Electrophysiologic studies in atrial fibrillation. Slow conduction of premature impulses: a possible manifestation of the background for reentry

Interactive teaching of medical 3D cardiac anatomy: atrial anatomy enhanced by ECG and 3D visualization

The most commonly applied way of teaching students to convey the foundations of human anatomy and physiology involves textbooks and lectures. This way of transmitting knowledge causes difficulties for students, especially in the context of three-dimensional imaging of organ structures, and as a consequence translates into difficulties with imagining them. Even despite the rapid uptake of knowledge dissemination provided by online materials, including courses and webinars, there is a clear need for learning programs featuring first-hand immersive experiences tailored to suit individual study paces. In this paper, we present an approach to enhance a classical study program by combining multi-modality data and representing them in a Mixed Reality (MR)-based environment. The advantages of the proposed approach have been proven by the conducted investigation of the relationship between atrial anatomy, its electrophysiological characteristics, and resulting P wave morphology on the electrocardiogram (ECG). Another part of the paper focuses on the role of the sinoatrial node in ECG formation, while the MR-based visualization of combined micro-computed tomography (micro-CT) data with non-invasive CineECG imaging demonstrates the educational application of these advanced technologies for teaching cardiac anatomy and ECG correlations.

Elevated liver fibrosis-4 index predicts recurrence after catheter ablation for atrial fibrillation in patients with heart failure

BACKGROUND

The fibrosis-4 (FIB-4) index is a noninvasive scoring system that is used to assess the progression of liver fibrosis. This study aimed to assess whether the FIB-4 index is associated with recurrent atrial fibrillation (AF) after catheter ablation in patients with and without heart failure (HF).

METHODS

We included 1,184 patients who underwent initial AF catheter ablation between 2016 and 2021. The patients were classified into low-risk (< 1.3), intermediate-risk (1.3-2.67), and high-risk (> 2.67) groups based on their FIB-4 indices at baseline. The patients were divided into HF (n = 552) and non-HF groups (n = 632); the HF group was further divided into paroxysmal AF (PAF) and non-PAF groups. AF recurrence after catheter ablation was then compared among the groups.

RESULTS

In the non-HF group, no significant differences in recurrence after ablation were observed between the low-(n = 219), intermediate-(n = 364), and high-risk (n = 49) groups. In contrast, in the HF group, the intermediate-(n = 341) and high-risk (n = 112) groups had significantly higher recurrence rates than the low-risk group (n = 99) (log-rank test, p = 0.005). This association remained significant after multivariate analysis (hazard ratio [HR]:1.374; p = 0.027). The FIB-4 index increased incrementally as the brain natriuretic peptide levels and severity of tricuspid regurgitation increased. The FIB-4 index was an independent predictor of recurrence in the non-PAF HF group (HR:1.498; p = 0.007) but not in the PAF group.

CONCLUSIONS

The FIB-4 index may be a useful predictor of AF recurrence after catheter ablation in patients with HF, particularly in those with non-PAF.

Electro-Mechanical Alterations in Atrial Fibrillation: Structural, Electrical, and Functional Correlates

Atrial fibrillation is the most common arrhythmia encountered in clinical practice affecting both patients’ survival and well-being. Apart from aging, many cardiovascular risk factors may cause structural remodeling of the atrial myocardium leading to atrial fibrillation development. Structural remodelling refers to the development of atrial fibrosis, as well as to alterations in atrial size and cellular ultrastructure. The latter includes myolysis, the development of glycogen accumulation, altered Connexin expression, subcellular changes, and sinus rhythm alterations. The structural remodeling of the atrial myocardium is commonly associated with the presence of interatrial block. On the other hand, prolongation of the interatrial conduction time is encountered when atrial pressure is acutely increased. Electrical correlates of conduction disturbances include alterations in P wave parameters, such as partial or advanced interatrial block, alterations in P wave axis, voltage, area, morphology, or abnormal electrophysiological characteristics, such as alterations in bipolar or unipolar voltage mapping, electrogram fractionation, endo-epicardial asynchrony of the atrial wall, or slower cardiac conduction velocity. Functional correlates of conduction disturbances may incorporate alterations in left atrial diameter, volume, or strain. Echocardiography or cardiac magnetic resonance imaging (MRI) is commonly used to assess these parameters. Finally, the echocardiography-derived total atrial conduction time (PA-TDI duration) may reflect both atrial electrical and structural alterations.

Size matters in atrial fibrillation: the underestimated importance of reduction of contiguous electrical mass underlying the effectiveness of catheter ablation

Evidence has accumulated over the last century of the importance of a critical electrical mass in sustaining atrial fibrillation (AF). AF ablation certainly reduces electrically contiguous atrial mass, but this is not widely accepted to be an important part of its mechanism of action. In this article, we review data showing that atrial size is correlated in many settings with AF propensity. Larger mammals are more likely to exhibit AF. This is seen both in the natural world and in animal models, where it is much easier to create a goat model than a mouse model of AF, for example. This also extends to humans-athletes, taller people, and obese individuals all have large atria and are more likely to exhibit AF. Within an individual, risk factors such as hypertension, valvular disease and ischaemia can enlarge the atrium and increase the risk of AF. With respect to AF ablation, we explore how variations in ablation strategy and the relative effectiveness of these strategies may suggest that a reduction in electrical atrial mass is an important mechanism of action. We counter this with examples in which there is no doubt that mass reduction is less important than competing theories such as ganglionated plexus ablation. We conclude that, when considering future strategies for the ablative therapy of AF, it is important not to discount the possibility that contiguous electrical mass reduction is the most important mechanism despite the disappointing consequence being that enhancing success rates in AF ablation may involve greater tissue destruction.

