Interpreting EKGs Flashcards
How does the his bundle/purkinje system divide?
Into left and right bundle branches
Left into anterior and posterior fascicles
Left supplied by LAD
What is the SA node?
In upper right atrium
Intrinsic rate of depolarization is 60-100 bpm
What does each waveform on the EKG correspond to?
P wave - atrial depolarization, impulse went from SA to AV node
PR interval - how well the AV node is functioning
QRS - ventricular depolarization
T wave - ventricular repolarization
U wave - delayed repolarization seen in hypokalemia
What is the j point?
End of S wave
Important during stress testing
What are the important measurements to remember with the EKG paper?
Speed is 25mm/sec
Small boxes are 1mm, large are 5mm
Every small box is .04 sec, large is .2
10 mm vertically is 1mV
What are the different kinds of leads?
Limb leads (I, II, III, aVF, aVR, aVL) from frontal plane Pecordial leads (V1-V6) from vertical plane
How can you calculate heart rate from an EKG?
Divide 300 by the number of LARGE boxes between QRS complexes
If rate below 50 or rhythm irregular, count number of QRS complexes on one page and multiply by 6
What is the av nodes intrinsic rate?
40-60 bpm
What are the different forms of bradycardia?
Idioventricular rhythm
Junction all rhythm
Sinus bradycardia
Wandering atrial pacemaker
What is idioventricular rhythm?
Wide QRS complex without a p wave
Usually result of increased vagal tone forcing ventricles to take ove as pacemaker
What is junctional rhythm?
Diseased SA node forces junctional area (AV node) to take over pacemaking
No p waves due to simultaneous depolarization of A and V - but pacemaker high in junction could get inverted p wave, low in junction could get inverted p wave after QRS
What are possible causes of junctional rhythm?
Hypoxia, ischemia, digitalis toxicity, electrolyte abnormalities, and chronic lung disease
Why is the sinus bradycardia rate and what conditions is it seen in?
Less than 60
Can be normal in athletes
Also seen with diseased SA node, MI, or drug toxicity
What is a wandering atrial pacemaker?
3 different p wave morphologies
PR intervals can be changing
Rate of 60-100
Seen in young and healthy, esp athletes
What are the different tachycardias?
Multifocal atrial Sinus Paroxysmal supraventricular Atrial tach Atrial flutter Atrial fibrillation Ventricular tach Ventricular fibrillation
What is multifocal atrial tachycardia and where is it seen?
3 different p wave morphologies followed by QRS
rate greater than 100
Seen in older patients with chronic lung disease, coronary artery disease, CHF, and infection
What is paroxysmal supraventricular tachycardias?
Regular rhythm between 150-250
Involves reentrant pathway triggered by premature atrial contraction
Distinct p waves usually not seen because they’re combining with the t wave
What is atrial tachycardia?
Regular rhythm fast because of reentry pathway in atria at focus other than SA node
P wave is regular but different than in sinus rhythm
Usually 1:1 conduction to ventricles
What is one clue distinguishing between sinus tach and atrial tach?
With atrial tach, patients is usually normal and then this suddenly happens
Sinus tach is more chronic
What is atrial flutter?
Reentry pathway in atrium causes rate of integer fractions of 300
AV blocks some and conducts usually in 2:1 or 4:1 pattern
Ablation is potential cure
If HR is 150, suspect this with 2:1 block rather than sinus tach
Saw tooth pattern on EKG
What is atrial fibrillation?
Rhythm due to multiple reentrant pathways in atria causing irregular rate over 350
Irregularly irregular
AV node blocks most - rate is actually 60-140
Usually no p waves due to chaotic activity in atria
NO saw toothsome on EKG
What is v tach?
Regular rate of 120-220
Wide QRS since ventricle has to depolarize itself by reentry pathway
What is ectopy?
Irregular beats can occur if something takes over from SA node for a brief period of time
Either premature atrial contraction or premature ventricular, then resets to SA node and regular rhythm after brief pause
If doesn’t reset and PVC occurs at fixed rhythm –> “bigeminy”
What is sinus arrhythmia?
Variation of rhythm with respiration that is not clinically significant
What is normal axis, lefty axis deviation and right axis deviation?
Normal - -30 to 90 degrees
LAD - 90 degrees
What gives you the correct axis?
Lead that is isoelectric
Add or subtract 90 degrees based on whether or not lead I shows RAD
Where is normal axis positive?
Lead I and aVF
How do the leads clue you into any axis deviation?
QRS negative in lead I means RAD
QRS negative in lead II means LAD
QRS negative in both means extreme left or right deviation
What are some causes of right axis deviation?
