Bradycardias and atrioventricular conduction block Scott Ewing, D.O. November 3, 2005

Sinus Bradycardia Common in normal individuals during sleep and high vagal tone (athletes and young healthy adults) P wave before every QRS complex and normal P axis PR interval is at least 0.12 s Most common pathological cause acute MI Particularly associated with inferior MI as the inferior myocardial wall and the SA and AV nodes are usually supplied by the RCA

Sick Sinus Syndrome SSS - dysfunction of the sinoatrial node, with impairment of its ability to generate and conduct impulses Usually idiopathic fibrosis of the SA node but is also associated with myocardial ischaemia, digoxin, and cardiac surgery EKG features include persistent sinus bradycardia periods of sinoatrial block sinus arrest junctional or ventricular escape rhythms tachycardia­bradycardia syndrome paroxysmal atrial flutter atrial fibrillation Most common EKG feature is an inappropriate, persistent, and often severe sinus bradycardia

Tachycardia­Bradycardia Syndrome Common in sick sinus syndrome Characterised by bursts of atrial tachycardia interspersed with periods of bradycardia Paroxysmal atrial flutter or fibrillation may also occur, and cardioversion may be followed by a severe bradycardia

Sinoatrial Block Characterised by a transient failure of impulse conduction to the atrial myocardium, resulting in intermittent pauses between P waves The pauses are the length of two or more P­P intervals

Sinus Arrest Transient cessation of impulse formation at the sinoatrial node Manifests as a prolonged pause without P wave Pause is unrelated to the length of the P­P cycle

Escape Rhythms Result of spontaneous activity from a subsidiary pacemaker, located in the atria, atrioventricular junction, or ventricles Takes over when normal impulse formation or conduction fails and may be associated with any profound bradycardia Junctional escape beat has a normal QRS complex shape with a rate of 40­60 beats/min Ventricular escape rhythm has broad complexes and is slow (15­40 beats/min)