Narrow-Complex Tachycardia With Intermittent Irregularity and Variable QRS Morphology.

CASE SUMMARY: We describe a case of an 83-year-old patient presenting with palpitations and a serial electrocardiogram demonstrating narrow-complex tachycardia with varying regularity and QRS morphology. This case highlights the diagnostic value of serial electrocardiogram analysis and detailed QRS morphological assessment in elucidating underlying arrhythmia mechanisms, enabling accurate diagnosis of complex tachyarrhythmias.

TAKE-HOME MESSAGES: Serial electrocardiogram analysis, particularly tracking QRS morphology changes, provides critical insights beyond pattern recognition in arrhythmia diagnosis. Although common conditions present familiar patterns, detailed morphological evaluation reveals underlying mechanisms, enabling precise identification of complex arrhythmias and guiding targeted interventions.