Idiopathic Ventricular Tachycardia In 10% of patients with VT Young (20-50 years, range, 6 to 80 years) Palpitation, dizziness, presyncope or syncope (rare) Sudden cardiac death is rare Excellent prognosis Can be a cause of tachycardia-mediated cardiomyopathy Certain anatomic locations with manifest specific ECG patterns which help identify their site of origin.
Automaticity 1. focal origin 2. may become incessant during isoproterenol 3. cannot be initiated or terminated by programmed electrical stimulation 4. sometimes suppressed by calcium or β blockers 5. adenosine transiently suppresses but does not terminate it. Triggered activity 1. focal origin 2. EAD or DAD ([Ca 2+ ] i overload due to HR↑, β adrenergic effect (cAMP↑) or digoxin) 3. Induced by burst pacing, isoproterenol infusion or atropine Mechanism of tachyarrhythmia RVOT VT: DAD, adensine sensitive
Reentry 1. a large circuit (macroreentry) or focal (microreentry) 2. slow conduction zone: small diastolic potential 3. can be initiated and terminated by programmed electrical stimulation 4. can be entrained from multiple sites Mechanism of tachyarrhythmia Idiopathic left VT: macroreentry, verapamil sensitive
Classification of idiopathic VT relative to the mechanism Adenosine-sensitive VT (triggered activity) Propranolol-sensitive VT (automaticity) Verapamil-sensitive VT (reentry)
RVOT VT 1. Nonsustained, repetitive, monomorphic VT. # Most common form (60-90%) # Characterised by frequent VPCs, couplets and salvos of non sustained ventricular tachycardia (NSVT) # LBBB morphology and inferior QRS axis. # Occurs at rest or following a period of exercise # Transiently suppressed by sinus tachycardia. They may diminish with exercise during stress testing. 1. Paroxysmal, exercise-induced sustained VT. # This VT may be initiated during exercise or recovery. # Exercise stress testing is frequently uses to initiate and evaluate RVOT VT, but is not clinically helpful in most cases.
Signal transduction schema for initiation and termination of cAMP-mediated DAD (triggered activity) Adenosine cAMP ↓ DAD ↓
Outflow tract ventricular tachycardia 90% of outflow tract VT comes from the RVOT - may above the pulmonary valves (rare) 10% may arise from LVOT - superior basal region of LV septum, free wall - aortic sinuses of Valsava - aortic cusps - the aorto-mitral continiuty - mitral annulus - His bundle area Epicardium
Management of OTVT 1. Acute termination: vagal maneuver or adenosine (6 mg until 24 mg), IV verapamil (10 mg given over 1 min. These drugs may suppress triggered rhythms; electrical cardioversion. 2. Long term treatment options # Medical therapy: β-blockers, verapamil, diltiazem (efficacy: 20 to 50%); Alternatively class IA, IC and III agents. # Radiofrecuency ablation has cure rates of 90% with a recurrence rate of 5%.
Indications for catheter ablation of idiopathic ventricular tachycardia Monomorphic VT that is causing severe symptoms Monomorphic VT when antiarrhythmic drugs are not effective, not tolerated, or not desired Tachycardia-induced cardiomyopathy
Contraindication for catheter ablation of idiopathic ventricular tachycardia Presence of a mobile ventricular thrombus Asymptomatic PVCs and/or non-sustained VT that are not suspected of causing or contributing to ventricular dysfunction VT due to transient, reversible causes, such as acute ischemia, hyper-/hypokalemia, or drug-induced torsade de points
How to ablate VT Mapping Basic electrophysiologic study Pace mapping (identical 12-lead ECG morphology) Activation mapping (earliest activation site) Electroanatomic mapping (Carto, Navx, Enside Array, Magnetic remote control) (voltage, anatomy) Ablation successful rate: 90 %
Mapping Tool for OT-VT ECG morphology: Could be non-inducible Pacing morphology could be large area 2 cm 2 : different chamber, scar, or epicardium Activation map More accurate: remain unsuccess: more mapping sites, epicardium
Management of RVOT VT 1. CAG and 2D echo are usually normal, but MRI may show abnormalities of the RV in up to 70% of patients (focal thinning, diminished systolic wall thickening and abnormal wall motion). 2. RVOT VT should be distinguished from ARVD: ECG morphologic features similar to RVOT VT but DOES NOT terminate with adenosine. 3. It should be strongly considered for the following patients with a potentially malignant form of OT VT: a) a history of syncope; b) very fast VT; c) ventricular premature beats with a short coupling interval.
Requirement of non-contact mapping system for VT mapping Pacing mapping may not sensitive to locate the sites of foci in certain patients with focal VT, in the presence of large scar area. VT could be non-sustained and unstable. It is difficult to map the entire chamber One beat analysis of dynamic substrate by NCM may be useful to treat these patients.
Mechanism of fascicular VT The most likely mechanism of idiopathic left ventricular tachycardia is reentry with an excitable gap and a zone of slow conduction since can be initiated and terminated with programmed stimulation as well as the demonstration of entrainment of the tachycardia with rapid pacing Verapamil sensitive
Management of fascicular VT The long-term prognosis of patients with fascicular VT without structural heart disease is very good. Arrhythmias in patients with sporadic, well- tolerated episodes of idiopathic left ventricular tachycardia may not progress despite absence of pharmacologic therapy. Treated with oral verapamil (120 to 480 mg/day). Ablation successful rate: >95%
Where to Target Diastolic potential (P1) in the midseptum of LV. P1-QRS=28-130 msec If P1 could not be identified, target the fused and earliest Purkinje potential (P2) Successful ablation revealed P1 during SR could be a marker of successful ablation. Ablation successful rate: >95% Complication: trivial
Role of electroanatomic mapping systems Refers to point by point (contact) mapping combined with the ability to display the location of each point in 3-dimensional space. Carto, Navx, Ensite array, Magnetic remote system Functions: 1. non-fluoroscopic localization of the ablation catheter 2. display of intracardiac electrograms (scar, low voltage zone) 3. interpretation of mechanism of arrhythmia (focal or macroreentry) Always useful in scar-related VTs; can be useful in idiopathic VTs.
Conclusion Idiopathic VT concerns a small subgroup of patients with VT. Depending on tachycardia mechanism, idiopathic VT may respond to β-blockers, Ca 2+ channel blockers or to vagal manueuvers, although radiofrequency ablation is curative in most patients. Patients usually continue to follow up to rule out latent progressive heart disease such as arrhythmogenic right ventricular dysplasia (ARVD) or other forms of cardiomyopathies.