The Electrophysiology of Atrial Fibrillation: From Basic Mechanisms to Catheter Ablation

The electrophysiology of atrial fibrillation (AF) has always been a deep mystery in understanding this complex arrhythmia. The pathophysiological mechanisms of AF are complex and often remain unclear despite extensive research. Therefore, the implementation of basic science knowledge to clinical practice is challenging. After more than 20 years, pulmonary vein isolation (PVI) remains the cornerstone ablation strategy for maintaining the sinus rhythm (SR). However, there is no doubt that, in many cases, especially in persistent and long-standing persistent AF, PVI is not enough, and eventually, the restoration of SR occurs after additional intervention in the rest of the atrial myocardium. Substrate mapping is a modern challenge as it can reveal focal sources or rotational activities that may be responsible for maintaining AF. Whether these areas are actually the cause of the AF maintenance is unknown. If this really happens, then the targeted ablation may be the solution; otherwise, more rough techniques such as atrial compartmentalization may prove to be more effective. In this article, we attempt a broad review of the known pathophysiological mechanisms of AF, and we present the recent efforts of advanced technology initially to reveal the electrical impulse during AF and then to intervene effectively with ablation.

Surface ECG interatrial block-guided treatment for stroke prevention: rationale for an attractive hypothesis

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with stroke, cognitive impairment, and cardiovascular death. Some predisposing factors − as aging, diabetes, hypertension − induce and maintain electrophysiological and ultrastructural remodeling that usually includes fibrosis. Interatrial conduction disturbances play a crucial role in the initiation of atrial fibrosis and in its associated complications. The diagnosis of interatrial blocks (IABs) is easy to perform using the surface ECG. IAB is classified as partial when the P wave duration is ≥120 ms, and advanced if the P wave also presents a biphasic pattern in II, III and aVF. IAB is very frequent in the elderly and, particularly in the case of the advanced type, is associated with AF, AF recurrences, stroke, and dementia. The anticoagulation in elderly patients at high risk of AF without documented arrhythmias is an open issue but recent data suggest that it might have a role, particularly in elderly patients with structural heart disease, high CHA₂DS₂VASc (Congestive heart failure/left ventricular dysfunction, Hypertension, Age ≥ 75 [doubled], Diabetes, Stroke [doubled] – Vascular disease, Age 65–74, and Sex category [female]), and advanced IAB. In this debate, we discuss the association of surface ECG IAB, a marker of atrial fibrosis, with AF and stroke. We also present the rationale that justifies further studies regarding anticoagulation in some of these patients.

Atrial Fibrillation Ablation Strategy: "Ready Made" or "Tailored"?

Atrial fibrillation (AF) is the most common arrhythmia leading to hospital admissions. Catheter ablation has evolved as an effective treatment strategy; however, ablation strategies continue to evolve due to the complex and multifactorial nature of atrial fibrillation. A standardized and primarily anatomical approach may not be sufficient to eliminate all mechanisms of atrial fibrillation. A tailored ablation strategy can target specific triggers and drivers of atrial fibrillation; however, it is limited by the accuracy and sensitivity of the methods used in identifying specific mechanisms of atrial fibrillation.

The Association of Serum Galectin-3 Levels with Atrial Electrical and Structural Remodeling

INTRODUCTION

Left atrial (LA) interstitial fibrosis is known to have a role in the initiation and maintenance of atrial fibrillation (AF). The role of galectin-3 in the pathogenesis of cardiac fibrosis has been demonstrated in previous studies. We aimed to determine whether serum galectin-3 level is associated with markers of atrial remodeling, including the extent of LA fibrosis detected by delayed enhancement magnetic resonance imaging (DE-MRI) and atrial electromechanical delay (AEMD) in paroxysmal AF patients with preserved left ventricular (LV) functions.

METHODS AND RESULTS

Thirty-three patients (58 [28-74] years, 51.5% male) with paroxysmal AF who underwent DE-MRI prior to cryoballoon-based AF ablation were included in the study. Serum galectin-3 levels were measured with ELISA. LA volume index (B ± SE: 0.424 ± 0.504, 95% CI: 0.560-2.627, P = 0.004) and serum galectin-3 levels (B ± SE: 0.549 ± 7.745, 95% CI: 16.874-47.550, P < 0.001) were found to be independently correlated with extent of LA fibrosis detected with DE-MRI in paroxysmal AF patients with preserved LV function. Correlation analysis between AEMD parameters and baseline characteristics showed that galectin-3 was significantly correlated with intra-left (ρ = 0.432, P = 0.012) and inter-AEMD (ρ = 0.395, P = 0.023). Duration of AF, LAD, and extent of LA fibrosis were also found to be significantly correlated with AEMD parameters.

CONCLUSION

This is a hypothesis-generating study pointing out that serum galectin-3 level is significantly associated with atrial remodeling in paroxysmal AF patients with preserved LV function. Further studies are necessary to provide exact pathophysiological mechanisms.

Mechanisms of Atrial Fibrillation - Reentry, Rotors and Reality

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice, yet our understanding of the mechanisms that initiate and sustain this arrhythmia remains quite poor. Over the last 50 years, various mechanisms of AF have been proposed, yet none has been consistently observed in both experimental studies and in humans. Recently, there has been increasing interest in understanding how spiral waves or rotors - which are specific, organised forms of functional reentry - sustain human AF and how they might be therapeutic targets for catheter-based ablation. The following review describes the historical understanding of reentry and AF mechanisms from earlier in the 20th century, advances in our understanding of mechanisms that are able to sustain AF with a focus on rotors and complex fractionated atrial electrograms (CFAEs), and how the study of AF mechanisms has resulted in new strategies for treating AF with novel forms of catheter ablation.

Interatrial conduction disturbance in postoperative atrial fibrillation: a comparative study of P-wave dispersion and Doppler myocardial imaging in cardiac surgery

Objective

Disturbances of interatrial conduction have been proposed as one of the contributing mechanisms of postoperative atrial fibrillation (AF). P-wave dispersion has been recognized as a sensitive tool for detecting interatrial conduction disturbances. Doppler myocardial imaging (DMI) has been validated as a non-invasive tool to indirectly reflect electrical atrial activation and therefore is used in this study to detect possible interatrial electromechanical disturbances after cardiac surgery.

