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
Sentinel node list, can be simplified remarkably using a sentinel node to demarcate the beginning and end of the list. Following is a Python implementation of a circular doubly-linked list: Notice how the codice_13 method takes the node that will be displaced by the new node in the parameter codice_14. For appending to the left, this is the head of a non-empty list, while for appending to right, it is the tail. But because of how the linkage is setup to refer back to the sentinel, the code just works for empty lists as well, where codice_14 will be the sentinel node.