bidirectional ventricular tachycardia ( bvt ) is defined as a tachycardia showing beat - to - beat alternation in the qrs axis .
the rate is typically between 140 and 180  bpm , with a frontal plane axis varying between 20 and 110. the most common causes of bvt include catecholaminergic polymorphic ventricular tachycardia and cardiac glycoside toxicity .
other previously described etiologies include myocarditis , long qt syndrome type 7 , congenital cardiomyopathies , cardiac tumors , and acute cardiac allograft rejection .
cardiac sarcoidosis is characterized by myocardial inflammation and interstitial fibrosis that can lead to slowed conduction and macro re - entrant arrhythmias .
we report a case of bvt in a patient with cardiac sarcoidosis and briefly discuss the proposed mechanisms underlying bvt .
a 73-year - old man with history of chronic pulmonary sarcoidosis was seen for an annual checkup , during which ventricular bigeminy was identified on a 12-lead electrocardiogram .
subsequent holter monitor assessment showed multiple premature ventricular beats and several short runs of non - sustained ventricular tachycardia ( vt ) , with two different qrs morphologies ( fig .
1 ) . a cardiac magnetic resonance tomography with delayed gadolinium showed a curvilinear region of patchy mid - myocardial enhancement within the inferolateral left ventricular myocardium near the base , consistent with cardiac sarcoidosis ( fig .
2 ) . the left and right ventricular ejection fractions were 47% and 37% , respectively .
a nuclear myocardial perfusion study using single - photon emission computed tomography showed no myocardial perfusion defects on stress or rest imaging , ruling out ischemia .
a fasting 18-fluorodeoxyglucose positron emission tomography ( pet ) demonstrated increased uptake in the same area of the myocardium that had shown late gadolinium enhancement , consistent with active cardiac sarcoid ( fig .
the patient was elected to have an implantable cardioverter defibrillator ( icd ) placed for prevention of sudden cardiac death .
he had not experienced any vt episodes during the one - year follow - up .
one of the proposed mechanisms of bvt include elevated intracellular calcium , causing delay after depolarization in anatomically separate parts of the conducting system .
proposed that two separate foci , with different rate thresholds for delayed after depolarization  induced ventricular bigeminy , were present in a rabbit model .
this would effectively double the heart rate , increasing the overall ventricular rate above the second threshold .
once this had developed , the two competing sites would simply alternate on a beat - to - beat basis .
this is likely the mechanism underlying bvt observed with digitalis toxicity and catecholaminergic polymorphic vt .
the other proposed mechanisms for bvt include an alternating bundle branch block related to bifocal automaticity and inscribed in opposite directions , or scar - mediated reentry around a circuit with two alternating exit sites .
described a mechanism including retrograde conduction over the mid septal fascicular pathway , with alternating block in the left anterior or posterior fascicles , to explain polymorphic fascicular vt patterns .
scarring is typically patchy , with a predilection for the basal septum , anterior wall , and perivalvular regions of the left ventricle .
it may also be confluent , affecting the right ventricular epicardium or endocardium . in sarcoidosis , it is plausible that multiform or bidirectional premature ventricular contractions ( pvcs ) are due to multiple exits from the areas of inflammation and/or scarring .
conduction disturbances in cardiac sarcoidosis are not uncommon , and often affect the his - purkinje system . in our case ,
the patient had an intraventricular conduction delay at baseline , with prolonged qrs complexes at relatively low atrial rates ( fig .
the majority of the retrospective data suggest that immunosuppression reduces the burden of arrhythmias , especially in the early phases of the disease .
previous case series have reported various success rates with vt ablation in patients with cardiac sarcoidosis , likely due to the small number of patients in each series , with varying degrees of disease burden .
the most common circuit for vt in one report was reentry in the peritricuspid area , which can be safely ablated . in another study , abolishing all inducible tachycardias was not always feasible because of septal intramural circuits , extensive right ventricular scarring , or sites of origin in close proximity to the left anterior descending , the ramus intermedius arteries , or the para - hisian region , which prohibit safe ablation . in the current case , it is likely that the presence of a septal focus leads to alternate exits into the right or left ventricle which shows the observed electrocardiogram pattern .
although the septal involvement was not visible by imaging until a year after diagnosis , it might have been present initially , but was microscopic in nature .
this is consistent with previous autopsy studies that have shown a heterogeneous distribution of sarcoid granulomas in the myocardium .
the recent expert consensus document is an excellent resource for management and risk stratification for cardiac sarcoidosis patients .
icd implantation for primary prevention is commonly performed due to the high burden of vt events ( estimated incidence rate of 15% per year ) in patients with cardiac sarcoidosis . in the current case ,
icd implantation was recommended due to the high burden of nonsustained vt episodes , left and right ventricular dysfunction , and the presence of fibrosis and active inflammation by imaging studies .
 a 73-year - old man with history of pulmonary sarcoidosis was found to have runs of non - sustained bidirectional ventricular tachycardia ( bvt ) with two different qrs morphologies on a holter monitor . 
 cardiac magnetic resonance delayed gadolinium imaging revealed a region of patchy mid - myocardial enhancement within the left ventricular basal inferolateral myocardium . 
 an 18-fluorodeoxyglucose positron emission tomography ( fdg - pet ) showed increased uptake in the same area , consistent with active sarcoid , with no septal involvement . 
 follow - up fdg - pet one year later showed disease progression with new septal involvement . 
 cardiac sarcoidosis , characterized by myocardial inflammation and interstitial fibrosis that can lead to conduction system disturbance and macro re - entrant arrhythmias , should be considered in differential diagnosis of bvt . 
 bvt may indicate septal involvement with sarcoidosis before the lesions are large enough to be detected radiologically . 