BPK 105 Study Guide - Final Guide: Qrs Complex, Qt Interval, Stroke Volume
27 Apr 2018
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Modules 7 & 8 - Review Questions - Part 5
9. Draw a typical Electrocardiogram (ECG) trace. Label each of the phases and describe
the electrical and contractile events in the heart during each phase. [6 marks]
Refer to figure 12.16 in textbook.
Electrocardiogram
Action potentials conducted through the heart during the cardiac cycle produce electrical
currents that can be measured at the surface of the body. Electrodes placed on the body
surface and attached to a recording device can detect the small electrical changes resulting
from the action potentials in all of the cardiac muscle cells. The record of these electrical events
is an electrocardiogram (figure 12.16).
- The normal ECG consists of a P wave, a QRS complex, and a T wave.
- The P wave results from depolarization of the atrial myocardium, and the beginning of
the P wave precedes the onset of atrial contraction.
- The QRS complex consists of three individual waves: the Q, R, and S waves. The
QRS complex results from depolarization of the ventricles, and the beginning of
the QRS complex precedes ventricular contraction.
- The T wave represents repolarization of the ventricles, and the beginning of the T
wave precedes ventricular relaxation. A wave representing repolarization of the atria
cannot be seen because it occurs during the QRS complex.
The time between the beginning of the P wave and the beginning of the QRS complex is the
PQ interval, commonly called the PR interval because the Q wave is very small. During the PQ
interval, the atria contract and begin to relax. At the end of the PQ interval, the ventricles
begin to depolarize.
The QT interval extends from the beginning of the QRS complex to the end of the T wave
and represents the length of time required for ventricular depolarization and
repolarization.
The ECG is not a direct measurement of mechanical events in the heart, and neither the force
of contraction nor the blood pressure can be determined from it. However, each deflection in the
ECG record indicates an electrical event within the heart and correlates with a subsequent
mechanical event.
10. After six months of training an individual has a lower resting heart rate than she did
prior to training when running at the same speed. Her cardiac output, however, is
essentially the same. What do you think accounts for this? Define cardiac output and its
components in your answer. Do you think her resting HR is different after training? Why?
[4 marks]
Document Summary
Modules 7 & 8 - review questions - part 5: draw a typical electrocardiogram (ecg) trace. Label each of the phases and describe the electrical and contractile events in the heart during each phase. Action potentials conducted through the heart during the cardiac cycle produce electrical currents that can be measured at the surface of the body. Electrodes placed on the body surface and attached to a recording device can detect the small electrical changes resulting from the action potentials in all of the cardiac muscle cells. The record of these electrical events is an electrocardiogram (figure 12. 16). The normal ecg consists of a p wave, a qrs complex, and a t wave. The p wave results from depolarization of the atrial myocardium, and the beginning of the p wave precedes the onset of atrial contraction . The qrs complex consists of three individual waves : the q, r, and s waves.
