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Bidirectional ventricular tachycardia (VT) is classically associated with digoxin toxicity, catecholaminergic polymorphic ventricular tachycardia (CPVT), and Anderson-Tawil syndrome1.We report a case of bidirectional VT in a post-operative patient with TMEM43 arrhythmogenic cardiomyopathy (AC) with a probable diagnosis of stress-induced cardiomyopathy. Despite a documented VT rate that exceeded the detect rate on the patient's implantable cardioverter defibrillator (ICD), no therapy was delivered by the device. This was due to failure to satisfy consecutive tachycardia intervals given the varying cycle lengths due to alternating QRS morphology characteristic of bidirectional VT. Bidirectional ventricular tachycardia (VT) is classically associated with digoxin toxicity, catecholaminergic polymorphic ventricular tachycardia (CPVT), and Anderson-Tawil syndrome1. We report a case of bidirectional VT in a post-operative patient with TMEM43 arrhythmogenic cardiomyopathy (AC) with a probable diagnosis of stress-induced cardiomyopathy. Despite a documented VT rate that exceeded the detect rate on the patient's implantable cardioverter defibrillator (ICD), no therapy was delivered by the device. This was due to failure to satisfy consecutive tachycardia intervals given the varying cycle lengths due to alternating QRS morphology characteristic of bidirectional VT. A 63-year-old woman with a history of TMEM43 arrhythmogenic cardiomyopathy was seen on post-operative day 5 following left thoracotomy and left lower lobectomy for resection of a squamous cell carcinoma. The post-operative course was complicated by hypoxemic respiratory failure requiring high flow nasal oxygenation to maintain adequate oxygen saturation. On the fifth post-op day, she had sudden onset of a wide-complex tachycardia noted on telemetry. A 12-lead electrocardiogram (ECG) of her arrhythmia is shown below: The rhythm was determined to be ventricular tachycardia (VT) with frequent periods of alternating frontal plane axis consistent with bidirectional VT. The patient was hemodynamically stable during this episode. She was taking amiodarone 400mg daily and sotalol 80mg twice daily chronically for a history of refractory ventricular tachycardia requiring device therapy which was continued in hospital. Other than these two medications, no other anti-arrhythmic medications had been given. There was no use of digoxin prior to this event. The QTc in sinus rhythm on ECG the same day as the VT ECG was 447 ms. Pre-operative transthoracic echocardiograph showed mildly decreased left ventricular systolic function with mid-distal inferolateral and inferoseptal wall hypokinesis and mild right ventricular (RV) dilatation with lower limits of RV systolic function. Right ventricular systolic pressure was estimated as normal and there was no significant valvular dysfunction. This was not significantly different from a prior echocardiogram in 2020. Electrolyte panel demonstrated a potassium of 4.2 mmol/L (normal 3.5-5.0 mmol/L), magnesium 0.86 mmol/L (normal 0.66-1.07 mmol/L) and corrected calcium of 2.4 mmol/L (normal 2.15 – 2.55 mmol/L). This episode of tachycardia resolved spontaneously, and she converted back to sinus rhythm with baseline repolarization/T wave abnormalities. There were no ischemic symptoms or new ECG changes to suggest ischemia. The patient was transferred to the coronary care unit where she received IV amiodarone infusion and treatment for pulmonary edema. On device interrogation, the VT episode was recorded in the monitor zone with a duration of 31 minutes and 50 seconds. No anti-tachycardia pacing (ATP) or defibrillation therapy was delivered by her ICD during this episode. The lower therapy zone of the device was set to 28 intervals at 370 ms (162 bpm). The upper therapy zones were 320 ms (188 bpm) VT via VF and 260 ms (231 bpm) for 30/40 intervals. The lower therapy zone was decreased to 410 ms (146 bpm) following this episode. The patient was monitored in the CCU following this episode with no recurrence of VT and transitioned back to oral amiodarone and sotalol. Follow-up myocardial perfusion imaging in hospital did not demonstrate any evidence of reversible ischemia. A post-operative echocardiogram demonstrated a new finding of a dyskinetic apex, which resolved on a follow-up study, suggestive of stress-induced (Takotsubo) cardiomyopathy. The patient was discharged in stable condition following the usual post-operative care for thoracic surgery. Classically, bidirectional VT is associated with digoxin toxicity, catecholaminergic polymorphic ventricular tachycardia (CPVT), and Anderson-Tawil syndrome1Sonmez O. Gul E.E. Duman Ç. Düzenli M.A. Tokaç M. Cooper J. Type II bidirectional ventricular tachycardia in a patient with myocardial infarction.J Electrocardiol. 