Midterm Flashcards
What is normal sinus rhythm (NSR)?
60-100 BPM
Syncope
Sudden fainting spell
Can indicate a decrease in CO / function
What causes angina?
Rapid arrhythmias that increase the oxygen demands of the myocardium
What is the most common arrhythmia that can lead to sudden death?
Ventricular arrhythmia
Why do arrhythmias happen?
- Mnemonic: HIS DEBS
- H - Hypoxia
- I - Ischemia & Irritability
- S - Sympathetic Stimulation (Exercise, etc)
- D - Drugs
- E - Electrolyte Disturbances (imbalances of Ca, Mg, hypokalemia)
- B - Bradycardia (sick sinus syndrome)
- S - Stretch
What lead yields the most information in rhythm strips?
Lead II
Holter Monitor vs. Event Monitor
Holter Monitor
- Ambulatory monitor
- Portable EKG w/ a memory
- Patient wears for 24-48 hrs
- 1-2 leads (1 limb, 1 precordial)
Event Monitor
- Better for rhythm disturbances that happen so infrequently that a Holter monitor is likely to miss it
- Record 3-5 mins of data, but is initiated by the patient when he/she experiences symptoms (palpitations)
- Sent over phone lines for evaluation
Rhythm Analysis Steps
- Calculate Rate
- Determine regularity
- Assess the P waves
- Determine PR interval
- Determine QRS duration
Rhythm Analysis
Step 1: Calculating Rate
Option 1:
- Count # R waves in a 6 sec rhythm strip, then multiply by 10
- Reminder: all rhythm strips in the modules are 6 seconds in length
- Interpretation: 9x10 = 90 BPM
Option 2
- Find an R wave that lands on a bold line
- Count the # of large boxes to the next R wave. If the 2nd R wave is 1 large box away, the rate is 300, 2 = 150, 3 = 100, 4 = 75, etc.
- Memorize the sequence: 300-150-100-75-60-50
- Interpretation: approx 95 BPM
Option 3
- Divide 300 by the # of large squares b/t R waves. Ex: 300/4 squares = 75
Option 4
- Count the total # of small squares b/t R waves and dividing 1500 by this total
- Most accurate but too TEDIOUS!
What does an absence of a P wave indicate?
What do irregular P waves indicate?
Absence: The rhythm originated below the atria
Irregular: Origins of depolarization are from different foci in the atria
PR Interval
Normal: 0.12 - 0.20 seconds (3 - 5 boxes)
PR interval is the beginning of atrial depolarization to the beginning of ventricular depolarization
Prolonged PR Interval = delay in conduction
QRS Complex Duration
Duration: Normal - 0.04 - 0.12 sec (1-3 boxes)
Wide QRS Complex = inefficient means of conduction, initiation of rhythm in ventricles
What are the 4 types of arrhythmias?
- Arrhythmias of Sinus Origin
- Sinus Tachycardia / Bradycardia
- Sinus Arrhythmia
- Sinus Arrest
- Asystole
- Nonsinus Pacemakers
- Junctional Escape Rhythm
- Ectopic Rhythms
- Paroxysmal Supraventricular Tachycardia
- Atrial Flutter
- Atrial Fibrillation
- Multifocal Atrial Tachycardia
- Paroxysmal Atrial Tachycardia
- Premature Ventricular Contractions (PVCs)
- Conduction Blocks
- Preexcitation Syndromes
Sinus Tachycardia
Rate > 100 BPM
Seen normally in exercise
Or abnormally in congestive heart failure (CHF), severe lung disease, or hyperthyroidism
Sinus Bradycardia
Rate < 60 BPM
Seen normally in well conditioned athletes or enhanced vagal tone resulting in fainting
or abnormally as an early stage in an acute MI
Sinus Arrhythmia
Normal, but slightly irregular
Reflects variation in HR w/ inspiration and expiration
Inspiration = accelerates HR
Expiration = decelerates HR
Sinus Arrest
Occurs when sinus node stops firing
If nothing else were to happen –> asystole (flat line)
Fortunately, other myocardial cells can spring in to action and take over pacing = escape beats
Asystole
Prolonged electrical inactivity
No CO / no blood flow
Treatment: CPR & Epinephrine IV
Nonsinus Pacemakers
- SA node: 60-100 bpm
- Atrial foci: 60-75 bpm
- Junctional foci (AV node): 40-60 bpm
- Ventricular foci (His bundle, bundle branches & purkinje system): 20-40 bpm
Anything below 40 bpm originates below atrium / AV node
Junctional Escape Rhythm
Of all escape rhythms, this is most common
Depolarization originates near AV node and usual pattern of atrial depolarization does not occur, thus…
NO P waves!
What are the mechanisms of Ectopic Rhythms?
