Inducible cardiomyocyte injury within the atrioventricular conduction system uncovers latent regenerative capacity in mice.

The cardiac conduction system (CCS) ensures regular contractile function, and injury to any of its components can cause cardiac dysrhythmia. Although all cardiomyocytes (CMs) originate from common progenitors, the CCS is composed of biologically distinct cell types with unique functional and developmental characteristics. In contrast to ventricular cardiomyocytes, which continue to proliferate after birth, most CCS cells terminally exit the cell cycle during fetal development. Although the CCS should thus provide a poor substrate for postnatal injury repair, its regenerative capacity remains untested. Here, we describe a genetic system for ablating CMs that reside within the atrioventricular conduction system (AVCS). Adult mouse AVCS ablation resulted in regenerative failure characterized by persistent atrioventricular conduction defects and contractile dysfunction. In contrast, AVCS injury in neonatal mice led to recovery in a subset of these mice, thus providing evidence for CCS plasticity. Furthermore, CM proliferation did not appear to completely account for the observed functional recovery, suggesting that mechanisms regulating recovery from dysrhythmia are likely to be distinct from cardiac regeneration associated with ventricular injury. Taken together, we anticipate that our results will motivate further mechanistic studies of CCS plasticity and enable the exploration of rhythm restoration as an alternative therapeutic strategy.

Histological topography of the atrioventricular node and its extensions in relation to the cardiothoracic surgical landmarks in normal human hearts.

BACKGROUND: Atrioventricular (AV) nodal injury which results in cardiac conduction disorders is one of the potential complications of heart valve surgeries and radiofrequency catheter ablations. Understanding the topography of the AV conduction system in relation to the tricuspid and mitral valves will help in reducing these complications. METHODS: A tissue block of 3cmx4cm, which contain the AV node, bundle of His and the AV nodal extensions, was excised at the AV septal junction in 20 apparently normal human hearts. The block was divided into three equal segments through vertical incisions perpendicular to the insertion of the septal leaflet of the tricuspid valve. Each segment was processed and stained with H&E and Gomori to study the different parts of the AV conduction system. RESULTS: The lower pole of the AV node was located vertically above the tricuspid septal leaflet (TSL) in 100% (20/20) of cases and at the level of the muscular interventricular septum in 65% (13/20) of cases. The upper pole of the compact AV node was located at the level of the mitral valve leaflet (MVL) in 50% (10/20) of cases. The penetrating bundle of His was seen at the level of the TSL, while the branching bundle of His was situated 1.9±1.5 mm inferior to the TSL. The right and left posterior extensions of the AV node spanned from the MVL to 2.9±1.3 mm above the TSL. CONCLUSIONS: A rectangular area (2.5 mm × 12 mm) in the Koch's triangle was devoid of AV nodal tissue and could be labeled as a safe area with no risk of conduction defects during valve surgeries. Information on the separation of AV nodal extensions from the TSL, MVL and muscular interventricular septum may play a crucial role in guiding and improving the safety of radiofrequency ablations.

Sudden death due to the atrioventricular node contusion: Three cases report.

INTRODUCTION: Atrioventricular node (AVN) contusion usually results in cardiogenic shock and arrhythmia and is a rare but fatal condition. The condition is difficult to diagnose and easily overlooked because it develops rapidly and is asymptomatic. We here report 3 cases that demonstrate blunt chest impact and hemorrhages of the posterior atrioventricular junction, eventually result in death. CLINICAL FINDINGS: Autopsy and histological examination were performed on all cases. External inspection revealed bruises in the hearts and fractures in the sternum and ribs. However, histological examinations were conclusive and showed cardiac contusion on the surface of the posterior atrioventricular junction of the individuals, and the death was due to the AVN contusion. The position of the AVN on the heart surface is determined by detailed examinations via an autopsy and microscopic, both of which are critical in the certification of cause of death. CONCLUSION: The report is intended to raise our understanding and make forensic pathologists aware of the surface of the posterior atrioventricular junction.

Linear lesion cryoablation for the treatment of atrioventricular nodal re-entry tachycardia in pediatrics and young adults.

