Electrocardiography in Bitches with Mammary Tumors
Authors: Bahr Arias Gabriela , De Oliveira Mariângela Kilpp Gomes , Schnitzer Josiana de Fátima , Di Santis Giovana Wingeter , Martins Maria Isabel Mello , Gava Fábio Nelson 
Published: December 2021

Background: The incidence of cancer has increased due to greater longevity of the animals as a consequence of better control of other diseases, improvement of nutrition and good practices in preventive medicine. Malignant tumors can cause paraneoplastic syndrome as hypercalcemia, anemia, cachexia, among others and consequent cardiovascular disorders. The electrocardiography (ECG) is a complementary exam that can reveal with its traces these rhythms disorders.  Based on that, the objective of this study was to evaluate the ECG in bitches with mammary tumors in order to detect in which type of tumor would be found significant changes as in cardiac rhythm, ECG waves, segments or cardiac axis.Material, Methods & Results: Twenty-nine female dogs were used in this study, being 19 bitches with mammary tumor, and they were allocated in three groups: G1: control group (n=10), G2: benign neoplasia group (n=6) and G3: malignant neoplasia group (n=13). The most prevalent type of neoplasia in G2 was the benign mixed tumor (83%), followed by adenoma (17%) whereas in G3: carcinoma in mixed tumor (61%); papillary carcinoma (23%). Regarding cardiac rhythm, it was found sinus arrhythmia (SA) and normal sinus rhythm (NS): G1: 50% SA and 50% NS; G2: 67% SA and 33% NS; G3: 54% SA and 46% NS. No ventricular or atrial arrhythmias were detected. For other parameters in G1, G2 and G3, respectively (mean±Std error): FC (bpm): 110±9.2, 120±8.5, 124±7,5; P (ms): 48±1.6, 51±1.8, 50±1.2; P (mV) 0.19±0.02, 0,2±0.02, 0,19±0.02; PR (ms): 94±4.3, 93±5.5, 89±3.9; QRS (ms): 56±1.54, 60±4, 62±1.2; R (mV): 1.1±0.06, 1.2±0.24, 0.9±0.13; QT (ms): 203±9.4; 204±7.9; 182±15.6; and cardiac axis (°): 66±6.2, 61±7.9, 70±7.5. There were no significant differences for all cardiac parameters and also for ST interval and T wave morphology.Discussion: All electrocardiographic parameters found are in accordance with other studies carried out in the canine species. The results regarding tumor types differ from what was found in another study, in which in 18 bitches with mammary tumors, 55% were benign, with prevalence of adenomas (38%) followed by benign mixed tumors, and 45% malignant, with adenocarcinoma prevailing (22%). In another study, it was verified in 63 bitches the predominance of tubular carcinoma (26.56%) and carcinoma in mixed tumor (23.44%). Diverging from the electrocardiographic parameters of this study, a significant difference was found in the R wave amplitude value in the research by Barros et al., (2015) who performed computerized electrocardiography in 50 dogs, not only with mammary neoplasms (55% mammary carcinomas), but also in mastocytomas, lymphomas, benign tumors and other sarcomas. This author found out that the R wave amplitude values of the neoplasia group were lower when compared to the control group. In addition, we suspect that other types of tumors could result in more paraneoplastic syndrome than the mammary neoplasms found in this research. Neoplasms as lymphomas (T cells), apocrine gland anal sac adenocarcinomas, multiple myelomas and thymomas are known as a cause of hypercalcemia of malignancy and histiocytic sarcomas, myelomas, leukemia and lymphomas causing anemia. In conclusion, ECG has no changes in benign or malignant mammary tumors in dogs. However, this fact does not exclude the importance of its performance in pre-anesthetic evaluations.