A challenging case of narrow complex tachycardia ☆ Vivek Reddy, MD, ⁎ Shanker Kundumadam, MD, Pradeep Kathi, MD, Nadia Nasser, MD, Mazhar Khan, MD Wayne State University/Detroit Medical Center Introduction Narrow Complex Tachycardia includes a large differen- tial of arrhythmias with varying pathophysiology and management. The differentiation of arrhythmias in this broad category can often prove to be challenging to diagnose on a surface ECG, with EP studies as the only definite modality for diagnosis. In this case we present a narrow complex tachycardia, indistinguishable on surface ECG. The rhythm however, was clearly decipherable after administra- tion of diltiazem with improved rate control. Case description An 85 year old female with a past medical history significant for hypertension, non-ischemic cardiomyopathy with an EF of 10% with moderate mitral regurgitation and mitral annular calcification, non-obstructive coronary artery disease, peripheral artery disease, old cerebrovascular accident and chronic kidney disease stage IV presented to the hospital with an elevated blood pressure of 170’s/130’s, an elevated HR of 180 and the remainder of vitals within normal limits. The patient remained clinically stable with a physical examination unchanged from baseline. Upon obtaining a 12-lead ECG shown in Fig. 1-1, she appeared to be in a regular narrow complex tachycardia at a rate of 170. With no previous history of an elevated heart rate, differentials included AVNRT, atrial Flutter 2:1 block, atrial tachycardia and sinus tachycardia. The patient was subsequently given a 20 mg IV push of diltiazem for improved rate control with the subsequent ECG shown below in Fig. (1-2). She remained asymptomatic during the remainder of her hospital course and was subsequently discharged with oral metoprolol for rate control and an outpatient cardiology follow up. Discussion In this case we describe a narrow complex tachycardia at an elevated heart rate of approximately 170 with no previous diagnosis of an arrhythmia in the past. On evaluation of the surface ECG it was difficult to ascertain the exact rhythm, however likely differentials included AVNRT, atrial flutter 2:1 conduction and atrial tachycardia. After the ventricular rate was appropriately controlled, the repeat ECG showed an inverted P wave in lead II with likely an underlying atrial tachycardia with 2:1 and 3:1 conduction and possibly underlying AV dissociation with a junctional escape rhythm. A digoxin level to rule out toxicity was deferred at this time as the patient had no exposure. The presence of 3:1 conduction and 5:1 conduction has been associated with bi-level AV nodal block in atrial flutter and in this case it may also represent a new significant AV block secondary to diltiazem [1,2]. During the hospital course subsequent ECGs showed normal sinus rhythm and atrial tachycardia with a 2:1 block further supporting the diagnosis of atrial tachycardia on admission. The incidence of sustained atrial tachycardia is low; approximately 5%–15% of supraventricular tachycardias and it is more common in those with structural heart disease. The efficacy of diltiazem in the treatment of atrial tachycardia is unclear; however, a previous study performed showed that diltiazem is an efficacious medication in the setting of paroxysmal supraventricular tachycardia, including paroxysmal atrial tachycardia [3]. In this study, albeit with a small population size, diltiazem terminated all twenty cases of paroxysmal atrial tachycardia; however, in our case it had a minimal effect on the atrial rate and appeared to induce significant AV block resulting in atrial tachycardia with variable block and possibly underlying AV dissociation with a junctional escape rhythm. The main-stay of management includes b-blockers and calcium channel blockers for rate control as well as EP studies for possible ablation [4]. Further studies are indicated to assess the efficacy of diltiazem Available online at www.sciencedirect.com ScienceDirect Journal of Electrocardiology xx (2017) xxx – xxx www.jecgonline.com ☆ Conflict of Interest: The authors declare that there is no conflict of interest regarding the publication of this paper. ⁎ Corresponding author. E-mail address: vreddy@med.wayne.edu http://dx.doi.org/10.1016/j.jelectrocard.2017.01.010 0022-0736/© 2017 Elsevier Inc. All rights reserved.