Heart 5 Flashcards
From what do cardiac arrhythmias result?
Disturbances in impulse formation or impulse conduction (or both in combination).
Define altered automaticity
Alterations in pacemaker rate that are mediated through changes in the pacemaker mechanisms that normally exist in pacemaker cells
Tachycardia vs bradycardia
> 100 BPM vs
Seven possible causes of tachy-dysrhythmias
- Norepinephrine
- Stimulants
- Ischemia
- Stretching
- Sick sinus syndrome
- Fever
- Hyperthyroidism
EKG manifestations in tachy-dysrhythmias
Sinus tachycardia, PAC’s, PVC’s, AT/VT, SVT
Five possible causes of brady-dysrhythmias
- Drugs
- Barbiturates
- Ischemia/infarct
- Sick sinus syndrome
- Aging
EKG manifestations of brady-dysrhythmias
- Sinus bradycardia
Where can re-entry of excitation happen?
Anywhere in the heart
What is the most common cause of dysrhythmias seen clinically?
Re-entry of excitation
Three general requirements for re-entry of excitation to occur
- Proper geometry for a conduction loop
- Slow or delayed conduction
- Unidirectional conduction block
Possible causes of re-entry of excitation
Ischemia, infarct, congenital bypass tracts
Possible EKG manifestations during episodes of re-entry of excitation
PVC's/PAC's AT/VT SVT Atrial flutter A-/V-fib
Where in the heart can triggered activity happen?
In the atrial or ventricular tissues
What is the cause of delayed afterdepolarization?
Abnormally elevated intracellular calcium concentration
When are delayed afterdepolarizations clinically documented?
With dysrhythmias resulting from digitalis toxicity
Possible causes of delayed afterdepolarizations
- Digitalis toxicity
- Elevated catecholamines
- Rapid heart rate
Combination of all the above
Possible manifestations from delayed afterdepolarizations
PAC/PVC’s
A-/V-tach
Mechanism of delayed afterdepolarization (it’s a long one.)
- Elevated calcium is taken up by the SR
- After SR is overloaded, AP can trigger abnormal release of Ca after AP has ended
- Extra released Ca extruded by Na/Ca exchanger
- Net inward current produced by exchange
- Triggers DAD
- If DAD amplitude is large enough to reach threshold, an AP is generated*
Early afterdepolarizations are related to . . .
prolongation of action potential duration.
Mechanism of early afterdepolarizations
Still not certain, but could be due to abnormal re-activation of the slow inward calcium current
To what else are early afterdepolarizations thought to be linked?
Prolonged Q-T syndrome
Possible causes of early afterdepolarizations
- Acidosis
- Hypokalemia
- Quinidine
- Slow heart rates
Possible EKG manifestations of early afterdepolarizations
PAC’s/PVC’s
A-/V-fib (torsades de pointes)
What does the voltage graph look like during stimulation of Purkinje fibers in cesium solution?
Multiple repetitive triggered action potentials at CL>10 seconds
What can single triggered action potentials result in?
Premature beats
What can repetitive triggered action potentials result in?
Runs of tachycardia
Anti-arrhythmic therapies
- Drugs
- Radio-frequency ablation
- DC cardioversion
- Implantable cardioverter-defibrillator
Normal range for P-R interval
120-200 ms
Normal range for QRS complex
70-100 ms
Normal range for Q-T interval
250-430 ms