Enhanced automaticity
Re-entry (beat from another circuit fires off)
Paroxysmal Supraventricular Tachycardia
- Regular narrow (QRS) complex tachycardia
- P waves are retrograde if visible
- Rate: 150-250 bpm
- Initiated by premature supraventricular beat and persisted by reentrant pathway
- Treatment: Carotid massage - slows or terminates
- Commonly involve re-entry loop mechanism
Carotid Massage
- Can help diagnose & terminate an episode of PSVT
- Baroreceptors sense changes in pressure which cause reflex response from brain to heart via vagus n. to slow HR (increase BP, decrease HR)
- Goals: Terminate the arrhythmia or slow it down to try and find p waves –> diagnosis
- Interrupts re-entry circuit
- You must listen for tubulent flow first b/c person may have a plaque blockage in carotid and you could loosen it and cause it to go to brain –> stroke
Atrial Fibrillation
- Irregularly irregular, w/o discernable P waves
- Undulating baseline
- Atrial rate: 350-500 bpm
- Ventricular rate: variable
- Carotid massage: may slow ventricular rate
- Narrow QRS complex
- Wavering baseline
*
Atrial Flutter
- Regular, saw toothed
- 2:1, 3:1, 4:1, etc. block (# of flutter waves: per QRS complex)
- Atrial rate: 250-350 bpm
- Ventricular rate: 1/2, 1/3, 1/4, etc. of atrial rate
- Carotid massage: increases block
Multifocal Atrial Tachycardia
- Irregular w/ a rate of 100-200 bpm
- At least 3 diff p wave morphologies from different atrial foci
- Aka. wandering atrial pacemaker when rate < 100 bpm
- Carotid massage: no effect
- Common w/ people w/ COPD
Paroxysmal Atrial Tachycardia
- Regular
- Rate: 100-200 bpm
- Characteristic warm up period in the automatic form
- Carotid massage: no effect, or only mild slowing
Premature Ventricular Contractions
- Aka. PVC’s most common of the ventricular arrhythmias
- QRS is wide and bizarre b/c ventricular depolarization does not follow normal conduction
- Bigeminy = 1 nl sinus beat to 1 PVC
- Trigeminy = 2 nl sinus beats to 1 PVC
- 3 PVCs in a row = run of V-Tach
When to worry:
- Frequent
- 3 or more in a row
- Multiform PVCs, in which they vary in their site of origin and hence their appearance
- PVCs falling on the wave of the previous beat –> R on T phenomenon; T-wave is a vulnerable period of cardiac cycle
- Any PVC occurring in the setting of an acute myocardial infarction
Ventricular Tachycardia
- Run of 3 or more consecutive PVCs
- Rate: 120-200 bpm and may be slightly irregular
- Sustained VT is an emergency preceding cardiac arrest
- Can be uniform or polymorphic (Torsades De Pointes)
Ventricular Fibrillation
- Preterminal event
- Seen almost solely in dying hearts
- Most frequently encountered in adults who experience sudden death
- Course or fine - no true QRS complexes
- No CO: CPR / defibrillation immediately
Accelerated Idioventricular Rhythm
- Benign rhythm seen during an AMI
- Regular rhythm occurring at 50-100 bpm
- Represents a ventricular escape focus that has accelerated sufficiently to drive the heart
- Rarely sustained, does not progress to VF, and rarely requires treatment
Torsades de Pointes
- “Twisting of the points”
- Form of VT usually seen in patients w/ prolonged QT intervals - prolonged QT can progress to this
- Prolonged QT: congenital or results from electrolyte disturbance (hypocalcemia, hypomagnesemia, hypokalemia), during MI, some drugs, PVC on T wave
- Replenishing Mg or Ca can often stop this
What is a myocyte?
- Cardiac cell
- Electrically polarized at rest
- Inside of cell is negatively charged compared to the outside
- Polarity is maintained by membrane pumps (controlling distributions of ions - sodium, potassium, chloride, and calcium) necessary to keep the inside of cells electronegative
Na+ / K+ Pump
Maintains membrane electrical polarity
3 Na+ outside for every 2 K+ inside
ATP is needed to keep cell polarized (in this state)
Types of Heart Cells
Pacemaker cells
Electrical Conducting Cells
Myocardial Cells
Pacemaker Cells
Electrical power source of the heart
- Depolarize spontaneously
- Rate of depolarization is determined by the innate electrical characteristics of that cell and the external neural and hormonal input
- Each depolarization serves as a source of a wave of depolarization that initiates one complete cycle of cardiac contraction and relaxation
Electrical Conducting Cells
The hard wiring of the heart
Myocardial Cells
The contractile machinery of the heart
Action Potential
- A record of one electrical cycle of depolarization and repolarization of a single cell
- This one action potential stimulates neighboring cells to depolarize until the entire heart has been depolarized and contracts