Methods

30 patients (23 men, age 62 ± 1 years) admitted for coronary bypass surgery with no prior history of AF were included in this investigation. Echocardiography and electrocardiograms (ECG) were obtained on the day before and after surgery. In addition to standard echocardiography, DMI-loops were acquired from the apical window. The following time intervals were derived off-line from the free right atrial (RA), left atrial (LA) lateral and LA posterior wall: onset P-wave to start (P to A’start), to peak (P to A’peak) and to end of atrial deformation (total electromechanical activity). These intervals were compared to each other and to P-wave dispersion derived from the recorded ECGs.

Results

All patients were in sinus rhythm during their postoperative assessment, but 11 patients presented episodes of AF within the first three postoperative days. Atrial electromechanical activation was earliest in the RA and latest in the lateral LA. In patients with AF, P-wave dispersion was significantly prolonged postoperatively (mean: +18.6 ms; 95% confidence interval (CI): 12.1–25.2 ms; p < 0.001) compared to non-AF patients (mean: -2.4 ms; CI: -6.6–1.9 ms). P dispersion was closely correlated to P to A’start intervals (from RA to LA lat.: preop.: rho = 0.74, postop.: rho = 0.87; p < 0.001). Prolonged right to left conduction interval was associated with an elevated risk for AF (from RA to LA lat.: odds ratio 1.13 (CI:1.03-1.24); p: 0.007.

Conclusion

DMI enabled detection of interatrial conduction disturbances in concordance to findings of prolonged postoperative P-wave dispersion. Equally effective to P-wave dispersion, this simple and reproducible tool might help to early identify the risk for postoperative AF, thus extending the informative value of routine postoperative echocardiography.

Angiotensin-(1-7) prevent atrial tachycardia induced sodium channel remodeling

BACKGROUND

Activation of the renin-angiotensin system plays an important role in atrial electrical remodeling; angiotensin-(1-7) (Ang-(1-7)) counterbalances the actions of angiotensin II. The aim of this study was to determine the effects of Ang-(1-7) on cardiac sodium current (INa ) in a canine model of atrial tachycardia.

METHODS

Eighteen dogs were randomly assigned to sham, pacing, or pacing + Ang-(1-7) groups (n = 6 in each group). Rapid atrial pacing (500 beats/min) was maintained for 2 weeks, while the dogs in the sham group were not paced. Ang-(1-7) (6 μg/kg/h) was administered intravenously during pacing. Whole-cell patch clamp techniques were utilized to record INa from canine atrial myocytes. Reverse transcription-polymerase chain reaction was used to assess possible underlying changes in cardiac Na(+) channels (Nav1.5).

RESULTS

Our results showed that INa density and expression of the Nav1.5 mRNA significantly decreased following pacing (P < 0.05 vs sham); however, the half-activation voltage (V1/2act ) and half-inactivation voltage (V1/2inact ) of INa were not significantly altered (P > 0.05 vs sham). Ang-(1-7) treatment significantly increased INa densities and hyperpolarized V1/2act without concomitant changes in V1/2inact but have no effect on the expression of the Nav1.5 gene.

CONCLUSIONS

Ang-(1-7) significantly increased INa densities, which contributed to improving intraatrial conduction and decreasing the likelihood of atrial fibrillation maintenance.

Number of P-wave fragmentations on P-SAECG correlates with infiltrated atrial fat

BACKGROUND

Although atrial fibrillation (AF) triggers are known, the underlying AF substrate is less well understood. The goal of our study was to explore correlations between electrophysiological and structural characteristics of atria in patients with paroxysmal AF and individuals at AF risk.

METHODS

Patients in sinus rhythm (N = 90; age 57 ± 10 year; 55 men [63.2%]) with structural heart disease and paroxysmal AF (n = 12 [13%]), or with AF risk factors and LVEF > 35% (n = 78), underwent SAECG and cardiac magnetic resonance study. Interatrial and epicardial fat was analyzed with a Dark-blood DIR-prepared Fat-Water-separated sequence in the horizontal longitudinal axis. All local P-wave extrema were identified on SAECG leads during sinus rhythm. A P-wave fragmentation (Pf) was defined as an absolute difference between adjacent extrema which was above three standard deviations of noise, and was normalized by the duration of the P wave in the corresponding lead.

RESULTS

The Pf was greater on the filtered than on the unfiltered P-SAECG signal (13.1 ± 3.8 vs. 3.4 ± 1.2; P < 0.0001). Pf was the greatest on the Y lead (13.0 ± 3.5 on Y lead vs. 12.1 ± 3.4 on Z lead; P = 0.003. Pf on Z lead correlated with interatrial fat index (r = 0.544; P = 0.001). Epicardial fat significantly correlated with body mass index (BMI; r = 0.302; P = 0.015). After adjustment for BMI, left atrium (LA) size, epicardial fat, and interatrial septum width, interatrial fat independently associated with the Pf on Z lead (β-coefficient 0.009 [95%CI 0.0003-0.019]; P = 0.043).

CONCLUSIONS

Infiltrated atrial fat correlates with discontinuous conduction on posterior LA wall and represents AF early substrate.

Short-term repeatability of electrocardiographic P wave indices and PR interval

BACKGROUND

P wave indices and PR interval from 12-lead electrocardiograms (ECGs) are predictors of cardiovascular morbidity and mortality, but their repeatability has not been examined.

OBJECTIVES

Determine the short-term repeatability of P wave indices (P axis, maximum P area and duration, P dispersion and P terminal force in V1) and PR interval.

METHODS

Participants (n=63) underwent two standard ECGs at each of two visits, two weeks apart. We calculated the intra-class correlation coefficient (ICC), weighted kappa, and minimal detectable change and difference.

RESULTS

ICCs were 0.93 for PR interval, 0.78 for P axis, 0.77 for maximum P area, and 0.58 for maximum P duration. Within- and between-visit Kappa were 0.30 and 0.11 for P dispersion, and 0.68 and 0.46 for P terminal force.

CONCLUSION

Repeatability of PR duration was excellent, that of P wave axis and maximum area was fair, and maximum P wave duration and terminal force was poor. Repeatability of P wave dispersion was fair within visit, yet poor between visits. These results illustrate potential biases when measurement error of some P wave indices is ignored in clinical and epidemiologic studies.

