Diagnostic Accuracy of the Electrocardiogram for Detection of Atrial and Ventricular Overloads in Dogs

Background: Analysis of the electrocardiogram may suggest atrial and ventricular overloads. However, it has a low sensitivity and specificity for diagnosis of cardiac chamber overload. The accuracy of electrocardiographic interpretation can be improve using new cut-offs for the duration and amplitude of the electrocardiographic waves. Our objective was to evaluate the use of the electrocardiogram in the diagnosis of atrial and ventricular overload, using echocardiography as the gold standard test for the diagnosis of atrioventricular overload. We aimed to define new cut-off values that would increase the sensitivity and specificity of the electrocardiogram for diagnosis of chamber overload in dogs.Materials, Methods & Results: Eletrocardiogram records were obtained in 81 dogs divided into 3 groups: Group 1A (healthy dogs 10 kg); Group 1B (dogs 10 kg with mitral or tricuspid valve disease); Group 2 (dogs weighing between 10.1 and 20 kg) and Group 3 (dogs > 20.1 kg). Duration in milliseconds (ms) and amplitude in millivolts (mV) of P waves and QRS complexes, PR and QT segment, T wave amplitude and ST segment were evaluated in lead DII. Using leads I and III, the mean cardiac electrical axis in the frontal plane, expressed in degrees, was determined as the mean of three consecutive measurements. For Group 1A and 1B the duration of P wave was < 45 ms and QRS duration < 55 ms. In Group 2 the duration of P wave was < 47 ms and QRS duration < 57 ms. In Group 3 the duration of P wave was < 50 ms and duration QRS < 64 ms. These values (duration of P wave and QRS duration) were compared with echocardiographic measurements of the left atrium, considering the reference value AE/Ao < 1.4 and measurements of the left ventricle in M-mode according to the body weight, respectively. A P wave amplitude < 0.4 mV suggested that the right atrium size was normal and this was compared with the area of the right atrium measured on the echocardiogram. The right ventricle was assessed using the amplitude of S wave and right axis deviation and compared with the right ventricular area obtained by echocardiography. The reference value of the right atrium and right ventricle is according to the body weight. For both the right and left atria, there was concordance between the diagnoses with electrocardiography and echocardiography. For the right and left ventricle was no agreement between the diagnoses. All criteria examined had low sensitivities, usually with high specificities. But it was not possible to determine a new cut-off that would improve the sensitivity of the electrocardiogram for diagnosis of atrial and ventricular overload in dogs. Discussion: The electrocardiogram analysis produced false interpretations for the measures indicative of atrioventricular overloads and should not be used alone, for diagnosis of cardiac chamber overload. The standard electrocardiographic reference values, for P wave duration and amplitude, were excellent for identification of normal atrial size. However, QRS duration, R wave amplitude (dependent of the dog’s weight) and S wave amplitude, associated with cardiac electrical axis cannot be used for diagnosis of ventricle overload. Electrocardiographic analysis should not be used as a tool to assess cardiac chamber overload, which should be diagnosed by echocardiography and clinical investigation. Based on our findings echocardiogram is the gold standard test indicated to identify overload of cardiac chambers.