Impact of weight adjusted high frequency low tidal volume ventilation and atrial pacing in lesion metrics in high-power short-duration ablation: Results of a pilot study.

INTRODUCTION: Lesion size index (LSI) was introduced with the use of Tacticath™ and as a surrogate of lesion quality. The metric used to achieve the predetermined values involves combined information of contact force (CF), power and radiofrequency time. Rapid atrial pacing (RAP) and high-frequency low-tidal volume ventilation (HFLTV) independently or in combination improve catheter stability and CF and quality of lesions. Data of the impact of body weight adjusted HFLTV ventilation strategy associated with RAP in the lesion metrics still lacking. The study aimed to compare the results of high-power short-duration (HPSD) atrial fibrillation ablation using simultaneous weight adjusted HFLTV and RAP and standard ventilation (SV) protocol. METHODS: Prospective, nonrandomized study with 136 patients undergoing de novo ablation divided into two groups; 70 in RAP (100 ppm) + HFLTV with 4 mL/kg of tidal volume and 25 breaths/min (group A) and 66 patients with SV in intrinsic sinus rhythm (group B). Ablation using 50 W, CF of 5-10 g/10-20 g and 40 mL/minute flow rate on the posterior and anterior left atrial wall, respectively. RESULTS: No procedure-related complications. Group A: Mean LSI points 70 ± 16.5, mean total lower LSI 3.4 ± 0.5, mean total higher LSI 8.2 ± 0.4 and mean total LSI 5.6 ± 0.6. Anterior and posterior wall mean total LSI was 6.0 ± 0.4 and 4.2 ± 0.3, respectively. Mean local impedance drop (LID) points were 118.8 ± 28.4, mean LID index (%) 12.9 ± 1.5, and mean LID < 12% points 55.9 ± 23.8. Anterior and posterior wall mean total LID index were 13.6 ± 2.0 and 11.9 ± 1.7, respectively. Recurrence in 11 (15.7%) patients. Group B: Mean LSI points 56 ± 2.7, mean total lower LSI 2.9 ± 0.7, mean total higher LSI 6.9 ± 0.9, and mean total LSI 4.8 ± 0.8. Anterior and posterior wall mean total LSI was 5.1 ± 0.3 and 3.5 ± 0.5, respectively. Mean LID points were 111.4 ± 21.5, mean LID index (%) 11.4 ± 1.2, and mean LID < 12% points 54.9 ± 25.2. Anterior and posterior wall mean total LID index were 11.8 ± 1.9 and 10.3 ± 1.7, respectively. Recurrence in 14 (21.2%) patients. Mean follow up was 15.2 ± 4.4 months. CONCLUSION: Weight adjusted HFLTV ventilation with RAP HPSD ablation produced lower recurrence rate and better LSI and LID parameters in comparison to SV and intrinsic sinus rhythm.

The power of three: Atrial rate limit power-on-reset - A non-electromagnetic cause of pacemaker-induced extracardiac stimulation.

BACKGROUND: Power-on reset (PoR) is most commonly due to electromagnetic interference. Full PoR results in a switch to an inhibited mode (VVI) pacing and resets pacing outputs to maximal unipolar settings, leading to extracardiac stimulation. METHODS: We present a case of PoR occurrence in the absence of electromagnetic interference, resulting in pectoral stimulation triggered by violation of the atrial rate limit. CONCLUSIONS: It is useful for clinicians to recognizethe occurrence of PoR in the setting of atrial limit violation andthe appropriate management in such circumstances.

Atrial pacing minimization in sinus node dysfunction and risk of incident atrial fibrillation: a randomized trial.

