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.

Atrial flutter, Radiofrequency ablation, Bradycardia, Slow ventricular response, Atrioventricular block.

Atrial flutter is a supraventricular arrhythmia. It is caused by organized and rapid atrial electrical activity. It often results in a fast ventricular rate due to regular conduction through the AV node. While the typical clinical picture involves tachycardia, a slower ventricular response may occasionally be observed. This is usually attributed to factors such as nodal blocking medications, degenerative conduction system disease, or metabolic disturbances.[1]

Here, we present a case of atrial flutter with a marked SVR in a patient without exposure to AV nodal inhibitors, highlighting the need for comprehensive evaluation and tailored treatment in such presentations.

An 86-year-old man with a medical history of hypertension and dyslipidemia presented with progressive shortness of breath and lightheadedness over one week. He denied chest discomfort, palpitations, or syncope. His medications included aspirin and atorvastatin.

Upon examination, he was hemodynamically stable with a blood pressure of 140/66 mmHg but had a significantly low heart rate of 36 bpm. Cardiopulmonary and neurological examinations were unremarkable. Laboratory tests showed elevated B-type natriuretic peptide (BNP) and C-reactive protein (CRP), while serum electrolytes, thyroid function, and cardiac enzymes were within normal limits. Chest X-ray showed no acute pathology.

The first electrocardiogram (ECG) showed atrial flutter with a usual atrial rate of 300 beats per minute (bpm) and variable AV block, varying from 6:1 to 7:1, which can result in a slow ventricular rhythm. The QRS complexes were narrow (Figure 1).

Figure 1: Initial ECG showing typical flutter waves and slow ventricular resistance (SVR) due to variable AV block

Anticoagulation was initiated using low molecular weight heparin, and intravenous furosemide was administered for mild fluid overload. Transthoracic echocardiography revealed no valvular abnormalities or intracardiac thrombus, with an estimated left ventricular ejection fraction above 45%. The cardiology and electrophysiology teams were consulted.

The patient underwent successful radiofrequency ablation (RFA) of the CTI, guided by intracardiac echocardiography. His ECG after the surgery showed sinus rhythm with the 1^st degree right bundle branch block and AV block with ventricular rate, which improved to 60 to 70 bpm (Figure 2).

Figure 2: Post-RFA ECG showing restored sinus rhythm and improved heart rate

Following the intervention, the patient experienced symptom resolution and was discharged with outpatient follow-up.

While atrial flutter occurs less commonly than atrial fibrillation, it has many clinical signs and complications. The typical ventricular response in atrial flutter falls between 100–150 bpm due to regular AV conduction ratios like 2:1 or 4:1. Reduced conduction is rare and often indicates either pharmacologic inhibition of AV nodal conduction or the intrinsic disease in the node itself.[1,2]

In the absence of medications that reduce AV nodal conduction and with normal electrolyte and thyroid status, intrinsic AV nodal dysfunction becomes the most likely cause of the bradycardic presentation. As seen in our patient, the variability in AV block ratios suggests an unstable conduction pathway, possibly influenced by age-related degenerative changes.[3]

Recognition of atypical atrial flutter patterns is essential in emergency and cardiology settings, as misdiagnosis can delay proper therapy. ECG is sufficient to determine the diagnosis and gives the unique sawtooth flutter waves in the inferior leads. Echocardiography can help rule out structural causes and guide anticoagulation decisions.[4,5] Slow ventricular response in atrial flutter, although rare, has been documented in the literature and can lead to hemodynamic instability, especially in older adults.[6]

Transthoracic echocardiography is valuable in assessing left ventricular function, valvular pathology, and the presence of intracardiac thrombi, which may influence both treatment strategy and the need for anticoagulation.[3,5] Interestingly, structural causes like cardiac tumors have also been implicated in some cases of atypical atrial flutter presentations [7].

Catheter-based RFA of the CTI has become the standard of care for typical atrial flutter, offering high success rates and low recurrence. Studies have shown that RFA provides superior rhythm control compared to pharmacological therapies, along with improved quality of life and reduced hospital admissions.[3,4,8]

Atrial flutter with SVR is an uncommon but clinically significant presentation that may indicate AV nodal pathology, specifically in the elderly. The clinicians must be aware that bradycardia cannot exclude the atrial flutter and must go for thorough diagnostic and therapeutic strategies. Catheter ablation remains an effective and potentially curative treatment.[3,8]

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.

Not reported

Not applicable

Corresponding Author:
Saeed Ur Rehman
Department of Internal Medicine
St. Luke’s General Hospital, Kilkenny, Ireland
Email: saeedkhattak460@gmail.com

Co-Authors:
Abdul Rehman
Department of Emergency
St. Luke’s General Hospital, Kilkenny, Ireland

Nisar Ahmad Khan
Department of Internal Medicine
St. Luke’s General Hospital, Kilkenny, Ireland

All authors contributed to the conceptualization, investigation, and data curation by acquiring and critically reviewing the selected articles and were involved in the writing – original draft preparation and writing – review & editing to refine the manuscript.

Informed consent was obtained from the patient and their attenders.

The authors declare no conflict of interest.

None

https://doi.org/10.63096/medtigo30623228

Rehman SU, Rehman A, Khan NA. Atrial Flutter with Variable High-Degree AV Block: An Atypical Case in an Elderly Patient. medtigo J Med. 2025;3(2):e30623228. doi:10.63096/medtigo30623228 Crossref