Differential diagnosis for polymorphous VT?

• A. Pulmonary embolism and pneumonia
• B. Atrial flutter, AVNRT, pericardial effusion
• C. Sinus tachycardia only
• D. VF/VT, toxic ingestion, hyperkalemia

Answer: (D)

Polymorphic VT is a ventricular tachyarrhythmia where the QRS morphology changes from beat to beat, reflecting a dynamic substrate or varying triggers. The key idea when evaluating this rhythm is to look for causes that can abruptly alter repolarization or conduction and provoke beat-to-beat changes or rapid degeneration to worse rhythms. The most pertinent contributors are disturbances that directly provoke ventricular irritability or destabilize the rhythm, such as the rhythm itself being present (VF/VT) and factors that can trigger or worsen ventricular arrhythmias: toxic ingestions that interfere with cardiac electrophysiology and electrolyte abnormalities that profoundly affect conduction and repolarization, like hyperkalemia.

Pulmonary embolism, pneumonia, or pericardial effusion, while they can cause acute symptoms and other rhythm disturbances, do not typically present as primary causes of polymorphic VT with beat-to-beat variability. Sinus tachycardia is a regular rhythm and does not produce the polymorphic pattern. In contrast, seeing polymorphic VT prompts urgent consideration of these drivers: the arrhythmia itself as a potential rhythm you’re trying to identify or manage, toxins that can provoke ventricular irritability, and severe electrolyte disturbances such as hyperkalemia that disrupt normal conduction and repolarization and can precipitate VT or degenerate into VF.