BACKGROUND AND AIMS: High percentages of atrial pacing have been associated with an increased risk of atrial fibrillation. This study is aimed at evaluating whether atrial pacing minimization in patients with sinus node dysfunction reduces the incidence of atrial fibrillation. METHODS: In a nationwide, randomized controlled trial, 540 patients with sinus node dysfunction and an indication for first pacemaker implantation were assigned to pacing programmed to a base rate of 60 bpm and rate-adaptive pacing (DDDR-60) or pacing programmed to a base rate of 40 bpm without rate-adaptive pacing (DDD-40). Patients were followed on remote monitoring for 2 years. The primary endpoint was time to first episode of atrial fibrillation longer than 6 min. Secondary endpoints included longer episodes of atrial fibrillation, and the safety endpoint comprised a composite of syncope or presyncope. RESULTS: The median percentage of atrial pacing was 1% in patients assigned to DDD-40 and 49% in patients assigned to DDDR-60. The primary endpoint occurred in 124 patients (46%) in each treatment group (hazard ratio [HR] 0.97, 95% confidence interval [CI] 0.76-1.25, P = .83). There were no between-group differences in atrial fibrillation exceeding 6 or 24 h, persistent atrial fibrillation, or cardioversions for atrial fibrillation. The incidence of syncope or presyncope was higher in patients assigned to DDD-40 (HR 1.71, 95% CI 1.13-2.59, P = .01). CONCLUSIONS: Atrial pacing minimization in patients with sinus node dysfunction does not reduce the incidence of atrial fibrillation. Programming a base rate of 40 bpm without rate-adaptive pacing is associated with an increased risk of syncope or presyncope.

Mapping-guided atrial lead placement determines optimal conduction across Bachmann's bundle: a rationale for patient-tailored pacing therapy.

AIMS: Conventional right atrial appendage (RAA) pacing is associated with increased atrial activation time resulting in higher incidences of atrial tachyarrhythmia. Optimal pacing sites ideally shorten inter-atrial conduction delay, thereby decreasing atrial excitation time. We therefore examined the impact of programmed electrical stimulation (PES) from the right atrium (RA) and left atrium (LA) on the electrophysiological properties of Bachmann's bundle (BB). METHODS AND RESULTS: High-resolution epicardial mapping of BB was performed during sinus rhythm (SR) and PES in 34 patients undergoing cardiac surgery. Programmed electrical stimulation was performed from the RAA, junction of the RA with inferior caval vein (LRA), and left atrial appendage (LAA). Pacing from either the RAA or LAA resulted in, respectively, right- and left-sided conduction across BB. However, during LRA pacing in most patients (n = 15), activation started in the centre of BB. The total activation time (TAT) of BB during RAA pacing [63 (55-78) ms] was similar to that of SR [61 (52-68) ms, P = 0.464], while it decreased during LRA [45 (39-62) ms, P = 0.003] and increased during LAA pacing [67 (61-75) ms, P = 0.009]. Reduction of both conduction disorders and TAT was most often achieved during LRA pacing (N = 13), especially in patients who already had a higher amount of conduction disorders during SR [9.8 (7.3-12.3) vs. 4.5 (3.5-6.6)%, P < 0.001]. CONCLUSION: Pacing from the LRA results in a remarkable decrease of TAT compared with pacing from the LAA or RAA. As the most optimal pacing site varies between patients, individualized positioning of the atrial pacing lead guided by mapping of BB may be one of the new frontiers for atrial pacing.

Alternative atrial pacing site to improve cardiac function: focus on Bachmann's bundle pacing.

Pacing from the right atrial appendage (RAA) prolongs the P wave duration and can induce interatrial and especially left-sided atrio-ventricular dyssynchrony. Pacing from Bachmann's bundle closely reproduces normal physiology and has the potential to avoid the electromechanical dysfunction associated with conventional RAA pacing. Interatrial conduction delay is associated with an increased risk of stroke, heart failure, and death. In addition to a reduction in atrial fibrillation, Bachmann's bundle pacing has emerging applications as a hemodynamic pacing modality. This review outlines the pathophysiology of atrial conduction disturbances and their potential remedies and provides the reader with a practical guide to implementing Bachmann's bundle pacing with an emphasis on the recapitulation of normal electrical and mechanical function.

Optimizing transesophageal atrial pacing in mice to detect atrial fibrillation.

