Atrial Ectopy Increases Asynchronous Activation of the Endo- and Epicardium at the Right Atrium.

The predisposition of atrial extrasystoles (AES) to trigger cardiac tachyarrhythmia may arise from intramural conduction disorders causing endo-epicardial asynchrony (EEA). This study aimed to determine whether spontaneous AES disturb endo-epicardial conduction. Simultaneous endo-epicardial mapping of the right atrium was performed in patients during cardiac surgery with two 128-electrode arrays. Sixty spontaneous AES were observed in 23 patients and were analyzed for incidence of conduction delay, conduction block and amount of EEA compared to the previous sinus rhythm beat. Both conduction delay and block occurred more often in AES compared to sinus rhythm. The difference in lines of conduction block between the epicardium and endocardium increased in AES causing a greater imbalance of conduction disorders between the layers. The incidence of EEA with differences ≥10 ms increased significantly in AES. AES caused delays between the epicardium and endocardium up to 130 ms and EEA to increase for up to half (47%) of the mapping area. Conduction disturbances between the epicardial and endocardial layer giving rise to EEA increase during AES. Asynchronous activation of the atrial layers increases during AES which may be a mechanism for triggering cardiac tachyarrhythmia under the right conditions but EEA cannot be recognized by current mapping tools.

Functional Atrial Endocardial-Epicardial Dissociation in Patients With Structural Heart Disease Undergoing Cardiac Surgery.

OBJECTIVES: The goal of this study was to describe functional endocardial-epicardial dissociation (FEED), signal complexities, and three-dimensional activation dynamics of the human atrium with structural heart disease (SHD). BACKGROUND: SHD commonly predisposes to arrhythmias. Although progressive remodeling is implicated, direct demonstration of FEED in the human atrium has not been reported previously. METHODS: Simultaneous intraoperative mapping of the endocardial and epicardial lateral right atrial wall was performed by using 2 high-density grid catheters during sinus rhythm, pacing drive (600 ms and 400 ms cycle length), and premature extrastimulation (PES). Unipolar electrograms (EGMs) were exported into custom-made software for activation and phase mapping. Difference of ≥20 ms between paired endocardial and epicardial electrodes defined dissociation. EGMs with ≥3 deflections were classified as fractionated. RESULTS: Sixteen patients (mean age 60.5 ± 4.1 years; 18.7% with a history of atrial fibrillation) with SHD (43% ischemia, 57% valvular disease) were included. A total of 9,218 EGMs were analyzed. Compared with sinus rhythm, phase and activation analyses showed significant FEED during pacing at 600 ms and 400 ms (phase mapping 22.4% vs. 10% [p < 0.0001] and 25.8% vs. 10% [p < 0.0001], respectively; activation mapping 25.4% vs. 7.8% [p < 0.0001] and 27.7% vs. 7.8% [p < 0.0001]) and PES (phase mapping 34% vs. 10% [p < 0.0001]; activation mapping 29.5% vs. 7.8% [p < 0.0001]). Fractionated EGMs occurred significantly more during PES compared with sinus rhythm (50.2% vs. 39.5%; p < 0.0001). Activation patterns differed significantly during pacing drive and PES, with preferential epicardial exit during the latter (15.9% vs. 13.8%; p = 0.046). CONCLUSIONS: Simultaneous endocardial-epicardial mapping revealed significant FEED with signal fractionation and preferential epicardial breakthroughs with PES. Such complex three-dimensional interaction in electrical activation provides mechanistic insights into atrial arrhythmogenesis with SHD.

The Effects of Valvular Heart Disease on Atrial Conduction During Sinus Rhythm.

Different arrhythmogenic substrates for atrial fibrillation (AF) may underlie aortic valve (AV) and mitral valve (MV) disease. We located conduction disorders during sinus rhythm by high-resolution epicardial mapping in patients undergoing AV (n = 85) or MV (n = 54) surgery. Extent and distribution of conduction delay (CD) and block (CD) across the entire right and left atrial surface was determined from circa 1880 unipolar electrogram recordings per patient. CD and CB were most pronounced at the superior intercaval area (2.5% of surface, maximal degree 6.6%/cm2). MV patients had a higher maximal degree of CD at the lateral left atrium than AV patients (4.2 vs 2.3%/cm2, p = 0.001). A history of AF was most strongly correlated to CD/CB at Bachmann's bundle and age. Although MV patients have more conduction disorders at the lateral left atrium, disturbed conduction at Bachmann's bundle during sinus rhythm indicates the presence of atrial remodeling which is related to AF episodes.

