Key Points
- Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
- Set objective targets and reassess frequently.
- Plan definitive source control or disease‑specific therapy when indicated; document follow‑up and patient education.
Algorithm
- If unstable → defibrillate; give IV magnesium immediately.
- Replete K/Mg/Ca; stop QT-prolonging agents; correct bradycardia with pacing/isoproterenol.
- Address underlying causes; consider ICD for congenital or recurrent high-risk cases.
Clinical Synopsis & Reasoning
Polymorphic VT with prolonged QT requires IV magnesium sulfate regardless of serum level, aggressive potassium repletion, and cessation of QT-prolonging drugs. Unstable patients need immediate defibrillation; recurrent cases benefit from overdrive pacing or isoproterenol if pause-dependent.
Treatment Strategy & Disposition
Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced/procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.
Epidemiology / Risk Factors
- Risk varies by comorbidity and precipitants; see citations for condition‑specific data.
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|
| ECG with QTc measurement and rhythm monitoring | Diagnosis | Prolonged QT with twisting QRS amplitude | Identify triggers |
| Electrolytes (K/Mg/Ca) and drug screen | Etiology | Correct abnormalities; stop culprits | — |
| Echo/genetics (selected) | Risk | Structural disease or congenital LQTS | — |
High-Risk & Disposition Triggers
| Trigger | Why it matters | Action |
|---|
| Hemodynamic instability or sustained polymorphic VT | Sudden death risk | Immediate defibrillation; ICU |
| Prolonged QTc >500 ms with syncope | High risk | IV magnesium; stop QT-prolonging drugs |
| Bradycardia-triggered TdP | Pause-dependent | Overdrive pacing or isoproterenol |
| Electrolyte abnormalities (low K/Mg/Ca) | Arrhythmogenic | Aggressive repletion |
| Congenital LQTS | Genetic risk | Beta-blockers; ICD consideration |
Pharmacology
| Medication/Intervention | Mechanism | Onset | Role in Therapy | Limitations |
|---|
| Magnesium sulfate 2 g IV over 10–15 min (repeat) | Stabilization | Minutes | First-line therapy | Even if normal Mg |
| Aggressive potassium repletion to 4.5–5.0 | Antiarrhythmic milieu | Hours | Reduce ectopy | — |
| Overdrive pacing or Isoproterenol infusion | Rate acceleration | Minutes | Treat pause-dependent TdP | Avoid in ischemia |
Prognosis / Complications
- Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.
Patient Education / Counseling
- Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.
References
- AHA/ACC arrhythmia statements — Link