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Dr. Sara Moreno Reviriego
Dr. Jose Luis Merino,
Idiopathic ventricular tachycardia (IVT), a term that has been used for ventricular tachycardia (VT) in the absence of clinically apparent structural heart disease (1), accounts for around 10% of all VTs evaluated in specialised arrhythmia services. Several types have been reported according to their clinical presentation, ventricular origin, response to drugs, electrocardiographic pattern, among others. The most common type is the so called ventricular outflow tract (VOT-T) or adenosine-sensitive tachycardia while other monomorphic forms of IVT, not explained in this review, include intrafascicular verapamil-sensitive reentrant tachycardia and ventricular tachycardia in patients with structural heart disease (1). Adenosine-sensitive tachycardia commonly originated in the right ventricular outflow tract (80% of all locations). Other less frequent sites of endocardial and epicardial origin are the left ventricular outflow tract (12% of all locations), the pulmonary artery, the basal area of interventricular septum, near mitral and tricuspid annulus and the aortic sinuses of Valsalva (2-4). All of them, including those originating in places remote from the ventricular outflow tract (such as the coronary sinus and cardiac veins, other ventricular regions, the atrioventricular annulus, etc), behave in a similar way. Therefore, classifying them according to its behaviour may be more appropriate than according to their anatomical location.
These tachycardias share a common mechanism: triggered activity (figure 1). Cytosolic calcium overload mediated by increased levels of cyclic adenosine monophosphate (cAMP) lead to delayed afterdepolarisations which, when reaching the cardiomyocite threshold, may cause another action potential and initiate tachycardia (5). Reentry and enhanced automaticity have been also postulated as other potential mechanisms of these tachycardias. However, the former is the most accepted one due to the following factors:
Nevertheless, it is not uncommon to observe the same response to verapamil and beta-blockers in other forms of IVT, such as intrafascicular reentrant tachycardia and IVT due to abnormal automatism respectively. Therefore, sensitivity to adenosine and response to stimulation may be the most specific criteria that support this mechanism.
Ventricular outflow tract tachycardia (VOT-T) typically presents in young people, usually in the second to fourth decades of life. It appears to have similar distribution between the two sexes, though it has been reported that it will depend on the anatomic location. According to this, a right ventricular outflow tract origin (RVOT-T) could occur more often in females (69.6%) while a left origin apparently predominates in males (2). The most frequent clinical complaint is palpitations (48-80%). Other common symptoms are lightheadness and presyncope (28-50%), chest pain, and, less frequently, syncope (10%). Since it typically affects young people without structural heart disease, it is usually well tolerated. Tachycardiomyopathy has also been described as part of this condition, although it is usually reversible after successful ablation. The adrenergic-dependent character of this arrhythmia has been well documented. The majority of patients experience episodes during or after exercise (7). Other common triggers are emotional stress, anxiety, stimulants such as caffeine and, in the hospital setting, the infusion of catecholamines. Interestingly, it has been described as responding to hormonal variations in women, with states of hormonal flux (premenstrual, gestational and perimenopausal periods and the administration of contraceptives) the most common recorded trigger (59%) (8). Although it is considered an arrhythmia with a benign course, some cases of sudden death and malignant polymorphic VT have been reported at follow-up (9, 10). In fact, ventricular fibrillation and polymorphic ventricular tachycardia initiated by ventricular premature complexes with a short coupling interval originated in RVOT have been recently described (11). As we will see further on, excluding other pathologies with similar presentation is essential to avoid the overestimation of malignant cases.
Ventricular outflow tract tachycardia typically shows an ECG pattern consisting of QS complex morphology of left bundle branch block and inferior axis. The QRS complex duration is usually <140 ms and longer durations should lead to ruling out mechanisms other than idiopathic VT (figure 2). Small differences in QRS complex morphology can be found during ongoing tachycardia but multiple morphologies should alert us about underlying structural heart disease. The most frequent form of presentation (90%) is the one originally described by Gallavardin (12): repetitive non-sustained ventricular tachycardia, couplets and ventricular ectopic beats present at rest (figure 3). On the other hand, it can also manifest as paroxysmal, exercise induced, sustained monomorphic VT. Considerable overlap exists between both forms of presentation that appear to be on a continuum of the same process. The electrocardiographical pattern is useful for diagnostic purposes and to help differentiate the site of origin of the tachycardia, as we will see later, to approach the electrophysiological study. Some useful features would be the following:
Several complex algorithms have been developed combining these ECG signs to predict VT location. However, we must consider that even if there is some correlation to anatomical position, it is not certain in all cases.
