Electrocardiographic Identification and Correction of Left Ventricular Pacing Latency.

Pacing latency, defined as the delay between a pacemaker stimulus and myocardial depolarization, is an uncommon but clinically relevant phenomenon in patients with permanent pacing systems. Its presence may be mistaken for a lead malfunction, exit block, or device failure, leading to unnecessary interventions. A 55-year-old male with a history of nonischemic dilated cardiomyopathy (left ventricular [LV] ejection fraction-30% on standard two-dimensional echocardiography; 17% on speckle-tracking assessment) and severe systolic dysfunction, previously implanted with a cardiac resynchronization therapy with defibrillator (CRT-D), was admitted with progressive abdominal distension, bilateral lower limb edema, and weight gain of 5-6 kg over 2 weeks. Examination revealed hypotension (90/60 mmHg), elevated jugular venous pressure, pedal edema, and basal crepitations. Laboratory evaluation showed elevated N-terminal pro-B-type natriuretic peptide (4750 pg/mL). He was treated with intravenous diuretics and guideline-directed medical therapy, resulting in clinical improvement and weight reduction from 75 to 70 kg. During hospitalization, device interrogation confirmed stable parameters. However, a 12-lead electrocardiography demonstrated consistent pacing latency with an 80 ms delay between the pacing spike and QRS onset. Electrolytes were normal, and no offending medications were identified. The patient was discharged in New York Heart Association Functional Class II after symptomatic improvement. This case highlights the mechanical and electrophysiological consequences of LV pacing latency in a patient with CRT-D and worsening heart failure. Pacing latency required active correction to restore effective biventricular resynchronization. Recognition of this entity is essential to guide targeted device optimization and prevent unnecessary interventions. Advanced echocardiographic techniques play a critical complementary role in assessing the mechanical impact of pacing latency and the efficacy of its correction.