Background: Left atrial (LA) size and function are routinely quantified by echocardiography using left atrial volume index (LAVI) and speckle-tracking LA strain. Electrocardiographic (ECG) criteria, such as P-wave duration, notching (“P-mitrale”), and P-wave terminal force in V1 (PTFV1), are widely used as low-cost surrogates, yet their agreement with echo-defined enlargement or dysfunction remains debated. Objective: To synthesize evidence comparing ECG criteria of “left atrial enlargement (LAE)” against echo-measured LA volume and/or LA strain, and to appraise diagnostic thresholds and clinical utility. Methods: Following PRISMA guidance, we searched major databases to October 19, 2025. We included original studies in adults that directly compared ECG indices with transthoracic echo reference standards (2D/3D LAVI and/or LA strain). Twelve studies met inclusion for the results synthesis; 10 additional papers informed background and interpretation. Results: Across heterogeneous cohorts, traditional ECG LAE criteria showed modest sensitivity and variable specificity for detecting increased LAVI. PTFV1 and P-wave peak time correlated most consistently with LAVI, while LA strain (reservoir) related inversely to P-wave indices and PTFV1. Proposed ECG cutoffs differed by population (hemodialysis vs. hypertension vs. valvular disease). Conclusions: ECG abnormalities reflect atrial electrical remodeling but incompletely capture echo-defined atrial dilation or dysfunction. Multiparametric ECG assessment may aid triage, yet LAVI and LA strain remain the reference for diagnosis and risk stratification.