cardiovascular disorders
Complications of Acute Coronary Syndromes
Conduction Defects
 Second-degree AV block (Wenckebach block, progressive prolongation of PR interval with eventual dropped beats) is relatively common with an inferior-diaphragmatic infarction (see figure The PR interval progressively lengthens with each beat until the atrial impulse is not conducted and the QRS complex is dropped (Wenckebach phenomenon); AV nodal conduction resumes with the next beat, and the sequence is repeated. Second-degree AV block (dropped beats) usually indicates massive anterior myocardial infarction, as does complete heart block with wide QRS complexes (atrial impulses do not reach the ventricle); both are uncommon. Frequency of Third-degree AV block (complete) block depends on site of infarction (see figure Mobitz type I block usually does not warrant treatment. For true Mobitz type II block with dropped beats or for AV block with slow, wide QRS complexes, temporary transvenous pacing is the treatment of choice. External pacing can be used until a temporary transvenous pacemaker can be placed. A permanent pacemaker is required for patients with 3rd degree block and those with persistent 2nd degree AV block, especially if symptomatic. 0.5 mg IV every 3 to 5 minutes to a total dose of 2.5 mg may be useful for narrow-complex Atrioventricular Block with a slow ventricular rate but is not recommended for new wide-complex atrioventricular block. 