Bradyarrythmias: Disorders of the Sinoatrial Node Flashcards
Autonomic Nervous System
Regulates the rate of phase 4 diastolic depolarization and thus the firing rate of both primary (SA node) and subsidiary pacemaker.
2 most common causes of pathologic bradycardia
SA node dysfunction
AV conduction block
Only reliable therapy for symptomatic bradycardia in the absence of extrinsic and reversible etiologies (inc vagal tone, hypoxia, Hypothermia)
Permanent pacemaking
Where is the SA node?
Sulcus terminalis on the epicardial surface at the right atrial superior vena cava junction
Where does the SA nodal artery arise from?
right coronary artery (55-60%)
left circumflex artery (40-45%)
Slow conduction within SA node explained by
Absence of I(Na) and poor electrical coupling
Most common causes of extrinsic SA node dysfunction
Drugs and autonomic nervous system influences
Other extrinsic causes of SA node dysfunction
Hypothyroidism, sleep apnea, Hypothermia, Hypoxia, and increased intracranial pressure (cushing’s response) and endotracheal suctioning via activation of the vagus nerve
Inflammatory disorders that are associated with SA nodal disease ( sinus bradycardia, sinus arrest and exit block)
Pericarditis, Myocarditis, Rheumatic Heart Disease
Infiltritative disorder in patients typically in the ninth decade of life
Deposition of amyloid protein in the atrial myocardium
Senile amyloidosis
Ophthalmoplegia
Pigmentary degeneration of the retina
Cardiomyopathy
Kearns-Sayre Syndrome
Coexisting diseases that may hasten deposition of fibrous tissue in SA node
CAD DIabetes Mellitus Hypertension Valvular diseases Cardiomyopathies
Incidence of persistent atrial fibrillation or atrial flutter in SA node dysfunction increases in the ff condition
Advanced age Hypertension Diabetes mellitus Left Ventricular Dilation Valvular Heart Disease Ventricular Pacing
ECG manifestation of SA node dysfunctin
sinus bradycardia Sinus pauses sinus arrest sinus exit block tachycardia (in SSS) Chronotropic incompetence
Chronotropic incompetence
inability to increase the heart rate in response to exercise
Normal IHR after administration of 0.2 mg/kg of propofol and 0.04 mg/kg atropine
117.2 - (0.53 x age)
in beats/min
low IHR is indicative of SA disease
Sinus node recovery time
longest pause after cessation of overdrive pacing of the right atrium near the SA node (normal <1500 ms or sinus cycle length <550 ms)
Sinoatrial conduction time (SACT)
1/2 the difference between intrinsic sinus cycle length and a noncompensatory pause after a premature atrial stimulus <125 ms
Pacemaker implantation
primary therapeutic intervention in patients with symptomatic SA node dysfunction
Which class/es of antiarrythmic drugs promote SA node exit block
Class I and Class III
These drugs increase SNRT in patients with SA node dysfunction
Beta blockers and calcium channel blockers
These IV drugs may be used to increase the heart rate acutely
Atropine and Isoproterenol
This drug may be used acutely or chronically to increase heart rate but has liabilities when used in patients with tachycardia-bradycardia syndrome and in patients with structural heart disease
Theophylline
Most commonly programmed modes of implanted singe and dual chamber pacemaker
VVIR
DDDR
Complications of transvenous pacemaker implantation
HIPCaDL Hematoma Infection Pneumothorax Cardiac perforation Diaphragmatic/Phrenic nerve stimulation Lead dislodgement
Limitations of chronic pacemaker therapy
Infection
Erosion
Lead failure
Abnormalities (Inappropriate programming or interaction with native electrical cardiac function)
Twiddler’s syndrome
Rotation of the pacemaker pulse generator in its subcutaneous pocket
Collection of symptoms that include neck pulsation, fatigue Palpitations cough Confusion Exertional Dyspnea Dizziness Syncope Elevation in jugular venous pressure canon A waves stigmata of congestive heart failure
Pacemaker syndrome
Stigmata of CHF
edema
rales
third heart sound
Most common causes of pathologic bradycardia
SA node dysfunction, AV conduction block
Composed of a cluster of small fusiform cells in the sulcus terminalis on the epicardial surface of the heart at the right atrial-superior vena caval junction
SA node
Alternate definition of chronotropic incompetence
Failure to reach 85% of predicted maximal heart rate at peak exercise or failure to achieve a heart rate > 100 beats per min with exercise or maximal heart rate less than 2 SD below that of age matched control population.
Normal IHR after administration of 0.2 mg/kg propanolol and 0.04 mg/kg atropine
117.2 - (0.53* age) in beats per min