Mice are routinely used to investigate molecular mechanisms underlying the atrial fibrillation (AF) substrate. We sought to optimize transesophageal rapid atrial pacing (RAP) protocols for the detection of AF susceptibility in mouse models. Hypertensive and control C57Bl/6J mice were subjected to burst RAP at a fixed stimulus amplitude. The role of parasympathetic involvement in pacing-related atrioventricular (AV) block and AF was examined using an intraperitoneal injection of atropine. In a crossover study, burst and decremental RAP at twice diastolic threshold were compared for induction of AV block during pacing. The efficacy of burst and decremental RAP to elicit an AF phenotype was subsequently investigated in mice deficient in the lymphocyte adaptor protein (Lnk-/-) resulting in systemic inflammation, or the paired-like homeodomain-2 transcription factor (Pitx2+/-) as a positive control. When pacing at a fixed stimulus intensity, pacing-induced AV block with AF induction occurred frequently, so that there was no difference in AF burden between hypertensive and control mice. These effects were prevented by atropine administration, implicating parasympathetic activation due to ganglionic stimulation as the etiology. When mice with AV block during pacing were eliminated from the analysis, male Lnk-/- mice displayed an AF phenotype only during burst RAP compared with controls, whereas male Pitx2+/- mice showed AF susceptibility during burst and decremental RAP. Notably, Lnk-/- and Pitx2+/- females exhibited no AF phenotype. Our data support the conclusion that multiple parameters should be used to ascertain AF inducibility and facilitate reproducibility across models and studies.NEW & NOTEWORTHY Methods were developed to optimize transesophageal rapid atrial pacing (RAP) to detect AF susceptibility in new and established mouse models. High stimulus intensity and pacing rates caused parasympathetic stimulation, with pacing-induced AV block and excessive AF induction in normal mice. For a given model, pacing at twice TH enabled improved phenotype discrimination in a pacing mode and sex-specific manner. Transesophageal RAP should be individually optimized when developing a mouse model of AF.

Epicardial atrial pacing after the extracardiac Fontan operation: Feasibility of an entirely transvenous approach.

This series describes an innovative technique for pacing in patients with sinus node dysfunction after extracardiac Fontan surgery. This transpulmonary approach to the left atrial epi-myocardium has been successfully applied to three patients at two centers and resulted in excellent acute and midterm pacing characteristics without known complications. The principal advantage of this procedure in comparison to prior iterations is the absence of pacing material within the pulmonary venous atrium, so that future systemic thromboembolism risk is minimized. The transpulmonary approach for permanent atrial pacing offers a novel solution to the unique challenges for patients after extracardiac Fontan operation.

Atrial Pacing Affects Left Atrial Morphological and Functional Parameters Early after Pacemaker Implantation.

Background and Objectives: Chronic atrial stimulation might impair left atrial (LA) function. We aimed to assess the impact of atrial pacing burden on LA volumetric and functional parameters after implantation of a dual-chamber pacemaker. Materials and Methods: The prospective study included 121 subjects with sinus node disease (SND) or atrioventricular block (AVB) that received a dual-chamber pacemaker. After device implantation, the subjects were divided into three groups: (1) SND with a lower rate (LR) set to 60 bpm and rate response enabled; (2) AVB with an LR set to 60 bpm and no rate response; and (3) AVB with an LR set to 40 bpm and no rate response. Subjects were followed at one and three months. Two subsets of patients with high and low atrial pacing burdens accompanied by low ventricular pacing percentage were analyzed. LA function was evaluated with volumetric and strain parameters from transthoracic echocardiography. Results: The high atrial low ventricular pacing group consisted of 38 subjects, and the low atrial low ventricular group consisted of 22 subjects. When looking at the change in volumetric parameters, we observed a tendency for volumes to increase in both groups; however, only minimal LA volume reached statistical significance at three months in the high atrial pacing group. A trend towards the lowering of an active emptying fraction at one month (p = 0.076) became significant at three months (p = 0.043), and was also only observed in the same group. Moreover, a decrease in the tendency to reach statistical significance at three months for reservoir and contractile strain parameters and stiffness index was only observed in the high atrial pacing group. Meanwhile, in the low atrial pacing burden group, all parameters remained significantly unchanged. Conclusions: The burden of right atrial pacing in patients with preserved left ventricular function negatively influences functional and morphologic LA parameters. Moreover, negative effects take place soon after pacemaker implantation and appear to be sustained.