The Bachmann bundle and interatrial conduction: comparing atrial morphology to electrical activity.

BACKGROUND: The Bachmann bundle (BB) is one of the major interatrial muscular connections. Macroscopic anatomy and electrophysiological properties of BB have so far not been linked, and differences in activation patterns are most likely due to anatomical variations. OBJECTIVES: The goals of this study were to analyze different activation patterns and couple those wavefronts to epicardial morphological structures on cadaveric hearts. METHODS: High-resolution epicardial mapping over BB during sinus rhythm was performed in 185 patients undergoing coronary artery bypass graft surgery. The epicardial atrial musculature was macroscopically examined in 19 postmortem dissected human hearts, which are different from those examined in the mapping study. The morphology of BB and surrounding interatrial connections were evaluated. Activation patterns were subsequently linked to morphological variance found in the dissected hearts. RESULTS: Epicardial mapping showed that BB is activated in a right-to-left direction in the majority of patients. In almost one-third of patients, a wavefront emerging or entering in the middle of BB was also observed. In some patients, left-to-right activation of BB was observed. BB was macroscopically present in all postmortem hearts. In addition, a newly found posterosuperior bundle was consistently seen, joining BB from the posterior border over the interatrial groove. Other connections identified were the septopulmonary bundle and posterior interatrial connections. CONCLUSION: The morphological interatrial connections correspond to the interatrial pathways observed with high-resolution epicardial mapping of BB. Of these connections, BB and the posterosuperior bundle seem to be most consistent, both morphologically and electrophysiologically.

Dysrhythmias in patients with a complete atrioventricular septal defect: From surgery to early adulthood.

OBJECTIVE: Outcomes after surgical repair of complete atrioventricular septal defect (cAVSD) have improved. With advancing age, the risk of development of dysrhythmias may increase. The aims of this study were to (1) examine development of sinus node dysfunction (SND), atrial and ventricular tachyarrhythmias, and (2) study progression of atrioventricular conduction abnormalities in young adult patients with repaired cAVSD. STUDY DESIGN: In this retrospective multicenter study, 74 patients (68% female) with a cAVSD repaired in childhood were included. Patients' medical files were evaluated for occurrence of SND, atrioventricular conduction block (AVB), atrial and ventricular tachyarrhythmias. RESULTS: Median age at repair was 6 months (interquartile range 3-10) and median age at last follow-up was 24 years (interquartile range 21-28). SND occurred after a median of 17 years (interquartile range 11-19) after repair in 23% of patients, requiring pacemaker implantation in two patients (12%). Regular supraventricular tachycardia was observed in three patients (4%). Atrial fibrillation and ventricular tachyarrhythmias were not observed. Twenty-seven patients (36%) had first-degree AVB, which was self-limiting in 16 (59%) and persistent in 10 (37%) patients. One patient developed third-degree AVB 7 days after left atrioventricular valve replacement. Spontaneous type II second-degree AVB occurred in a 28-year-old patient. Both patients underwent pacemaker implantation. CONCLUSIONS: Clinically significant dysrhythmias were uncommon in young adult patients after cAVSD repair. However, three patients required pacemaker implantation for either progression of SND or spontaneous type II second-degree AVB. Longer follow-up should point out whether dysrhythmias will progress or become more prevalent with increasing age.

Intraoperative Inducibility of Atrial Fibrillation Does Not Predict Early Postoperative Atrial Fibrillation.

BACKGROUND: Early postoperative atrial fibrillation (EPoAF) is associated with thromboembolic events, prolonged hospitalization, and development of late PoAF (LPoAF). It is, however, unknown if EPoAF can be predicted by intraoperative AF inducibility. The aims of this study are therefore to explore (1) the value of intraoperative inducibility of AF for development of both EPoAF and LPoAF and (2) the predictive value of de novo EPoAF for recurrence of LPoAF. METHODS AND RESULTS: Patients (N=496, 75% male) undergoing cardiothoracic surgery for coronary and/or valvular heart disease were included. AF induction was attempted by atrial pacing, before extracorporeal circulation. All patients were on continuous rhythm monitoring until discharge to detect EPoAF. During a follow-up period of 2 years, LPoAF was detected by ECGs and Holter recordings. Sustained AF was inducible in 56% of patients. There was no difference in patients with or without AF before surgery (P=0.159), or between different types of surgery (P=0.687). In patients without a history of AF, incidence of EPoAF and LPoAF was 37% and 2%, respectively. EPoAF recurred in 58% patients with preoperative AF, 53% developed LPoAF. There were no correlations between intraoperative inducibility and EPoAF or LPoAF (P>0.05). EPoAF was not correlated with LPoAF in patients without a history of AF (P=0.116), in contrast to patients with AF before surgery (P<0.001). CONCLUSIONS: Intraoperative AF inducibility does not predict development of either EPoAF or LPoAF. In patients with AF before surgery, EPoAF is correlated with LPoAF recurrences. This correlation is absent in patients without AF before surgery.

