Margarita Murillo

Anatomic evaluation of the left phrenic nerve relevant to epicardial and endocardial catheter ablation: Implications for phrenic nerve injury

BACKGROUND/OBJECTIVE The purpose of this study was to clarify the spatial relationship between the left phrenic nerve (LPN) and key cardiac structures in order to minimize the risk of phrenic nerve injury during interventions. METHODS The course and relationship of the LPN to various cardiac structures were examined by gross dissection and histologic sections of 22 human cadavers. RESULTS The nerve descended on the fibrous pericardium along one of three courses: over the anterior surface of the left ventricle (18%), over the lateral margin of the left ventricle (59%), and in a posteroinferior direction (23%). The endocardium of the roof of the left atrial appendage was <4 mm from the LPN in 2 (9%) specimens. The nerve passed <2.5 mm from the epicardium of the apex of the left atrial appendage in 7 (31%) specimens. Regardless of the position of the nerve in relation to the high left ventricular wall, the nerve was <3 mm from the epicardial surface in 8 (36%) specimens and passed <6 mm from the epicardium of the right ventricular outflow tract in 2 (9%) specimens. CONCLUSION During electrophysiologic interventions, the LPN is especially at risk when procedures are performed in the vicinity of the left atrial appendage and high left ventricular wall.

Morphological evidence of muscular connections between contiguous pulmonary venous orifices: Relevance of the interpulmonary isthmus for catheter ablation in atrial fibrillation

BACKGROUND Electrophysiological studies in patients with atrial fibrillation demonstrated the presence of electrical conduction between superior and inferior left pulmonary veins (PVs) that makes electrical disconnection of individual PVs difficult. Anatomically, the prevalence, sizes, and locations of the interpulmonary connections have not been investigated systematically. METHODS We retrieved 112 PVs from 28 patients who died from noncardiac causes (43 +/- 13 years, 17 males). Dissections of subepicardial myocardial strands at the venoatrial junctions were made in 10 hearts, and histological sections were made in the remaining 18 hearts. RESULTS We found histological variations in the muscular width of the interpulmonary isthmus between ipsilateral left and right PVs (2.7 +/- 0.5 mm vs 1.7 +/- 0.5 mm; P <.05). Histologic sections of 15 hearts revealed myocardial strands 0.2-3.5 mm thick crossing obliquely at the left isthmus in 53%, at the right isthmus in 33%, and at both isthmuses in 14% of hearts to connect with the myocardial sleeves of adjacent veins. In 40% of hearts there were additional direct bridges connecting the anterior or posterior walls of the veins. The crossing myocardial strands were at the epicardial (27% of hearts), subendocardial (53% of hearts), and both (20%) aspects of the PV wall. The mean distance between the endocardium of the interpulmonary isthmus to the muscular connections was 2.5 +/- 0.5 mm in the left-sided PVs and 1.5 +/- 0.5 mm in the right-sided PVs. CONCLUSIONS Crossing myocardial strands and bridges at the interpulmonary isthmus may be the anatomical substrate for electrical connection between superior and inferior PVs and may have implications for local PV isolation in patients with atrial fibrillation.

Triggers and Anatomical Substrates in the Genesis and Perpetuation of Atrial Fibrillation

The definition of atrial fibrillation (AF) as a functional electrical disorder does not reflect the significant underlying structural abnormalities. Atrial and Pulmonary Vein (PV) muscle sleeve microstructural remodeling is present, and establishes a vulnerable substrate for AF maintenance. In spite of an incomplete understanding of the anatomo-functional basis for AF, current evidence demonstrates that this arrhythmia usually requires a trigger for initiation and a vulnerable electrophysiological and/or anatomical substrate for maintenance. It is still unclear whether the trigger mechanisms include focal enhanced automaticity, triggered activity and/or micro re-entry from myocardial tissue. Initiation of AF can be favored by both parasympathetic and sympathetic stimulation, which also seem to play a role in maintaining AF. Finally, evolving clinical evidence demonstrates that inflammation is associated with new-onset and recurrent AF through a mechanism that possibly involves cellular degeneration, apoptosis, and subsequent atrial fibrosis.

