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 is sinus exit block?
Failure of sinus depol to be transmitted out of node into atria
What are two major causes of nonsinus arrhythmias?
Ectopic and reentrant rhythms
What are ectopic rhythms?
- Disorder of impulse formation: abn rhythms arising elsewhere from SA node
- Single + isolated or sustained
- Cause:
- Enhanced automaticity of non-SA node, overdrives normal sinus mechanism
- Often due to digitalis toxicity and beta adrenergic stim from inhalaer therapies used to treat asthma + COPD
*
- Often due to digitalis toxicity and beta adrenergic stim from inhalaer therapies used to treat asthma + COPD
- Enhanced automaticity of non-SA node, overdrives normal sinus mechanism
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
