In our opinion, the choice between an endocardial versus an epicardial approach to target VT should depend on the patient’s underlying disease substrate, and the location of the arrhythmogenic substrate within the myocardial wall, which can be best assessed with a cardiac MRI. Certain patient-specific characteristics including ECG criteria, previously failed ablations, the presence of intracardiac thrombi or intraprocedural mapping data may further impact on the decision to proceed with an epicardial mapping and ablation approach. In patients with idiopathic outflow tract arrhythmias, a transcutaneous subxiphoid approach is rarely needed, even if the arrhythmia has an epicardial origin.
- Critical components of a ventricular tachycardia (VT) reentry circuit may be confined to locations deep in the subendocardium, the midmyocardium or the epciardium, and may be beyond the reach of current endocardial ablation techniques.
- ECG criteria suggesting an epicardial VT exit site include a delayed precordial maximal deflection index of ≥0.55, a pseudo ‘delta wave’ QRS of ≥34 ms, the shortest RS complex of ≥121 ms and the presence of q wave in lead I. While these criteria may be helpful in patients with idiopathic arrhythmias, their value in patients with structural heart disease has been debated.
- The type of structural heart disease and the resulting location of the arrhythmogenic substrate indicate, in most patients, whether an epicardial procedure will be necessary.
- The value of a preprocedural MRI with respect to a planned epicardial access is highest when an epicardial or intramural scar is identified within the left ventricular free wall, especially in patients with nonischaemic cardiomyopathy.
- For idiopathic outflow tract ventricular arrhythmias, a coronary venous approach combined with an endocardial method is most beneficial. The subxiphoid epicardial access is rarely beneficial in these patients.