibrillation

To study the effects of an atrial premature beat on atrial refractory periods, we investigated 11 patients (group A) who were the control group, 12 patients suffering from paroxysmal atrial fibrillation (group B), and 10 patients (group C) without arrhythmias but with cardiopathy or cardiomyopathy. At every eighth complex of a constant atrial electrostimulated rhythm a fixed premature extrastimulus was introduced, and effective and functional refractory periods (ERP and FRP) were measured in three different sites of the right atrium, before and after introduction of this extrastimulus. Average ERP and FRP shortened respectively in group A, from 220.28 +/- 25.68 msec and 281.17 +/- 28.15 msec before extrastimulation, to 190.58 +/- 22.74 msec and 245.88 +/- 19.86 msec after; in group B, from 219.44 +/- 27.38 msec and 284 +/- 30.06 msec to 191.66 +/- 28.72 msec and 253.23 +/- 34.01 msec; and in group C from 229.03 +/- 29.65 msec and 289.67 +/- 51.62 msec to 194.19 +/- 24.6 msec and 237.74 +/- 39.59 msec. The average dispersions of ERP and FRP in group A were, respectively: 41.81 +/- 21.36 msec and 36.36 +/- 18.04 msec before extrastimulation, 28.18 +/- 18.14 msec and 35.45 +/- 15.72 msec after. In group B: 26.66 +/- 19.46 msec and 41.66 +/- 16.96 msec versus 45.83 +/- 23.91 msec and 45 +/- 34.77 msec and in group C: 27 +/- 11.59 msec and 45 +/- 29.15 msec versus 29 +/- 18.52 and 27 +/- 18.88.(ABSTRACT TRUNCATED AT 250 WORDS)