Can antihistamines (anti-allergic medications) like diphenhydramine be used to resolve palpitations (irregular heartbeats)?

Antihistamines Do Not Resolve Palpitations and May Cause Cardiac Complications

Antihistamines, particularly diphenhydramine, should not be used to treat palpitations as they can potentially worsen cardiac symptoms and may even cause cardiac arrhythmias through sodium channel blockade.

Understanding Palpitations and Their Causes

Palpitations are sensations of a rapid or irregular heartbeat that can be described as racing, fluttering, pounding, skipping, or thumping of the heart 1, 2. They have various potential causes:

• Cardiac arrhythmias (sinus tachycardia, atrial fibrillation, premature ventricular contractions, ventricular tachycardia) 1
• Non-arrhythmic cardiac problems (mitral valve prolapse, pericarditis, heart failure) 1
• Non-cardiac causes (anxiety, hyperthyroidism, vasovagal syncope, hypoglycemia) 1
• Medication or substance-related (stimulants, certain prescription medications) 2

Antihistamines and Cardiac Effects

First-Generation Antihistamines (e.g., Diphenhydramine)

• Diphenhydramine has sodium channel blocking properties similar to tricyclic antidepressants, which can cause ECG changes and cardiac arrhythmias 3, 4
• Can cause QRS prolongation and potentially dangerous wide-complex dysrhythmias 3
• May induce bradycardia followed by transient hypertension 5
• In overdose cases, diphenhydramine can cause palpitations rather than resolve them 4

Second-Generation Antihistamines

• Some non-sedating antihistamines like terfenadine (now restricted) have been associated with QT prolongation and torsades de pointes, a life-threatening ventricular arrhythmia 6
• Terfenadine has been shown to cause hypotension, bradycardia, and significant arrhythmogenic activity in experimental studies 5

Appropriate Management of Palpitations

The management of palpitations should be directed at the underlying cause rather than using antihistamines:

• Diagnostic evaluation should include detailed history, physical examination, laboratory studies, and 12-lead ECG 2
• For cardiac-induced palpitations, treatment may include reassurance, education, trigger avoidance, or atrioventricular nodal blockers 2
• For tachyarrhythmias, cardiac ablation may be required 2
• Nondihydropyridine calcium channel blockers and certain antiarrhythmic medications may be appropriate for symptom relief 6

Risks of Antihistamine Use in Patients with Cardiac Symptoms

• Antihistamines with anticholinergic effects (like diphenhydramine) can cause cognitive decline, particularly in elderly patients 6
• First-generation antihistamines may impair driving ability and are concerning for patients prone to cardiovascular events 6
• Diphenhydramine overdose can present with anticholinergic toxicity affecting multiple organ systems, including cardiac toxicity 3

When Antihistamines May Be Indicated

While antihistamines are not appropriate for treating palpitations directly, they may be indicated in specific situations:

• For treating allergic reactions where palpitations are secondary to the allergic response 6
• H1 and H2 receptor antagonists may be used for symptoms of mast cell activation syndrome, which can include palpitations as part of the syndrome 6
• In these cases, later-generation non-sedating antihistamines (e.g., fexofenadine, cetirizine) are generally preferred over first-generation options like diphenhydramine 6

Conclusion

Antihistamines, particularly diphenhydramine, should not be used to treat palpitations. Instead, proper diagnostic evaluation should be performed to identify the underlying cause, and appropriate targeted therapy should be initiated. For cardiac-related palpitations, consultation with a cardiologist may be warranted for proper management.