C244: BRADYARRHTYMIAS: DISORDERS OF SA NODE Flashcards
____________sinoatrial (SA) node serves as the natural pacemaker of the heart
sinoatrial (SA) node serves as the natural pacemaker of the heart
If the sinus node is dysfunctional or suppressed a subsidary pacemaker in the ________ or ________ will take over leading to a slower junctional or ventricular rhythm
If the sinus node is dysfunctional or suppressed a subsidary pacemaker in the atrioventricular node or specialized conduction system will take over leading to a slower junctional or ventricular rhythm
Once irreversible sinus node dysfunction is confirmed, ________the only reliable therapy for symptomatic bradycardia.
Once irreversible sinus node dysfunction is confirmed, permanent pacemaker implantation is the only reliable therapy for symptomatic bradycardia.
LOCATION OF SA NODE:
the sulcus terminalis on the epicardial surface of the heart at the right atrial–superior vena caval junction
Action potential depolarization in the SA node is normally at a resting rate of ________beats/min.
Action potential depolarization in the SA node is normally at a resting rate of 60–100 beats/min.
The autonomic nervous system exhibits control over the sinus node, with a preponderance of ________ innervation at baseline
The autonomic nervous system exhibits control over the sinus node, with a preponderance of parasympathetic innervation at baseline
Cells in the SA node exhibit the most rapid phase ________depolarization and thus are the dominant pacemakers in a normal heart.
Cells in the SA node exhibit the most rapid phase 4 depolarization and thus are the dominant pacemakers in a normal heart.
Unlike atrial and ventricular cells, sinus node pacemaker cells have no true resting potential, but instead depolarize automatically and repetitively after the end of an action potential. True or False…
True
depolarizing current in the SA node myocytes results primarily from slow ________currents instead of fast________channels, which are absent in SA node cell
depolarizing current in the SA node myocytes results primarily from slow calcium currents instead of fast sodium channels, which are absent in SA node cell
Spontaneous phase 4 depolarization results from a combination of (3)
- slow inward depolarizing sodium currents (i f , “funny currents”)
- T-type calcium channel
- L-type calcium channel
Phase 0 is the ________ phase of the action potential
Phase 0 is the depolarization phase of the action potential
Intrinsic heart rate declines________ beats/min for each decade of age.
Intrinsic heart rate declines 5–6 beats/min for each decade of age.
Intrinsic sinus node disease is sometimes referred to as _______
sick sinus syndrome or sinus node dysfunction (SND)
Correlation between sleep apnea and bradyarrythmia:
Many patients with sleep apnea will have high vagal tone during sleep and especially during apneic events. Sinus bradycardia and sinus pauses frequently are seen
Formula for intrinsic heart rate:
118.1 – (0.57 × age)
SA nodal dysfunction subtyprs (6)
- Sinus node exit block
- Tachy-brady syndrome
- Chronotropic incompetence
- Sinus node fibrosis
- SA nodal ischemia and infarction
- Carotid sinus hypersensitivity and neurally mediated bradycardia
results from failure of impulse formation within the sinus node
sinus arrest
Type of sinus node exit block that involves progressive delay THEN intermitten failure to propagate to the atriu
Mobitz I SA block
Type of sinus node exit block that involves FIXED delay THEN intermitten failure to propagate to the atrium
Mobitz II SA block
This type of SA exit block can be inferred on the ECG if the sinus rate abruptly transitions to a sinus rate that is half the previous rate (every other sinus depolarization is blocked from exiting to the atrium)
Mobitz II SA block
This type of SA exit block can be inferred on the ECG in the setting of progressive shortening of the P-P interval leading up to a sinus paus
SA Wenckeback (type I)
Type of SA nodal dysfunction consisting of high heart rates (most commonly atrial fibrillation) with alternating symptomatic bradycardia or offset pauses
Tachy-Brady Syndrome
Type of SA nodal dysfunction consisting of high heart rates (most commonly atrial fibrillation) with alternating symptomatic bradycardia or offset pauses
Tachy-Brady Syndrome
Inability of the heart to increase its rate to meet activity or demand
Chronotropic incompetence
Pacing nomenclature… what do the 4 letters represent
- First letter - chamber paced
- Second letter - chamber sensed
- Third letter - response to sensed event
- Fourth letter - rate response is turned on
What is RATE RESPONSE
essential for the treatment of CI as it attempts to mimic the natural physiologic increase in heart rate in response to exertion.
Single chamber atrial pacemaler could be used in what condition
pure sinus node dysfunction
Indicatons for permanent pacing in sinus node dysfunction (5)
CLASS I INDICATION for pacing
- documented symptomatic bradycardia
- SND-associated long-term drug therapy for which there is no alternative
- Symptomatic CI
CLASS IIA INDICATION for pacing
- those outlined previously in which SND is suspected but not documented
- for syncope of unexplained origin in the presence of major abnormalities of SA node dysfunction
CLASS IIB INDICATION for pacing
Mildly symptomatic individuals with heart rates consistently <40 beats/min constitute a class IIb indication for pacing
Refers to rotation of the pacemaker pulse generator in its SQ pocket, either intentionally or inadvertently
Twiddler’s syndrome
ANTI HTN MEDS THAT CAN CAUSE SINUS NODE DYSFUNCTION
- Beta blockers
- Clonidine
- Methyldopa
- Non-DHP CCBs
