The Study of Arrhythmias Using Surgical Scars
All tissue, including myocardium, subjected to irreversible damage heals by forming scars that consist of fibrocytes that do not conduct electrical activity. From GR Mines’ first description of reentry in 1914 to Will Sealy’s first surgical procedure to interrupt an accessory pathway responsible for the Wolff-Parkinson-White syndrome in 1968 (54 years between the procedures), scars were used exclusively to study arrhythmias. Sealy’s operation marked the first time that a surgical scar had ever been used to treat an arrhythmia, though it was also important in establishing the mechanism of the arrhythmia. Until that successful surgical procedure, many prominent cardiologists of the day believed that longitudinal dissociation of the His bundle was the underlying electrophysiologic abnormality responsible for WPW syndrome. Although Sealy’s successful WPW operation was crucial to the final documentation of the underlying electrophysiology of WPW syndrome, it was also the basis for all subsequent interventional therapy for cardiac arrhythmias.
The Maze procedure served a similar function in elucidating the underlying mechanisms responsible for sustained atrial fibrillation (AF). Although AF is infinitely more complex than WPW syndrome, the Maze procedure’s success in the treatment of patients with paroxysmal, persistent, and long-standing persistent AF has provided several undeniable facts regarding the electrophysiology of AF. For example, if AF were sustained by the continuous firing of focal triggers in the atrium, the Maze procedure would simply not work because the focal triggers located between the lesions of the Maze procedure would continue to cause the atria to fibrillate (see Chapter 4 , Fig. 4.21 ). Indeed, this was the basis of Gordon Moe’s original experiments in the early 1960s.
Isolation of the focal triggers in and around the pulmonary veins decreases the likelihood that an AF episode will occur, but it does not make the atria incapable of fibrillating. Thus the focal triggers are largely irrelevant in the more sustained types of AF. As a result, their isolation or ablation has a salutary effect on paroxysmal AF but a suboptimal effect on persistent AF and long-standing persistent AF. The occasional successful ablation of persistent and long-standing persistent AF by pulmonary vein isolation (PVI) is not because the PVI isolates the triggers that induce AF but rather because the PVI has inadvertently interrupted the macro-reentrant circuits sustaining AF in that particular patient.
The Concept of Ablation and Isolation Procedures
Regardless of whether the cause of an arrhythmia is automatic, micro-reentrant, macro-reentrant, or some combination of these mechanisms, the interventional approach to its treatment follows certain principles that should be understood by all arrhythmia surgeons and interventional electrophysiologists. We have found it helpful to categorize interventional procedures for cardiac arrhythmias into either isolation procedures or ablation procedures. Isolation procedures do not actually ablate arrhythmias; rather, they confine them and/or their triggers to a specific region of the heart that minimizes their adverse effects in the remainder of the heart. Examples of isolation procedures are elective His bundle ablation, the left atrial (LA) isolation procedure, and PVI.
On the other hand, ablation procedures preclude arrhythmias from developing either by destroying their trigger mechanisms or by altering (or removing) the substrate that allows the arrhythmia to be induced and sustained. Examples of ablation procedures are the interruption of accessory pathways responsible for WPW syndrome, discrete cryosurgery of the atrioventricular node for atrioventricular node reentry tachycardia, and the Maze procedure for AF.
Adoptability of Interventional Procedures
The adoption of a new interventional procedure is inversely related to its complexity; that is, as the complexity of a procedure increases, its adoptability decreases ( Fig. 10.1 ). The impact of the procedure’s efficacy (success rate) on its adoptability is negligible ( Fig. 10.2 ). Despite the high success rate of the Maze procedure in ablating AF, the complexity of the procedure has prevented its widespread adoption by surgeons ( Fig. 10.3 ). On the contrary, despite the known lower success rate of catheter ablation for AF, its lower complexity and lower degree of invasiveness have resulted in its widespread adoption by interventional electrophysiologists ( Fig. 10.4 ). Procedures that are deemed to be too complex or that have too many failures are not widely adopted ( Fig. 10.5 ).
There is an inverse relationship between the complexity of an interventional procedure and its adoption by physicians and surgeons.
The efficacy of an interventional procedure has little or no effect on its adoption by physicians and surgeons.
Because of the complexity of the Maze procedure, it has not been widely adopted despite its outstanding efficacy. As a result, the absolute number of patients treated successfully for atrial fibrillation by the Maze procedure is relatively small.
Because the complexity and degree of invasiveness of catheter ablation is relatively low, it has been widely adopted despite its suboptimal efficacy compared with a Maze procedure. As a result, the absolute number of patients treated successfully for atrial fibrillation by catheter ablation is relatively large and far exceeds the absolute number of patients treated successfully by the Maze procedure.
