Mechanisms of Bradyarrythmias Flashcards
3 forms of sinus node dysfunction?
Sinus bradycardia.
Chronotropic incompetence
Tachy-brady syndrome (Sick sinus syndrome)
2 main categories of bradyarrhythmia?
Problems with impulse generation (SA node)
Problems with conduction
What does chronotropic incompetence refer to?
The patient can’t increase their heart rate, even with exercise.
This doesn’t necessarily mean that the resting HR is low.
What 2 processes underly tachycardia-bradycardia syndrome?
A fib + sinus node dysfunction.
What happens in SA exit block?
SA depolarization fails to reach atria -> no P wave.
The heart skips a beat.
(intracardiac electrograms can show you that the SA node is really still depolarizing, it just doesn’t make it out)
Review: 3 degrees of AV block?
1st degree: Delayed conduction through AV node - PR elongation.
2nd degree: Intermittent failure of P wave to be transmitted through AV node.
3rd degree: Complete heart block - P waves and QRS’ are unrelated.
PR interval cutoff for first degree heart block?
200ms
What happens in Mobitz type 1 (Wenckebach), 2nd degree heart block?
Is this benign or malignant?
PR intervals get progressively longer until finally a P wave doesn’t conduct. Then the PR interval following the skipped QRS is short.
This is benign.
What happens in Mobitz type II, 2nd degree AV block?
Benign or malignant?
There’s a wide QRS, with consistent PRs, but dropped QRSs at unpredictable intervals.
This indicates significant problems with the conduction system and has a high risk of progressing to complete AV block.
Review: What does the QRS complex look like in Right bundle branch block (RBBB)?
Early narrow left-pointing depolarization, with wide right-pointing depolarization afterward.
Review: What does the QRS complex look like in LBBB?
It’s mostly one big, wide, left-pointing depolarization.
The right-pointing depolarizations get lost in the ECG.
How does rate of escape rhythm relate to location of its origin?
The higher in the conduction system it originates, the faster the escape rhythm.