Alpha-lipoic acid prevents atrial electrical and structural remodeling via inhibition of NADPH oxidase in a rabbit rapid atrial pacing model.

BACKGROUND: Alpha-lipoic acid (ALA) is a natural compound, one of the natural antioxidants with high activity. In the NADPH oxidase family, NADPH oxidase 4 (NOX4) is an important subunit participating in the production of ROS. NADPH oxidase 2 (NOX2) can form active NADPH oxidase complexes when binding to several other subunits in the cytoplasm, and NOX2 is its major functional subunit. Rapid atrial pacing (RAP) model was constructed to study the effects of ALA on electrical and structural remodeling in rabbits. METHODS: Thirty rabbits were divided into SHAM group, RAP group and ALA+RAP group. Their right atriums were paced at a speed of 600 beats/min for 12 h in the RAP and ALA+RAP groups, and the atrial effective refractory period (AERP) and AERP frequency adaptability were determined during the pace. In ALA+RAP group, ALA (30 mg/kg) was administered intraperitoneally daily to the rabbits for 3 days before RAP. Atrial tissue was collected from each group to detect malondialdehyde (MDA), superoxide dismutase (SOD) and reactive oxygen species (ROS) to observe the effect of oxidative stress. The pathological structure of the atrial tissue was observed through hematoxylin-eosin (HE) staining. Ultrastructural changes in the atrial myocytes were observed by transmission electron microscopy (TEM), and the expression levels of Nox2 and Nox4 were detected by immunohistochemistry, western blot and ELISA. RESULTS: AERP gradually shortened, while ALA injection could remarkably delay this process. HE staining showed that the most of the nuclei appeared normal, the myocardial fibers did not show ruptures, and their arrangement was slightly ordered, and myofilament dissolution and mitochondrial swelling and deformation were rarely observed by TEM in the ALA+RAP group. Compared with the RAP group, the contents of MDA and ROS were reduced, SOD activity was enhanced, and the expression of NOX2 and NOX4 was decreased in the ALA+RAP group. DISCUSSION: ALA can inhibit atrial electrical remodeling and structural remodeling, and its mechanism may be related to inhibiting the activity of NADPH oxidase.

Efficacy of intentional permanent atrial pacing in the long-term management of congenital long QT syndrome.

BACKGROUND: Unfortunately, some patients with long QT syndrome (LQTS) experience breakthrough cardiac events (BCEs) despite maximal therapy. Small studies have shown that refractory LQTS cases may benefit from intentional permanent atrial pacing (IPAP). As such, we sought to determine the genotype-specific utilization and efficacy of IPAP in a single-center LQTS registry. METHODS AND RESULTS: In this retrospective study, electronic medical records from 1065 patients diagnosed with LQTS were used to identify individuals that received IPAP. Pre- and post-IPAP heart rate, heart rate-corrected QT (QTc) values, annual BCE rate, and IPAP-related complications were compared between genotypes. BCEs were defined as LQTS-associated syncope/seizures, sustained ventricular arrhythmia (VA)-terminating ICD therapies, and sudden cardiac arrest/death. Overall, 52 out of 1065 LQTS patients received adjunctive IPAP therapy (77% female; median age 18.5 [interquartile range, 1-35.5] years; 73% with prior VA). Over an average IPAP follow-up of 121 ± 82 months, the average heart rate increased from 65.8 ± 20.4 bpm to 78.9 ± 17.1 bpm; (p < .01) and the average QTc decreased from 533.4 ± 66.6 to 488.3 ± 52.4 ms; (p < .01). The mean BCE rate dropped from 0.88 to 0.19 per patient-year (p = .01), driven by a marked decrease in the LQT2 cohort (1.01 BCE/year to 0.02 BCE/year; p = .003). No serious IPAP-related complications were observed. CONCLUSION: In high-risk LQTS patients, namely those with recalcitrant LQT2, IPAP appears to be a safe and efficacious adjunct therapy. The beneficial effects of IPAP may stem from attenuating the QTc and circumventing a pause-dependent trigger. Whether IPAP might obviate the need for an ICD in some instances warrants further study.

