Idiopathic VPC: Distribution Of FOCI And Tips Of Ablation

Abstract

Idiopathic Ventricular Premature Contraction (VPC) is currently more routinely referred for electrophysiology evaluation. Usually it carries a good prognosis but, when symptomatic or suspected to produce ventricular dysfunction, will require treatment. Nowadays, RF ablation has great advantages over antiarrhythmic drugs. Classically the outflow tract (right or left), with the typical inferior axis with left (eventually right) bundle brunch block like ECG morphology, is considered the most frequent site of origin for idiopathic VPC, but with the widespread of EP procedures and advancement of technology making possible to map and ablate difficult locations, it is possible to see a growing and changing population referred for idiopathic VPC ablation, displaying that, almost any region of the heart may be source of this kind of arrhythmia that can be successfully treated. A well-planned procedure, with the presumed region of origin settled and employing the current technology and knowledge (tips), will have a high chance of cure.

Keywords: Ablation; Idiopathic; Outflow tract; Ventricular Premature Contraction.

Figure 1. Scheme of the main ECG morphologies of the basal PVCs. There is a progressive modification of the QRS from negative to positive in lead V1 according the origin of the PVC from the anterior RVOT to the epicardium of the posterior left ventricle.

Figure 2. Algorithm developed by Betensky BP et al.15 for OTA ECG localization. If the PVC transition to an R>S occurs later than the SR transition then the PVC origin is the RVOT (100% specificity). If the PVC transition occurs at or earlier than the SR transition (i.e., SR transition lead V3 or later), then the V2 transition ratio is measured. If the transition ratio is <0.6, then RVOT origin is likely. If the transition ratio is ≥0.6, then LVOT origin is likely (sensitivity 95%, specificity 100%).

Figure 3. Scheme of the methodology for vagal stimulation during EP studies developed by authors. The RF catheter, temporarily detached from the RF generator and connected to a neurostimulator, is advanced to the internal jugular vein. This position usually has a great proximity with the vagus nerve allowing its stimulation. This maneuver must be only accomplished after being the patient anesthetized.

Figure 4. Case of a patient who was symptomatic due to a very frequent monomorphic VPC. However, in the EP laboratory the arrhythmia was completely absent. A: during vagal stimulation there is an immediate asystole followed by a junctional beat and one PVC (red arrow). This response was typically reproducible. All other attempts to reproduce the PVC were unsuccessful. B: The PVC triggered by the vagal stimulation was mapped and a good precocity was obtained allowing the ablation; C: After ablation, vagal stimulations were unable to reinduce new VPCs. Currently, this patient is asymptomatic and has no more arrhythmia.

Figure 5. Computerized aid for pace mapping. Pace mapping is extremely useful in the PVC ablation however, it has some disadvantages like the time consuming and a huge dependency of the subjective interpretation of the operator. This software, developed by the authors, as other products on the market, has promoted great agility and efficiency in the pace mapping technique. In A and B there are two examples of pace mapping inappropriate for ablation, however in C the mapping is excellent that is, a place with a high probability of ablation success (all the flags are green).

Figure 6. Scheme of the cardiac fibrous skeleton and its relationship with Valsalva sinuses. The non-coronary sinus is related with fibrous tissue only and is the solely one that does not gives rise to PVCs. The coronary sinuses are relatively frequent source of PVCs and the ablation in these places must have special care for avoiding coronary injury.

Figure 7. Forbidden PVC ablation. Method proposed and routinely employed by the authors using the irrigation system of the ablation catheter, placed in the best mapping position, by injecting X-ray dye for verifying if it is in a risk position, associated with a coronary ostium. In this example, a young woman had a ventricular tachycardia originated from the left coronary sinus. The best place for ablation was located in the left coronary ostium. The ablation catheter was relocated and the ablation was finally successful but performed outside the ostium, despite being a suboptimal position.