A 52-year-old woman with dilated cardiomyopathy (ejection fraction 25%) presents with recurrent episodes of rapid palpitations. Her 12-lead ECG during an episode shows a wide-complex tachycardia with a rate of 160 bpm. The QRS morphology varies beat-to-beat with changing axis. Blood pressure is maintained at 110/70 mmHg. What is the most likely diagnosis?

## Clinical Diagnosis **Key Point:** Polymorphic ventricular tachycardia (PVT) is characterized by continuously changing QRS morphology and axis on the same ECG strip, in contrast to monomorphic VT which maintains a fixed morphology. ## Distinguishing Features of Polymorphic vs Monomorphic VT | Feature | Monomorphic VT | Polymorphic VT | |---------|---|---| | **QRS morphology** | Fixed, identical | Varies beat-to-beat | | **Axis** | Fixed | Changing | | **Rate** | Usually 140–250 bpm | Often 150–300 bpm | | **Etiology** | Scar-related reentry (post-MI, cardiomyopathy) | Long QT, short QT, Brugada, catecholaminergic | | **Hemodynamics** | Often unstable if fast | May be stable initially | | **Treatment** | Amiodarone, ICD, ablation | Beta-blockers, ICD, correct QT | **High-Yield:** The phrase **"changing axis and morphology"** is pathognomonic for polymorphic VT. This patient's dilated cardiomyopathy is a risk factor for both types, but the ECG description (varying QRS morphology beat-to-beat) is diagnostic of polymorphic VT. ## Polymorphic VT in Cardiomyopathy ```mermaid flowchart TD A[Dilated cardiomyopathy]:::outcome --> B{Polymorphic VT?}:::decision B -->|Yes| C{QT interval normal?}:::decision C -->|Yes| D[Catecholaminergic PVT or structural]:::outcome C -->|No: Prolonged| E[Long QT syndrome]:::outcome C -->|No: Short| F[Short QT or Brugada]:::outcome A --> G[Monomorphic VT risk]:::outcome G --> H[Scar-based reentry]:::outcome ``` **Clinical Pearl:** In a patient with dilated cardiomyopathy presenting with polymorphic VT: 1. Check the QT interval (normal, prolonged, or short). 2. Obtain genetic testing if family history of sudden cardiac death. 3. Initiate beta-blockers and consider ICD for secondary prevention. 4. Avoid QT-prolonging drugs (antiarrhythmics, antipsychotics). **Mnemonic: "POLYMORPHIC = Pleomorphic (many forms)"** — the QRS shape changes from beat to beat, like a shape-shifter. In contrast, monomorphic VT is "monotonous" — same shape every time. **Warning:** Do not confuse polymorphic VT with atrial fibrillation with rapid ventricular response; AF has irregular intervals and chaotic baseline, whereas PVT has a regular or semi-regular rate with organized (albeit changing) QRS complexes.