Variable Arrangement of the Atrioventricular Conduction Axis Within the Triangle of Koch: Implications for Permanent His Bundle Pacing.

OBJECTIVES: This study sought to describe, in detail, the angiographic, gross macroscopy, and histological dissection of the conduction axis in humans. BACKGROUND: The recent upsurge of interest in specific pacing of the atrioventricular conduction axis has emphasized the need for precise knowledge of the location of the atrial and penetrating components of the atrioventricular conduction axis. METHODS: A total of 41 human hearts were studied by serial histological sectioning and an additional 3 hearts by gross dissection. One of the hearts studied histologically was also dissected to show the location of the conduction axis prior to serial sectioning. The anatomical findings were then compared with the results of angiography undertaken in the catheter laboratory in 60 patients undergoing electrophysiological studies. RESULTS: Marked variation of the location of the transition from atrioventricular conduction axis to the penetrating atrioventricular bundle, or the bundle of His, relative to the landmarks of the triangle of Koch was observed. In just over one-half of both the specimens and the patients, the site of penetration was on the atrial aspect of the hinge of the septal leaflet of the tricuspid valve, with further variation noted relative to the apex of the triangle of Koch. Based on measurements of the histological sections, marked variation in the dimensions of the axis and its adjacency to the right-sided endocardium were also found. In almost three-fifths of hearts, an interventricular component of the fibrous membranous septum was not able to be identified. The significance of these findings to those who seek to perform selective pacing of the atrioventricular conduction axis are discussed. CONCLUSIONS: Marked variability of the location of the conduction axis within the triangle of Koch is reported. In three-fifths of hearts, the interventricular component of the fibrous membranous septum is nonexistent.

Changes in Local Atrial Electrograms and Surface ECG Induced by Acute Atrial Myocardial Infarction.

BACKGROUND: Atrial coronary branch occlusion is a hardly recognizable clinical entity that can promote atrial fibrillation. The low diagnostic accuracy of the ECG could deal with the characteristics of the ischemia-induced changes in local atrial electrograms, but these have not been described. OBJECTIVES: We analyzed the effects of selective acute atrial branch occlusion on local myocardial structure, atrial electrograms, and surface ECG in an experimental model close to human cardiac anatomy and electrophysiology. METHODS: Six anesthetized open-chest anesthetized pigs underwent surgical occlusion of an atrial coronary branch arising from the right coronary artery during 4 h. Atrial electrograms and ECG were simultaneously recorded. One additional pig acted as sham control. In all cases, the hearts were processed for anatomopathological analysis. RESULTS: Atrial branch occlusion induced patchy atrial necrosis with sharp border zone. During the first 30 min of occlusion, atrial electrograms showed progressive R wave enlargement (1.8 ± 0.6 mV vs. 2.5 ± 1.1 mV, p < 0.01), delayed local activation times (28.5 ± 8.9 ms vs. 36.1 ± 16.4 ms, p < 0.01), ST segment elevation (-0.3 ± 0.3 mV vs. 1.0 ± 1.0 mV, p < 0.01), and presence of monophasic potentials. Atrial ST segment elevation decreased after 2 h of occlusion. The electrical border zone was ∼1 mm and expanded over time. After 2 h of occlusion, the ECG showed a decrease in P wave amplitude (from 0.09 ± 0.04 mV to 0.05 ± 0.04 mV after 165 min occlusion, p < 0.05) and duration (64.4 ± 8.0 ms vs. 80.9 ± 12.6 ms, p < 0.01). CONCLUSION: Selective atrial branch occlusion induces patchy atrial infarction and characteristic changes in atrial activation, R/S wave, and ST segment that are not discernible at the ECG. Only indirect changes in P wave amplitude and duration were appreciated in advanced stages of acute coronary occlusion.

Epicardial Connections Involving Pulmonary Veins: The Prevalence, Predictors, and Implications for Ablation Outcome.

BACKGROUND: The presence of epicardial connections (ECs) between pulmonary veins (PVs) and other anatomic structures may hinder PV isolation. In this study, we analyzed their prevalence, location, associated factors, and clinical implications. METHODS: Five hundred thirty-four consecutive patients with atrial fibrillation undergoing radiofrequency ablation were included. We considered that an EC was present if: (1) the first pass around the PV antrum did not produce PV isolation and (2) subsequent atrial activation during PV pacing showed that the earliest site was located away from the ablation line and later activation sites were observed near the ablation line. Clinical and electrophysiological variables were collected from all patients. Patients were followed during 12.9±9.4 months, and any documented atrial tachyarrhythmia after the 3-month blanking period was classified as a recurrence. RESULTS: Out of the 534 patients included, 72 (13.5%) were found to have 81 ECs. There was a significant association between the presence of ECs and structural heart disease (15.3% in patients without ECs versus 36.5% in patient with ECs; P<0.001) and patent foramen ovale (4.6% versus 13.5%; P=0.002). The presence of a left common trunk was significantly associated with the absence of ECs (29.6% in patients without ECs versus 16.2% in patients with ECs; P=0.014). Patients with ECs had lower acute success in PV isolation compared with patients without ECs (99.1% versus 86.1%; P<0.001). After adjusting for age, sex, type of atrial fibrillation, left atrium area, hypertension, structural heart disease, presence of left common trunk, patent foramen ovale, and time for atrial fibrillation diagnosis to the ablation, we found a significantly higher risk of atrial tachyarrhythmia recurrences in patients with ECs compared with patients without ECs (hazard ratio, 1.7 [95% CI, 1.1-2.9]; P=0.04). CONCLUSIONS: ECs between PVs and other adjacent structures are frequent in patient with atrial fibrillation (prevalence: 13.5%). Structural heart disease and a patent foramen ovale are strongly associated with the presence of ECs. ECs reduce the acute and chronic success of PV isolation.