The QT interval and risk of incident atrial fibrillation

BACKGROUND

Abnormal atrial repolarization is important in the development of atrial fibrillation (AF), but no direct measurement is available in clinical medicine.

OBJECTIVE

To determine whether the QT interval, a marker of ventricular repolarization, could be used to predict incident AF.

METHODS

We examined a prolonged QT interval corrected by using the Framingham formula (QT(Fram)) as a predictor of incident AF in the Atherosclerosis Risk in Communities (ARIC) study. The Cardiovascular Health Study (CHS) and Health, Aging, and Body Composition (ABC) study were used for validation. Secondary predictors included QT duration as a continuous variable, a short QT interval, and QT intervals corrected by using other formulas.

RESULTS

Among 14,538 ARIC study participants, a prolonged QT(Fram) predicted a roughly 2-fold increased risk of AF (hazard ratio [HR] 2.05; 95% confidence interval [CI] 1.42-2.96; P < .001). No substantive attenuation was observed after adjustment for age, race, sex, study center, body mass index, hypertension, diabetes, coronary disease, and heart failure. The findings were validated in Cardiovascular Health Study and Health, Aging, and Body Composition study and were similar across various QT correction methods. Also in the ARIC study, each 10-ms increase in QT(Fram) was associated with an increased unadjusted (HR 1.14; 95% CI 1.10-1.17; P < .001) and adjusted (HR 1.11; 95% CI 1.07-1.14; P < .001) risk of AF. Findings regarding a short QT interval were inconsistent across cohorts.

CONCLUSIONS

A prolonged QT interval is associated with an increased risk of incident AF.

Cardiac responses to 24 hrs hyperoxia in Bmp2 and Bmp4 heterozygous mice

BACKGROUND

Hyperoxia or clinical oxygen (O2) therapy is known to result in increased oxidative burden. Therefore, understanding susceptibility to hyperoxia exposure is clinically important. Bone morphogenetic proteins (BMPs) 2 and 4 are involved in cardiac development and may influence responses to hyperoxia.

METHODS

Bmp2(+/)(-). Bmp4(+/)(-) and wild-type mice were exposed to hyperoxia (100% O2) for 24 hrs. Electrocardiograms (ECG) were recorded before and during exposure by radio-telemetry.

RESULTS

At baseline, a significantly higher low frequency (LF) and total power (TP) heart rate variability (HRV) were found in Bmp2(+/)(-) mice only (p < 0.05). Twenty-four hours hyperoxia-induced strain-independent reductions in heart rate, QTcB and ST-interval and increases in QRS, LF HRV and standard deviation of RR-intervals were observed. In Bmp4(+/)(-) mice only, increased PR-interval (PR-I) (24 hrs), P-wave duration (P-d; 18 and 21-24 hrs), PR-I minus P-d (PR - Pd; 24 hrs) and root of the mean squared differences of successive RR-intervals (24 hrs) were found during hyperoxia (p < 0.05).

DISCUSSION

Elevated baseline LF and TP HRV in Bmp2(+/)(-) mice suggests an altered autonomic nervous system regulation of cardiac function in these mice. However, this was not related to strain specific differences in responses to 24 hrs hyperoxia. During hyperoxia, Bmp4(+/-) mice were the most susceptible in terms of atrioventricular conduction changes and risk of atrial fibrillation, which may have important implications for patients treated with O2 who also harbor Bmp4 mutations. This study demonstrates significant ECG and HRV responses to 24 hrs hyperoxia in mice, which highlights the need to further work on the genetic mechanisms associated with cardiac susceptibility to hyperoxia.

Atrial arrhythmia, triggering events and conduction abnormalities in isolated murine RyR2-P2328S hearts

AIM

RyR2 mutations are associated with catecholaminergic polymorphic tachycardia, a condition characterized by ventricular and atrial arrhythmias. The present experiments investigate the atrial electrophysiology of homozygotic murine RyR2-P2328S (RyR2(S/S)) hearts for ectopic triggering events and for conduction abnormalities that might provide a re-entrant substrate.

METHODS

Electrocardiograph recordings were made from regularly stimulated RyR2(S/S) and wild type (WT) hearts, perfused using a novel modified Langendorff preparation. This permitted the simultaneous use of either floating intracellular microelectrodes to measure action potential (AP) parameters, or a multielectrode array to measure epicardial conduction velocity (CV).

RESULTS

RyR2(S/S) showed frequent sustained tachyarrhythmias, delayed afterdepolarizations and ectopic APs, increased interatrial conduction delays, reduced epicardial CVs and reduced maximum rates of AP depolarization ((dV/dt)(max)), despite similar effective refractory periods, AP durations and AP amplitudes. Effective interatrial CVs and (dV/dt)(max) values of APs following ectopic (S2) stimulation were lower than those of APs following regular stimulation and decreased with shortening S1S2 intervals. However, although RyR2(S/S) atria showed arrhythmias over a wider range of S1S2 intervals, the interatrial CV and (dV/dt)(max) of S2 APs provoking such arrhythmias were similar in RyR2(S/S) and WT.

CONCLUSIONS

These results suggest that abnormal intracellular Ca(2+) homoeostasis produces both arrhythmic triggers and a slow-conducting arrhythmic substrate in RyR2(S/S) atria. A similar mechanism might also contribute to arrhythmogenesis in other conditions, associated with diastolic Ca(2+) release, such as atrial fibrillation.

Misleading long post-pacing interval after entrainment of typical atrial flutter from the cavotricuspid isthmus

OBJECTIVES

The purpose of this study was to evaluate the prevalence and mechanism of a misleading long post-pacing interval (PPI) upon entrainment of typical atrial flutter (AFL) from the cavotricuspid isthmus (CTI).

BACKGROUND

In typical AFL, the PPI from entrainment at the CTI is expected to closely match the tachycardia cycle-length (TCL).

