Chapter 3 Flashcards
Why are normal, everyday cardiac rhythms called normal sinus rhythm?
Because each beat originates with depol of SA
What rate does heart normally beat?
60-100 bpm
Define arrythmia.
Any disturbance in rate, regularity, site of origin, conduction of electrical impulse
What are several characteristic sx of arrhythmias?
- Palpitations (awareness of one’s own heartbeat - accel/decel/regular/irregular)
- Syncope/light-headedness (due to decreased CO)
- Angina (chest pain, due to increased O2 demands of myocardium –> can precipitate CHF)
- Sudden death
What arrhythmogenic factors should be considered for pts w arrythmias?
- HIS DEBS
-
Hypoxia
- Myocardium deprived of O2 = irritable
- Pulm disorders = major precipitants of cardiac arrythmias
-
Ischemia + irritability
- Myocardial infarctions + angina w or w/o cell death = major precipitants
- Myocarditis (inflamm of heart muscle, often caused by routine viral infections) can also induce arrhythmia
-
Sympathetic stim
- Can be from hyperthyroidism, CHF, nervousness, exercise
- Drugs, even antiarrhythmic drugs (e.g. quinidine)
-
Electrolyte disturbances
- Hypokalemia
- Ca + Mg imbalances
- Bradycardia (incl. bradytachycardia aka sick sinus syndrome)
- Stretch (englargement + hypertropy of atria/ventricles, CHF, cardiomyopathies, valvular disease)
(T/F) 12-lead EKG is sufficient to view heart rhythm if arrhythmia is suspected.
F, run rhythm strip (long tracing of single or mult leads)
What is the diff b/w Holter and event monitors?
- Holter or ambulatory monitor
- Worn for 24-48h
- Monitor can employ 1-2 leads (1 precordial and 1 limb lead)
- Rhythm stored for later analysis of arrhythmias
- Best for infrequent occurance
- Event monitor
- Worn over course of several months
- Initiated by pt during palpitations
- Records only 3-5min of rhythm strip
- Best for even less frequent occurances
How to det HR from EKG?
- Find R wave that falls on heavy lines
- Count number of boxes until next R wave
- Determine rate:
- 1 lg square: 300bpm
- 2 lg squares: 150bpm
- 3 lg squares: 100bpm
- 4 lg squares: 75bpm
- 5 lg squares: 60bpm
- 6 lg squares: 50bpm
- Can divide 300 by number of lg squares or 1500 by number of sm squares
*Can also count number of cycles within two 3s intervals and mult by 10
What are the 5 basic types of arrhythmias?
- Arrhythmias of sinus origin - follows usual conduction pathways (too fast/slow/irregular)
- Ectopic rhythms - electrical activity originates elsewhere than SA node
- Reentrant arrhythmias - electrical activity trapped within electrical racetrack, can occur anywhere within heart
- Conduction blocks - electrical activity originates in sinus node, follows usual pathways but encounters unexpected blocks and delays
- Preexcitation syndromes - electrical activity follows accessory conduction pathway other than normal –> electrical shortcut/ short circuit
Describe sinus tachycardia and sinus bradycardia.
- Depol originates in SA node
- Above 100bpm or below 60bpm
- Can be normal or pathologic as with sig heart disease
- CHF, severe lung disease, hyperthyroidism in elderly –> tachy
- Early stages of acute MI, enhanced vagal tone –> brady
- Brady can lead to fainting
Define sinus arrhythmia.
- Slightly irregular but in all else appears NSR = normal phenomenon
- Variation in HR accompanies inspir + expir
- Inspir –> accel HR
- Expir –> decreases HR
- Diminishes w age, obesity, in pt w long-standing HTN, DM pt w autonomic neuropathy
What is the difference between sinus arrest, asystole, and escape beats?
- Sinus arrest –> SA node stops firing
- Prolonged arrest = asystole
- Escape beats –> all cells have pacemaker ability –> other pacemakers spring into action
- SA node: usually has overdrive suppresion of other foci
- Atrial automaticity focus: 60-80bpm
- Junctional automaticity focus: 40-60bpm (most common; AV node typically won’t take over if SA node fails)
- Ventricular automaticity focus: 30-45bpm (any of purkinje fibers)
- What can happen at any of these foci is reentrant rhythm (e.g. Afib
What is a junctional escape rhythm?
- Depolarization occuring at/near AV node
- Usual pattern of atrial depol doesn’t occur –> no normal P wave but may see retorgrade P wave
What is retrograde P wave?
- Depol of atrium moving backwards from normal direction
- Axis of P wave reversed 180 degrees –> inverted P wave
(T/F) It is impossible to determine whether prolonged sinus pause is due to sinus arrest or sinus exit block.
T, but sometimes can be distinguished
- Sinus arrest: resumption of sinus electrical activity occurs at random time
- Sinus exit block: resumption in some integer multiple of normal cycle (fired regularly but silently)
What are reentrant rhythms?
- Disorder of impulse transmission: Depol arriving at two adjacent regions of myocardium and one wave transmits more slowly than the other (e.g. from ischemic disease/fibrosis/diff degrees of ANS input) –> wave of depol pushes through slower pathway –> revoling circuit with current sending waves of depol in all directions
- Normally: depol arriving at two adjacent regions of myocardium, conducting current at same rate –> depol continues normally
