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Pseudotachycardia in a Teenager With Recurrent Syncope

To identify the key insights or developments described in this article
1 Credit CME

A teenager with a history of cardiomyopathy and recurrent syncope was admitted to the pediatric unit with a urinary tract infection. Levofloxacin was started along with outpatient medications of metoprolol and valsartan. The patient had symptomatic improvement of the urinary tract infection and was ready for discharge on day 3 after hospital admission. However, the patient lost consciousness suddenly and had seizurelike activities with urine incontinence. The patient regained consciousness with a blood pressure of 86/45 mm Hg and pulse oximetry of 95% on oxygen via nasal cannula after brief cardiopulmonary resuscitation. A 12-lead electrocardiogram (ECG) was urgently obtained and is shown in the Figure. A bedside 2-dimensional echocardiography revealed biatrial enlargement, left ventricular hypertrophy with ejection fraction of 47%, and no pericardial effusion.

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The initial impression of tachycardia was largely misled by the unusually large amplitude P waves accompanied by atrial T waves with an opposite polarity to that of the P waves because atrial repolarization does not normally register a visible wave on an ECG. However, the quick bedside findings, including markedly slow heart sound by auscultation and pulse wave on the pulse oximeter, were additional clues for a diagnosis of complete AV block. Additionally, the heart sound and pulse wave that occurred simultaneously with those slow and wider QRS complexes on the ECG (Figure) further supported the diagnosis.

The P waves with amplitude up to 8 mm plus prominent atrial T waves indicated either an isolated markedly enlarged right atrium or possible combined right and left atrial dilatation. The bedside 2-dimensional echocardiography revealed that the right and left atriums were measured at 42 mm and 38 mm, respectively, which are considerably larger than the top normal limits at the patient’s age in the setting of left ventricular hypertrophy. These echocardiographic findings were consistent with hypertrophic restrictive cardiomyopathy. The lesson learned in this case is that a P wave resulting from marked biatrial enlargement can be large enough that it could be mistakenly viewed as a QRS complex, particularly when prominent atrial T waves are also present. Failure to recognize it would have led to wrong treatments for pseudo–ventricular tachycardia in the presence of complete AV block, for example, that could have potentially put the patient at life-threatening risk if an intravenous antiarrhythmic drug such as amiodarone or direct current cardioversion was started.

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Article Information

Corresponding Authors: Kui Hong, MD, PhD, Department of Cardiovascular Medicine, the Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, China (hongkui88@163.com); Gan-Xin Yan, MD, PhD, Lankenau Medical Center, Main Line Health, 100 E Lancaster Ave, Wynnewood, PA 19096 (yang@mlhs.org).

Published Online: February 27, 2023. doi:10.1001/jamainternmed.2022.6455

Conflict of Interest Disclosures: Prof Yan reported grants from the Sharpe-Strumia Research Foundation outside the submitted work. No other disclosures were reported.

References
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Lee  RJ , Liem  LB , Cohen  TJ , Franz  MR .  Relation between repolarization and refractoriness in the human ventricle: cycle length dependence and effect of procainamide.   J Am Coll Cardiol. 1992;19(3):614-618. doi:10.1016/S0735-1097(10)80281-5PubMedGoogle ScholarCrossref
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Algeo  SS , Ewy  GA .  Pseudo-atrial rhythm due to electrical ventricular separation.   Am Heart J. 1985;109(4):900-902. doi:10.1016/0002-8703(85)90656-8PubMedGoogle ScholarCrossref
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Sirinvaravong  N , Heimann  M , Liskov  S , Yan  GX .  Dual atrial rhythms: a case report of an unusual cause of pacemaker syndrome.   Eur Heart J Case Rep. 2022;6(1):ytab531. doi:10.1093/ehjcr/ytab531PubMedGoogle ScholarCrossref
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