Unipolar atrial electrogram morphology from an epicardial and endocardial perspective.

BACKGROUND: Endo-epicardial asynchrony (EEA) and the interplay between the endocardial and epicardial layers could be important in the pathophysiology of atrial arrhythmias. The morphologic differences between epicardial and endocardial atrial electrograms have not yet been described, and electrogram morphology may hold information about the presence of EEA. OBJECTIVE: The purpose of this study was to directly compare epicardial to endocardial unipolar electrogram morphology during sinus rhythm (SR) and to evaluate whether EEA contributes to electrogram fractionation by correlating fractionation to spatial activation patterns. METHODS: In 26 patients undergoing cardiac surgery, unipolar electrograms were simultaneously recorded from the epicardium and endocardium at the inferior, middle, and superior right atrial (RA) free wall during SR. Potentials were analyzed for epi-endocardial differences in local activation time, voltage, RS ratio, and fractionation. The surrounding and opposite electrograms of fractionated deflections were evaluated for corresponding local activation times in order to determine whether fractionation originated from EEA. RESULTS: The superior RA was predisposed to delayed activation, EEA, and fractionation. Both epicardial and endocardial electrograms demonstrated an S-predominance. Fractionation was mostly similar between the 2 sides; however, incidentally deflections up to 4 mV on 1 side could be absent on the other side. Remote activation was responsible for most fractionated deflections (95%) in SR, of which 4% could be attributed to EEA. CONCLUSION: Local epi-endocardial differences in electrogram fractionation occur occasionally during SR but will likely increase during arrhythmias due to increasing EEA and (functional) conduction disorders. Electrogram fractionation can originate from EEA, and this study demonstrated that unipolar electrogram fractionation can potentially identify EEA.

Intraoperative arrhythmias in children with congenital heart disease: transient, innocent events?

Aims: The significance and incidences of intraoperative arrhythmias occurring in the operating room (OR) in children with congenital heart disease (CHD) are unknown. Aims of this study were to determine incidences of intraoperative arrhythmias in children with CHD and to examine whether they are associated with persistent arrhythmias during follow-up. Methods and results: Continuous ECG recordings obtained from 134 consecutive paediatric CHD patients were manually examined from the moment the aortic cross-clamp (ACC) was removed [use of ACC and cardiopulmonary bypass (CPB)], when CPB was stopped (use of only CPB) or when the sternum was closed (no use of ACC and CPB) until departure from the OR. In the OR, 2nd (60%) and 3rd (34%) degree atrioventricular conduction block (AVB), ectopic atrial rhythm (30%), and junctional rhythm (32%) were most often observed in patients who underwent surgery with both ACC and CPB. Incidences of these arrhythmias decreased after cessation of CPB (P < 0.01). (Supra)ventricular premature beats were mostly observed between end of ACC time and sternum closure (64-84%), but decreased before departure from the OR (6-16%, P < 0.01). During a median follow-up of 37 months, 17 patients (13%) had new onset, late post-operative arrhythmias. Of these patients, 88% had intraoperative arrhythmias compared with 85% of patients without late post-operative arrhythmias (P = 1). Conclusion: Intraoperative arrhythmias, mainly 2nd degree AVB and (supra)ventricular premature beats, were frequently observed in children with CHD undergoing cardiac surgery with use of CPB and ACC. Most arrhythmias were short-lasting and transient and appeared not to be related to late post-operative arrhythmias.

Quantification of the Arrhythmogenic Effects of Spontaneous Atrial Extrasystole Using High-Resolution Epicardial Mapping.

