Development of a sheep model of atrioventricular block for the application of novel therapies.

INTRODUCTION: Sheep have been adopted as a pre-clinical large animal for scientific research as they are good models of cardiac anatomy and physiology, and allow for investigation of pathophysiological processes which occur in the large mammalian heart. There is, however, no defined model of atrioventricular block in sheep to allow for pre-clinical assessment of new cardiac treatment options. We therefore aimed to develop an adult sheep model of atrioventricular block with the focus on future novel applications. METHODS AND RESULTS: We utilized six sheep to undergo two procedures each. The first procedure involved implantation of a single chamber pacemaker into the right ventricular apex, for baseline assessment over four weeks. The second procedure involved creating atrioventricular block by radiofrequency ablation of the His bundle, before holding for a further four weeks. Interrogation of pacemakers and electrocardiograms determined the persistence of atrioventricular block during the follow up period. Pacemakers were inserted, and atrioventricular block created in 6 animals using a conventional approach. One animal died following ablation of the His bundle, due to procedural complications. Four unablated sheep were assessed for baseline data over four weeks and showed 5.53 ± 1.28% pacing reliance. Five sheep were assessed over four weeks following His bundle ablation and showed continuous (98.89 ± 0.81%) ventricular pacing attributable to persistent atrioventricular block, with no major complications. CONCLUSION: We have successfully developed, characterized and validated a large animal model of atrioventricular block that is stable and technically feasible in adult sheep. This model will allow for the advancement of novel therapies, including the development of cell and gene-based therapies.

Electroanatomically estimated length of slow pathway in atrioventricular nodal reentrant tachycardia.

The length of the slow pathway (SP-L) in atrioventricular (AV) nodal reentrant tachycardia (NRT) has never been measured clinically. We studied the relationship among (a) SP-L, i.e., the distance between the most proximal His bundle (H) recording and the most posterior site of radiofrequency (RF) delivery associated with a junctional rhythm, (b) the length of Koch's triangle (Koch-L), (c) the conduction time over the slow pathway (SP-T), measured by the AH interval during AVNRT at baseline, and (d) the distance between H and the site of successful ablation (SucABL-L) in 26 women and 20 men (mean age 64.6 ± 11.6 years), using a stepwise approach and an electroanatomic mapping system (EAMS). SP-L (15.0 ± 5.8 mm) was correlated with Koch-L (18.6 ± 5.6 mm; R 2 = 0.1665, P < 0.005), SP-T (415 ± 100 ms; R 2 = 0.3425, P = 0.036), and SucABL-L (11.6 ± 4.7 mm; R 2 = 0.5243, P < 0.0001). The site of successful ablation was located within 10 mm of the posterior end of the SP in 38 patients (82.6 %). EAMS-guided RF ablation, using a stepwise approach, revealed individual variations in SP-L related to the size of Koch's triangle and AH interval during AVNRT. Since the site of successful ablation was also correlated with SP-L and was usually located near the posterior end of the SP, ablating anteriorly, away from the posterior end, is not a prerequisite for the success of ablation procedures.

Associated cardiac lesions in patients with radiation-induced complete heart block.

We investigated the clinical, electrophysiological, haemodynamic and angiographic aspects of four patients (two men and two women, aged 31-46 years) who developed complete heart block 13-20 years after therapeutic irradiation of the chest for Hodgkin's disease. The initial cardiac symptom was syncope in three, effort intolerance in one. The electrocardiogram recorded third-degree atrioventricular block in three patients, right bundle branch block and posterior fascicular block in one. The electrophysiological study, performed in three cases, showed that the block was infranodal in two. Three patients had significant coronary arterial stenoses, that involved the ostia in two. All patients had mild-to-moderate aortic and mitral regurgitation. One patient had haemodynamic signs of constriction. Another patient had recurrent pericardial effusions. All had echocardiographic evidence of a thickened pericardium. Cardiac involvement can be extensive in patient with radiation-induced heart block. Because coronary artery disease can be particularly severe, coronary angiography appears to be warranted in such patients.

Tromboembolia pulmonar masiva con desviación del eje eléctrico a la izquierda y bajo voltaje / Masive pulmonary embolism with left axis desviation and ion voltaje

En la Tromboembolia Pulmonar masiva o submasiva se han considerado como cambios electrocardiográficos clásicos en ausencia de cardiopatíe y/o neumopatía, la presencia de S1Q3T3 desviación del eje eléctrico a la derecha, P pulmonar, desnivel positivo o negativo del segmento ST, isquemia subepicárdica y bloqueo intermitente de la rama derecha del haz de His de grado intemedio o avanzado. Con que la desviación del eje eléctrico a la izquierda secundario a tromboembolia pulmonar se describió en 1949, éste hallazgo, así como la presencia de bajo voltaje en el plano frontal, se ha informado aisladamente en las últimas décadas, y su conocimiento ha tenido poca difusión. El objetivo del presente trabajo es comunicar el caso de una paciente con sistema cardiopulmonar previamente sano, con tromboembolia pulmonar masiva, que electrocardiográficamente presentó desviación del eje eléctro a la izquierda y bajo voltaje en el plano horizontal, atribuidos a éste padecimiento. Los mecanismos que dan lugar a éstos cambios electrocardiográficos en la tromboembolia pulmonar se desconocen. Dado que el electrocardiograma es un método inespecífico en el diagnóstico de éste padecimiento, la presencia de éstos cambios dan lugar a un mayor grado de dificultad en el diagnóstico, por lo que consideramos importante su comunicación