The concept of ventricular or atrial myocardium extension in large blood vessels has already been known for a long time. It has been full three decades since the extensions of atrial myocardium in the pulmonary veins were systematically described for the first time until we realized that these isolated tissue fibers are electrically unstable and may trigger arrhythmias, in the case the atrial fibrillation (3). Two reasons lie in the substrate, first, the isolated myocardium loses electrical stability because it is not a part of the syncytium. The cell to cell coupling is lost, thus creating the foundation for autonomous electrical activity. The second reason is described as heterogeneity of the rate of impulse conduction (anisotropy) providing thus the conditions for localized reentry. For idiopathic ventricular arrhythmias of supravalvular origin it is considered that the isolation of such fibers from the remaining myocardium is the basic foundation of their autonomous activities.

An important concept for the explanation of this entity is the understanding of association of these fibers with myocardium. Looking at the intimate anatomical relations LVOT, RVOT and coronary cusps, it becomes clear why for example, the focus from the left coronary cusp can have multiple exit sites, usually towards the LVOT, but also to the septal RVOT which makes the use of electrocardiographic criteria for the localization of the origin of arrhythmias unreliable (4) (Figure 1). Understanding this phenomenon, the so-called preferential conduction of impulses, is very important because it explains why the same patient can have ventricular arrhythmias of different QRS morphologies, and all of them can be ablated in the same focus (Figure 2). Traditionally, multiple QRS morphologies would discourage the attempts of ablation and result in an extensive diagnostic cardiac work up, both non-invasive and invasive, in terms of seeking an organic substrate for such a form of ventricular arrhythmias.

As in other types of idiopathic ventricular arrhythmias, the entire spectrum can be recorded in an individual patient from isolated ventricular extrasystoles, often in the form of bigeminies or trigeminies through non-sustained ventricular tachycardia (NSVT) to sustained VT. Depending on the ectopic activity burden, the entity can make for only symptomatic phenomenon for years, however, arrhythmia induced cardiomyopathy often develops.

Traditionally, these arrhythmias are treated by beta-blockers as the drugs of choice, but our own experience and experience of other centers suggests that these arrhythmias are generally not induced by adrenergic tone, that is, they differ from traditional RVOT tachycardias which are triggered, mediated by intracellular cAMP. The proof for this is that the suppression of ectopic activity typically occurs during the exercise stress test, to be more precise, that the dominance of sinus rhythm occurs due to the length of the cycle. Group 1c antiarrhythmics (propafenone in Croatia) can in particular cases lead to significant suppression of ectopic activity, but it is really necessary to exclude structural heart disease before the treatment is initiated.

Due to the failure of the medical therapy, but also the fact that these are mainly young, active patients, the ablation should be early offered as a therapeutic solution. No matter whether the focus is in the pulmonary artery or aortic sinuses of Valsalva (and above the coronary cusps), no particularly demanding ablation maneuvers are concerned. On contrary, the mapping by applying retrograde aortic approach is straightforward, but the use of radiofrequency (RF) energy has to be discreet because of the proximity of the coronary arteries. For example, since the pulmonary valve is about 1- 2 cm above the aorta, the ablation of the focus just above the pulmonary valve may be only 5-6 mm distant from the left main coronary artery, while the danger of an injury to the orifice of the coronary arteries for aortic ablation is clear and intrinsic, so the use of RF energy must necessarily be controlled by some imaging method, either by direct coronary angiography (Figure 3) or by monitoring the position of ablation catheter via intracardiac echocardiography (ICE) (Figure 4). As for ablations in the right coronary cusp, there is a danger of an injury to the bundle of His that can be avoided by careful monitoring of signals and stimulation with a high power output that can not achieve the stimulation of His. In recent years we highlight the necessity of registering very typical electrograms to find the exact origin of arrhythmia. Specifically isolated myocardial fibers in the aorta or pulmonary artery provide a very specific potential which is identical to that which can be recorded in the pulmonary veins or on the bundle of His (5). This potential, called the great arterial potential drops during the ectopic activity very early before the QRS complex, which proves that this myocardial fiber of the origin of arrhythmias marks an appropriate target for ablation (6). These signals have a very high predictive value for the long-term success of RF ablation, and ablation guided by these signals typically results in almost immediate disappearance of ventricular ectopic activity.

The success of ablation of supravalvular arrhythmias is better than the classical intramyocardial focuses, because the region that the ventricular activity comes from is well defined which needs not be the case in classical RVOT arrhythmias where the application of multiple radiofrequency lesions for the elimination of arrhythmias is required. Ablation guided by great arterial potential is the modern standard and provides a 95% probability of long-term absence of arrhythmias.

Regarding the complications, the injuries to coronary arteries and cusps with consequential valvular insufficiency have been described. They are both at the level of anecdotal descriptions, and with today’s availability of imaging methods, particularly ICE, they should not occur.

During the period from April 2011 to December 2013, the ablation was performed in supravalvular regions in 13 patients (10 in the aortic cusps, 3 in the pulmonary artery), which accounts for 25% of the total number of patients who underwent the ablation of idiopathic ventricular arrhythmias. Arterial potentials were registered in 8 out of 10 patients with successful ablation in the aortic cusps, and in all patients with the focus in the pulmonary artery (Figure 5).

Only conventional equipment for electrophysiology (electrophysiological stations EP Tracer 70, Cardiotek, Netherlands and EP Med 3, SJM, USA) was used for the ablation, without the help of the electroanatomical mapping system. The early signal range before QRS was 50-114 ms for the ablations in coronary cusps and 30-44 ms for foci in the pulmonary arteries. 4 patients were redo cases and in all these cases the earlier unsuccessful ablation in subvalvular RVOT was described. Acute success in terms of the complete elimination of ectopic activity was observed in all 13 patients, and recurrence of arrhythmia was recorded in only one patient in the postprocedural follow up (at 1-30 months). The ablation in coronary cusps was monitored in all patients by direct coronary angiography or ICE. Not a single complication was observed in terms of an injury to coronary arteries or valvular insufficiency.