Arrhythmias Flashcards
What is the most common cause of sudden cardiac death?
• Preferred treatment?
- Ventricular Fibrillation
* Need Defibrillator implanted
What is represented by the P waves, PR interval, Q waves, and ST segment?
P-waves = atrial depolarization
PR-interval = current traversing the AV node
Q-wave = Septal Depolarization
ST-segement = ischemia/infarct
What part of the action potential was is most affected by arrhythmias?
Phase 4 - aka the diastolic/resting phase
How does ventricular hypertrophy show up on EKG?
Look at V6:
• T wave Reversal
- HUGE R-wave - this make sense given that the R wave corresponds to depolarization near the Apex
- Normal R waves should be about 10mm (2 large boxes), these R waves will be about 20-30mm (4-6 large boxes)
If we take an EKG on someone and their T waves or ST segment are already inverted, how will we investigate this further?
• Nuclear medicine because you don’t want to do a stress test on someone whose heart is already apparently ischemic at rest
What constitutes a widened QRS?
• what conditions is this seen in?
• reason for widening?
QRS greater than 120mm aka greater than 3 small boxes is widened QRS
- See in BUNDLE BRANCH BLOCK related to ischemia or infarction
- QRS is widened because AP can’t propagate through fast conducting purkinje fibers and must take slow way through ventricles
**Note: Q, R, or S portions may get enlarged depending on where the block is
Someone rolls in the the ED with Widened QRS along with palor, anxiety, and chest pain. What do you do next?
TAKE them to the CATH lab
Is a prologued QRS ever physiologic?
• if so when?
NO, QRS is never physiologic, its always pathologic but its not specific to any particular disorder
Why we see T wave/ST segment inversion in ischemia?
T is usually a positive hump because it is the result of two negative (away actions)
1st - repolarizaiton is the opposite of polarization so we would expect a negative slope BUT
2nd - in NORMAL tissue repolarization takes place from epicardium to endocardium which we would also expect to give a negative slope BUT these two actions happening together causes a POSTIVTIVE hump
**IN ISCHEMIA 2ND PROCESS IS MESSED UP AND DECREASED CORONARY PERFUSION LEADS TO ENDOCARDIUM GETTING REPOLARIZED BEFORE EPICARDIUM AND WE NEGATIVE DIP*
Why is the Q wave enlarged in MI?
• Action Potential must take a back route that is slower instead of traveling down the purkinje fibers - bundle branch has been blocked
***WHAT ARE THE TWO PRINCIPAL MECHANISMS THAT CAUSE ARRHYTHMIAS?
- Altered/Enhanced Automaticity
2. Re-entry
What is the general underlying cause of Altered/Enhanced Automaticity?
- Cells are JUMPY - they are depolarizing when they shouldn’t
- caused by a PHASE 4 DIASTOLIC DEPOLARIZATION that rises to quickly
What are some Autonomic, Metabolic, Drug, and Ion factors that can increase Automaticity?
AUTONOMIC:
• MORE: Sympathetic Tone/ Catecholamines
• LESS: parasympathetic Tone
METABOLIC:
• MORE: CO2/Acidity (aka HYPOXIA), Temp.
• LESS: O2
DRUGS:
•Digitalis
IONS: Most common cause
• MORE: calcium
• LESS: potassium
What are some causes of Re-entry?
- Ischemia
- Valve Disease
- Cardiac Surgery
- Electrolyte Imbalance
What are some of the clinical effects of re-entry?
- Premature Atrial Depolarization
- SUPRAVENTRICULAR TACHYCARDIA
- VENTRICULAR TACHYCARDIA
- WOLFF-PARKINSON-WHITE
- Arrythmia in Pre-excitation Syndromes