BACKGROUND: Radiofrequency (RF) ablation is a relatively safe and effective method for treatment of atrioventricular nodal re-entry tachycardia (AVNRT), but carries a 1-2% risk of AV nodal injury. Cryothermal ablation reduces the risk of AV block, but has had decreased procedural success and increased recurrence of tachycardia. We sought to evaluate the technique of linear lesion cryoablation (LLC) for treatment of AVNRT. METHODS: Single institution retrospective cohort study. Each patient underwent slow pathway modification using either RF, single lesion cryoablation, or LLC. Procedural success, recurrence, freedom from tachycardia 12 months following ablation and fluoroscopy time were compared between ablation methods. RESULTS: A total of 125 patients, median age 15.5 (4.7-23.1) years, underwent ablation: 32 RF energy, 31 single lesion cryoablation, 62 LLC. Procedural success was obtained in 94% of the LLC group compared to 58% using single lesion cryoablation (P ≤ 0.001). Ninety-seven percent of the LLC group was free from tachycardia recurrence, significantly higher than with single lesion cryoablation (68%, P = 0.001) and equal to that of RF (97%, P = NS). Fluoroscopy time was reduced in the LLC group compared to both single lesion and RF groups (P = 0.02). There was no permanent AV nodal injury in the cryoablation groups. CONCLUSION: LLC is an effective means of treatment for AVNRT and is associated with significantly improved procedural success and freedom from recurrence compared to single lesion methods, while at the same time obtaining equivalent efficacy to RF.

Catheter-induced mechanical trauma to fast and slow pathways during radiofrequency ablation of atrioventricular nodal reentry tachycardia: incidence, predictors, and clinical implications.

BACKGROUND: Data on the incidence and significance of catheter-induced trauma to fast and slow pathways are scarce. OBJECTIVES: To evaluate the incidence, predictors, and clinical implications of inadvertent catheter-induced mechanical trauma to fast and slow pathways during radiofrequency ablation (RFA) of atrioventricular nodal reentry tachycardia (AVNRT). METHODS: A total of 901 consecutive patients (aged 9-92 years old) with inducible sustained AVNRT underwent RFA of the slow pathway. All procedures were closely monitored for appearance of catheter-induced mechanical block of fast or slow pathways. RESULTS: Catheter-induced mechanical trauma to fast and/or slow pathways was observed in 121 (13.4%) patients: 86 (71%) patients had trauma of the fast pathway, three (2.4%) had trauma of the slow pathway, and 32 (26.4%) had trauma of both pathways. Mechanical trauma lasted <1 minute in 87 (72%) patients, 1-30 minutes in 23 (19%) and >30 minutes in 11 (9%). A significantly increased procedure discontinuation rate was observed in patients with mechanical trauma as compared to those with no trauma (P < 0.0001). Young patient age (<35) was a strong predictor for the occurrence of mechanical trauma to AV nodal pathways. No significant difference between the trauma and non-trauma groups was found in respect to the number of catheters used during the procedure, the incidence of AV block, and the need for permanent pacemaker implantation. CONCLUSIONS: Mechanical trauma to fast and slow pathways during ablation of AVNRT is more common than previously recognized, occurring especially in patients aged <35 years.

Radiofrequency ablation of accessory pathways. Contemporary success rates and complications in 323 patients.

INTRODUCTION: 17 years ago the first radiofrequency catheter ablation of an accessory pathway (AP) was performed. The aim of this study was to describe the contemporary success rates and procedure related complication rates of radiofrequency (RF) ablation of accessory pathways (APs). In addition, the present study describes the anatomical distribution of APs according to the new nomenclature introduced by NASPE and ESC in 1999. METHODS: The analysis included all patients, who underwent RF ablation of an AP in the Heart Center Leipzig between January 2000 and December 2003. RESULTS: Over a 4 year period 336 APs were ablated in 323 patients. 201 APs (60%) presented with antegrade and retrograde conduction and showed preexcitation on ECG. For the remaining 135 APs (40%), only retrograde conduction over the AP was documented. According to the new nomenclature APs were classified as left-sided, right sided, septal and paraseptal APs. 188 APs (56%) were located on the left, 41 (12%) on the right, 64 (19%) in the paraseptal space and 31 APs (9%) presented with a septal or parahisian localization, respectively. Because of atypical course and/or characteristics 12 APs (4%) could not be classified. Ablation of all pathways were successful in 315 patients (98%). In 289 patients (89%) success was achieved within a single ablation session. The left-sided pathways had a re-intervention rate of 5%, which was significantly lower compared to the remaining localizations. The highest re-intervention rate was observed in the septal APs (23%). Complications were observed in less than 2% of all treated patients. CONCLUSIONS: 17 years after the first RF catheter ablation of an AP this therapy is established as a highly effective procedure. The success rate has improved to 98% and the complication rate has been minimized to less than 2%. The most frequent localization of APs is left posterior. Left sided APs also presented with the lowest re-intervention rate. The introduction of the new nomenclature in 1999 by NASPE and ESC has simplified the description of the exact anatomical localization of an AP.