Effect of atrial artificial electrical stimulation on depolarization and repolarization and hemodynamics of the heart ventricle in rainbow trout Oncorhynchus mykiss.

The spatial-temporal organization of the activation, repolarization and hemodynamics of the heart ventricle in rainbow trout, Oncorhynchus mykiss, adapted to a temperature of 5-7 °C, were studied from the normal sinus rhythm (21.6 ± 4.9 bpm) to the highest possible heart rhythm (HR) (60 bpm), during which deterioration of the contractile activity of the myocardium occurred. Regardless of the HR, the main pattern of excitation of the heart ventricle was the movement of the depolarization wave from the dorsal areas of the base in the base-apical and ventral directions with the capture of the entire thickness of the walls, with a slight difference in the time of activation of the subendocardium compared to the subepicardium. The increase in HR above the sinus rhythm caused significant shortening of local repolarization durations in all areas and layers (endocardial, intramural and subepicardial) of the heart ventricle. Changes in local durations of repolarization led to an increase in the heterogeneity of repolarization of the ventricular myocardium; as a result, a deterioration of its contractility was observed. In relation to the sinus rhythm, the maximal systolic pressure in the heart ventricle decreased, the diastolic and end-diastolic pressure increased, and the maximum rates of pressure rise and fall decreased. In rainbow trout adapted to a temperature of 5-7 °C at sinus rhythm, the pumping function of the heart was probably within the upper limit of the physiological norm, and a further increase in the heart rate led to a decline in myocardial contractility.

Regular ventricular rate and "reverse bigeminy" in 3:2 Wenckebach periodicity.

One of the more common causes of bigeminy at the ventricular level is type 1 second-degree atrioventricular (AV) block with 3:2 conduction ratio. In 3:2 Wenckebach, the shorter cycles reflect the consecutively conducted impulses and the longer cycles coincide with the blocked P waves. Theoretically, however, depending on the degree of conduction delay between the first and second transmitted impulses, other types of spacing of the QRS complexes may become possible. In this retrospective study of 180 patients who underwent electrophysiologic studies for symptomatic arrhythmias, atrial pacing-induced 3:2 Wenckebach periodicity resulted in a regular ventricular rate and/or in "reverse bigeminy" in 16 cases (8.9%). Reverse bigeminy was characterized by the shorter R-R intervals including both the blocked P waves and the first conducted beats of the subsequent cycles, and the longer R-R intervals coinciding with the second conducted beats during 3:2 Wenckebach. In 14 cases, regular ventricular rate and reverse bigeminy was triggered by marked conduction delay in the AV node and in 2 cases, the conduction delay was in the His-Purkinje system. Reverse bigeminy appeared to be related to dual AV nodal physiology in 8 patients. In 2 cases, sophisticated maneuvers such as termination of atrial pacing at critical intervals during the AV Wenckebach were required to expose the true conduction pattern. This study demonstrates that during rapid atrial rhythms, one cannot always be sure which P wave is responsible for which QRS complex. Rarely, extreme conduction delays can result in P waves conducting across the subsequent ventricular beats and be responsible not for the first, but for the following QRS complexes.

Programming Pacemakers to Reduce and Terminate Atrial Fibrillation.

