We present an educational case of a verapamil-sensitive fascicular VT with typical ECG characteristics, which developed immediately following an overdose of promethazine and which was terminated successfully with verapamil, in a young person with a structurally normal heart.
Key Findings
Background
Promethazine overdose precipitated verapamil-sensitive fascicular ventricular tachycardia in a young patient with a structurally normal heart.
This is reported as the first published case of promethazine precipitating a fascicular VT.
The patient was a young person with no underlying structural cardiac abnormality.
The VT developed immediately following the promethazine overdose.
The case is described as presenting an 'unusual link' between promethazine and this specific arrhythmia type.
Results
The fascicular ventricular tachycardia displayed typical ECG characteristics of verapamil-sensitive fascicular tachycardia.
The arrhythmia involved the specialised cardiac conducting tissue (the fascicles).
The presentation was a broad complex tachycardia.
ECG characteristics were described as 'typical' for verapamil-sensitive fascicular VT.
This type of VT is distinct from the Torsades de Pointes arrhythmia more commonly associated with antihistamine toxicity.
Results
The ventricular tachycardia was successfully terminated with intravenous verapamil.
Verapamil, a calcium channel blocker, was used as the specific treatment.
The arrhythmia was 'terminated successfully with verapamil.'
Verapamil-sensitivity is a defining pharmacological characteristic of this subtype of VT.
Early recognition of the ECG pattern was highlighted as important for appropriate management.
Discussion
Promethazine's arrhythmic mechanism in this case differed from the typical pro-arrhythmic pathway associated with antihistamines.
Multiple antihistamines are known to be pro-arrhythmic, but 'these tend to precipitate Torsades de Pointes via drug-induced QT prolongation.'
In this case, the arrhythmia was fascicular VT rather than Torsades de Pointes.
The case highlights that antihistamine overdose can precipitate arrhythmias through mechanisms beyond QT prolongation.
Drug overdose is described as 'an important cause to consider when assessing patients with a new presentation of a broad complex tachycardia.'
What This Means
This research describes a rare case report of a young person who developed a specific type of dangerous heart rhythm problem called fascicular ventricular tachycardia immediately after taking an overdose of promethazine, a common antihistamine and anti-nausea medication. This type of irregular heart rhythm involves the specialized electrical wiring of the heart and shows a distinctive pattern on an electrocardiogram (ECG). The heart rhythm disturbance was successfully stopped by giving the patient a medication called verapamil, which is a calcium channel blocker known to be effective specifically against this type of arrhythmia.
This research suggests that promethazine can trigger a type of heart rhythm problem that is different from what is typically expected with antihistamine medications. Usually, antihistamines cause a different arrhythmia called Torsades de Pointes by prolonging a specific electrical interval in the heart. This case shows a previously unreported mechanism where promethazine triggered fascicular ventricular tachycardia instead, and the authors note there are no previously published reports of promethazine causing this specific arrhythmia.
The practical importance of this case is that it highlights the need for clinicians to consider drug overdose as a possible cause when a patient presents with a new broad complex (fast, abnormal) heart rhythm, and to be aware that the appropriate treatment depends on correctly identifying which type of arrhythmia is present. Recognizing the typical ECG pattern of fascicular VT is important because it guides treatment toward verapamil rather than other interventions, and misidentification could lead to inappropriate management.
Hassan S, Carpenter A, Nisbet A. (2026). Verapamil-sensitive fascicular ventricular tachycardia precipitated by promethazine overdose.. BMJ case reports. https://doi.org/10.1136/bcr-2025-271685