Atrial Flutter with Variable High-Degree AV Block: An Atypical Case in an Elderly Patient

Background: Atrial flutter is a common supraventricular arrhythmia, typically presenting with a rapid ventricular response due to regular atrioventricular (AV) conduction. However, in rare circumstances, atrial flutter may manifest with a slow ventricular response (SVR), which can lead to significant bradycardia and hemodynamic compromise. Such atypical presentations, especially in the absence of AV nodal blocking medications or metabolic disturbances, pose diagnostic challenges and may reflect intrinsic conduction system disease. Case report: We present the case of an 86-year-old male with a history of hypertension and dyslipidemia who presented with progressive dyspnea and lightheadedness. He was found to have marked bradycardia with a heart rate of 36 bpm. Electrocardiography revealed atrial flutter with a regular atrial rate of approximately 300 bpm and a variable AV block ranging from 6:1 to 7:1, resulting in SVR. The patient was not on any medications that affect AV nodal conduction, and laboratory tests, including thyroid function and electrolyte levels, were normal. He underwent successful cavotricuspid isthmus (CTI) radiofrequency ablation, which restored sinus rhythm and resolved bradycardia. Conclusion: This case highlights an uncommon presentation of atrial flutter with SVR in an elderly patient without reversible causes. Clinicians should maintain a high index of suspicion for arrhythmic causes of bradycardia, even in the absence of typical risk factors. Catheter ablation remains a definitive and effective treatment, offering both diagnostic clarity and therapeutic resolution.