Concomitant Short QT Syndrome and Sick Sinus Syndrome: A Case Report

DOI: 10.19102/icrm.2026.17053

FARZAD MASOUDKABIR, MD, MPH,¹ HAMID KHEDERLOU, MD,² and VANOUSHE AZIMI PIRSARAEI, MD³

¹Cardiac Primary Prevention Research Center, Cardiovascular Diseases Research Institute, Tehran University of Medical Sciences, Tehran, Iran

²Department of Cardiology, Zanjan University of Medical Sciences, Zanjan, Iran

³Student Research Committee, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran

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ABSTRACT. Short QT syndrome (SQTS) is a rare inherited cardiac channelopathy disease resulting from mutations in potassium channels. It has been associated with several dysrhythmias, including ventricular tachycardia, ventricular fibrillation, atrial fibrillation, and atrial flutter. We report, for the first time, a case of a 19-year-old man presenting with recurrent syncope due to SQTS concomitant with sick sinus syndrome, who underwent implantation of an implantable cardioverter-defibrillator.

KEYWORDS. Case report, implantable cardioverter-defibrillator, short QT syndrome, sick sinus syndrome.

The authors report no conflicts of interest for the published content. No funding information was provided. ORCID IDs: F.M., 0000-0001-8098-7121; H.K., 0000-0001-8606-2381; V.A.P., 0000-0002-3701-6431.
Manuscript received October 08, 2025. Final version accepted December 22, 2025.
Address correspondence to: Hamid Khederlou, MD, Department of Cardiology, Zanjan University of Medical Sciences, Zanjan, Iran. Email: dr.khederlou@gmail.com.

Introduction

Channelopathies are among the crucial causes of syncope or sudden cardiac death (SCD) in patients with structurally normal hearts. Short QT syndrome (SQTS) is a rare inherited cardiac channelopathy that predisposes individuals—particularly the young—to cardiac arrest and SCD.¹ Previous studies have demonstrated its association with ventricular tachycardia (VT), ventricular fibrillation (VF), atrial fibrillation (AF), and atrial flutter (AFL).^2,3 We report, for the first time to the best of our knowledge, a case of a patient with concomitant SQTS and sick sinus syndrome (SSS).

Case presentation

A 19-year-old man was admitted to the emergency department with syncope. He reported a history of frequent syncopal episodes for 4–5 years, occurring in various positions and often preceded by palpitations. He did not have dizziness, sweating, shortness of breath, or chest pain before or after syncope. He denied any past medical history, medication use, or family history of SCD. On examination, his blood pressure was 128/83 mmHg, temperature was 36.8°C, and respiratory rate was 17 breaths per minute. Neurological, cardiac, and systemic examinations were unremarkable.

The admission electrocardiogram revealed sinus bradycardia (heart rate, 54 bpm), normal axis, normal P-waves, a normal P–R interval, normal QRS voltage and duration with appropriate R-wave progression, and a short QT interval (corrected QT [QTc], 318 ms) resulting from a shortened ST segment (Figure 1). Transthoracic echocardiography showed no structural, functional, or valvular abnormalities.

The patient’s initial serum potassium, magnesium, calcium, and phosphorus levels were 4.3 mg/dL (reference range, 3.5–5.2 mg/dL), 2.4 mg/dL (reference range, 1.6–3.0 mg/dL), 8.9 mg/dL (reference range, 8.4–10.2 mg/dL), and 5.1 mg/dL (reference range, 3.5–6 mg/dL), respectively. Venous blood gas analysis showed no evidence of acidosis or alkalosis. Results of additional laboratory evaluations, including of parathyroid hormone, vitamin D, urea, creatinine, and serum albumin levels, were within normal limits. Thyroid function, liver function, and complete blood count findings were also normal. Based on these findings, secondary causes of short QT interval were excluded, and the diagnosis of SQTS was confirmed given the patient’s recurrent syncope and QTc interval of <360 ms.

Seven-day Holter monitoring showed no dysrhythmia, and the patient reported no syncopal episodes during the monitoring period. Automated QTc measurements provided by the Holter system demonstrated a shortened QTc interval, with a mean QTc of 336 ms. An electrophysiological study was planned to further evaluate potential causes of syncope, as no documented malignant ventricular arrhythmia had been identified. During the study, no ventricular arrhythmia was inducible; however, prolonged sinoatrial (SA) pauses were observed, with a corrected sinus node recovery time (CSNRT) of approximately 2300 ms (Figure 2).

The final diagnosis was SQTS associated with SSS. The case was presented at our institution’s electrophysiology conference, and, in view of the patient’s recurrent syncope and prolonged SA arrest, implantation of a dual-chamber implantable cardioverter-defibrillator (ICD) was recommended. The device was successfully implanted, and the patient remains under regular follow-up (Figure 3).

Written informed consent was obtained from the patient for the submission and publication of this case report, in accordance with the guidelines of the Committee on Publication Ethics.

Discussion

In this case, we describe a patient with a structurally normal heart and recurrent syncope, diagnosed with SQTS concomitant with SSS, who ultimately underwent implantation of an ICD.

Channelopathies are important causes of syncope and SCD in patients with structurally normal hearts.² SQTS is a rare inherited cardiac channelopathy caused by mutations in potassium channels. The condition may be inherited from a parent or arise from a de novo mutation of unknown cause.¹ Mutations in potassium channel genes, such as HERG and KCNQ1, increase the rapid delayed rectifier potassium current and slow delayed rectifier potassium current, leading to shortening of the QT interval.⁴ SQTS was first described in 2000.⁵ Currently, SQTS is defined by either a QTc of ≤330 ms or by a QTc of <360 ms in combination with one or more of the following: (1) a history of cardiac arrest or syncope, (2) a family history of SCD at ≤40 years, (3) AF, or (4) a malignant ventricular arrhythmia.⁶ Recent studies report that SQTS is associated with SCD in approximately 34% of cases, AF in 31%, and syncope in about 25%. The association of SQTS with VT, VF, AF, and AFL has been well documented^2,3,7; however, to the best of our knowledge, no previous report has described SQTS coexisting with SSS. Our patient represents the first reported case of concomitant SQTS and SSS.

SSS, also known as sinus node dysfunction, is a clinical disorder first described in 1967.⁸ Mutations in the cardiac sodium channel genes, including SCN5A, have been shown to cause SSS, which manifests as inappropriate sinus bradycardia, sinus arrest, chronotropic incompetence, and tachycardia–bradycardia syndrome. Unlike our patient, who was only 19 years old, SSS typically occurs in the context of structural heart disease or advanced age, with a mean age of onset of around 73 years.⁹

ICD implantation is generally recommended for patients with SQTS who have survived sudden cardiac arrest or have documented malignant ventricular arrhythmias. However, in patients without documented ventricular arrhythmias, particularly those with recurrent unexplained syncope and markedly shortened QTc intervals, individualized decision-making is advised. Additionally, implantable loop recorder implantation has been suggested as a consideration in children and young asymptomatic SQTS patients. Quinidine is the only drug shown to be effective in SQTS and may be prescribed for patients who decline ICD implantation or for younger individuals.^3,10 In the present case, the coexistence of SQTS, recurrent syncope episodes, and significant sinus node dysfunction further influenced the choice of implanting a dual-chamber ICD rather than a pacemaker alone, while prolonged rhythm monitoring with a loop recorder was considered insufficient given the patient’s clinical risk profile. During the 3-month follow-up period after ICD implantation, the patient remained symptom-free, with no recurrence of syncope.

Genetic testing was not performed in this case; therefore, the underlying molecular substrate could not be identified, which represents a limitation of this report.

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