Ventricular tachycardia in a patient with tetralogy of Fallot

ECG: Sinus rhythm at 60 beats/minute; right bundle branch block, very broad QRS (180 ms) and extremely fragmented; followed by wide QRS tachycardia at a rate of 150 bpm; left delay pattern; QRS transition in V3; high positivity of the QRS in the inferior leads and in lead I suggestive of a reentry cycle at the level of the isthmus delimited by the pulmonary infundibulum and the ventricular septal defect closure patch;

Comments: Patients who have undergone tetralogy of Fallot repair surgery have an increased risk of sudden death and a high incidence of ventricular rhythm disorders has been described. As with atrial arrhythmias, the association between surgical electrophysiological sequelae (ventricular septal defect closure patch, infundibular patch, ventriculotomy) and altered long-term right ventricular load and pressure conditions contribute to the occurrence of re-entry induced arrhythmias. Left ventricular dysfunction observed after a prolonged evolution, whether systolic or diastolic, could also be a determining factor in the genesis of ventricular arrhythmias compromising the patient’s vital prognosis. The finding of this high prevalence and the understanding of the underlying mechanisms of the arrhythmias has favored the modification of surgical practices with preference for an atrial approach rather than by a more disruptive ventriculotomy for right ventricular function and activation.

The electrocardiogram enables to partly assess the risk of sudden death. Indeed, the presence of a widened QRS (> 180 ms) as well as the rapid increase in QRS duration are factors recognized as associated with an increased risk of sudden death. It is likely that a more comprehensive analysis of the QRS pattern (search for significant fragmentation, reflecting the abnormal and disorganized activation of the ventricles) could also, in the future, be integrated into a risk assessment algorithm.

The majority of described ventricular arrhythmias are organized with the highlighting of ventricular tachycardias rotating around anatomical and electrophysiological obstacles. Ventricular myocardial remodeling induced by pressure and/or volume overload, fibrosis, and change in fiber orientation contribute to the development of slow conduction zones. Various anatomical regions (valves, patches, surgical incisions) can favor the occurrence of conduction blocks and isthmuses propitious for ventricular reentry around non-excitable tissues. Ventricular mapping can reveal four preferential isthmuses in patients with a surgically-repaired tetralogy of Fallot: an isthmus between the tricuspid annulus and the right ventricular anterior infundibular scar or patch (the isthmus most often involved in the occurrence of ventricular arrhythmias); an isthmus between the pulmonary annulus and the lateral right ventriculotomy; an isthmus between the pulmonary annulus and the ventricular septal defect closure patch; an isthmus between the ventricular septal defect closure patch and the tricuspid annulus. The ablation procedure consists in inducing ventricular tachycardia, identifying the arrhythmia circuit and the isthmus(es) involved, then creating a block line between the two anatomical obstacles, verifying the presence of a bidirectional block and the non-inducibility at the end of the procedure.

Take-home message: Patients with a tetralogy of Fallot frequently present ventricular tachycardias with left delay in conjunction with a reentry circuit around anatomical obstacles and involving four different isthmuses.