Exam 1 Review: Chapter 18: Electrocardiogram
electrocardiogram = ECG or EKG - A diagnostic test which records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.
Einthoven's triangle - An imaginary equilateral triangle with the heart at its centre, its equal sides representing the three standard limb leads of the electrocardiogram.
electrocardiograph - The output of an ECG which records the electrical activity of the heart on the Y axis and time on the X axis; it is a complex curve whose deflection points are noted by the letters P, Q, R. S, and T.
deflection waves - The three characteristic segments of the electrocardiograph which distinguish the main electrochemical events of the cardiac cycle, the P wave denoting depolarization of the SA node and the depolarization (contraction) of the atria; the QRS wave, denoting ventricular depolarization (contraction) while masking the simultaneous repolarization (relaxation) of the atria; and the T wave which denotes the repolarization (relaxation) of the ventricles.
P wave - The first of the three deflection waves of the electrocardiograph which denotes depolarization of the SA node and the depolarization (contraction) of the atria.
atrial depolarization - The coordinated transmission of the stimulus for the contraction of the atria which is carried from the sino-atrial node throughout the walls of the atria by conduction fibers; the event may be referred to as atrial systole and is denoted on the electrocardiograph by the P wave.
QRS complex - The second of the three deflection waves of the electrocardiograph which denotes ventricular depolarization (contraction) while masking the simultaneous repolarization (relaxation) of the atria.
ventricular depolarization - The coordinated transmission of the stimulus for the contraction of the ventricles which is carried from the atrio-ventricular node throughout the walls of the ventricles by the bundle and conduction fibers; the event may be referred to as ventricular systole and is denoted on the electrocardiograph by the QRS complex; contraction proceeds from the apex of the heart to the base of the heart.
T wave - The third of the three deflection waves of the electrocardiograph which denotes the repolarization (relaxation) of the ventricles.
ventricular repolarization - The restoration of the resting potential in the ventricular myocardium which begins with the closure of the slow calcium channels and the opening of the potassium channels; repolarization proceeds from the apex of the heart to the base of the heart.
P-Q (PR) interval - The time period indicated on the electrocardiograph encompassing atrial depolarization up to but not including the start of ventricular depolarization; a major portion of the PR interval reflects the slow conduction through the AV node which is controlled by the sympathetic-parasympathetic balance within the autonomic nervous system. (If the PR Interval is longer than 0.22 secs, it is called a Prolonged PR Interval and may indicate the presence of an AV Block.)
S-T segment - The pause after the QRS Complex - the interval between the end of the QRS Complex and the beginning of the T wave; it symbolizes the end of ventricular depolarization to the start of ventricular repolarization. (When the ST Segment is elevated in a patient with known disease, it is usually a sign of an evolving transmural infarction - an MI in progress.)
Q-T interval - The time period indicated on the electrocardiograph encompassing the time from the beginning of the Q or R wave through the end of the T wave; it represents 40% of the normal cardiac cycle whether at rest or during exercise.
stress electrocardiogram - A diagnostic electrocardiogram (ECG or EKG), performed to measure how the heart rate, heart rhythm, and blood pressure change during exercise; it is often done while the subject walks or runs on a treadmill or rides on an exercise bike; it may show problems in the heart that do not show up on a resting electrocardiogram but appear only during exercise, when the heart is working harder and needs more oxygen. aka - exercise stress test
Sketch and Label:
7. the waves, intervals, & segments of a normal ECG.
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Describe:
4. the relationship between the electrical activity of the heart and ECG.
| The electrical activity of the heart is due to the series of ion flows (Na+, Ca++, K+, etc.) which occur as cardiac muscle depolarizes and repolarizes. The electrocardiograph detects these electrical events at the surface of the body and translates them into a graph with voltage potential changes depicted on the Y axis and time on the X axis. The specific relationships between individual waves are summarized below: | ||||||||||||||||
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