Changing P wave polarity. Intermittent posterior internodal conduction

Role of lead aVR in evaluation of 12-lead electrocardiogram

Diagnostic information obtained from the evaluation of the unipolar lead aVR in electrocardiography (ECG) is not fully appreciated, and therefore, the lead aVR is often overlooked in the routine evaluation of the 12-lead ECG. Lead aVR may supplement clinical information, aiding in the management of several cardiovascular conditions. The role of the lead aVR in evaluation of various clinical conditions is reviewed.

Fine structure of cells and their histologic organization within internodal pathways of the heart: clinical and electrocardiographic implications

The fine structure of the normal internodal pathways was studied in 1 human and 2 canine hearts and correlated with histologic observations on more than 100 human and 10 canine hearts. From the electron microscopic studies six different kinds of myocardial cells were classified from two locations: the Eustachian ridge (posterior internodal pathway) and the Bachmann bundle (anterior internodal pathway). Five of the six kinds of cells (working myocardial cells, Purkinje-like cells, either broad or slender transitional cells and P cells, all previously described) were present in both locations. A sixth cell, pleomorphic and dark in appearance, with a special intertwined relation to P cells, is newly designated as an ameboid cell. It was found solely in the Eustachian ridge. In the same area a rare direct contact between a nerve and a myocardial cell was observed. The importance of these different kinds of cells, their respective cell connections, and their topographic locations inside the internodal pathways are discussed relative to certain functions such as rapid conduction and subsidiary pacemaking. The possible influence of these factors on clinical electrocardiographic changes is considered.