BACKGROUND: Atrial extrasystoles (AES) can initiate atrial fibrillation. However, the impact of spontaneous AES on intra-atrial conduction is unknown. The aims of this study were to examine conduction disorders provoked by AES and to correlate these conduction differences with patient characteristics, mapping locations, and type of AES. METHODS AND RESULTS: High-resolution epicardial mapping (electrodes N=128 or N=192; interelectrode distance, 2 mm) of the entire atrial surface was performed in patients (N=164; 69.5% male; age 67.2±10.5 years) undergoing open-chest cardiac surgery. AES were classified as premature, aberrant, or prematurely aberrant. Conduction delay and conduction block were quantified during sinus rhythm and AES and subsequently compared. Median incidence of conduction delay and conduction block during sinus rhythm was 1.2% (interquartile, 0%-2.3%) and 0.4% (interquartile, 0%-2.1%). In comparison, the median incidence of conduction delay and conduction block during 339 AES was respectively 2.8% (interquartile, 1.3%-4.6%) and 2.2% (interquartile, 0.3%-5.1%) and differed between the types of AES (prematurely aberrant>aberrant>premature). The degree of prematurity was not associated with a higher incidence of conduction disorders (P>0.05). In contrast, a higher degree of aberrancy was associated with a higher incidence of conduction disorders; AES emerging as epicardial breakthrough provoked most conduction disorders (P≥0.002). AES caused most conduction disorders in patients with diabetes mellitus and left atrial dilatation (P<0.05). CONCLUSIONS: Intraoperative high-resolution epicardial mapping showed that conduction disorders are mainly provoked by prematurely aberrant AES, particularly in patients with left atrial dilation and diabetes mellitus or emerging as epicardial breakthrough.

Time course and interrelationship of dysrhythmias in patients with surgically repaired atrial septal defect.

BACKGROUND: Atrial fibrillation (AF) and other supraventricular tachycardias (SVTs) are known complications after surgical repair of atrial septal defect (ASD), but sinus node dysfunction (SND) and complete atrioventricular conduction block (cAVB) may also occur. OBJECTIVE: The aim of this study was to examine time course and interrelationship of various dysrhythmias in patients with ASD. METHODS: Adult patients (N = 95) with surgically repaired secundum ASD (n = 40), partial atrioventricular septal defect (n = 37) or sinus venosus defect (n = 18), and documented SND, cAVB, AF, and/or other SVT were included. The median age at repair was 13 years (interquartile range [IQR] 6-45 years), and patients were followed for 26 years (IQR 15-37 years) after ASD repair. RESULTS: SND was observed in 34 patients (36%), cAVB in 14 (14%), AF in 48 (49%), and SVT in 44 (45%); 37 patients (39%) had ≥2 dysrhythmias. All dysrhythmias presented most often after ASD repair (P < .01), with a median duration of 12 years (IQR 17 days - 32 years) to 16 years (IQR 4 - 28 years) between repair and onset. Development of SND and cAVB late after ASD repair was not related to a redo procedure in 100% and 60% of patients, respectively. SND preceded atrial tachyarrhythmias in 50% (P = .31) and SVT preceded AF in 68% (P = .09) of patients with both dysrhythmias. CONCLUSION: A substantial number of dysrhythmias presented (very) late after ASD repair. In most patients, development of late SND and cAVB was not related to redo procedures. In patients with multiple dysrhythmias, a specific order of appearance was not observed.

Relevance of Conduction Disorders in Bachmann's Bundle During Sinus Rhythm in Humans.

BACKGROUND: Bachmann's bundle (BB) is considered to be the main route of interatrial conduction and to play a role in development of atrial fibrillation (AF). The goals of this study are to characterize the presence of conduction disorders in BB during sinus rhythm and to study their relation with AF. METHODS AND RESULTS: High-resolution epicardial mapping (192 unipolar electrodes, interelectrode distance: 2 mm) of sinus rhythm was performed in 185 patients during coronary artery bypass surgery of whom 13 had a history of paroxysmal AF. Continuous rhythm monitoring was used to detect postoperative AF during the first 5 postoperative days. In 67% of the patients, BB was activated from right to left; in the remaining patients from right and middle (21%), right, central, and left (8%), or central (4%) site. Mean effective conduction velocity was 89 cm/s. Conduction block was present in most patients (75%; median 1.1%, range 0-12.8) and was higher in patients with paroxysmal AF compared with patients without a history of AF (3.2% versus 0.9%; P=0.03). A high amount of conduction block (>4%) was associated with de novo postoperative AF (P=0.02). Longitudinal lines of conduction block >10 mm were also associated with postoperative AF (P=0.04). CONCLUSIONS: BB may be activated through multiple directions, but the predominant route of conduction is from right to left. Conduction velocity across BB is around 90 cm/s. Conduction is blocked in both longitudinal and transverse direction in the majority of patients. Conduction disorders, particularly long lines of longitudinal conduction block, are more pronounced in patients with AF episodes.

