Cardiac Medicine Certification (CMC) Practice Exam

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Prepare for your Cardiac Medicine Certification (CMC) Test with comprehensive quizzes, case studies, and helpful materials. Enhance your knowledge and gain confidence before the big day!

Each practice test/flash card set has 50 randomly selected questions from a bank of over 500. You'll get a new set of questions each time!

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What defines third-degree heart block?

Regular P to P intervals without any QRS complex
No conduction between the SA and AV nodes
Normal heart rate with dropped beats
Gradual lengthening of the PR interval

The correct answer is: No conduction between the SA and AV nodes

Third-degree heart block, also known as complete heart block, is characterized by a complete absence of conduction between the atria and ventricles. In this condition, the electrical impulses generated in the sinoatrial (SA) node do not reach the atrioventricular (AV) node, which results in the atria and ventricles beating independently of one another. In this scenario, the atrial pacing is intact with P waves occurring at regular intervals, but these P waves do not correlate with QRS complexes, which can lead to varying ventricular rates that may be slow and irregular. Since there is a complete block in conduction between the SA and AV nodes, the atrial and ventricular rhythms are dissociated, making this condition distinctly recognizable on an electrocardiogram (ECG). In contrast to the other options, where P waves might still lead to QRS complexes in the case of a lesser degree of block or have a certain relationship with the QRS complexes, third-degree heart block is specifically defined by the total lack of communication between the SA and AV nodes, making the choice that describes this lack of conduction the correct one.