Atrial T (Ta) loop in patients with A-V block: a trial to differentiate normal and abnoral groups.

The P and the Ta waves were recorded with high fidelity and high amplification. The P and the Ta loops were constructed from these waves. Human subjects with A-V block were used, so that the Ta waves could be completely visualized. Subjects were separated into two groups: one group with minimal clinical evidence of heart disease and another with more severe disease. There were great and important differences in the Ta loops between the two groups with minimal differences in the P loops. In the patients with minimal heart disease, the Ta loop was always oriented to the right and superiorly. The P-Ta angle was approximately 180 degrees and all patients in this group showed a small spatial atrial gradient oriented to the left and inferiorly. These findings are similar to those found in normal dogs reported separately in the Journal. In the group of four patients with more severe heart disease, the P-Ta angle varied widely and deviated greatly form 180 degree. The satial atrial gradient was very large in three cases. The findings and others such as the direction of the maximum Ta vectors were diagnostically useful in separating the Ta loops of the two patient groups. Results indicate that the Ta loop may be very useful in separating normal from diseased atria in individuals with A-V block. There are some frequency differences between the Ta wave and the QRS complex. If the Ta wave could be extracted from the QRS complex by the use of some kind of filter when A-V block dose not exist, most of the Ta wave could be visualized. This, along with high fidelity recording techniques, may help detect atrial abnormalities in patients without A-V block. Future development of this equipment as a clinical tool is hoped for.