Idiopathic ventricular tachycardia is a diagnosis of exclusion. It is important to distinguish idiopathic VOT-T from VT related to structural heart diseases, arrhythmogenic right ventricular cardiomyopathy (ARVC) in particular. VT often originates from the RVOT in both entities (18) but treatment and prognosis are completely different. Traditional tests for this purpose include:
Although ARVC exclusion is critical for its therapeutic and prognostic implications, differential diagnosis of VOT-T also includes tachycardias associated with atriofascicular fibers (Mahaim fibers), atrioventricular reentrant tachycardia using a right-sided accessory pathway, and VT occurring in patients after repair of tetralogy of Fallot.
A) Acute management
As in other cases of wide QRS tachycardia, we should evaluate the hemodynamic status of the patient. Electrical cardioversion is emergent in case of tachycardia intolerance. In stable patients, we could recommend the following steps (Figure 2):
B) Long-term management
Taking into account the fact that truly VOT-T is not considered a life-threatening arrhythmia, decisions upon its treatment depend on the frequency and severity of the symptoms. Treatment options include antiarrhythmic drugs and catheter ablation.
• Antiarrhythmic drugs
Although RVOT VT shows a better response to antiarrhythmic drugs than VT related to structural heart disease, their overall efficacy is moderate with 30 to 40% recurrences. Beta-blockers and calcium channel blockers (including verapamil and diltiazem) are the first line therapy in symptomatic patients (27). Their efficacy has been proved to be from 25 to 50% with a synergistic effect when administered in combination. Alternative therapy includes class I and class III antiarrhythmic drugs. Gill et al (28) reported that even if flecainide, sotalol and verapamil can suppress RVOT_VT, sotalol was the most frequently effective drug (>89%) in their population.
• Catheter ablation
The procedure is usually initiated by tachycardia induction (usually facilitated by the infusion of isoproterenol and burst pacing), followed by mapping of the same either looking for the site with the earliest activation or by stimulating and comparing with the morphology of paced QRS complex with that one recorded during VT. The choice of mapping method will depend on the easiness of VT induction. In case of impossibility, premature ventricular complex and runs of non sustained VT can be really useful. Mapping usually begins at the RVOT and, if necessary, is followed by mapping the pulmonary artery, great cardiac vein, LVOT, and aortic cusps. Once localised, radiofrequency delivery from a 4-mm-tip ablation catheter usually ablates the tachycardia. Acute success rate has been reported to be over 80%. The most common cause of failure is an inability to induce tachycardia. After successful ablation, a 5% of VT recurrences has been reported, the majority within the first year and successfully ablated with a second procedure (1). Serious complications are rare (< 1% of procedures) and include:
The recommendations for electrophysiology testing and catheter ablation according to the last guidelines for the management of patients with ventricular arrhythmias are listed in the table below (27):
Drug therapy with beta blockers and/or calcium channel blockers (and/or IC agents in RVOT VT) can be useful in patients with structurally normal hearts with symptomatic VT arising from the RV.
ICD implantation can be effective therapy for the termination of sustained VT in patients with normal or near normal ventricular function and no structural heart disease who are receiving chronic optimal medical therapy and who have reasonable expectation of survival for more than 1 y
Traditionally, medical therapy has been considered of first choice, especially in patients with mild and infrequent symptoms. Catheter ablation was reserved for patients with frequent and drug-refractory symptoms, severe symptoms (such as syncope or tachycardiomyopathy), or drug intolerance. However, the curative character of ablation, the low risk of serious complications and the young age of patients with VOT-T, makes it an attractive initial treatment in many patients.
Figure 1. Mechanism of triggered activity Figure 2. Typical electrocardiographical pattern of ventricular outflow tract tachycardia Figure 3. Repetitive non-sutained ventricular outflow tract tachycardia Figure 4. Acute management
Tachycardia originating from the ventricular outflow tracts constitutes the most frequent form of idiopathic ventricular tachycardia. Triggered activity related to delayed afterdepolarizations seems to be its main mechanism. It is typical of young people without overt structural heart disease and usually presents with palpitations related to exercise. It shows a typical ECG pattern consisting of left bundle branch block configuration and inferior axis of the QRS complex. It can presents in repetitive or sustained forms. VOT-T is a diagnosis of exclusion and imaging techniques should be performed to exclude other causes, above all ARVC. Treatment options include antiarrhythmic drugs and catheter ablation. The curative character of ablation, the low risk of serious complications and the young age of patients with VOT VT, makes of this procedure an attractive initial treatment in many patients. Antiarrhythmic therapy is considered of fist choice in patients with mild and infrequent symptoms.
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Sara Moreno Reviriego and Jose L. Merino. FESC Dr Jose L. Merino, FESC, Member of the Europace 2009 Programme Arrhythmia Research Unit, Hospital Universitario La Paz, Madrid, Spain. firstname.lastname@example.org