Contractility
the ability of atrial and ventricular muscle cells to shorten their fiber length in response to electrical
stimulation, causing sufficient pressure to push blood forward through the heart. In other words, this is
the mechanical activity of the heart.
AV Node
where impulses slow down or are delayed before proceeding to the ventricles. This delay is reflected in
the PR segment on the ECG. This slow conduction provides a short delay, allowing the atria to contract
and the ventricles to fill.
SA Node
the heart’s primary pacemaker. It can spontaneously and rhythmically generate electrical impulses at a
rate of 60-100 beats per min and therefore has the greatest degree of automaticity.
Purkinje Cells
composed of the bundle of HIS, bundle branches, and these fibers. Responsible for the rapid conduction
of electrical impulses throughout the ventricles, leading to ventricular depolarization and the
subsequent ventricular muscle contraction.
Semi-Reclined
While obtaining a 12-lead ECG, remind the patient be as as still as possible in a
____________ position, breathing normally.
Clea, Dry, Moist
For continous ECG monitoring, be sure to ______ skin and clip hairs/shave. Ensure that
the electrode placement is _ and the gel on each electrode is __ and fresh.
P Wave
a deflection on an ECG representing atrial depolarization. When the electrical impulse is consistently
generated form the SA node, this wave has a consistent shape in a given lead. If an impulse is then
generated from a different (ectopic) focus, such as atrial tissue, the shape of this wave changes in the
lead, indicating that an ectopic focus has fired.
PR Segment
the isoelectric line from the end of the P wave to the beginning of the QRS complex, when the electrical
impulse is traveling through the AV node, where it is delayed.
PR Interval
measured form the beginning of the P wave to the end of the PR segment. Represents the time required
for atrial depolarization, the impulse delay in the AV node, and the travel time to the Purkinje files.
Normally measures from 0.12-0.20 seconds (five small blocks).