417 DOI: 10.5935/2359-4802.20150061 Internacional Journal of Cardiovascular Sciences. 2015;28(5):417-423 Corresponding author: Carlos Henrique Miranda Rua Bernardino de Campos, 1000 – Centro – 14015-130 – Ribeirão Preto, SP – Brazil E-mail: chmiranda@fmrp.usp.br Diagnostic Accuracy of the P Wave in the Lewis and Gallop Leads for Atrial Enlargement Detection Carlos Henrique Miranda 1 , Gustavo P Gerolim 2 , Ana Marta Salgado Gali 3 , Antônio Pazin-Filho 1 1 Universidade de São Paulo – Faculdade de Medicina de Ribeirão Preto – Departamento de Clínica Médica – Divisão de Emergências Clínicas – Ribeirão Preto, SP – Brazil 2 Universidade de São Paulo – Hospital das Clínicas – Serviço de Ecocardiografia – Ribeirão Preto, SP – Brazil 3 Universidade de São Paulo – Faculdade de Medicina de Ribeirão Preto – Departamento de Clínica Médica – Divisão de Cardiologia – Ribeirão Preto, SP – Brazil Background: The diagnostic accuracy (DA) of the conventional electrocardiogram (ECG) for detecting atrial enlargement (AE) is low. Lewis (L) and Gallop (G) enable better viewing the P wave in the ECG. Objective: Checking whether the P wave parameters in the leads of Lewis and Gallop increase the diagnostic accuracy of the conventional ECG AE criteria. Methods: The P wave characteristics in the L and G leads were standardized in 27 healthy individuals. The percentile of 99 was considered as limit of normality for those parameters. These new criteria were evaluated in 117 patients through conventional ECG and the L and G leads. The atrial sizes under the echocardiogram were considered as golden standard for defining the AE. The area under the ROC (receiver operating characteristic) curve (AUC) was used for determining the DA of each parameter. Results: Conventional ECG presented low DA for detecting the AE. Morris index was the only showing significant DA: AUC 0.57 (95%CI: 0.48-0.66); p=0.03. The inclusion of the P wave >100 ms (L and G) has not increased the DA for detecting left AE compared to the traditional criteria: AUC 0.58 (95%CI: 0.50-0.65) vs. AUC 0.57 (95%CI: 0.49-0.65); p=0.80. Including P wave with amplitude >2 mm (L) and/or >3 mm (G) has not increased DA for detecting right AE either: AUC 0.53 (95%CI: 0.46-0.61) vs. AUC 0.53 (95%CI: 0.45-0.60); p=0.31. Conclusion: Including the P wave in the accessory leads of L and G did not result in increment of DA for detecting AE. Keywords: Electrocardiography; Atrial function, left; Atrial function, right Abstract Manuscript received on October 19, 2015; approved on November 02, 2015; revised on November 30, 2015. ORIGINAL MANUSCRIPT Introduction Detecting atrial enlargement, especially that of the left atrial function, is important during the clinic evaluation, considering that its presence may identify individuals with higher risk of developing atrial fibrillation 1-3 . The electrocardiographic criteria normally used for evaluating atrial enlargement present low diagnostic accuracy 4 . Lewis (L) and Gallop (G) accessory leads were described in the past century and enable better viewing the P wave in the surface electrocardiogram. Those bipolar accessory leads are attained by placing the electrodes of the upper limbs on the chest, the electrode of the right arm being placed on the second right parasternal intercostal space, and the left arm electrode, on the fourth right parasternal intercostal space in Lewis, and on the left parasternal in Gallop 5 . The objective of this study was verifying whether the use of the P wave electrocardiographic parameters attained