Cardiac Safety of Mirtazapine and Bupropion in Supraventricular Tachycardia
Mirtazapine poses minimal cardiac risk in SVT patients and can be safely continued, while bupropion is also safe to resume given its favorable cardiovascular profile in cardiac patients.
Mirtazapine and Cardiac Complications
Limited Cardiac Risk Profile
Mirtazapine does not appear on the ACC/AHA/HRS guideline lists of medications requiring caution or contraindication in SVT patients 1. The comprehensive SVT management guidelines specifically detail drugs with SA/AV nodal effects, QT prolongation risks, and other cardiac concerns—mirtazapine is notably absent from these precautionary lists 1.
Documented Adverse Events Are Rare
The primary cardiac concerns with mirtazapine are:
Orthostatic hypotension: The European Society of Cardiology advises caution with mirtazapine in elderly patients due to orthostatic hypotension risk, particularly in those with falls history 2. However, your 30-year-old patient does not fall into this high-risk category.
Bradyarrhythmias in overdose: Case reports document junctional bradycardia and first-degree AV block, but these occurred exclusively with supratherapeutic doses (300+ mg) 3, 4. At therapeutic doses of 7.5 mg, these risks are not clinically relevant.
No tachyarrhythmia exacerbation: Mirtazapine does not worsen tachyarrhythmias or SVT 5. Its mechanism involves α2-adrenergic blockade and serotonin receptor modulation without direct effects on cardiac conduction at therapeutic doses 5.
Clinical Context
The patient's concern about cardiac risks appears unfounded at her 7.5 mg dose. The American Heart Association does not list mirtazapine among antidepressants requiring avoidance in cardiovascular disease 2. The guideline concern is primarily orthostatic hypotension in elderly patients, not arrhythmia exacerbation in young adults with SVT 2.
Bupropion Safety in SVT
Favorable Cardiac Profile
Bupropion is safe to resume at 150 mg daily in patients with cardiac disease, including those with arrhythmias 6. A dedicated study of 36 depressed patients with preexisting cardiac disease (including ventricular arrhythmias and conduction disease) demonstrated that bupropion:
- Did not cause significant conduction complications 6
- Did not exacerbate ventricular arrhythmias 6
- Had low rates of orthostatic hypotension 6
- Had no effect on pulse rate 6
Dose-Related Safety
At therapeutic doses up to 900 mg in unintentional single ingestions, bupropion outcomes are predominantly mild 7. Your patient's 150 mg daily dose is well below concerning thresholds. The median dose associated with seizures was 900 mg, with seizure risk being the primary concern rather than cardiac arrhythmias 7.
SVT-Specific Considerations
Bupropion does not appear on ACC/AHA/HRS lists of medications contraindicated or requiring caution in SVT 1. The comprehensive drug interaction tables for SVT management do not include bupropion among agents with SA/AV nodal effects or proarrhythmic potential 1.
Drug Interaction with Metoprolol
No clinically significant interactions exist between bupropion or mirtazapine and metoprolol. The SVT guidelines detail extensive drug-drug interactions for beta-blockers, and neither antidepressant appears in these lists 1. Metoprolol's side effects (nausea, fatigue) are unrelated to the antidepressants and should be addressed with her cardiologist independently.
Clinical Recommendation
Resume both medications as previously tolerated:
- Bupropion XL 150 mg daily: Excellent safety profile in cardiac patients, no SVT exacerbation risk 6
- Clonazepam 0.5 mg twice daily as needed: Continue for anxiety management
- Discontinue mirtazapine 7.5 mg: Reasonable if patient prefers, though cardiac concerns are not evidence-based at this dose
The patient's decision to stop all psychiatric medications due to "drug interaction concerns" was unnecessary and has resulted in untreated anxiety. Beta-blockers like metoprolol are actually recommended for SVT management and may help mitigate any theoretical tachycardic effects 1, 8.