Sinoatrial block a lag between the time that the SA node fires and actual depolarization of the atria. This rhythm is not recognizable on an ECG strip because a strip does not denote when the SA node fires. It can be detected only during an electrophysiology study when a small wire is placed against the SA node from within the heart and the electrical impulses can be recorded as they leave the p-cells in the centre of the node [ see pacemaker potential ], followed by observing a delay in the onset of the p wave on the ECG. Second degree SA
Lymph node and fixed macrophages. The subcapsular sinus has clinical importance as it is the most likely location where the earliest manifestations of a metastatic carcinoma in a lymph node would be found. The cortex of the lymph node is the outer portion of the node, underneath the capsule and the subcapsular sinus. It has an outer superficial part and a deeper part known as the paracortex. The subcapsular sinus drains to the trabecular sinuses, and then the lymph flows into the medullary sinuses. The outer cortex consists mainly of the B cells arranged as follicles, which may develop a germinal center