METHODS

Sixty patients with confirmed CTI-dependent AFL were retrospectively analyzed and grouped into short (≤30 ms) or long (>30 ms) PPI-TCL. Thereafter, we prospectively studied 16 patients to acquire the PPI-TCL at 4 CTI sites with entrainment at pacing cycle-lengths (PCLs) 10 to 40 ms shorter than the TCL. Conduction times during AFL and entrainment were compared in 5 segments of the AFL circuit.

RESULTS

Eleven patients (18%) in the retrospective analysis had a long PPI-TCL after entrainment from the CTI. Subjects with long PPI-TCL had similar baseline characteristics but greater beat-to-beat TCL variability. In the prospective cohort, PPI-TCL was influenced by the difference between PCL and TCL and site of entrainment. Conduction delays associated with a long PPI-TCL were located predominantly in the segment activated first by the paced orthodromic wave front, and were mainly due to local pacing latency, as confirmed by the use of monophasic action potential catheters.

CONCLUSIONS

A long PPI upon entrainment of typical AFL from the CTI is common and due to delayed conduction with entrainment. Whether these findings apply to other macro-re-entrant tachycardias warrants further investigation.

P-wave dispersion in children with acute rheumatic fever

As a new and simple electrocardiographic marker, P-wave dispersion is reported to be associated with inhomogeneous and discontinuous propagation of sinus impulses. The current study aimed to investigate P-wave dispersion in children with acute rheumatic fever. The study population consisted of 47 children with acute rheumatic fever (29 patients with carditis and 18 patients without carditis) and 31 healthy control subjects. Maximum and minimum P-wave durations were measured from the 12-lead surface electrocardiogram. The P-wave dispersion was calculated as the difference between maximum and minimum P-wave durations. The maximum P-wave duration and the P-wave dispersion of the patients with and without carditis were significantly greater than those of the control subjects. The P-wave dispersion of the patients with carditis was significantly greater than that of the patients without carditis. In conclusion, the P-wave dispersion was higher in the children with acute rheumatic fever than in the healthy control subjects.

Is there a relationship between complex fractionated atrial electrograms recorded during atrial fibrillation and sinus rhythm fractionation?

BACKGROUND

Ablation of persistent atrial fibrillation (AF) may require adjunctive methods of substrate modification. Both ablation-targeting complex fractionated atrial electrograms (CFAEs) recorded during AF and fractionated electrograms recorded during sinus rhythm (sinus rhythm fractionation [SRF]) have been described. However, the relationship of CFAEs with SRF is unclear.

METHODS

Twenty patients (age 62 ± 9 years, 13 males) with persistent AF and 9 control subjects without organic heart disease or AF (age 36 ± 6 years, 4 males) underwent detailed CFAE and SRF left atrial electroanatomic maps. The overlap in left atrial regions with CFAEs and SRF was compared in the AF population, and the distribution of SRF was compared among patients with AF and normal controls. Propagation maps were analyzed to identify the activation patterns associated with SR fractionation.

RESULTS

SRF (338 ± 150 points) and CFAE (418 ± 135 points) regions comprised 29% ± 14% and 25% ± 15% of the left atrial surface area, respectively. There was no significant correlation between SRF and CFAE maps (r = .2; P = NS). On comparing patients with AF and controls, no significant difference was found in the distribution of SRF between groups (P = .74). Regions of SRF overlapped areas of wave-front collision 75% ± 13% of the time.

CONCLUSIONS

(1) There is little overlap between regions of CFAEs during AF and regions of SRF measured in the time domain or the frequency domain, (2) the majority of SRF appears to occur in regions with wave-front collision, (3) the distribution of SRF is similar in patients with AF and normal controls, suggesting that this may not have an important role in AF maintenance and may not be a suitable ablation target.

Increased dispersion of atrial repolarization in Brugada syndrome

AIMS

Patients with Brugada syndrome (BS) often experience atrial fibrillation (AF) and atrial vulnerability, as measured by increased atrial conduction time. To date, however, dispersion of atrial repolarization has not been reported in these patients.

METHODS AND RESULTS

Monophasic action potentials (MAPs) recorded from four sites of the right atrium were analysed in 11 patients (10 men, 1 woman; mean age, 40 ± 9 years) with BS and in 10 controls (8 men, 2 women; mean age, 35 ± 8 years). None of these patients had a history of AF. Monophasic action potentials were recorded during right atrial pacing at a drive cycle length of 600 ms after continuous pacing. Dispersion of MAP duration (D-MAPD90) was defined as the difference between the maximum and minimum MAP duration measured at 90% repolarization (MAPD90). Inducibility of AF and repetitive atrial firing were also determined. The MAPD90 did not differ significantly between the BS and control groups (245 ± 42 vs. 228 ± 24 ms, P = ns), but D-MAPD90 was significantly higher in the BS group (69.1 ± 35.0 vs. 41.4 ± 10.3 ms, P < 0.05). Atrial fibrillation was induced in six BS patients and repetitive atrial firing in four, but neither was induced in any of the control subjects.

CONCLUSION

The significantly increased dispersion of MAPD90 observed in patients with BS suggests that the heterogeneity of atrial repolarization may contribute to the development of atrial fibrillation in patients with BS.

Electrophysiological Changes of the Atrium in Patients with Lone Paroxysmal Atrial Fibrillation

Introduction: Paroxysmal atrial fibrillation (PAF) is a common arrhythmia, and it is associated with various cardiac conditions. On the other hand, lone PAF has no identifiable underlying cause, and can occur any time for no apparent reason. The underlying causes may modify the electrophysiological properties of the atrium in different ways and extent. However this setting may be different in patients with lone PAF. We sought to investigate the atrial electrophysiological properties in lone PAF. Material and Methods: This study included 62 control subjects (Control group) and 58 patients with lone PAF (LAF group). The following atrial vulnerability parameters induced by programmed atrial stimulation were assessed and quantitatively measured: 1) the atrial effective refractory period (ERP), 2) the atrial conduction delay (CD) zone, and 3) the maximum CD. Results: The mean atrial ERP of the Control group was 215±29 ms, and that of LAF group was 208±28 ms, p<0.05. The mean atrial CD zone of the LAF group was (50±28 ms) significantly greater than that of controls (34±22 ms) (p<0.01). The mean maximum CD of the LAF group (62±29 ms) was also significantly greater than that of controls (43±20 ms) (p<0.01). Conclusions : There is a greater conduction delay of the atrium and shorter refractoriness in patients with lone PAF. Patients without underlying causes for the development of PAF exhibit abnormalities in the electrophysiological properties of the atrium.

