Mobitz Type II AV block is defined by which feature?

Mobitz Type II AV block is defined by which feature?

• A. Intermittent dropped QRS without PR prolongation
• B. Intermittent dropped QRS with unchanged PR interval
• C. Progressive PR lengthening before dropped QRS
• D. All P waves are missing

Answer: (B)

Mobitz Type II AV block is defined by intermittent non-conducted atrial impulses that fail to conduct to the ventricles, producing dropped QRS complexes, while the PR interval of the conducted beats remains constant. This stability of the PR interval (no progressive lengthening) indicates a block below the AV node, often in the His-Purkinje system. It contrasts with Mobitz Type I, where the PR interval lengthens progressively before a drop. It also is different from complete heart block, where atrial and ventricular activities are completely dissociated. Because the block tends to be infranodal, Mobitz II can be more dangerous and may require pacing.

Mobitz Type II AV block is defined by intermittent non-conducted atrial impulses that fail to conduct to the ventricles, producing dropped QRS complexes, while the PR interval of the conducted beats remains constant. This stability of the PR interval (no progressive lengthening) indicates a block below the AV node, often in the His-Purkinje system. It contrasts with Mobitz Type I, where the PR interval lengthens progressively before a drop. It also is different from complete heart block, where atrial and ventricular activities are completely dissociated. Because the block tends to be infranodal, Mobitz II can be more dangerous and may require pacing.