CHAPTER 30Origin of the Heartbeat & the Electrical Activity of the Heart 505the QRS complex (ventricular depolarization), and the T wave
(ventricular hyperpolarization). Various arrhythmias can be de-
tected in irregular ECG recordings.
■ Because of the contribution of ionic movement to cardiac mus-
cle contraction, heart tissue is sensitive to ionic composition of
the blood. Most serious are increases in [K+] that can produce
severe cardiac abnormalities, including paralysis of the atria and
ventricular arrhythmias.MULTIPLE-CHOICE QUESTIONS
For all questions, select the single best answer unless otherwise directed.
- Which part of the ECG (eg, Figure 30–5) corresponds to ventric-
ular repolarization?
A) the P wave
B) the QRS duration
C) the T wave
D) the U wave
E) the PR interval - Which of the following normally has a slowly depolarizing
“prepotential”?
A) sinoatrial node
B) atrial muscle cells
C) bundle of His
D) Purkinje fibers
E) ventricular muscle cells - In second-degree heart block
A) the ventricular rate is lower than the atrial rate.
B) the ventricular ECG complexes are distorted.
C) there is a high incidence of ventricular tachycardia.
D) stroke volume is decreased.
E) cardiac output is increased.
4. Currents caused by opening of which of the following channels
contribute to the repolarization phase of the action potential of
ventricular muscle fibers?
A) Na+ channels
B) Cl– channels
C) Ca2+ channels
D) K+ channels
E) HCO 3 – channels
5. In complete heart block
A) fainting may occur because the atria are unable to pump
blood into the ventricles.
B) ventricular fibrillation is common.
C) the atrial rate is lower than the ventricular rate.
D) fainting may occur because of prolonged periods during
which the ventricles fail to contract.
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