Polymorphic ventricular tachycardia--part II: the channelopathies

Polymorphic Wide QRS Complex Tachycardia: Differential Diagnosis

Polymorphic wide QRS complex tachycardia is defined as a tachyarrhythmia showing variable and frequently alternating morphologies of the QRS complex with irregular R-R intervals. It may present with a specific and reproducible pattern including torsade de pointes and bidirectional ventricular tachycardia or with a nonspecific and very irregular pattern, different from ventricular fibrillation. Polymorphic ventricular tachycardia is a challenging diagnosis and is associated with a high risk for sudden cardiac death. Although rare, preexcited atrial fibrillation over multiple accessory pathways can also generate a polymorphic wide QRS complex tachycardia mimicking polymorphic ventricular tachycardia.

Nonsustained Ventricular Tachycardia in the Normal Heart: Risk Stratification and Management

Nonsustained ventricular tachycardia (NSVT) may trigger concern, particularly in patients with known congestive heart failure, structural heart disease, or prolonged QT interval. When NSVT occurs in patients with normal hearts, it usually has a benign prognosis. Therefore, establishing the presence or absence of structural or inherited heart disease is a critical step in each patient's evaluation. It is important to approach a wide-complex tachycardia in a systematic manner, to ensure correct diagnosis and treatment. When NSVT occurs in a patient with a normal heart, treatment is targeted toward symptoms and may consist of observation, medical therapy, or catheter ablation.

Pro-arrhythmogenic effects of CACNA1C G1911R mutation in human ventricular tachycardia: insights from cardiac multi-scale models

Mutations in the CACNA1C gene are associated with ventricular tachycardia (VT). Although the CACNA1C mutations were well identified in patients with cardiac arrhythmias, mechanisms by which cardiac arrhythmias are generated in such genetic mutation conditions remain unclear. In this study, we identified a novel mechanism of VT resulted from enhanced repolarization dispersion which is a key factor for arrhythmias in the CACNA1C G1911R mutation using multi-scale computational models of the human ventricle. The increased calcium influx in the mutation prolonged action potential duration (APD), produced steepened action potential duration restitution (APDR) curves as well as augmented membrane potential differences among different cell types during repolarization, increasing transmural dispersion of repolarization (DOR) and the spatial and temporal heterogeneity of cardiac electrical activities. Consequentially, the vulnerability to unidirectional conduction block in response to a premature stimulus increased at tissue level in the G1911R mutation. The increased functional repolarization dispersion anchored reentrant excitation waves in tissue and organ models, facilitating the initiation and maintenance of VT due to less meandering rotor tip. Thus, the increased repolarization dispersion caused by the G1911R mutation is a primary factor that may primarily contribute to the genesis of cardiac arrhythmias in Timothy Syndrome.

'Refractory epilepsy': what lies beneath?

A 30-year-old woman presented to the emergency room with recurrent seizures for 5 days. She had been diagnosed with epilepsy 2 years previously but stopped treatment due to the side effects of her medications. She was now experiencing episodes every 15-30 min. While undergoing a brain MRI to investigate for structural central nervous system pathology, she experienced another episode, preceded by prodromal symptoms. Polymorphic ventricular tachycardia was noted during the event. Further investigation revealed a normal QT interval, normal electrolyte panel, normal coronaries and severe left ventricular systolic dysfunction. Cardiac MRI revealed non-ischaemic cardiomyopathy. The patient was managed with heart failure and antiarrhythmic medications and an implantable cardioverter defibrillator. She remained symptom free at 6-month follow-up. This case highlights the importance of differentiating between cardiogenic syncope and epilepsy and reiterates the importance of re-evaluating a diagnosis of epilepsy when presentation is atypical or symptoms are refractory.