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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
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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)