Atrioventricular (AV) Blocks Flashcards

A rhythm analysis technician observes an ECG strip where the PR interval is consistently 0.26 seconds for every beat. The rhythm is regular, with an atrial and ventricular rate of 68 bpm. Each P wave is followed by a QRS complex. What is the correct interpretation?

Answer: First-Degree AV Block

First-Degree AV Block is characterized by a prolonged but constant PR interval greater than 0.20 seconds. [9, 11] In this rhythm, every P wave is conducted to the ventricles, resulting in a 1:1 relationship between P waves and QRS complexes. [1] The rate is within the normal sinus range, and the PR interval of 0.26 seconds is the key diagnostic feature.

Which of the following ECG findings is the defining characteristic of Second-Degree AV Block, Mobitz I (Wenckebach)?

Answer: Progressive lengthening of the PR interval until a QRS complex is dropped.

The hallmark of Second-Degree AV Block, Mobitz I (Wenckebach) is the progressive prolongation of the PR interval over several beats, culminating in a P wave that is not followed by a QRS complex (a dropped beat). [2, 6, 18] After the dropped beat, the cycle typically repeats.

A patient's ECG shows a regular atrial rate of 80 bpm and an irregular ventricular rate of approximately 40 bpm. The PR interval for all conducted beats is constant at 0.22 seconds. There are P waves that are not followed by a QRS complex. This pattern is most consistent with which arrhythmia?

Answer: Second-Degree AV Block, Mobitz II

Second-Degree AV Block, Mobitz II is characterized by intermittently non-conducted P waves without progressive PR interval prolongation. The PR interval of the conducted beats remains constant. [14, 20] This type of block is more serious than Mobitz I because it often occurs below the AV node and can progress to complete heart block. [3, 17]

A CRAT is analyzing a rhythm strip and observes complete AV dissociation. The atrial rate (P-P interval) is regular at 100 bpm, and the ventricular rate (R-R interval) is regular at 42 bpm. There is no consistent relationship between the P waves and the QRS complexes. What is this rhythm?

Answer: Third-Degree AV Block

Third-Degree (Complete) AV Block is defined by the complete absence of conduction between the atria and ventricles. [4, 13] This results in AV dissociation, where the atria and ventricles beat independently of each other, each controlled by its own pacemaker. [15, 16] The ECG shows regular P-P intervals and regular R-R intervals, but the two are not related.

Which of the following atrioventricular blocks is considered more clinically significant and has a higher risk of progressing to a complete heart block, often requiring pacemaker implantation?

Answer: Second-Degree AV Block, Mobitz II

Second-Degree AV Block, Mobitz II is considered more dangerous than Mobitz I because the block is typically located in the His-Purkinje system, which is less stable. [14, 20] This rhythm has a significant risk of progressing suddenly to Third-Degree (Complete) AV Block and causing severe bradycardia or asystole, which is why a permanent pacemaker is often indicated. [3, 27]

A technician reviews a rhythm strip showing an atrial rate of 75 bpm and a ventricular rate of 38 bpm. The P-P interval is regular, and the R-R interval is regular. P waves can be seen marching through the QRS complexes, with some appearing just before, some buried within, and some after the QRS. This describes:

Answer: Third-Degree AV Block

This scenario describes the classic features of Third-Degree (Complete) AV Block. There is complete AV dissociation, meaning the atrial impulses (P waves) have no relationship to the ventricular responses (QRS complexes). [13, 15] The atria and ventricles beat at their own regular, independent rates, with the atrial rate being faster than the ventricular escape rate. [4, 28]