INTRODUCTION

This chapter is based on the experience of two authors of different origins, who work in countries with distinctive realities but who both experienced the introduction and development of numerous techniques for catheter ablation of cardiac arrhythmias. In the next few pages, the historical aspects and motivations that set the stage for the minimally invasive techniques used in arrhythmia management for access and instrumentation of the pericardial space will be reported.

ARRHYTHMIA INTERVENTIONS AND RF ABLATION: THE EARLY YEARS

The interventional treatment of cardiac arrhythmias has experienced major advances in last 40 years. In the Heart Institute (InCor) of São Paulo University Medical School, arrhythmia ablation was initially performed using open-chest surgery, introduced by Dr. Eduardo Sosa and Dr. Miguel Barbero Marcial in 1979. The surgical treatment of supraventricular and scar-related ventricular tachycardias (VTs) were performed with reasonable frequency in that institution until the mid-1990s.^1–9

Indisputably, radiofrequency (RF) energy delivered by catheters with deflectable tips was responsible for a great revolution in the interventional treatment of tachyarrhythmias in the clinical setting. In a short period of time, conventional open-chest surgery to ablate arrhythmias was replaced by vascular access interventions with very good efficacy and low risk, and this success was reproduced in different centers worldwide.^10–14

RF application from the endocardium was effective and had low risk of complications, including when applied to patients with recurrent sustained VT associated with previous myocardial infarction.^10–12 Consequently, catheter-based ablation gave rise to a new medical specialty, the “Interventional Electrophysiology,” which has been growing over the years and enabling the curative treatment of numerous patients with cardiac arrhythmias.

THE CHAGAS DISEASE CHALLENGE

Although very successful in several types of atrial and ventricular arrhythmias, the efficacy of endocardial ablation has been more limited in patients with nonischemic VT. Deeper intramyocardial circuits, especially those involving subepicardial fibers, preclude effective endocardial RF energy delivery.¹⁵ This limitation was particularly evident in a special type of nonischemic heart disease, very common in Brazil and Latin America: Chagas heart disease, which frequently presents with episodes of recurrent VT and electrical storm.^16,17

Traditional endocardial activation and entrainment mapping techniques, useful in the identification of VT circuits of ischemic origin, were frequently ineffective in patients with Chagas VT. Although the substrate of these VTs is usually segmental fibrosis, its location and anatomopathological aspects are different when compared to the scars observed in patients with previous myocardial infarction in which subendocardial RF applications can frequently reach the circuits.¹⁹

It was already known that the mechanism of sustained VT in Chagasic cardiomyopathy was reentry, because of its behavior during programmed ventricular stimulation.¹⁸ However, it was not possible to demonstrate the participation of subepicardial fibers in the reentrant mechanism when doing endocardial mapping and ablation. Indirect observations, like fractionated late potentials documented from coronary sinus catheter recordings, the absence of presystolic and mid-diastolic activity during extensive endocardial mapping of sustained VT, and endocardially applied RF interruption of sustained VT followed by its easy reinduction, raised the hypothesis that the slow conducting channels could involve subepicardial fibers.

The first plan to clarify this point was to perform surgical mapping, simultaneously exploring the endocardial and epicardial ventricle surfaces, as had already been previously demonstrated in intraoperative studies of patients with ischemic heart disease.19–21 Due to technical difficulties in the development of an intraoperative mapping system (which were not commercially available at that time in Brazil), exploring the endocardium and epicardium surfaces of the heart would prove challenging. A good-quality intraoperative map was not easy to achieve during open-chest surgery in patients with Chagas disease. In Chagas disease, different VT morphologies were usually induced during programmed stimulation and were difficult to reproduce due to the deep anesthesia and the ventricular incisions required to access the endocardial ventricular surface. Additionally, during surgery, it was not easy to identify the specific 12-lead electrocardiographic morphology of the induced and the clinical VTs, given that complete surface 12-lead ECG registration was not feasible due to the anterior sternotomy used to gain access to the heart.

DEVELOPING THE NONSURGICAL EPICARDIAL MAPPING TECHNIQUES

The first nonsurgical effort designed to investigate the subepicardial origin of cardiac arrhythmias with catheters was suggested by Dr. Warren Jackman and colleagues from Oklahoma City, who used multi-microelectrode catheters through the coronary venous system to access epicardial fibers.²² The great advantage of this technique was the low risk of complications of the transvenous epicardial mapping. However, although ideal for left-sided atrioventricular (AV) pathways and VT substrate confined to the immediate perivalvular mitral region, detailed epicardial mapping was constrained by the location of large epicardial venous vessels.²³ Currently, only the distal great cardiac veins, the proximal anterior interventricular vein, and the middle cardiac vein are routinely used to map the epicardium in the setting of idiopathic VTs with a suspected epicardial origin.

At the Heart Institute of Sao Paulo University, the initial plan to reach the entire epicardial surface of the ventricles, without open thoracic surgery, was to introduce the catheters by video thoracoscopy, a technique that had just been initiated in the institution for the diagnostic and therapeutic approaches of various thoracic diseases. However, this procedure had to be performed in the surgical center and not in the electrophysiology (EP) laboratory, a fact that displeased the entire team.

Many discussions were made with much debate on how to best access the pericardial space in the EP lab. At that time, after a subxiphoid puncture and drainage procedure of a pericardium tamponade that occurred from perforation during an ablation, Dr. João Luis Piccioni, the anesthesiologist of the EP team, suggested the same access to perform the epicardial mapping despite the difference regarding the pericardial access risk when performing a subxiphoid puncture in a patient with a pericardial effusion compared to another without an effusion. He opened a new opportunity for epicardial space exploration once he remembered that anesthesiologists currently used the Tuohy needle, specially designed to access the virtual space of the epidural membranes and that this needle could also be used to safely access the pericardial space.

With this hypothesis in mind, Dr. Mauricio Scanavacca started to elaborate a method to perform the puncture and then to introduce guidewires, sheaths, and multielectrode catheters into the virtual pericardial space. “We hypothesized that if an accidental perforation and epicardial bleeding occurred, it could be immediately drained through the same access, with a low probability of requiring surgical intervention.”

The technical strategy was presented to Dr. Eduardo Sosa, the director of the Arrhythmia Unit, who accepted it immediately and worked to obtain authorization from the ethical committee of the hospital, in order to start a pilot study in Chagasic patients who were already scheduled for surgical treatment of their sustained VTs.

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