Case reports. 1. An autopsy case of fatal arrhythmia induced by injuries of the atrioventricular conduction system: a case report.

A 65-year-old woman died three days after being involved in a traffic accident, following an episode of ventricular fibrillation. She was diagnosed as having suffered cardiac contusion, liver contusion, mediastinal hematoma and rib fracture on admission. Her electrocardiogram showed complete right bundle branch block, complete atrioventricular block, and right axis deviation. Aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase and creatine kinase-MB were found to be elevated on biochemical blood analysis. These findings recovered and her condition appeared to improve daily. At autopsy, epicardial and intramyocardial haemorrhage were macroscopically seen in the posterior wall of the bilateral ventricles. On microscopic examination, there was evidence of fresh haemorrhage and coagulative necrosis with inflammatory reaction in the ordinary myocardium and adipose tissue around the atrioventricular node, which had spread to the proximal portion of the His' bundle. It is considered that these findings caused ventricular fibrillation to occur, and that the cause of death in this case was myocardial contusion due to blunt thoracic injury. This case would indicate that myocardium nearby atrioventricular junction is vulnerable to external force. Moreover, it would seem that fatal arrhythmia occasionally occurs during the follow-up stage, despite the lack of any significant clinical findings.

Dual AV nodal pathway physiology after injury with radiofrequency energy in a patient without a history of reentrant tachycardia.

Radiofrequency (RF) atrioventricular (AV) nodal modification has been reported to occasionally produce a proarrhythmic effect. Dual AV nodal pathway physiology in patients without reentrant tachychardia has also been reported. This case describes AV nodal modification with RF energy in an anatomically intermediate area resulting in the appearance of discontinuous antegrade conduction curves and reentry in a patient in which these were previously not present. This suggests that AV nodal injury may be a mechanism for acquired AV nodal reentry.

Reduction of symptoms from LVOT tachycardia following inadvertent fast pathway ablation.

VT was mapped to above the aortic valve in a young patient with troublesome palpitations. A single 15-second RF application was inadvertently delivered to a reference His catheter producing permanent first-degree heart block. The patient has been completely asymptomatic since.

Transient complete atrioventricular block following radiofrequency ablation of left free wall accessory pathway.

We report the case of a forty-six-year-old female with symptomatic WPW syndrome. The accessory pathway was located on the left free wall, for which ablation was attempted from the retrograde aortic approach. The ablation catheter was positioned at the appropriate site on the mitral anulus. A single radiofrequency energy application resulted in complete AV block with no escape rhythm, necessitating ventricular pacing. The AV conduction soon resumed with no evidence of pre-excitation. This phenomenon was thought to be related to trauma to the AV node during catheter entry in to the left ventricle.

Catheter ablation of canine myocardium with radiofrequency energy.

High energy direct-current shocks delivered via an electrode catheter have been used to ablate the atrioventricular junction since 1981. This technique has also been adapted for ablation of other cardiac tissues including the atrium, posterior interatrial septum and ventricular myocardium. The limitations of this technique include inadequate control of the energy source, poor understanding of the mechanisms of myocardial injury, and untoward complications possibly related to barotraumatic injury. Radiofrequency energy has been shown to create ablative injury when delivered to the myocardium via standard electrode catheters. This report will review our experience with radiofrequency catheter ablation of the canine myocardium with specific emphasis on the biophysical aspects of lesion formation.

Atrial fibrillation resulting from cardiac trauma.

Reports in the literature concerning isolated traumatic lesions of the conductive system of the heart following blunt injury to the thorax are rare. A 69-year-old woman who was a front-seat passenger developed disturbances of conduction with atrial fibrillation after blunt injury to the thorax. She died 7 days later. Autopsy and subsequent histological investigation of the conductive system of the heart showed isolated contusion in the right atrium close to the atrio-ventricular node.