there was no family history of similar complaints or history of sudden death in family . there was no obvious dysmorphic features except small proximal phalanges of little fingers of both hands , giving an impression of fifth finger clinodactyly ( fig .  1 ) . the child 's height was normal as per his age and mid - parental height . differential diagnosis of catecholaminergic polymorphic ventricular tachycardia and anderson - tawil syndrome ( ats ) were entertained . exercise testing , carried out after prolonged exercise , showed initial increase in compound muscle action potential ( cmap ) amplitude with a progressive drop and slow recovery . in view of genetic heterogeneity for bidirectional vt , genomic dna was subjected to exome sequencing by next generation sequencing ( ngs ) technique . genes responsible for catecholaminergic polymorphic ventricular tachycardia ( cpvt ) and anderson - tawil syndrome were analysed for sequence variations . the patient was found to harbour a known , pathogenic , heterozygous variant p.arg218trp caused by a substitution ( c.652c  >  t ) in exon 2 of the kcnj2 gene . none of them was found to harbour this variation , suggesting that the variation is denovo in the affected child . apart from digitalis toxicity , other etiologies include myocarditis , myocardial infarction , metastatic cardiac tumour , herbal aconite poisoning and cardiac channelopathies i.e. catecholaminergic polymorphic vt ( cpvt ) and anderson - tawil syndrome ( ats ) . absence of drug or herbal medicine intake , structurally normal heart with normal bi - ventricular function pointed towards channelopathy in our patient . in ats , unlike cpvt , ventricular arrhythmias are associated with extra cardiac manifestations like episodic flaccid muscle weakness and dysmorphic features . characteristic dysmorphologies include low - set ears , hypertelorism , small mandible , clinodactyly and syndactyly . our patient did not have any of the described dysmorphic features except fifth finger clinodactyly . in 60% patients ( also called type 1 ats ) pathogenic mutation in kcnj2 gene is evident . reduced ik1 resulting from kcnj2 mutations alters late cardiac repolarization and leads to both distinctive t - u wave morphology and an increased propensity to ventricular arrhythmias . in a series by haruna et  al . , 30% patients presented with classical triad of symptoms and 70% patients presented with any two of three symptoms . characteristic t - u  wave pattern is present in 90% of type 1 ats and this pattern has 84% sensitivity and 97% specificity in diagnosing ats . ventricular tachyarrhythmia has been observed in about 65% patients , bidirectional vt being most common followed by polymorphic vt , monomorphic vt and rarely vf . cardiac conduction abnormalities   and dilated cardiomyopathy   has also been reported . in absence of flaccid muscle paralysis , long exercise protocol may reveal an immediate post -exercise increment followed by an abnormal decrement in the compound motor action potential after prolong exercise , as in our patient . differentiation of ats from cpvt is crucial because later situation is much more fatal than former and sudden cardiac death is rare in ats . although ats can be differentiated from cpvt by classical extra - cardiac features , there is a probability of phenotypic expression of cardiac derived symptomatology only , as in our case . however a nonfatal course , prominent u wave with prolongs qu interval and subclinical neuro - electrophysiological finding pointed towards ats . at least 50% patients diagnosed with ats have an affected parent . up to 50% of cases present sporadically without family history and these cases are due to denovo mutation , as in our case . the mutation also carries high degree of variable phenotypic expression and incomplete penetrance , with as much as 20% mutation positive carriers being asymptomatic . despite high arrhythmia burden , patients with kcnj2 mutation ( ats i ) have low rate of syncope and cardiac arrest . no single pharmacological agent has been found to be effective in preventing arrhythmia load . while few patients showed improvement with calcium channel blockers or amiodarone , same drugs are ineffective in other cases   or even exacerbate torsades de pointes . although beta - blockers and sodium channel blockers ( mexiletine , propafenone , and flecainide ) have been described ineffective , a good response was seen in our patients with combination of beta - blocker and flecainide . pacing in combination with nicorandil has been described to be effective in some cases . apart from reducing the arrhythmia load by pharmacotherapy , implantable cardioverter - defibrillator ( icd ) is indicated to prevent sudden cardiac death ( scd ) . although presence of ats itself is considered a class iib indication for icd placement , history of cardiac arrest due to ventricular fibrillation or vt should be regarded as a class i indication for icd placement in ats . until further data regarding risk stratification becomes available , icd therapy should be reserved for ats patients with a history of cardiac arrest , syncope , or sustained rapid and/or symptomatic vt . to conclude we report a case of bdvt of rare etiology and diagnosis of ats should be considered in presence of bdvt with structurally normal heart , even in absence of classical diagnostic criteria .
bidirectional ventricular tachycardia ( bdvt ) is a rare form of ventricular arrhythmia , characterized by changing qrs axis of 180 degrees . 
 digitalis toxicity is considered as commonest cause of bdvt ; other causes include aconite toxicity , myocarditis , myocardial infarction , metastatic cardiac tumour and cardiac channelopathies . 
 we describe a case of bdvt in a patient with anderson - tawil syndrome .