A 43-Year-Old Man Is Evaluated for Occasional Palpitations Provoked by Anxiety

A 43-year-old man is evaluated for occasional palpitations provoked by anxiety.  The patient describes a sudden-onset pounding sensation in the chest followed by lightheadedness and shortness of breath.  He has never had syncope.  The patient has no history of heart disease, and family history is unremarkable.  After initial evaluation, he is treated with verapamil and reports marked improvement in the frequency of palpitation episodes.  The tracing below shows the electrical activity of a specific type of cardiac cell in the patient's heart. Which of the following effects would verapamil administration most likely have on these cells?

A) Decreased excitation and contraction coupling
B) Increased action potential amplitude
C) Lowered threshold potential
D) Reduced refractory period
E) Slowed spontaneous depolarization

Correct Answer:

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