Complete AV block

Hypersensitivity or idiosyncrasy to quinidine or other cinchona derivatives manifested by thrombocytopenia, skin eruption or febrile reactions myasthenia gravis history of thrombocytopenic purpura associated with quinidine administration digitalis intoxication manifested by arrhythmias or AV conduction disorders complete heart block left bundle branch block or other severe intraventricular conduction defects exhibiting marked QRS widening or bizarre complexes complete AV block with an AV nodal or idioventricular pacemaker aberrant ectopic impulses and abnormal rhythms due to escape mechanisms history of drug-induced torsade de pointes history of long QT syndrome. 

Atrial fibrillation or flutter, pulmonary edema, and complete AV block occur occasionally. 

Cardiotoxic effects occur most commonly with IV administration and appear as conduction changes (50% widening of QRS complex, frequent ventricular premature contractions, ventricular tachycardia, and complete AV block). 

Contraindications Complete AV block, development of thrombocytopenic purpura during prior therapy with quinidine or quinine, intraventricular conduction defects (widening of QRS complex)... 

Cardiac uses Adrenaline may be used to stimulate the heart in cardiac arrest. Adrenaline can also be used in Stokes-Adam syndrome, which is a cardiac arrest occurring at the transition of partial to complete heart block. Isoprenaline or orciprenaline maybe used for the temporary treatment of partial or complete AV block. 

Adverse effects include bleeding, thrombocytopenia, human antichimeric antibody development, atrial fibrillation/flutter, complete AV block, palpitation, SVT, constipation, ileus, abnormal thinking, dizziness. 

Verapamil and diltiazem are prototypic calcium channel blockers. As indicated previously, these drugs influence cardiac function by blocking inward calcium movement through L channels. In so doing they block conduction velocity in SA and AV node cells. They are used therapeutically to treat reentry arrhythmias through the AV node as well as paroxysmal supraventricular tachycardias. In fact, verapamil has been reported to terminate 60-80 percent of paroxysmal supraventricular tachycardias within several minutes. However, because of their potent effect on AV conduction, these drugs are contraindicated in patients with preexisting conduction problems since they may produce complete AV block. 

Schoenmakers M, Ramakers C, van Opstal JM et at. (2003) Asynchronous development of electrical remodeling and cardiac hypertrophy in the complete AV block dog. Cardiovascular Research 59 351-359 Van Opstal JM, Leunissen JDM, Wellens HJJ, Vos MA (2001) Azimilide and dofetilide produce similar electrophysiolog-ical and proarrhythmic effects in a canine model of Torsade de Pointes arrhythmias. European Journal of Pharmacology 412 67-76... 

An 80-year-old woman with gastrointestinal bleeding had a sinus bradycardia (52/minute) despite acute blood loss. The only drug she had used that was an AV nodal depressant was timolol maleate 0.5%, one drop to both eyes every day. Continuous electrocardiography showed transient complete AV block without ventricular escape for nearly 6 seconds about 1 hour after instillation of timolol eye drops. She also reported having previously had episodes of dizziness and occasional falls 1-2 hours after instillation of her eye drops. 

This is the first report of complete AV block and prolongation of the QT interval after co-administration of erythromycin and verapamil, both of which are principally metabolized by CYP3A4. Both drugs are potent inhibitors of CYP3A4 and P-glycoprotein, which may be the basis of this interaction. 

Contraindications Complete AV block second- and third-degree AV block without pacemaker, abnormal impulses/rhythms because of escape mechanism... 

Increased risk of toxicity with drugs that alter serum electrolytes (potassium -depleting diuretics, corticosteroids, thiazide and loop diuretics, amphotericin B, quinidine, amiodarone). Blockers of p adrenergic receptors, calcium channels, or acetylcholinesterase increase risk of complete AV block. Drugs which alter Gl absorption may alter bioavallabillty. 

Prophylactic Temporary Pacemaker Insertion. Approximately 1% of patients with acute myocardial infarction develop a Type n second-degree AV block. Although this rhythm is often tolerated hemodynamically, because there can be sudden progression to complete AV block, temporary pacing should be considered. New bundle-branch block (BBB) has been associated with an 18% risk of transient complete AV block (9-11). The development of BBB usually signifies an extensive infarction, typically involving the anterior wall. Death in these patients usually results from left ventricular pump failure, although 9% of deaths have been attributable to complete AV block (9). 

---