ECG Ch2 Flashcards
True or False, In most ECG leads, a normal Q wave is less than 0.04 second in duration and less than one third the amplitude of the R wave in that lead.
True. With the exception of leads III and aVR, a normal Q wave in the limb leads is less than 0.04 second (one small box) in duration and less than one third the height of the R wave in that lead. An abnormal (pathologic) Q wave is more than 0.04 second in duration or more than one third the height of the following R wave in that lead. Myocardial infarction is one possible cause of abnormal Q waves.
_____ is the ability of cardiac pacemaker cells to spontaneously initiate an electrical impulse without being stimulated from another source, such as a nerve.
The ability of cardiac pacemaker cells to create an electrical impulse without being stimulated from another source is called automaticity.
True or False, If the wave of depolarization (electrical impulse) moves toward the positive electrode, the waveform recorded on ECG graph paper will be upright (positive deflection).
True
How do you determine whether the atrial rhythm on an ECG tracing is regular or irregular?
To evaluate the regularity of the atrial rhythm on a rhythm strip, the interval between two consecutive P waves is measured.
_____ cells are working cells of the heart that contain contractile filaments and form the muscular layer of the atrial walls and the thicker muscular layer of the ventricular walls.
Myocardial cells (working or mechanical cells) contain contractile filaments.
_____ is a term used to describe the period of recovery that cells need after being discharged before they are able to respond to a stimulus.
Refractoriness is a term used to describe the period of recovery that cells need after being discharged before they are able to respond to a stimulus. In the heart, the refractory period is longer than the contraction itself.
In most patients, the sinoatrial (SA) and atrioventricular (AV) nodes are supplied by the _____ coronary artery.
The SA node receives its blood supply from the SA node artery that runs lengthwise through the center of the node. The SA node artery originates from the right coronary artery in about 60% of people. The AV node is supplied by the right coronary artery in 85% to 90% of the population.
True or False, Depolarization is the same as contraction.
False. Depolarization is not the same as contraction. Depolarization (an electrical event) is expected to result in contraction (a mechanical event).
The intrinsic rate of the atrioventricular (AV) bundle is _____ beats/min.
The AV bundle has pacemaker cells capable of firing at a rate of 40 to 60 beats/min.
Lead II records the difference in electrical potential between the _____ leg and _____ arm.
Lead II records the difference in electrical potential between the left leg and right arm electrodes. The positive electrode is placed on the left leg and the negative electrode is placed on the right arm.
What does the QRS complex represent?
When the ventricles are stimulated, a QRS complex is recorded on the ECG. Thus, the QRS complex represents ventricular depolarization.
True or False, In the limb leads, the ST segment is normally isoelectric, or less than 1 mm above or below the isoelectric line.
True. The normal ST segment begins at the isoelectric line, extends from the end of the S wave, and curves gradually upward to the beginning of the T wave.
On the ECG, the T wave represents _____.
Ventricular repolarization is represented on the ECG by the T wave.
On the ECG, the P wave represents atrial _____ and the QRS complex represents ventricular _____.
On the ECG, the P wave represents atrial depolarization and the QRS complex represents ventricular depolarization.
Leads II, III, and aVF view the _____ surface of the left ventricle.
Leads II, III, and aVF view the inferior surface of the left ventricle.
On an ECG, what is the first negative deflection seen after the P wave?
A QRS complex normally follows each P wave. The QRS complex begins as a downward deflection—the Q wave. A Q wave is always a negative waveform.
The portion of the ECG tracing between the QRS complex and the T wave is called the ____.
The portion of the ECG tracing between the QRS complex and the T wave is the ST segment.
The PR interval is considered prolonged if it is more than _____ seconds in duration.
A PR interval is considered short if it is less than 0.12 second and long if it is more than 0.20 second.
Which of the following is the first positive deflection seen on the ECG after the P wave?
If the QRS complex consists entirely of a positive waveform, it is called an R wave.
The normal pacemaker of the heart is the _____ node, which is found in the _____ atrium, and has an intrinsic firing rate of _____ beats/min.
The sinoatrial (SA) node is normally the primary pacemaker of the heart because it has the fastest firing rate of all of the heart’s normal pacemaker sites (60 to 100 beats/min).
