CARDIAC LECTURE 4: DYSRHYTHMIAS Flashcards
What are the 2 functions of the autorhythmic fibers of the heart?
- Spontaneously depolarize to create action potentials
- Propagate/conduct action potentials through the heart
What is the name of the pacemaker of the heart, and where is it located?
Sinuatrial node, located in the right atrium superiorly
What is the function of the AV node?
Delays signals before transmission to AV bundle
After transmission to the AV bundle, where do electrical signals travel?
Right and left bundle branches
After transmission to bundle branches, where do electrical signals travel?
Subendocardial conducting network (Purkinje fibers)
After spontaneous depolarization, what causes rapid depolarization in the SA node?
Sodium influx through voltage gated fast channels
What causes the plateau/maintained depolarization in the sinoatrial node?
- Calcium influx through voltage gated slow channels
- Potassium outflow through some channels
What causes repolarization of the sinoatrial node?
- Calcium channels close
- Potassium outflow when more channels open
What prevents the membrane from depolarizing too soon after the previous action potential?
Refractory period
What are 3 possible mechanisms that cause dysrhythmias, and which is most common?
- Abnormal automaticity
- Triggered activity from depolarization
- Reentrant circuits (most common)
What is the meant by abnormal automaticity?
- Too fast/slow rate of depolarization generation
- Ectopic impulse generation
What is an example of a cause for abnormal automaticity?
Ischemia causes ATP depletion, which disrupts ion gradients
What is meant by triggered activity from depolarization?
Impulse generated during or just after repolarization
What is an example of a cause for triggered activity?
Genetic abnormalities/drugs alter calcium homeostasis
What is meant by reentrant circuits?
Cardiac impulse continues depolarizing a part of the heart after repolarization
What are 2 examples of causes for reentry?
- Cardiac scarring
- Mutations of genes that code for gap junction proteins
What is the purpose of a 12-lead ecg?
Measure the electrical activity of the heart from all angles
What does the P wave indicate?
SA node and atrial depolarization
What does the QRS complex indicate?
Ventricular depolarization
What does the T wave indicate?
Ventricular repolarization
What unit of time does one large box indicate on the ECG strip?
0.2 seconds
What are the 3 major types of cardiac dysrhythmias?
- Abnormal rates of sinus rhythm
- Ectopic sites of impulse initiation
- Disturbances in conduction pathways
What are treatments for sinus bradycardia?
- Drugs that activate sympathetic nervous system
- Drugs that block parasympathetic nervous system
What are 2 causes for ectopic sites of initiation?
- If the SA node fails then a slower pacemaker will take over
- Any premature depolarization that overrides the SA node
What does an atrial flutter look like on the ECG?
Sawtooth pattern, regular ventricular rate/rhythm
What is the most common reason for atrial flutter?
Reentrant rhythm in atria (continue depolarizing in atria even after repolarization everywhere else)
Why does atrial flutter not cause the ventricles to flutter as well?
AV node has a long refractory period so not all atrial depolarizations get through
What does atrial fibrillation look like on an ECG?
Irregular atrial rhythm (squiggles), irregular ventricular rhythm (not evenly spaced)
What is the cause of atrial fibrillation?
Rapid depolarizations from numerous ectopic sites
Why does atrial fibrillation involve irregular ventricular rhythm?
Ventricles only contract during occasional depolarizations near the AV node
What does ventricular tachycardia look like on an ECG?
“Tombstones” Wide QRS complexes at >100bpm
What is the mechanism that causes v-tach?
Ectopic site within ventricle spreads throughout ventricular region
What may induce v-tach?
- Hypoxia
- Hypokalemia
- HF
- Sympathetic stimulation
What does ventricular fibrillation look like on an ECG?
No discernable waves, just one long squiggle
What is the mechanism behind v-fib?
Multiple foci fire in a chaotic manner, producing quivering myocardium (no pumping)
What is the term for a dysrythmia where there is a problem between sinus impulse and ventricular response, either slowed or completely blocked?
Atrioventricular block
What type of AV block shows a prolonged PR interval (slowed ventricular contraction) and is usually asymptomatic?
1st degree block
Which type of AV block involves intermittent atrial conduction to ventricles?
2nd degree
What are 2 types of 2nd degree AV block?
- Irregular rate: PR intervals progressively lengthen until one QRS complex is dropped
- Regular rate: A few P waves before a QRS complex
Which type of AV block involves complete block of atrial conduction to ventricles, where the ventricles are paced by an independent pacemaker site?
3rd degree
What is the treatment for 3rd degree AV block?
Transcutaneous pacing or pacemaker
What are 4 methods of treatment for dysrhythmias?
- Vagal maneuvers (stimulate parasympathetic nervous system)
- Ablation (destroy abnormal tissue)
- Electrical interventions
- Anti-arrhythmic drugs
What are 3 electrical interventions for dysrhythmias?
- Pacemakers
- Cardioversion (with pulse)
- Defibrillation (without pulse)
What are 4 kinds of anti-arrhythmic drugs?
Class 1: Sodium channel blockers
Decrease depolarization and atrial contraction
Class 2: Beta blockers
Decrease SNS activity to slow heart rate and decrease contractility
Class 3: Potassium channel blockers, and Class 4: Calcium channel blockers
Prolong AP time and refractory period
