274 Bradyarrhythmias: Disorders of the SA Node Flashcards
It is the predominant pacemaker of the heart
SA Node
It results from a failure of either impulse initiation or impulse conduction.
Bradycardia
Most common causes of pathologic bradycardia
SA node dysfunction and AV conduction block
It is the only reliable therapy for symptomatic bradycardia in the absence of extrinsic and reversible etiologies such as increased vagal tone, hypoxia, hypothermia, and drugs
Permanent pacemaking
The most common causes of extrinsic SA node dysfunction
Drugs and autonomic nervous system influences
Extrinsic causes of SA Node Dysfunction
Autonomic Carotid sinus hypersensitivity Vasovagal (cardioinhibitory) stimulation Drugs Beta blockers Calcium channel blockers Digoxin Ivabradine Antiarrhythmics (class I and III) Adenosine Clonidine (other sympatholytics) Lithium carbonate Cimetidine Amitriptyline Phenothiazines Narcotics (methadone) Pentamidine Hypothyroidism Sleep apnea Hypoxia Endotracheal suctioning (vagal maneuvers) Hypothermia Increased intracranial pressure
Intrinsic causes of SA node dysfunction
Sick-sinus syndrome (SSS) Coronary artery disease (chronic and acute MI) Inflammatory Pericarditis Myocarditis (including viral) Rheumatic heart disease Collagen vascular diseases Lyme disease Senile amyloidosis Congenital heart disease TGA/Mustard and Fontan repairs Iatrogenic Radiation therapy Postsurgical Chest trauma Familial
The electrocardiographic manifestations of SA node dysfunction include_____
sinus bradycardia, sinus pauses, sinus arrest, sinus exit block, tachycardia (in SSS), and chronotropic incompetence.
It results from progressive prolongation of SA node conduction with intermittent failure of the impulses originating in the sinus node to conduct to the surrounding atrial tissue.
Type I second-degree SA block
True or False
SA node dysfunction is most commonly a clinical or electrocardiographic diagnosis.
True
Failure to increase the heart rate with exercise
Failure to reach 85% of predicted maximal heart rate at peak exercise or failure to achieve a heart rate >100 beats/min with exercise or a maximal heart rate with exercise less than two standard deviations below that of an age-matched control population.
Chronotropic incompetence