Ablation strategies for atrial fibrillation

Atrial fibrillation remains the most common arrhythmia in the USA and is associated with an increased risk for stroke, congestive heart failure and overall mortality. There has been a tremendous advance in the field of catheter ablation of atrial fibrillation that has resulted in better outcomes for patients. The approach for ablation of atrial fibrillation can be different depending on patients' presentation of paroxysmal or persistent atrial fibrillation. Pulmonary vein isolation remains the cornerstone of any ablation strategy for atrial fibrillation; however, further ablation, end points of the procedure, clinical end points for successful ablation and appropriate follow-up remain controversial. We aim to discuss these different approaches and the major controversies in catheter ablation of atrial fibrillation.

High-density biatrial pacing protects against atrial fibrillation by synchronizing left atrial tissue

PURPOSE

The induction and sustainability of atrial fibrillation (AF) are most commonly due to pulmonary vein (PV) triggers and left atrial (LA) substrate. We hypothesized that simultaneous pacing of the PV ostia, LA, and right atrium (RA) reduces AF susceptibility by synchronizing atrial activity.

METHODS

Mongrel dogs were rapidly paced and maintained in AF for 3 months before cardioversion. Pacing leads were then placed at PV ostia, LA, and RA sites. For single-site pacing (SSP), a drive train (S1) and premature stimulus (S2) were delivered from the same electrode. Multisite pacing (MSP) consisted of S1 at all leads simultaneously and S2 at one site. Pacing trials were performed with decremental S2 coupling intervals (CI) to endpoints of AF induction or refractoriness.

RESULTS

AF induction was reduced by 40.0% with MSP vs. SSP (7.2% vs. 12.0%, p < 0.001). LA S2 sites were more likely to induce AF than RA sites (11.5% vs. 2.6%, p < 0.0001), with benefit of MSP over SSP at LA sites (8.6% vs. 14.6%, p < 0.0001). The CI for AF induction was longer with SSP vs. MSP (119.4 +/- 13.3 vs. 104.4 +/- 11.2 ms, p < 0.05). Atrial activation times were shortened with MSP vs. SSP (87.4 +/- 4.9 vs. 97.1 +/- 10 ms, p < 0.005).

CONCLUSIONS

Atrial synchronization was shown by the decreased activation times with MSP. AF induction was reduced by 40.0% with MSP, supporting the hypothesis of decreased AF susceptibility with synchronization. This is the first study demonstrating AF protection with high-density pacing at LA sites associated with triggers and substrate for the induction and maintenance of AF.

Paroxysmal lone atrial fibrillation is associated with an abnormal atrial substrate: characterizing the "second factor"

OBJECTIVES

The purpose of this study was to determine whether patients with paroxysmal "lone" atrial fibrillation (AF) have an abnormal atrial substrate.

BACKGROUND

While "AF begets AF," prompt termination to prevent electrical remodeling does not prevent disease progression.

METHODS

Twenty-five patients with paroxysmal lone AF, without arrhythmia in the week prior, and 25 reference patients with left-sided accessory pathways were studied. Multipolar catheters placed at the lateral right atrium (RA), crista terminalis, coronary sinus, septal RA, and sequentially within the left atrium (LA) determined the effective refractory period (ERP) at 10 sites, conduction time along linear catheters, and conduction characteristics at the crista terminalis. Bi-atrial electroanatomic maps were created to determine regional differences in conduction velocity and voltage.

RESULTS

Patients with AF demonstrated the following compared with reference patients: larger atrial volumes (RA: 94 +/- 18 ml vs. 69 +/- 9 ml, p = 0.003; LA: 99 +/- 19 ml vs. 77 +/- 17 ml, p = 0.006); longer ERP (at 600 ms: 255 +/- 25 ms vs. 222 +/- 16 ms, p < 0.001; at 450 ms: 234 +/- 20 ms vs. 212 +/- 14 ms, p = 0.004); longer conduction time along linear catheters (57 +/- 18 ms vs. 47 +/- 10 ms, p = 0.01); longer bi-atrial activation time (128 +/- 17 ms vs. 89 +/- 10 ms, p < 0.001); slower conduction velocity (RA: 1.3 +/- 0.3 mm/ms vs. 2.1 +/- 0.5 mm/ms; LA: 1.2 +/- 0.2 mm/ms vs. 2.2 +/- 0.4 mm/ms, p < 0.001); greater proportion of fractionated electrograms (27 +/- 8% vs. 8 +/- 5%, p < 0.001); longer corrected sinus node recovery time (265 +/- 57 ms vs. 185 +/- 60 ms, p = 0.002); and lower voltage (RA: 1.7 +/- 0.4 mV vs. 2.9 +/- 0.4 mV; LA: 1.7 +/- 0.7 mV vs. 3.3 +/- 0.7 mV, p < 0.001).

CONCLUSIONS

Patients with paroxysmal lone AF, remote from arrhythmia, demonstrate bi-atrial abnormalities characterized by structural change, conduction abnormalities, and sinus node dysfunction. These factors are likely contributors to the "second factor" that predisposes to the development and progression of AF.

High-density mapping of atrial fibrillation in humans: relationship between high-frequency activation and electrogram fractionation

INTRODUCTION

Sites of complex fractionated atrial electrograms (CFAE) and dominant frequency (DF) have been implicated in maintaining atrial fibrillation (AF); however, their relationship is poorly understood.

