Cardiac orientation: Is there a correlation between the anatomical and the electrical axis of the heart?

Abstract

Data have suggested that in vivo cardiac orientation has the greatest effect on the cardiac electric field, and, thus, surface electrical activity. We sought to determine the correlation between in vivo cardiac orientation using cardiac computed tomography (CT) and the electrical cardiac axis in the frontal plane determined by surface electrocardiogram (ECG). Patients aged between 30 and 60 years old with a normal body mass index (BMI), who underwent CT coronary angiography between July 2010 and December 2012 were included. Patients with diabetes, hypertension, arrhythmias, structural heart disease or thoracic deformities were excluded. In vivo cardiac orientation was determined along the long axis and correlated with the electrical cardiac axis on surface ECG. There were 59 patients identified, with 47% male, mean age of 49.9 years and a mean BMI of 22.39 kg/m2. The mean cardiac axis on CT was 38.1 ± 7.8°, while the mean electrical cardiac axis on ECG was 51.8 ± 26.6°. Bi-variate analysis found no correlation between the two readings (Pearson r value 0.12, p=0.37). We conclude, there is no simple relationship between the anatomical cardiac axis and the ECG determined electrical axis of the heart. The electrical axis of the heart, however, showed more variability, reflecting possible underlying conduction disturbances.