The ability to recognize normal and abnormal cardiac rhythms, called dysrhythmias, is
an essential skill for the nurse.
Four properties of cardiac cells (automaticity, excitability, conductivity, and contractility)
enable the conduction system to initiate an electrical impulse, transmit it through the
cardiac tissue, and stimulate the myocardial tissue to contract.
o A normal cardiac impulse begins in the sinoatrial (SA) node in the upper right
o The signal is transmitted over the atrial myocardium via Bachmann’s bundle and
internodal pathways, causing atrial contraction.
o The impulse then travels to the atrioventricular (AV) node through the bundle of
His and down the left and right bundle branches, ending in the Purkinje fibers,
which transmit the impulse to the ventricles, resulting in ventricular contraction.
The autonomic nervous system plays an important role in the rate of impulse formation,
the speed of conduction, and the strength of cardiac contraction.
o Components of the autonomic nervous system that affect the heart are the right
and left vagus nerve fibers of the parasympathetic nervous system and fibers of
the sympathetic nervous system.
The electrocardiogram (ECG) is a graphic tracing of the electrical impulses produced in
ECG waveforms are produced by the movement of charged ions across the
semipermeable membranes of myocardial cells.
There are 12 recording leads in the standard ECG.
o Six of the 12 ECG leads measure electrical forces in the frontal plane (leads I, II,
III, aVR, aVL , and aVF).
o The remaining six leads (V thr1ugh V ) me6sure the electrical forces in the
horizontal plane (precordial leads).
o The 12-lead ECG may show changes that are indicative of structural changes,
damage such as ischemia or infarction, electrolyte imbalance, dysrhythmias, or
Continuous ECG monitoring is done using leads II, V , 1nd MCL . 1
o MCL is a1modified chest lead that is similar to V an1 is used when only three
leads are available for monitoring.
o Monitoring leads should be selected based on the patient’s clinical situation.
The ECG can be visualized continuously on a monitor oscilloscope, and a recording of
the ECG (i.e., rhythm strip) can be obtained on ECG paper attached to the monitor. ECG leads are attached to the patient’s chest wall via an electrode pad fixed with
electrical conductive paste.
Telemetry monitoring involves