[Alternating bundle branch block in a supraventricular tachycardia: Which is the mechanism ?] / Bloqueo de rama alternante en una taquicardia supraventricular ¿ Cuál es el mecanismo subyacente ?

Functional bundle branch block during a supraventricular tachycardia can be observed with shorter cycle lengths and represent a physiologic response by the specialized intraventricular conduction system to accelerated AV nodal conduction. The present case corresponds to a young patient with exercise induced orthodromic A-V reentrant tachycardia and alternating bundle branch block. This unusual response is explained by the finding obtained during the electrophysiology study. An accelerated AV nodal conduction made the depolarizing wave front reach the bundle branches during their refractory period. Once block in one bundle was stablished, block persisted due to the linking phenomenon that is repetitive retrograde concealed conduction from the contralateral bundle. After catheter ablation of a concealed left-sided accessory A-V pathway, rapid atrial pacing at the same cycle length of the tachycardia reproduced the same aberrancies observed during tachycardia. This response proved that functional bundle branch block is due to the short cycle length and not the presence of an accessory A-V pathway.

El bloqueo de rama funcional durante una taquicardia supraventricular puede ser observado con longitudes de ciclo cortas y representa una respuesta fisiológica del sistema de conducción intraventricular por la existencia de conducción nodal auriculo ventricular acelerada. Presentamos el caso de un paciente joven con taquicardia reentrante aurículo-ventricular ortodrómica y bloqueo de rama alternante. Esta respuesta infrecuente se explica por el hallazgo obtenido durante el estudio electrofisiológico. Una conducción nodal aurículo-ventricular acelerada produce un frente de onda que despolariza las ramas durante sus períodos refractarios. Una vez que ocurrió el bloqueo en una de las ramas, dicho bloqueo persistió debido al fenómeno de linking, que es por conducción oculta retrógrada repetitiva de la rama contralateral. Después de la ablación transcatéter de una vía accesoria oculta lateral izquierda, el marcapaseo auricular rápido a la misma longitud de ciclo de la taquicardia, reprodujo la misma aberrancia observada durante la taquicardia. Este procedimiento demostró que el bloqueo de rama funcional fue debido a la longitud de ciclo corto y no a la presencia de una vía accesoria aurículo-ventricular.

[Induction of atrioventricular nodal reentrant tachycardia by radiofrequency application]. / Inducción de taquicardia reentrante nodal aurículo-ventricular por aplicación de radiofrecuencia.

Atrioventricular nodal reentrant tachycardia is the most common form of sustained regular narrow QRS complex tachycardia. It is caused by the presence of a dual atrioventricular nodal anatomy and physiology, with a fast and a slow pathway forming a substrate for re-entry. Electrophysiology study confirms the diagnosis when the tachycardia is induced, although in some cases this is not possible. Casuistry is here presented where the application of radiofrequency induced atrioventricular nodal reentrant tachycardia, when the electrophysiological study could not do it; we explain here its electrophysiological mechanism.

Inducción de taquicardia reentrante nodal aurículo-ventricular por aplicación de radiofrecuencia / Induction of atrioventricular nodal reentrant tachycardia by radiofrequency application

La taquicardia reentrante nodal aurículo ventricular es la forma más común de taquicardia sostenida, regular con QRS angostos. Fisiopatológicamente está determinada por una anatomía y fisiología nodal aurículo ventricular dual, con una vía rápida y otra lenta que forman el sustrato de la reentrada. El estudio electrofisiológico determina el diagnóstico de certeza si es inducida, aunque en algunos casos no es posible. Presentamos nuestra casuística donde la aplicación de radiofrecuencia indujo taquicardia reentrante nodal aurículo ventricular cuando el estudio electrofisiológico no pudo hacerlo, y explicamos su mecanismo electrofisiológico.

Atrioventricular nodal reentrant tachycardia is the most common form of sustained regular narrow QRS complex tachycardia. It is caused by the presence of a dual atrioventricular nodal anatomy and physiology, with a fast and a slow pathway forming a substrate for re-entry. Electrophysiology study confirms the diagnosis when the tachycardia is induced, although in some cases this is not possible. Casuistry is here presented where the application of radiofrequency induced atrioventricular nodal reentrant tachycardia, when the electrophysiological study could not do it; we explain here its electrophysiological mechanism.