METHODS AND RESULTS

Twenty patients underwent biatrial high-density contact mapping (507 +/- 150 points/patient) during AF. CFAE were characterized using software to quantify electrogram complexity (CFE-mean). Spectral analysis determined the frequency with greatest power and sites of high DF with a frequency gradient. CFE-mean was higher (less fractionated) for right compared with left atria (P < 0.001) and in paroxysmal compared with persistent AF (P < 0.001). DF was lower for right compared with left atria (P = 0.02) and in paroxysmal compared with persistent AF (P < 0.001). There was significant regional variation in DF in paroxysmal (P < 0.001) but not persistent AF. Highest DF points clustered together with 5.2 +/- 1.7 clusters/patient. Correlation between CFE-mean and DF was poor on a point-by-point basis (r =-0.17, P < 0.001), but moderate on an individual basis (r =-0.50, P = 0.03). Exploration of their spatial relationship demonstrated CFAE areas in close proximity (median 5 mm, IQR 2-10) to high DF sites; within 10 mm in 80% and 10-20 mm in 10%. Simultaneous activation mapping at these sites further supports this observation.

CONCLUSION

Greater fractionation and higher DF are seen in persistent AF and left atria during AF. Preferential areas of high DF are observed in paroxysmal but not persistent AF. CFAE and DF correlate within an individual but not point-by-point. Exploration of their spatial relationship demonstrates CFAE in areas adjacent to high DF, and this is supported by activation mapping at these sites.

Prediction of atrial fibrillation in patients with cardiac dysfunctions†

AIMS

Atrial fibrillation (AF) is a common arrhythmia in advanced heart failure. The occurrence of AF increases the risk of death and hospitalization for patients with heart failure. The results of different studies indicated that patients with paroxysmal AF have a longer filtered P wave duration (FPD), a lower root mean square voltage of the last 20 ms of the P wave (RMS 20), and a lower chemoreflexsensitivity (CHRS). Our study bases on these observations in order to examine the methods for predicting AF in patients with a left ventricular ejection fraction below 40% without a prior documentation of AF.

METHODS AND RESULTS

The ratio between the difference of RR intervals in ECG and venous pO(2) before and after 5-min oxygen inhalation was measured (ms/mmHg) in order to determine the CHRS. A P wave signal-averaged ECG was performed for the measurement of FPD and RMS 20. The measurements were only performed in 94 patients with sinus rhythm. AF occurred during the mean follow-up of 39.9 months in 24 patients (26%). There were no significant differences concerning age, heart diseases, sex, ejection fraction, heart rate, or the use of drugs. The FPD (130.3 +/- 4.2 vs. 118.9 +/- 12.4 ms, P < 0.0001) was significantly longer and the RMS 20 (3.03 +/- 0.95 vs. 3.83 +/- 1.58 microV, P = 0.02) was significantly lower in patients with AF than in sinus rhythm. The CHRS did not differ significantly between both groups (3.57 +/- 1.49 vs. 3.48 +/- 1.62 ms/mmHg, P = 0.81). The chi(2) test showed that the threshold of FPD>or=125 ms and RMS 20 <or=3.3 microV revealed the best predictive value for AF. A stepwise logistic regression analysis of all variables identified the threshold of FPD>or=125 ms and RMS 20 <or=3.3 microV (OR 18.71; 95% CI, 4.85-72.16, P < 0.0001) as independent predictors for AF.

CONCLUSIONS

In summary, our data show that the results of a P wave signal-averaged ECG can predict the risk for new onset of AF in patients with heart failure. The value of signal-averaged FPD is probably the result of reflecting the intra-atrial conduction delay, which is a pathophysiological condition for AF. The CHRS is not a suitable method for predicting AF.

P-wave dispersion in panic disorder

BACKGROUND

P-wave dispersion (PWD) is defined as the difference between the maximum and the minimum P-wave (Pmax and Pmin, respectively) duration. Significant variation in cardiac atrial PWD has been correlated with changes in systemic autonomic tone such as during periods of anxiety. It is also known that the degree of PWD seen on 12-lead electrocardiogram (ECG) may be a predictor of susceptibility of the atrial myocardium to future atrial fibrillation (AF). Therefore, we firstly aimed to show an association between PWD and panic disorder, a state of high sympathetic tone.

METHODS

PWD was measured in 40 outpatients with panic disorder and in 40 physically and mentally healthy age- and gender-matched controls. In addition, the Panic Agoraphobia Scale (PAS) and the Hamilton Depression Rating Scale (HDRS) were scored concomitantly.

RESULTS

Both Pmax and Pmin were significantly higher than those of healthy controls. PWD was significantly greater in the panic disorder group than in the controls. As expected, the mean score on PAS was significantly higher for the panic disorder group than for the controls and correlated significantly with PWD. Heart rate (measured as RR intervals in milliseconds on electrocardiogram) did not differ significantly between the groups.

CONCLUSIONS

The findings of the present study suggest that the disorder may be associated with an increase in PWD. This association may result from prolonged anxiety and increase in sympathetic modulation, which are main characteristics of panic disorder.

Characterization of the electroanatomical substrate in human atrial fibrillation: the relationship between changes in atrial volume, refractoriness, wavefront propagation velocities, and AF burden

INTRODUCTION

Progressive remodeling occurs in experimental models of AF whereby slowing of conduction, shortening of refractoriness, and atrial dilatation are associated with an increased vulnerability to atrial fibrillation (AF). This study investigates the relative changes in atrial geometry and electrophysiology with increasing AF burden in humans.

METHODS AND RESULTS

Patients undergoing ablation of AF or left-sided accessory pathways were recruited. Atrial volumes were determined by echocardiography. Wavefront propagation velocities (WPV), specifically in the direction of activation, were calculated from pre-ablation activation (Carto) maps of both atria. Dispersion, adaptation of, and effective refractoriness (ERP) were measured at 3 sites. A composite arrhythmogenic index (Atrial Volume/WPV x ERP) was derived to compare the degree of electroanatomical remodeling with AF burden. Fifty-nine patients (22 paroxysmal AF, 19 recurrent persistent AF, and 18 controls) were recruited. AF subjects had slower right atrial WPV (P = 0.01), but no difference in left atrial WPV compared with controls. ERP was reduced globally (P < 0.05), with increased dispersion (P < 0.05). WPV and ERP did not distinguish between patients with paroxysmal or persistent AF. Biatrial volumes were greater only in patients with persistent AF (P < 0.01). There was a stepwise increase in the AI with increasing AF burden (P < 0.0001).

