29-09-2012, 10:31 AM
Event Detection
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Epochs in an ECG waveform:
The P wave:
Contraction of the atria triggered by the SA node.
The PQ segment:
AV node provides delay to facilitate completion of
atrial contraction and transfer of blood to ventricles
before ventricular contraction is initiated.
Normally flat or isoelectric.
The QRS wave:
Purkinje fibers stimulate contraction of ventricles.
The ST segment:
Normally flat or isoelectric
– related to the plateau
in action potential of left ventricular muscle cells.
Myocardial ischemia or infarction could change the
action potentials of left ventricular musculature:
ST segment depressed or elevated.
The T wave:
Related to the last phase of the
action potential of ventricular muscle cells:
ventricular repolarization or relaxation.
The first heart sound S1:
S1 reflects a sequence of events related to
ventricular contraction —
closure of the atrioventricular
valves,
isovolumic contraction,
opening of the semilunar valves, and
ejection of the blood from the ventricles.
Murmurs:
Systolic murmur of aortic stenosis—
turbulent ejection of blood from the left ventricle
through a restricted opening of the aortic valve.
Diastolic murmur in case of aortic insufficiency —
regurgitation of blood from the aorta back into the
left ventricle through a leaky aortic valve.
The dicrotic notch in the carotid pulse
Closure of the aortic valve causes a sudden drop in
aortic pressure on a downward slope at end of systole.
Dicrotic notch in the carotid pulse is a delayed, upstream
manifestation of the incisura in the aortic pressure wave.