PURPOSE OF REVIEW: The goal of this paper is to review present knowledge regarding preventive and antitachycardia pacing algorithms, aimed to reduce atrial fibrillation (AF) burden in patients when pacing is indicated. RECENT FINDINGS: Reactive antitachycardia pacing (ATP), the new generation of ATP, is significantly associated with a reduced risk of AF. In patients with indication for pacing and history of AF, pacemakers endowed with atrial preventive pacing and atrial ATP combined with managed ventricular pacing proved superior to standard dual-chamber pacing. Managed ventricular pacing is an algorithm that minimizes unnecessary right ventricular pacing. Progression to persistent AF is prevented by ventricular pacing minimization in patients with normal PR interval. The synergistic effect of pacemakers that combine atrial preventive pacing with reactive ATP and with algorithms that minimize ventricular pacing can reduce AF incidence and decrease the combined endpoint of permanent AF, hospital admissions, and mortality.

Activation of TGF-ß1/α-SMA/Col I Profibrotic Pathway in Fibroblasts by Galectin-3 Contributes to Atrial Fibrosis in Experimental Models and Patients.

BACKGROUND/AIMS: This study aimed to evaluate whether galectin-3 (Gal-3) contributes actively to atrial fibrosis both in patients and experimental atrial fibrillation (AF) models. METHODS: Mouse HL-1 cardiomyocytes were subjected to rapid electrical stimulation (RES) to explore Gal-3 expression and secretion levels by western blotting (WB) and enzyme linked immunosorbent assay (ELISA). Neonatal rat cardiac fibroblasts were treated with conditioned culture medium and recombinant human Gal-3 to evaluate the activation of the transforming growth factor (TGF)-ß1/α-smooth muscle actin (SMA)/collagen I (Col I) profibrotic pathway (WB) and fibroblast proliferation with a Cell Counting Kit-8 (CCK-8). Furthermore, in the rapid atrial pacing (RAP) rabbit AF model, atrial Gal-3 expression and its effects on the profibrotic pathway were evaluated (WB and Masson's trichrome staining). Moreover, 44 consecutive patients who underwent single mitral valve repair/replacement were included, consisting of 28 patients with persistent AF (PeAF) and 16 with sinus rhythm (SR). Coronary sinus blood was also sampled to test circulating Gal-3 levels (ELISA), and atrial myocardium Gal-3 and its downstream TGF-ß1/α-SMA pathway were also measured by WB and immunohistochemical staining. RESULTS: Gal-3 expression in HL-1 cells and its secretion level in culture medium were greatly increased after 24 h RES. Treatment of neonatal rat cardiac fibroblasts with conditioned media collected from the RES group or recombinant human Gal-3 protein (10 and 30 µg/mL) for 72 h induced the activation of the TGF-ß1/α-SMA/Col I profibrotic pathway. RAP increased Gal-3 levels and activated the TGF-ß1/α-SMA/Col I pathway in rabbit left atria, while the Gal-3 inhibitor N-acetyllactosamine, injected at 4.5 mg/kg every 3 days, mitigated these adverse changes. Furthermore, Gal-3 levels in coronary sinus blood samples and myocardial Gal-3 expression levels were higher in the PeAF patients than in the SR patients, and higher level profibrotic pathway activation was also confirmed. CONCLUSIONS: Activation of Gal-3 expression in the atria can subsequently activate the TGF-ß1/α-SMA/Col I pathway in cardiac fibroblasts, which may enhance atrial fibrosis.

Identification and characterization of circular RNAs in rapid atrial pacing dog atrial tissue.