Prevention of recurrences in patients with lone atrial fibrillation. The dose-dependent effect of angiotensin II receptor blockers.

BACKGROUND: Atrial fibrillation (AF) leads to the activation of the renin-angiotensin system (RAS), which seems to play an important role in atrial remodelling. It is not known yet whether RAS blockade may prevent recurrences in patients with lone AF. METHODS AND RESULTS: Patients with an episode of persistent AF for >7 days, in the absence of cardiac or extracardiac causes and with normal blood pressure values (lone AF), were recruited. Ninety patients were randomised and scheduled for electrical cardioversion. Three groups of patients were compared: Group I was treated with amiodarone 400 mg daily (30 patients), group II was treated with amiodarone 400 mg daily plus irbesartan 150 mg daily (30 patients) and group III with amiodarone 400 mg daily plus irbesartan 300 mg daily (30 patients). The primary endpoint was the time to a first recurrence of AF. The patients were cardioverted and followed. The Kaplan-Meier analysis of time to first recurrence during the follow-up period showed that patients treated with amiodarone 400 mg plus irbesartan 300 mg had a greater probability of remaining free of AF (77% vs. 52% for amiodarone and 65% for amiodarone+irbesartan 150 mg), hazard ratio for a recurrence in group III: 0.47 (95% CI 0.27-0.82; p=0.001). CONCLUSIONS: The combination of irbesartan plus amiodarone decreased the rate of AF recurrences, with a dose-dependent effect, in lone AF patients.

Saline irrigated catheter ablation for pulmonary vein isolation in pigs: an experimental model.

Focal AF is amenable to radical cure by RF ablation within the PV. The primary purpose of this study was to compare lesion characteristics for irrigated versus standard ablation using three power settings for PV isolation in pigs. Secondary analyses were the comparisons of ablation time and temperature characteristics, and evaluation of short-term safety in the pig model. In 20 pigs from 25 to 35 kg in weight, transseptal catheterization was performed and then the ablation catheter was advanced into the PV. RF energy was delivered to the ostium of the PV until its isolation was achieved. The animals were euthanized 1 week after ablation for pathological examination. Electrophysiological isolation of the PV was achieved, although it was difficult to achieve a complete circumferencial lesion in the ostium of the PV. Both of these catheters can produce transmural necrosis, even using 15 W of power. The authors did not see any stenosis of the PV. This might be due to the low energy delivery and the short follow-up. Pulmonary hemorrhage was present in two animals with 50 W of power, high energy output is dangerous for the ablation of the PV.

[Lesions produced by radiofrequency ablation of the cavotricuspid isthmus in an experimental model]. / Lesiones producidas por la ablación con radiofrecuencia del istmo cavotricuspídeo en un modela experimental.

INTRODUCTION AND OBJECTIVES: Experimental studies have shown that deeper and wider lesions (up to 10 mm long or deep) can be safely created using an 8 mm or irrigated tip catheter for ablation to treat atrial flutter. However, potential damage to the tricuspid valve or inferior cava vein has not been systematically evaluated. PATIENTS AND METHOD: The cavotricuspid isthmus was ablated in 26 pigs (body weight 26-52 kg), with a total of 187 radiofrequency pulses. Standard 4 mm, 8 mm and irrigated tip catheters were used at random. For each ablation, energy, impedance and temperature were recorded continuously. RESULTS: The lesions were larger with irrigated tip and 8-mm catheters than with standard ones. In 7 animals (1 with an irrigated tip, 4 with an 8-mm, and 2 with a standard tip) the tricuspid valve was damaged. The tricuspid valve was severely damaged in 3 pigs and lesions were moderate in 4. In animals with tricuspid valve lesions, maximal energy was higher (59 +/- 27 vs. 51 +/- 24 W; p=0,03) and higher temperatures were reached (63 +/- 4 vs. 55 +/- 11 degrees C; p<0.001). Low energy pulses measured before ablation were also more intense in animals in which damage was produced (0.55 +/- 0.24 vs. 0.35 +/- 0.29; p=0.001), indicating greater contact pressure. CONCLUSIONS: The tricuspid valve may be severely damaged during the ablation of the cavotricuspid isthmus for atrial flutter: damage was seen most often with high energy pulses and with 8-mm catheters, but can also occur with usual energy levels and standard catheters. To minimize damage this technique should not be used from the inside of the right ventricle just above the tricuspid valve.