2009; 42: 631-632https://doi.org/10.1016/j.jelectrocard.2009.06.011Crossref PubMed Scopus (17) Google Scholar. It has also been rarely described in myocarditis, hypokalemic periodic paralysis, and herbal aconitine poisoning1Sonmez O. Gul E.E. Duman Ç. Düzenli M.A. Tokaç M. Cooper J. Type II bidirectional ventricular tachycardia in a patient with myocardial infarction.J Electrocardiol. 2009; 42: 631-632https://doi.org/10.1016/j.jelectrocard.2009.06.011Crossref PubMed Scopus (17) Google Scholar. There have been other rare reports of bidirectional VT in dilated cardiomyopathy, metastatic cardiac tumors, acute ischemia, and active cardiac sarcoidosis1Sonmez O. Gul E.E. Duman Ç. Düzenli M.A. Tokaç M. Cooper J. Type II bidirectional ventricular tachycardia in a patient with myocardial infarction.J Electrocardiol. 2009; 42: 631-632https://doi.org/10.1016/j.jelectrocard.2009.06.011Crossref PubMed Scopus (17) Google Scholar, 2Benjamin M.M. Hayes K. Field M.E. Scheinman M.M. Hoffmayer K.S. Bidirectional ventricular tachycardia in cardiac sarcoidosis.J Arrhythmia. 2017; 33: 69-72https://doi.org/10.1016/j.joa.2016.05.003Crossref PubMed Scopus (8) Google Scholar, 3Norwood D.A. Dominguez L.B. Dominguez R.L. Winders W.T. Bidirectional Ventricular Tachycardia in a Women with Dilated Cardiomyopathy: A Case Report.Adv J Emerg Med. 2019; 4: e12https://doi.org/10.22114/ajem.v0i0.287Crossref Google Scholar, 4Schreiber A, Gardner M, Sossou C, Greene N, Ahsan C. Bidirectional Ventricular Tachycardia with Stress-Induced Cardiomyopathy. Sciarra L, ed. Case Rep Cardiol. 2022;2022:1-5. doi:10.1155/2022/1065847Google Scholar. Bidirectional VT is not an arrhythmia typically associated with AC. However, a case published in 2015 described a patient with phenotypic features of both AC and CPVT who had bidirectional VT. This patient was genotype negative, with no pathogenic variant identified on genetic testing for CPVT or AC5Patel H. Shah P. Rampal U. Shamoon F. Tiyyagura S. Arrythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) and cathecholaminergic polymorphic ventricular tachycardia (CPVT): A phenotypic spectrum seen in same patient.J Electrocardiol. 2015; 48: 874-878https://doi.org/10.1016/j.jelectrocard.2015.06.005Crossref PubMed Scopus (10) Google Scholar. Bidirectional VT was also recently described in a patient with stress-induced (Takotsubo) cardiomyopathy following multiple traumatic injuries and methamphetamine use 4Schreiber A, Gardner M, Sossou C, Greene N, Ahsan C. Bidirectional Ventricular Tachycardia with Stress-Induced Cardiomyopathy. Sciarra L, ed. Case Rep Cardiol. 2022;2022:1-5. doi:10.1155/2022/1065847Google Scholar. This patient had subsequent recovery of the apical wall motion abnormality initially noted on echocardiogram. Our patient had a primary prophylaxis defibrillator implanted in 2002 for a manifest phenotype with the high-risk p.S358L TMEM43 variant. She had received multiple appropriate shocks for ventricular tachycardia and ventricular fibrillation over long-term follow-up. She was started on sotalol in 2004 and later transitioned to amiodarone in 2016 for recurrent episodes of ventricular arrhythmia. On most recent follow-up in Nov of 2023, she was taking both amiodarone and sotalol for recurrent episodes of refractory ventricular arrhythmia. In this case, the cause of bidirectional VT was felt to be most likely secondary to stress-induced cardiomyopathy although it is unclear if the underlying AC contributed to its development. In addition, it is possible that the use of amiodarone and sotalol in combination contributed to development of this arrhythmia. However, these medications have not been previously attributed to this type of VT and the patient had been on stable chronic therapy prior to this event. There have only been single reports of bidirectional VT in AC and stress cardiomyopathy, both of which were present in this patient. An additional interesting aspect of this