Circular RNAs (circRNAs) have emerged as novel molecules of interest in gene regulation as other noncoding RNAs, and participating in the process of many diseases. However, the expression and functions of circRNAs in Rapid atrial pacing (RAP) dog atrial tissue still unknown. 12 canines were randomly assigned to control and pacing group. RAP at 500 beats per minute was maintained 14 days in the pacing group. The expression characterization of circRNAs were revealed by high-throughput sequencing. We totally predicted 15,990 circRNAs in dog atrial tissues. Moreover, we found 146 differentially expressed circRNAs between control and RAP dogs. Five circRNAs were selected for subsequent RT-PCR validation, and four circRNAs confirmed with the high throughput sequencing analysis. GO analysis showed that the differentially expressed circRNAs might involve in the process of "structural constituent of cytoskeleton, ion channel activity". We explored the circRNA-miRNA interaction network, and found extensive interaction among differentially expressed circRNAs and AF related miRNAs and mRNAs. Our work firstly identified the characterization of circRNAs in the dog atrial, and revealed the differentially expressed circRNAs in the RAP dog, this might lay a solid foundation on the function of circRNA in the mechanisms of AF.

Selective ablation of the ligament of Marshall attenuates atrial electrical remodeling in a short-term rapid atrial pacing canine model.

INTRODUCTION: Cardiac sympathetic activation facilitates atrial electrical remodeling during atrial fibrillation (AF). Selective ablation of the distal part of the ligament of Marshall (LOMLSPV ) could decrease cardiac sympathetic innervation. This study aimed to investigate the effects of LOMLSPV ablation on atrial electrical remodeling in a short-term rapid atrial pacing (RAP) model. METHODS: In 16 anesthetized dogs, 6 hours of RAP (20 Hz, 2 × threshold) was delivered before LOMLSPV ablation (group 1, N  =  8) or after (group 2, N  =  8). Heart rate variability (HRV), serum norepinephrine (NE), atrial electrophysiological indices were analyzed. Six times of burst pacing (20 Hz, 2 × threshold, lasting for 5 seconds, were performed to induce AF, the number of episodes and the duration of AF were compared. RESULTS: LOMLSPV ablation decreased sympathetic indices of HRV and serum NE. Atrial effective refractory period (ERP) was shortened during RAP in both groups with higher reduction degrees in group 1. In group 1, the shortening of atrial ERP, elevating of ERP dispersion and sum of window of vulnerability (ΣWOV), facilitating of AF induced by RAP were subsequently reversed by LOMLSPV ablation. In group 2, LOMLSPV ablation prolonged atrial ERP, decreased ΣWOV, eliminated AF induction. The subsequent RAP failed to alter these indices. Histological studies showed abundant sympathetic nerve fibers in LOMLSPV . CONCLUSION: LOMLSPV ablation could inhibit atrial electrical remodeling during short-term RAP by reducing the cardiac sympathetic activity. LOMLSPV may be a potential target in AF ablation, especially in patients with highly cardiac sympathetic activation or atrial electrical remodeling.

Pediatric heart transplantation-What are the risk factors for pacemaker implantation and how much pacing is required?

BACKGROUND: In an attempt to improve pacemaker therapy after pediatric transplantation, we investigated risk factors, indication for pacing, and pacing burden after pediatric heart transplantation. METHODS AND RESULTS: In this retrospective study, 139 pediatric heart transplant recipients, of whom 122 did not and 17 did require pacemakers, were investigated. Eleven of the 17 patients requiring a permanent pacemaker (PPM) received their heart from a female donor (68.8%); this compares to 48 of 122 patients (43.2%, P  =  0.082) in the group not requiring a pacemaker (No PPM). The donor age and height were significantly greater in the PPM group at a median of 25.26 years (16.29-48.00) and 160 cm (153-170) compared with 11.96 years (1.73-19.95) and 141 cm (89-165) in the No PPM group (P  =  0.003 and 0.015, respectively). Of the 17 patients requiring pacemakers, 13 presented with sinus node dysfunction (SND) and four with atrioventricular block. The atrial pacing burden in patients with SND remained above 60% within the 5 years of follow-up investigated. There was no significant difference in mortality between those patients requiring a PPM and those not (Log-Rank test: P  =  0.672). CONCLUSION: We found that in our cohort donor characteristics were key risk factors for pacemaker implantation in transplanted children. The data suggest that when patients require a pacemaker in posttransplant SND, they will require a relevant amount of pacing for at least 5 years. The pacing burden after this point remains to be investigated. Mortality does not differ between pediatric heart transplant patients with and without pacemakers.