Cryoablation time-dependent dose–response effect at minimal temperatures (−80°C): an experimental study

Aims To establish a temporal safety window for cryoablation at minimal temperatures and to assess the electrophysiological and histological changes as a function of the application duration. Methods and results Twenty mini-pigs underwent AV nodal cryoablation at −80°C without prior cryomapping. The duration of the cryoapplication following atrioventricular block (AVB) was randomized to 0, 10, 20, 40, or 60 s. Atrioventricular block was obtained in all animals after a median of 3 (1–8 interquartile range) applications. One week later, AV nodal conduction fully recovered in animals with application duration <10 s, whereas persistent AVB incidence increased as a function of time in animals with longer applications duration. Cryoablation application duration following AVB was the only independent predictor of persistent AVB (OR, 1.116; 95% CI, 1.013–1.229; P = 0.026). There was no difference in lesion location or size between animals with vs. those without persistent AVB at 1 week. However, animals randomized to longer application duration demonstrated higher degree of cell destruction and fibrotic content. Conclusion In this closed-chest pig model, there was a relation between cryoapplication duration following AVB at −80°C and recovery of conduction. A safety window of at least 10 s was observed in all cases.

Capillary Supply to the Sinus Node in Subjects with Long-Term Atrial Fibrillation

BACKGROUND Atrial ischemia, and sinus node ischemia in particular, may be involved in the pathogenesis of atrial fibrillation. In this study we compared the sinus node blood capillary content in normal hearts in sinus rhythm and in pathologic hearts with chronic atrial fibrillation and we analyzed the ultrastructural features of such capillaries. METHODS Sinus node biopsy specimens were obtained from 16 patients in chronic atrial fibrillation undergoing open heart surgery. Control sinus node specimens of normal hearts were obtained at autopsy from 7 subjects. Specimens were processed for immunohistochemical, light microscopy and transmission electron microscopy analysis and compared grossly and with morphometric techniques. RESULTS The proportion of sinus node tissue corresponding to capillaries, defined as blood vessel density (or BVD), was estimated as 1.06 +/- 1.47% for the atrial fibrillation group versus 2.12 +/- 2.0% for controls (p < 0001). Internal capillary diameter averaged 21.6 microm in the atrial fibrillation group and 24.2 microm in controls (p = 0.175), whereas external diameter averaged 32.2 microm in the atrial fibrillation group and 38.9 microm in controls (p = 0.052). Ultrastructural analysis demonstrated scarce and interrupted myoendocardial bridges and abnormal deposits of elastic fibers under the endothelial basal membrane at the level of precapillary sphincters and metaarterioles of atrial fibrillation specimens. CONCLUSIONS There is a significant reduction in the amount of capillaries in the sinus node of hearts in chronic atrial fibrillation. Our findings would support a potential association between sinus node tissue ischemia and chronic atrial fibrillation.

Models of Ventricular Structure and Function Reviewed for Clinical Cardiologists

The architectural arrangement of cardiomyocytes aggregated together within the ventricular walls remains controversial. Two models currently attract clinical attention, with neither model standing rigorous anatomical scrutiny. The first is based on the notion that ventricular mass can be unraveled consistently to produce a unique myocardial band. The second model was initially based on the notion that cardiomyocytes were bundled together in uniform fashion, with fibrous shelves interposed in transmural fashion. This concept was subsequently modified to accept the fact that the fibrous matrix supporting the cardiomyocytes within the ventricular walls does not form transmural sheets. Current observations demonstrate that not all cardiomyocytes are aggregated together in tangential fashion. A significant netting component is aligned in obliquely intruding and transversal fashion. The interaction between the tangential and transversal chains of cardiomyocytes with the fibrous matrix produces antagonistic forces, with both unloading and auxotonic forces necessary to explain normal and abnormal cardiodynamics. This article is part of a JCTR special issue on Cardiac Anatomy.

