The
electrocardiogram (ECG or EKG) records
the electrical activity of the heart. The ECG is used to
measure the rate and regularity of heartbeats, as well as the size and position
of the chambers, the presence of any damage to the heart, and the effects of drugs
or devices used to regulate the heart, such as a pacemaker.
During each heartbeat, a healthy heart will
have an orderly progression of electrical activity that starts in the pacemaker
(natural or artificial), spreads through the upper chambers and then travels to
the lower chambers. The lower chambers (ventricles) provide the main pumping
action of the heart.
The ECG can measure and diagnose abnormal heart
rhythms caused by electrolyte imbalance or damage to the heart muscle. In the
event of a heart attack, the damaged area can be identified. The ECG can also
discern scar tissue resulting from a heart attack.
Serial ECGs are a valuable diagnostic tool.
Comparison of an ECG during chest pain to one performed during a health
examination can help determine if the chest pain is cardiac. In the case of a
heart attack, the progression can be mapped over time or can monitor
therapeutic interventions.
The ECG is also of great value in evaluating
valvular heart disease, thickening of the heart wall and inflammation around
the heart. A stress test will measure
electrical activity when the heart is working hard, a resting ECG is just that.
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