Cardiac resynchronization therapy resulting from atrial pacing: An unusual case of intraventricular conduction delay.

Cardiac resynchronization therapy device implantation is complicated by a significant rate of failure to place a left ventricular lead via the coronary sinus. The present case describes one such failure ironically leading to resynchronization. The patient's QRS narrowing subsequent to postimplant atrial pacing alone suggests that bradycardia-dependent phase 4 block was the indirect but exclusive cause of the patient's intraventricular conduction delay. Thus, phase 4 block should be considered when atrial pacing at a faster rate resolves a wide QRS interval.

Correlation between the sudden jump-like increases of the atrio-Hisian interval induced during burst atrial pacing and during programmed atrial stimulation in patients with atrioventricular nodal reentrant tachycardia.

PURPOSE: To study the correlation between the sudden prolongations of the atrio-Hisian (AH) interval with ≥50 ms during burst and programmed atrial stimulation, and to define whether the AH jump during burst atrial pacing is a reliable diagnostic criterion for dual AV nodal physiology. METHODS: Retrospective data on 304 patients with preliminary ECG diagnosis of AV nodal reentrant tachycardia (AVNRT), confirmed during electrophysiological study, was analyzed for the presence of AH jump during burst and programmed atrial stimulation, and for correlation between the pacing modes for inducing the jump. Wilcoxon signed-ranks test and Spearman's bivariate correlation coefficient were applied, significant was P-value <0.05. RESULTS: The population was aged 48.5 ± 15.7 (12-85) years; males were 38.5%. AH jump occurred during burst atrial pacing in 81% of the patients, and during programmed stimulation - in 78%, P = 0.366. In 63.2% AH jump was induced by both pacing modes; in 17.8% - only by burst pacing; in 14.8% - only by programmed pacing; in 4.2% there was no inducible jump. There was negative correlation between both pacing modes, ρ = -0.204, Р<0.001. CONCLUSION: Burst and programmed atrial stimulation separately prove the presence of dual AV nodal physiology in 81 and 78% of the patients with AVNRT, respectively. There is negative correlation between the two pacing modes, allowing the combination of the two methods to prove diagnostic in 95.8% of the patients.

Single lead atrial vs. dual chamber pacing in sick sinus syndrome: extended register-based follow-up in the DANPACE trial.

AIMS: The DANPACE trial randomized patients with sick sinus syndrome (SSS) to single lead atrial (AAIR) or dual chamber (DDDR) pacemaker (PM). After 5 years follow-up, no difference in overall survival, stroke or heart failure (HF) was observed, whereas risk of atrial fibrillation (AF) and PM reoperation were increased in the AAIR group. The present study aimed to investigate very long term risk of death, AF hospitalization, stroke, HF and rate of change in pacing mode using national register-based data. METHODS AND RESULTS: The study population consisted of all 1384 patients included at Danish PM centres in the DANPACE trial randomized to AAIR (n = 696) or DDDR (n = 688). Long-term follow-up data was obtained from Danish national registers. Analysis was intention-to-treat. results: During mean follow-up of 8.9 years, 413 patients (59.3%) died in the AAIR-group compared to 367 (53.3%) in the DDDR-group (adjusted hazard ratio 1.03; 95% confidence interval 0.90-1.19; P = 0.65). We observed no difference in risk of AF hospitalization, stroke or HF. During extended follow-up, annual rate of pacing mode change to DDDR in the AAIR group was 4.5%, and higher than the 2.3% observed during trial conduct. CONCLUSION: This register-based long-term follow-up study indicates that there is no difference in mortality among patients with SSS randomized to AAIR or DDDR pacing, even with very long follow-up. Nor is there any difference in risk of AF hospitalization, stroke or HF. The higher rate of pacing mode-change to DDDR in the AAIR group suggests a different management of patients with an AAIR PM after the DANPACE trial.