El triángulo de Koch y el nodo AV en la anomalía de Ebstein: implicaciones en la ablación con catéter

Introduccion y objetivos. Los avances realizados en los procedimientos de ablacion de arritmias supraventriculares en la anomalia de Ebstein (AE) han creado la necesidad de un mejor entendimiento de la morfologia del triangulo de Koch (TK) y disposicion en dicha estructura del nodo auriculoventricular (AV). Metodos. Se han estudiado 17 corazones humanos, 11 con AE (intervalo de edades, 37 semanas a 1 semana despues de nacer) y 6 estructuralmente normales (intervalo de edades, 35 semanas a 2 dias despues de nacer). Se calculo el area del TK y se midio la longitud del nodo AV y el haz de His. Resultados. El area del TK es significativamente mas pequena en los especimenes con AE que en los controles (17,5 ± 4,5 mm2 frente a 25,5 ± 6,5 mm2; p < 0,05). En los corazones con AE, el nodo AV y sus extensiones son similares en longitud a los corazones normales. El nodo AV en los especimenes con AE se desplaza hacia la base del triangulo en el 73% y las extensiones inferiores llegan al nivel del istmo cavotricuspideo (ICT). En el 91% de los especimenes con AE, la entrada del haz de His se produce antes de llegar al apex del triangulo, y su longitud es mas corta. Conclusiones. Con base en los hallazgos morfologicos obtenidos en este estudio, se puede deducir su utilidad en los procedimientos de ablacion en las proximidades de la base del TK por la posibilidad de producir un bloqueo del nodo AV en pacientes con AE.

Fatty infiltration around the cardiac nodes.

La hipertrofia lipomatosa del septum interauricular (HLSI) es un tumor benigno raro caracterizado por depositos de grasa en el septum interauricular sin participacion de la fosa oval, que frecuentemente se asocia con arritmias cardiacas, generalmente de origen supraventricular (contraccion auricular prematura, sindrome del seno enfermo, flutter y fibrilacion auricular), insuficiencia cardiaca y, en ocasiones, muerte subita. Presentamos el caso de una mujer de mediana edad (47 anos), con obesidad morbida, miocardiopatia dilatada de posible origen enolico e insuficiencia cardiaca congestiva que fallecio subitamente; la autopsia cardiaca puso de manifiesto una HLSI. El estudio macroscopico muestra un tumor graso localizado en el interior del surco interauricular (fig. 1, estrella) que, tras su reseccion (fig. 1, flechas), mostro un tamano de 5 2,5 cm y la histologia tipica de esta entidad, es decir, adipocitos maduros (fig. 2A) entremezclados con miocitos auriculares (fig. 2B). Al analizar los nodos sinoauricular y auriculoventricular mediante tinciones histologicas con tricromico de Masson (fig. 3), se observo que la infiltracion grasa (asteriscos) los rodeaba externamente aunque no los aislaba por completo del miocardio auricular de trabajo circundante. La etiologia de la HLSI es desconocida, pero se suele producir en personas de edad avanzada, obesas y de sexo femenino. Uno de los mecanismos de las arritmias auriculares en la HLSI podria ser la infiltracion grasa desde la masa principal del tumor hacia los nodos, lo que puede interferir en la arquitectura muscular y la transmision electrica entre los miocitos nodales y auriculares de trabajo y originar fenomenos de reentrada. A B C

Anatomía quirúrgica de las arritmias

El interes por la anatomia cardiaca se ha visto incrementado con la utilizacion de las tecnicas de ablacion mediante cateter para el tratamiento de las taquiarritmias en el corazon humano. La cardiologia intervencionista vuelve a estudiar la morfologia macroscopica y las caracteristicas estructurales del corazon. En suma, una onda nueva ha nacido para revisitar la anatomia cardiaca dado que la informacion de que disponiamos hasta el momento era incompleta o llanamente erronea. Como resultado de este interes, recientes estudios han revelado las caracteristicas anatomicas, aspectos arquitectonicos y detalles histologicos de ciertos componentes del corazon que son de interes para el entendimiento del sustrato de las arritmias y su ablacion. El proposito de este estudio ha sido revisar detalles de la morfologia cardiaca tales como el istmo inferior o istmo cavotricuspideo, la region sinoatrial y la cresta terminal, el triangulo de Koch y su contenido, los orificios de las venas pulmonares y su vecindad con la auricula izquierda, la arquitectura de la union venoatrial y de la pared auricular posterior. En resumen, describimos la anatomia y arquitectura de la orejuela izquierda y de la cresta lateral izquierda, la vena de Marshall y el seno coronario, asi como la inervacion autonoma de las auriculas y su relacion con el esofago y los nervios frenicos. Finalmente, estudiamos las caracteristicas anatomicas de los ventriculos derecho e izquierdo.