case is the implications for programming of the ICD for tachycardia therapy. The rate of the VT on the ECG shown in Figure 1 is an average of 162 bpm. This happened to be the exact rate of the lower therapy zone of the ICD which resulted in some intervals falling below the detect rate. VT at or below the detect rate of a device is a common issue. However, the presence of alternating QRS morphologies added an additional challenge for tachycardia detection in this case that is interesting to consider. Some tachycardia therapy zones are reliant on consecutive counts of tachycardia intervals while others are probabilistic. The lower zone for this device was set to 28 consecutive intervals. This means that 28 consecutive intervals greater than 162 bpm need to be seen to trigger therapy. A single interval outside of the tachycardia therapy zone will reset the counter. Although the tachycardia averaged at a rate close to the lower therapy zone, beat to beat variations in the morphology produced uneven cycle length intervals with some intervals satisfying detect while others fall out of detect. This is illustrated in Figure 2A below:Figure 2AVarying Beat-to-beat cycle length during Bidirectional VT. Figure 2B. Short (*) and Long (**) Interval Pairs noted during VT. (TS = tachycardia zone interval, VS = interval outside the tachycardia zone)View Large Image Figure ViewerDownload Hi-res image Download (PPT) As demonstrated in Figure 2A, the QRS complexes demonstrate short intervals followed by long intervals. The average of these intervals is 358 ms (168 bpm). If this was a regular monomorphic tachycardia at 168 bpm, all intervals would have satisfied conditions for treatment with the patients current programming (lower zone of 370 ms/162 bpm). However, only intervals labelled TS fall into tachycardia therapy zones whereas VS intervals fall out. This cycle length variation is due to the alternating QRS morphology. Since the episode lasted for 32 minutes and the device suspends recording for part of this record, the exact electrogram annotation on the device corresponding to our 10 second ECG was not available. However, part of the episode was recorded on the device and confirms intermittent short and long interval pairs corresponding to bidirectional beats. This is shown in Figure 2B. Typically bidirectional VT shows frontal axis alterations occurring beat-to-beat. In this case, the rhythm appears to be intermittently monomorphic with periods of sustained bidirectionality (Figure 1). The reason for this is unclear but may be due to simultaneous and competing bidirectional VT from triggered activity and re-entrant VT due to arrhythmogenic cardiomyopathy. In the part of the episode shown in Figure 2B, the cycle length did slow considerably lower than the lower therapy zone throughout the 32 minutes. However, the episode may have been treated by the device earlier if the alternating QRS did not result in cycle length variations. The average rate of the tachycardia recorded by the ICD throughout its duration was 164 bpm. The lower therapy zone of the device was reduced from 162 bpm to 146 bpm following this event. In summary, this case describes the rare finding of bidirectional VT in a patient with AC seen post-operatively who likely also had a diagnosis of stress-induced cardiomyopathy. Despite the average rate of the tachycardia exceeding the lower therapy zone of the defibrillator, no therapy was delivered by the device. Beat-to-beat alteration in the QRS morphology produced a varying cycle length that prevented appropriate recognition and treatment of VT by the ICD. This case demonstrates how bidirectional VT may not trigger device therapy in an ICD despite meeting the rate criteria for a tachycardia zone. Therapy zones that require consecutive intervals to satisfy detection may avoid detection of this rare arrhythmia. 1.Bidirectional VT is a rare arrhythmia with a relatively short list of possible causes.2.Bidirectional VT in this case may be secondary to AC or stress-induced cardiomyopathy, both of which have been rarely reported.3.ICD therapy may be inappropriately withheld due to failure to meet consecutive interval requirements when the QRS morphology is alternating beat to beat in bidirectional VT. There are no author disclosures related to this article. No funding was provided for this article.
Duffett et al. (Sat,) studied this question.