By Claudio Tondo
Idiopathic ventricular tachycardia (VT) refers to all arrhythmias originating from the ventricles not linked to any detectable structural heart disease. These arrhythmias are usually due to focal triggered activity or re-entry between fascicular bundles. Detailed mapping of these arrhythmias is crucial because it can guide subsequent ablative intervention that is often curative.
Idiopathic VTs comprise different ventricular arrhythmias, amongst those:
- Outflow tract ventricular tachycardia
- Tricuspid annulus ventricular tachycardia
- Mitral annulus ventricular tachycardia
- Interfascicular ventricular tachycardia
- Papillary muscle ventricular tachycardia
Outflow tract VT
Amongst the group of idiopathic VTs, outflow tract VT is probably the most frequent occurring arrhythmia due to a discrete focus. Classically, its origin is suggested by QRS morphology and axis. Patients are often symptomatic for non-sustained episodes or long period of premature ventricular contractions (PVCs) with the same ECG morphology of VT. Almost 80% of outflow tract VTs arise from the right ventricular outflow tract and the majority from site 1–2cm below the pulmonary valve1.
Precise mapping of single PVCs is required to specifically identify the site of origin and guide successful ablation. Earliest local activation at successful ablation site precedes surface QRS by 20–45ms; bipolar electrograms often show sharp rapid deflections whilst unipolar recordings typically demonstrate QS morphology. The presence of PVCs of the same VT morphology is critical to mapping and successful ablation; in those cases of sporadic occurrence of PVCs, pace-mapping can be employed to identify the successful ablation site.
Less frequently, outflow tract VTs–PVCs originate from the left ventricle, the aortic valve cusps or the great arteries. On the other hand, some varieties can originate from the aorto-mitral continuity (the base of the septum or left ventricular epicardium). In these circumstances, QRS complexes show inferior axis, but prominent R waves in V1–V2. Detailed mapping is often improved by using intracardiac echocardiography (ICE) as an adjunctive mean to properly localise the anatomic structures potentially involved. Proximity to coronary arteries may limit radiofrequency energy applications in these locations and, in some circumstances coronary angiograms are warranted. Aortic cusps VTs originate from sleeves of left ventricular myocardium above the aortic annulus2.
One critical issue is the differential diagnosis between a true idiopathic VT and VTs otherwise due to subtle structural heart diseases. In some patients, arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) at initial phase with prominent epicardial involvement and scarce endocardial signs may produce ventricular arrhythmias mimicking idiopathic right ventricular outflow tract VTs. In those circumstances, an attentive EKG morphology evaluation along with 3D electroanatomic mapping is advisable to improve the likelihood to make the final diagnosis. In some occasions, endomyocardial biopsy may be required to distinguish different pathologic entities (right ventricular dysplasia/cardiomyopathy, amyloidosis, sarcoidosis, etc).
Tricuspid annulus VT
Spontaneous PVCs or VTs (approximately 8% of idiopathic VTs) could arise from the lower body of right ventricular regions 1–2cm below the tricuspid valve. All these arrhythmias present LBBB pattern. Accurate mapping and subsequent ablation can be effective in promoting prevention of recurrence in >80% of cases thus, highlighting the critical role of catheter ablation in these forms of arrhythmias. Also, in these patients it is important to rule out the occurrence of areas of right ventricular scars, as possible signs of arrhythmogenic cardiomyopathy3.
Mitral annulus VT
Less frequently, idiopathic VTs/PVCs arise from the mitral annulus (about 5% of all idiopathic ventricular arrhythmias). In these circumstances, the most frequent involved area is the antero-septal region of the annulus. Similar to aortic cusp VTs, a delayed potential is recorded during sinus rhythm at the valve annulus and, this potential precedes the QRS electrogram by 50–70ms during VT or spontaneous PVCs. Endocardial ablation is highly effective in suppressing the arrhythmia; occasionally, an epicardial approach via coronary sinus system may be required.
Interfascicular ventricular tachycardia (Belhassen VT)
This form of VT classically involves the posterior fascicles of the left ventricle and demonstrates a RBBB, left axis deviation pattern. It occurs in otherwise healthy patients, sometimes elicited by physical stress and could be terminated by verapamil infusion. Two other forms of verapamil-sensitive VT have been described; a left anterior fascicular VT with a narrow QRS complex, RBBB and right axis deviation and an upper septal fascicular VT with narrow QRS complex and normal axis. Due to the possible beneficial effects of intravenous verapamil, it has been Ca-dependent mechanism. Long-term therapy with verapamil is not as effective as radiofrequency catheter ablation. For the classic form of posterior fascicular VT, radiofrequency is directed at the anterograde apical Purkinje potential; the success rate of ablation is >85-90%.
Papillary muscle ventricular tachycardia
This is a distinct form of left ventricular VT arising from the papillary muscles and it can demonstrate a QRS pattern similar to fasciscular VT. This arrhythmia can be cathecolamine-sensitive and exercise-sensitive and clinically characterised by frequent PVCs rather than run of sustained VT. It is thought they have a focal automatic mechanism with spontaneous QRS variations that lack in fascicular VTs. Intracardiac echocardiography is the ideal guide to detect the region of the papillary muscle that is the location of the early activation and for guiding the ablation catheter.
Even though in the majority of circumstances, idiopathic VTs are not considered life-threatening arrhythmias, prevention of recurrences by means of antiarrhythmic drugs is often ineffective and, the patients’ quality of life remains unchanged. Different treatment options need to be discussed with the patient, portraying the whole scenario of possibilities. With catheter ablation, the overall acute success rate is about 85-90% with a long–term prevention of arrhythmia recurrence of about 75-80%. The overall complication rate is about 2%, with severe complication rate <1%. It is advisable that this kind of procedure is carried out by electrophysiologists with expertise in VT catheter ablation as to ensure a high success rate and reduce the likelihood of major complications.
- Aliot EM, Stevenson WG, Almendral-garrote JM, et al: EHRA/HRS expert consensus on catheter ablation of ventricular arrhythmias: developed in a partnership with the European Heart Rhythm Association (EHRA), a registered branch of the European Society of Cardiology (ESC), and the Heart Rhythm Society (HRS); in collaboration with the American College of Cardiology (ACC) and the American Heart Association (AHA). Heart Rhythm 2009; 6:886-933.
- Yamada T, McElderry HT, Doppalapudi H, et al. Idiopathic ventricular arrhythmias originating from the left ventricular summit: anatomic concepts relevant to ablation. Circ Arrhythm Electrophysiolol 2010; 3:616-23
- Van Herendael H, Garcia F, Lin D, et al. Idiopathic right ventricular arrhythmias not arising from the outflow tract: prevalence, electrocardiographic characteristics, and outcome of catheter ablation. Heart Rhythm 2011;8:511-8
Claudio Tondo is director of the Arrhythmia Research Centre, Centro Cardiologico Monzino, IRCCS, University of Milan, Milan, Italy