Atrioventricular Blocks

This presentation is about causes, clinical features and management of atrioventricular blocks.

1. بسم الله الرحمن الرحیم

2. A trioventricular Blocks causes, clinical features and management

3. First Degree Block First degree AV block may be associated with electrolyte disturbances, use of digitalis, Beta-blockers or calcium channel blockers , and acute myocardial infarction (usually inferior wall). It is usually asymptomatic. In the ECG, the P-R interval is prolonged to more than 0.20 seconds. All the P waves are conducted and the QRS is normal as the delay is most often in the AV node. Treatment includes correction of any electrolyte imbalance and removal of an offending agent. If it occurs as a result of acute MI, the patient should be observed to detect any progression to higher degrees of blocks.

4. Second Degree Block It can be subdivided into Mobitz type I and Mobitz type II blocks. Mobitz type I ( Wenckebach ) second degree AV block. It usually occurs in acute inferior wall myocardial infarction and use of digitalis, Beta-blockers or calcium channel blockers. The block is usually transient and the patient is usually asymptomatic. It is characterized by progressive slowing of AV conduction until it is totally blocked. The ECG typically shows progressive prolongation of successive P-R intervals until one P wave is not conducted. The QRS is usually normal. If the patient is symptomatic, atropine should be administered. Pacing is usually not required .

5. Mobitz type II second degree AV block. This type of block usually occurs after anterior wall Ml. The patients are usually symptomatic (see complete heart block) and there are high chances of its progression to third degree AV block The block is characterized by a constant P-R interval with intermittent failure of atrial impulses to conduct to the ventricles. The block is defined by a ratio in which the first digit represents the total number of P waves and the second digit represents the number of P waves conducted, i.e. the number of QRS complexes. Thus, in a 3: 1 block, of three P waves, one is conducted while two are blocked. It occurs most often due to delay in conduction in the His-bundle and Purkinje system and, therefore, the QRS is often abnormal. Patients generally require a pacemaker. Atropine is of little use while response to isoproterenol is variable .

6. Third Degree or Complete AV Block In complete heart block, none of the atrial impulses reach the ventricles. The atria are thus activated by one pacemaker, usually the sinus pacemaker. The ventricles are activated by another pacemaker situated either in the bundle of His or ventricles

7. Causes of Complete Heart Block Congenital Acquired • Lenegre's disease • Lev's disease • Myocardial ischemia or infarction • lntra -cardiac surgery •Digitalis intoxication •Infective endocarditis • Tumors and infections involving the conducting system • Lenegre's disease is idiopathic sclera-degenerative disease of conducting system. • Lev's disease is calcification and sclerosis of conducting system.

8. Clinical Features • Regular and slow pulse (30-40/minute) • High volume pulse • Irregular cannon waves on JVP • Varying intensity of first heart sound • Stokes-Adams attacks • The ECG shows constant P-P and R-R intervals but with complete AV dissociation, i.e. the atria and ventricles beat independently and there is no relation between the P waves and the QRS complexes . • The ECG shows constant P-P and R-R intervals but with complete AV dissociation, i.e. the atria and ventricles beat independently and there is no relation between the P waves and the QRS complexes . • The ECG shows constant P-P and R-R intervals but with complete AV dissociation, i.e. the atria and ventricles beat independently and there is no relation between the P waves and the QRS complexes.

9. Management Complete heart block complicating acute inferior myocardial infarction usually does not require any treatment. If the patient deteriorates clinically, it may be treated with intravenous atropine (0.6 mg) that may be repeated every 3-5 minutes for a total of 3 mg. Doses of atropine <0.6 mg may paradoxically result in further slowing of the heart rate. If bradycardia is unresponsive to atropine, intravenous infusion of Beta-adrenergic agonists with rate-accelerating effects (dopamine , epinephrine) or transcutaneous pacing can be effective while the patient is prepared for emergent trans-venous temporary pacing .

10. •However , administration of atropine or other drugs should not delay implementation of external pacing for patients with poor perfusion (e.g. bradycardia causing shock, altered level of consciousness, acute heart failure or ischemic chest pain). Complete heart block complicating acute anterior myocardial infarction should be treated by immediate insertion of temporary pacemaker Chronic complete heart block should be treated by the implantation of a permanent pacemaker.