Chest pain with slow rate

Learning Objectives:

1. Describe ECG criteria for type I second-degree AV block.

2. Describe ECG criteria for type II second-degree AV block.

3. Describe ECG criteria for third-degree AV block.

4. List serious signs and symptoms of bradycardia.

5. Describe the treatment algorithm for bradycardia.

Type I Second-Degree AV Block (Wenkebach):

1. The heart rate is slow to normal. The rhythm is not regular since some QRS complexes are missing.

2. The QRS complex is narrow.

3. The P waves are upright.

4. There are more P waves than QRS complexes. The PR interval progressively lengthens until a QRS complex is dropped. The shortest PR interval follows the dropped beat.

5. Second degree type I AV block is also known as Mobitz Type I or Wenkebach. The conduction block occurs in the AV node. The PR interval progressively lengthens until the impulse is not conducted to the ventricles.

6. Second degree type I AV block is most commonly associated with right coronary artery occlusion with inferior wall infarctions. This block generally has a good prognosis.

Type II Second-Degree AV Block:

1. The heart rate is slow to normal and the rhythm is not regular. QRS complexes are missing.

2. The QRS complex is usually wide.

3. The P waves are upright.

4. There are more P waves than QRS complexes. The PR interval is fixed and usually has normal duration.

5. Second degree type II AV block is also known as Mobitz Type II. The conduction block is infranodal. The PR interval is fixed duration until the impulse is not conducted to the ventricles.

6. Second degree type II AV block is most commonly associated with anterior wall infarctions. This block has a propensity to progress to third degree AV block.

Third-Degree AV Block:

1. The heart rate is slow to normal and the rhythm is regular.

2. The QRS complex is wide.

3. The P waves are upright.

4. There are usually more P waves than QRS complexes. There is usually atrial and ventricular regularity, but they are independent of each other. P waves march through QRS complexes.

5. Third degree AV block is complete heart block. The atria beat at their rate while the ventricular rate is determined by a junctional or ventricular pacemaker. P waves "march through" or are unrelated to QRS complexes.

Serious Signs and Symptoms of Bradycardia:

1. Chest pain

2. Shortness of breath

3. Decreased level of consciousness

4. Low blood pressure

5. Congestive heart failure

Bradycardia Algorithm:

Treat bradycardia if there are serious signs or symptoms due to the bradycardia.

1. Assess patient; observe if no signs or symptoms.

2. Atropine 0.5-1.0 mg IV if signs or symptoms, repeat every 3-5 minutes if continued signs or symptoms. Note that the denervated, transplanted heart will not respond to atropine.

3. Consider pacemaker if available.

4. Infuse dopamine 2-10 mcg/kg per min or epinephrine 2-10 mcg/min if continued signs or symptoms.

5. If no serious symptoms, but Mobitz II or Third degree heart block:

a. Prepare for transvenous pacer.

b. Prepare TCP (TransCutaneous Pacemaker) as a potential bridge device.