Lesiones producidas por la ablación con radiofrecuencia del istmo cavotricuspídeo en un modelo experimental / Lesions produced by radiofrequency ablation of the cavotricuspid isthmus in an experimental model

Introducción y objetivos. El empleo de catéteres con punta de 8 mm o irrigados para la ablación del aleteo auricular produce lesiones más anchas y profundas que los estándares, hasta de 10 mm de longitud y profundidad. El daño potencial sobre la válvula tricúspide o la vena cava inferior no se ha evaluado de forma reglada. Pacientes y método. Se hizo ablación del istmo cavotricuspídeo en 26 animales (cerdos, con un peso de 2652 kg) con un total de 187 aplicaciones, empleando aleatoriamente catéteres estándar de 4 y 8 mm, y catéteres irrigados, con control de la potencia, la impedancia y la temperatura. Resultados. Los catéteres irrigados y de 8 mm produjeron lesiones de mayor tamaño. En 7 animales (uno con catéter irrigado, 4 con catéter de 8 mm y 2 con catéter estándar) se dañó la válvula tricúspide, la lesión fue severa en 3 casos y moderada, en 4. Los casos con lesión valvular habían recibido mayor potencia (59 ñ 27 frente a 51 ñ 24 W; p = 0,03) y alcanzado temperaturas más altas (63 ñ 4 frente a 55 ñ 11 °C; p < 0,001). La medición del pulso de baja energía preablación fue también mayor cuando se produjeron lesiones (0,55 ñ 0,24 frente a 0,35 ñ 0,29; p = 0,001), lo que indicó una mayor presión de contacto del catéter. Conclusiones. El daño valvular durante la ablación del istmo cavotricuspídeo puede ser más frecuente con el uso de alta energía y con catéteres de 8 mm e irrigados, pero también se puede producir con catéteres estándares y energías habituales. Para evitarlo, no se deben hacer aplicaciones en el interior del ventrículo derecho, justo encima de la válvula tricúspide (AU)

Angiotensin receptor blocker as adjunctive therapy for rhythm control in atrial fibrillation: results of the irbesartan-amiodarone trial.

Atrial fibrillation (AF) is a common arrhythmia associated with increased risk of stroke and mortality. The early appearance of electrical remodeling is followed by structural remodeling of the atrial tissue. Direct current cardioversion of persistent AF is the most effective treatment for the restoration of sinus rhythm, but it is hampered by a high percentage of recurrences. Recurrences may be the consequence of both electrical and structural remodeling. A study on the use of irbesartan to maintain sinus rhythm in patients with long-lasting persistent AF showed that this angiotensin II receptor blocker combined with amiodarone prolonged sinus rhythm after cardioversion. Irbesartan may have antifibrotic effects due not only to the ability to diminish the synthesis of collagen type I molecules but also to its capacity to stimulate the degradation of collagen type I fibers, as has been demonstrated with losartan, another angiotensin II receptor blocker. This suggests that efforts to reduce the structural changes that occur during AF may be more useful in preventing recurrences than efforts designed to minimize the electrical changes alone. The AFFIRM trial compared two approaches to the treatment of AF: cardioversion with antiarrhythmic drugs to maintain sinus rhythm and the use of rate-controlling drugs. The results show that management of AF with the rhythm-control strategy offers no survival advantage over the rate-control strategy. However, non-antiarrhythmic drugs to prevent recurrences, like irbesartan, were not controlled and amiodarone was used in a low percentage of the patients. The treatment strategies proposed in both AFFIRM and RACE, in our opinion, may not be the optimal. The modern clinical approach to AF involves an early intervention to restore sinus rhythm, therefore preventing atrial remodeling. The pretreatment of patients with AF who undergo electrical cardioversion is very important and will be the subject for continuous improvement.