CHAPTER 2 • ELECTRICAL ACTIVITY OF THE HEART
For each question, choose the one best
Which one of the following depolar-
izes the resting membrane potential in a
a. Decreased calcium conductance
b. Decreased sodium conductance
c. Increased potassium conductance
d. Inhibition of the sarcolemmal Na+/K+-
In nonnodal cardiac tissue, fast sodium
channels are inactivated
a. During phase 0.
b. When the h-gates open.
c. By slow depolarization of the cell.
d. More slowly than L-type calcium
channels are inactivated.
The relative potassium conductance
is highest during which of the fol-
lowing phases of a ventricular action
a. Phase 0
b. Phase 2
c. Early phase 3
d. Late phase 4
The rate of sinoatrial (SA) nodal action
potential firing increases during exercise.
Which of the following mechanisms can
cause this increase in rate?
a. P-adrenoceptor activation increasing
“funny” currents (If)
b. Decreasing the slope of phase 4 by
vagal (parasympathetic) activation
c. Inactivation of fast sodium channels
d. Increased potassium conductance
during phase 4
The normal sequence of conduction
within the heart is
a. SA node —> atrioventricular (AV)
node —> bundle of His —» bundle
branches —» Purkinje fibers
h. SA node —> bundle of His —» AV node
—»bundle branches —> Purkinje fibers
c. AV node —» SA node —» bundle of His
—» bundle branches —» Purkinje fibers
d. SA node —» AV node —» bundle of His
—» Purkinje fibers —> bundle branches
A patient is found to have a PR interval
that is >0.2 seconds. Which of the fol-
lowing interventions would most likely
reduce the PR interval?
a. Blocking P-adrenoceptors
b. Blocking muscarinic (M2) receptors
c. Blocking L-type calcium channels
d. Enhancing vagal nerve activity
In a normal ECG,
a. The PR interval is >0.2 seconds,
h The ST segment represents the dura-
tion of the ventricular action potential.
c. The T wave represents ventricular
d. The duration of the QRS is >0.2 seconds.
A patient is found to have normal QRS
hut inverted T waves in leads II, III, and
aVF Which of the following is the most
likely explanation for these findings?
a. The direction of ventricular repolari-
zation is reversed from normal,
h. The polarity of the recording elec-
trodes is reversed.
c. Ventricular depolarization and
repolarization are occurring in
d. Ventricular depolarization is abnormal.