CONCLUSION

An arrhythmogenic substrate exists in human AF, characterized by globally decreased refractoriness with greater dispersion, slower right atrial conduction, and atrial dilatation. Persistence of AF is not accompanied by any further electrical remodeling, but only atrial dilatation. The degree of electroanatomical remodeling is associated with the clinical pattern of AF.

Prediction of Conversion from Paroxysmal to Permanent Atrial Fibrillation

BACKGROUND

Paroxysmal atrial fibrillation (PAF) transits to permanent atrial fibrillation (PEAF). The current study was to determine whether a P wave-triggered P wave signal averaged electrocardiogram (P-SAECG) and chemoreflexsensitivity (CHRS) are useful to predict a conversion to PEAF in patients with PAF.

METHODS

The filtered P wave duration (FPD) and the root mean square voltage of the last 20 ms of the P wave (RMS 20) were measured by P-SAECG. The ratio between the difference of RR intervals in the ECG and venous pO2 before and after 5-minutes oxygen inhalation is measured (ms/mmHg) for the determination of CHRS.

RESULTS

A total of 180 patients with PAF were enrolled and followed for a mean of 22.5 months. PEAF occurred in 38 patients (21%) and these patients had a significantly larger left atrial size (43.2 +/- 4.9 vs. 41.0 +/- 5.4 mm, P = 0.021), a significantly longer FPD (158.8 +/- 18.2 vs. 136.7 +/- 16.6 ms, P < 0.0001), and a significantly lower CHRS (1.96 +/- 0.99 vs. 2.44 +/- 1.19 ms/mmHg, P = 0.024) than patients with PAF. Patients with PEAF tended to have a lower RMS 20 (2.38 +/- 0.65 vs. 2.75 +/- 1.18 microV, P = 0.067) than patients with PAF. The chi(2) test showed that the combination of FPD > or = 145 ms, RMS 20 < or = 3.0 microV, left atrial size > or = 41 mm, and CHRS < or = 2.0 ms/mmHg had the best predictive power for PEAF. Patients who fulfilled these criteria had a 12-fold increased risk for a conversion from PAF to PEAF.

CONCLUSIONS

Our results show that a P-SAECG, an analysis of CHRS, and left atrial enlargement are clinical predictors of a progression from PAF to PEAF.

Acute coronary syndrome: short-term effects of early intravenous metoprolol on maximum P wave duration and P wave dispersion

In patients with acute coronary syndrome (ACS), the presence of atrial fibrillation (AF) results in worse inpatient outcomes than in those without AF. Two electrocardiographic markers, maximum P wave duration (P(maximum)) and P wave dispersion (P(dispersion)), have been assessed because they reflect conduction abnormalities in patients with paroxysmal AF. b blockers are known to have beneficial effects in patients with ACS. This prospective study was conducted to investigate whether early intravenous (IV) metoprolol injection acutely decreases P(maximum) and P(dispersion) in patients with ACS. This study involved 100 consecutive patients with ACS who were divided into 2 groups according to whether or not they received early IV metoprolol. Group 1 consisted of 19 patients who received IV metoprolol within 3 h after onset of symptoms, and group 2 consisted of 81 patients who did not receive IV metoprolol within 3 h after symptom onset because of late admission. P(maximum) and P(dispersion) were measured on admission and again at 2 h after admission. Two-dimensional echocardiographic examination was also performed. For patients who received early IV metoprolol, P(maximum) and P(dispersion), measured 2 h after admission, were shorter than values at admission (P<.001). Conversely, P(maximum) and P(dispersion), measured 2 h after admission, did not differ significantly from values at admission in patients who did not receive early IV metoprolol (P=.292 and P=.236, respectively). IV administration of metoprolol reduced values for P(maximum) and P(dispersion), measured 2 h after admission, among patients with ACS who were admitted within 3 h after onset of symptoms.

P wave dispersion predicts recurrence of paroxysmal atrial fibrillation in patients with atrioventricular nodal reentrant tachycardia treated with radiofrequency catheter ablation

BACKGROUND

Paroxysmal atrial fibrillation (AF) recurs in up to one-third of patients with atrioventricular nodal reentrant tachycardia (AVNRT) treated with slow pathway ablation. Therefore, identification of patients at risk for recurrence of AF after slow pathway ablation is important because of the necessity for additional therapies. The purpose of this study was to determine whether successful slow pathway ablation influences P wave parameters and whether these parameters predict the recurrence of paroxysmal AF in patients with both AVNRT and paroxysmal AF after ablation.

METHODS

Thirty-six patients with AVNRT and documented paroxysmal AF (Group 1) were compared to 36 age-matched controls with AVNRT only (Group 2). P wave durations and P dispersion were measured before and after ablation.

RESULTS

No significant differences were observed between P wave parameters observed before and after ablation. Maximum P wave durations (Pmax) and P dispersion (Pdisp) were significantly higher in Group 1 than in Group 2 (P < 0.001 for both) whereas minimum P wave durations did not differ between groups, both before and after ablation. Ten patients (28%) in Group-1 had recurrence of AF during a mean follow-up of 34 +/- 11 months. Univariate predictors of AF recurrence were Pdisp > or =35.5 ms (P < 0.010), left atrial diameter >40 mm (P < 0.010), mitral or aortic calcification (P < 0.010), Pmax > or =112 ms (P < 0.050), valvular heart disease (P < 0.050), and atrial vulnerability (induction of AF lasting >30 second) after ablation (P < 0.050). However, only Pdisp > or =35.5 ms (P < 0.050) and left atrial diameter >40 mm (P < 0.010) were independent predictors of AF recurrences.

CONCLUSION

This study suggests that P wave dispersion could identify patients with AVNRT susceptible to recurrence of AF after slow pathway ablation.