QUest for the Arrhythmogenic Substrate of Atrial fibRillation in Patients Undergoing Cardiac Surgery (QUASAR Study): Rationale and Design.

The heterogeneous presentation and progression of atrial fibrillation (AF) implicate the existence of different pathophysiological processes. Individualized diagnosis and therapy of the arrhythmogenic substrate underlying AF may be required to improve treatment outcomes. Therefore, this single-center study aims to identify the arrhythmogenic areas underlying AF by intra-operative, high-resolution, multi-site epicardial mapping in 600 patients with different heart diseases. Participants are divided into 12 groups according to the underlying heart diseases and presence of prior AF episodes. Mapping is performed with a 192-electrode array for 5-10 s during sinus rhythm and (induced) AF of the entire atrial surface. Local activation times are converted into activation and wave maps from which various electrophysiological parameters are derived. Postoperative cardiac rhythm registrations and a 5-year follow-up will show the incidence of postoperative and persistent AF. This project provides the first step in the development of a tool for individual AF diagnosis and treatment.

Atrial tachyarrhythmias after atrial switch operation for transposition of the great arteries: Treating old surgery with new catheters.

The arterial switch operation has been the procedure of first choice for correction of transposition of the great arteries (TGA) for several decades now. However, a large number of adult patients with TGA nowadays were palliated previously by either a Mustard or a Senning procedure. Atrial tachyarrhythmias (ATs) are frequently observed during long-term follow-up of patients with TGA after these atrial switch corrections and are associated with both morbidity and mortality. Because of the complex postoperative anatomy in these patients, ablative therapy for these tachyarrhythmias can be challenging. The goals of this review are to discuss the most prevalent ATs in patients after the Mustard or Senning procedure and to summarize (long-term) outcomes of ablative therapy. In addition, recent developments in ablative therapy for ATs in this patient population are outlined.

Time Course of Atrial Fibrillation in Patients With Congenital Heart Defects.

BACKGROUND: The incidence of atrial fibrillation (AF) is rising in the aging patients with congenital heart defects (CHD). However, studies reporting on AF in patients with CHD are scarce. The aim of this multicenter study was to examine in a large cohort of patients with a variety of CHD: (1) the age of onset and initial treatment of AF, coexistence of atrial tachyarrhythmia and (2) progression of paroxysmal to (long-standing) persistent/permanent AF during long-term follow-up. METHODS AND RESULTS: Patients (n=199) with 15 different CHD and documented AF episodes were studied. AF developed at 49±17 years. Regular atrial tachycardia (AT) coexisting with AF occurred in 65 (33%) patients; 65% initially presented with regular AT. At the end of a follow-up period of 5 (0-24) years, the ECG showed AF in 81 patients (41%). In a subgroup of 114 patients, deterioration from paroxysm of AF to (long-standing) persistent/permanent AF was observed in 29 patients (26%) after only 3 (0-18) years of the first AF episode. Cerebrovascular accidents/transient ischemic attacks occurred in 26 patients (13%), although a substantial number (n=16) occurred before the first documented AF episode. CONCLUSIONS: Age at development of AF in patients with CHD is relatively young compared with the patients without CHD. Coexistence of episodes of AF and regular AT occurred in a considerable number of patients; most of them initially presented with regular AT. The fast and frequent progression from paroxysmal to (long-standing) persistent or permanent AF episodes justifies close follow-up and early, aggressive therapy of both AT and AF.

Management of atrial fibrillation in patients with congenital heart defects.

Due to improved surgical technologies and post-operative care, long-term survival has improved in patients with congenital heart disease. Atrial fibrillation (AF) is increasingly observed in this aging population and is associated with morbidity and mortality; however, reports about the pathophysiology and the outcome of different treatment modalities of AF are still scarce in patients with congenital heart disease. In this review, the authors describe the epidemiology, pathophysiology and outcome of the different therapies of AF in this specific patient population.