A first-degree heart block has a PR interval greater than 0.20 seconds because:
A) depolarization of the atria occurs at a slightly slower rate than one would expect.
B) each impulse that reaches the AV node is delayed slightly longer than expected.
C) impulses generated by the SA node traverse the AV node at an accelerated rate.
D) the primary pacemaker is not the SA node, but rather an ectopic atrial pacemaker.
Answer: B) each impulse that reaches the AV node is delayed slightly longer than expected.
Health Professions
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