Bradycardia Flashcards
What are some modulators of heartrate?
age, gender, physical training, activity of pharmacologic agents
intrinsic causes of sinus node dysfunction
disorder of impulse formation
failure of conduction
causes: age associated fibrosis, coronary atherosclerosis, fibrosis due to hypertension and diabetes, cardiovascular disease, familial disease, pericardial disease, amyloidosis
extrinsic causes of sinus node dysfunction
increased vagal tone
medications
electrolyte abnormalities
severe hypotension or hypoxemia
pharmacologic agents that can suppress sinus node function
beta-blockers, calcium blockers, digoxin, antiarrhythmic drugs, and psychotropic medications
treatment of external dysfunction
removing offending stimulus
treatment of internal dysfunction
pacemaker implantation
estimation of maximum sinus rate
220 - age
sinus bradycardia ECG
normap p-wave axis with heart rate of <60 bpm
every P wave is followed by a QRS complex
sinus arrest
normal P-wave axis
every P-wave followed by a QRS complex
pauses of >3 seconds without atrial activity
SA exit block
normal P-wave axis
progressive shortening of PP interval until one P wave fails to conduct or sinus pause is an exact multiple of the baseline PP interval
bradycardia-tachycardia syndrome
alternating periods of atrial tachycardia and bradycardia
types of AV block
first-degree
second degree - mobitz I and II
2:1 AV block
high-grade
complete heart block
symptoms of bradyarrhythmia
syncope
presyncope/dizziness
poor exercise tolerance/fatigue
congestive heart failure
can also have no symptoms
What is the depolarization rate of the AV node?
40-60 bpm
What is the depolarization rate of the ventricles?
20-40 bpm
first-degree AV block
delay, no dropped beats
second degree AV block - Mobitz Type I (Wenckebach)
progressive delay with dropped beats
2nd degree AV block - Mobitz Type II
fixed delay with dropped beats
block is in the His-Purkinje system, which is more severe than the Type I block
3rd degree AV block
complete AV block, no conduction from atria to ventricles
right bundle branch block
left bundle and left ventricle depolarize normally and rapidly
right ventricle depolarizes slowly via cell-to-cell mechanism
leads to a wide QRS complex and rabbit ears phenomenon
left bundle branch block
right bundle and right ventricle depolarize normally and rapidly
left ventricle depolarizes slowly via a cell-to-cell mechanism
wide QRS, low and lobbing in lead V1