Normal in infants and tall thin adults Right ventricular hypertrophy Chronic lung disease even w/o pulm HT anterolateral MI left posterior hemiblock PE WPW with left side accessory pathway Septal defects
What are causes of left axis deviation?
Left anterior hemiblock Emphysema Hyperkalemia WPW with right side accessory pathway Tricuspid atresia Ostium primum ASD
What is lown-ganong-Levine?
Short PR interval without delta wave
Accessory pathway merges his-purkinje system below AV node
What is a first degree heart block?
Prolonged PR interval (>0.2sec) with QRS after every P wave
Significant only in setting of MI (indicates recurrent ischemia) or endocarditis on aortic valve (indicates perivalvular abscess)
What is a mobitz type I (wenkebach) second degree heart block?
Prolonged PR interval that gets longer and longer until QRS finally drops
Block usually in (higher) AV node - can result from aging, drug toxicity, hyperkalemia, myocarditis, restrictive cardiomyopathy, and endocarditis
What is mobitz type II second degree heart block?
PR interval is constant with sporadic dropped QRS complexes
Same causes as type I
Block usually below AV node and can progress - likely need pacemaker
What is third degree heart block?
Complete dissociation between atria and ventricles
AV dissociation with bradycardia
Block higher in the node causes narrow complex, lower in the node causes wider complexes
Temporary pacemaker needed with acute MI
What kind of blocks does the QRS interval indicate?
Bundle branch blocks
Normal is .08-.1 seconds, .1-.12 is hemiblock or fasicular block
What does an EKG of a LBBB show?
Widened QRS
RSR’ in v5 and v6 - first r wave is RV depolarization, R’ is later LV depolarization
No S wave in lead I
What are the causes of a LBBB?
Idiopathic/degenerative CAD Hypertrophic cardiomyopathy HT new LBBB suggests anterior MI because its supplied by LAD
What are the EKG findings in RBBB?
Wide QRS complex
RSR’ in v1
Rabbit ears in V1
Broad S wave in lead I
What are some causes of RBBB?
Ischemia
Idiopathic/degenerative
Pulmonary disease
With st elevations in v1-v3 = brugadas syndrome - high risk for SCD secondary to v fib
What is a left anterior fascicular block or left anterior hemiblock?
QRS between .1-.12 with LBBB looking pattern and left axis deviation
Wave of depolarization now starts from bottom of heart
Benign unless in context of acute MI
No S wave
What is a left posterior fascicular block or left posterior hemiblock?
QRS complex between .1-.12 with LBBB looking pattern and right axis deviation
Benign unless in acute MI
S wave
What is a bifasicular block?
Can be combo of RBBB with either LAFB or LPFB
What kinds of abnormalities does the QTc interval show?
Electrolyte abnormalities that regulate repolarization of ventricles
Normal is .4 for a man and .44 for a woman
What are causes of prolonged QTc?
Congenital - risk of SCD from v fib - jervell-Lange-Nielsen (AR and associated with deafness), Romano-ward (AD) Acquired - decreased serum ca, mg, and k, CNS lesions, ischemia, class Ia, Ic, and III antiarrhythmics, erythro, phenothiazines
What are causes of short QTc?
Hyperkalemia, hypermagnesemia, and hypercalcemia
Not as worrisome as long QTc
What is important to remember when diagnosing hypertrophy and enlargement off an EKG?
Voltage criteria only applies if QRS is otherwise normal
How does left ventricular hypertrophy present on an EKG?
Amplitude of r wave in lead aVL >11 mm or amplitude of r wave in v4-6 >25 mm
Amplitude of S wave in leads v1 + amplitude of r wave in v5 or v6 >35 mm
What four conditions can LVH be seen with?
HT
Constrictive pericarditis
Hypertrophic cardiomyopathy
Infiltration diseases of myocardium
What does right ventricular hypertrophy look like on EKG?
Tall r wave in v1 with amplitude >7 mm
Amplitude of r wave in v1 + amplitude of S wave in v6 >10 mm
What does left atrial enlargement (p mitrale) look like on EKG?
Wide and deep p wave in v1
Both >1 mm
What does right atrial enlargement (p pulmonale) look like on EKG?
P waves >2.5 mm in leads II, III, or aVF
When is ST depression significant?
If depressed by 1 mm
What are some causes of st depression?
Ischemia
LVH with strain
Digitalis
Benign
What is the pathophysiology of ST depression?
Decreased blood supply to subendocardial layer
Doesn’t extend to all layers - no q wave
Enough potassium lost from tissue in deep layers to alter repolarization
What are some causes of t wave inversion?
Ischemia LVH with strain Abdominal pain Digitalis CNS hemorrhage
What is significant ST elevation?
1 mm in limb leads and 2 mm in precordial leads
What are some causes of ST elevation?
MI early repolarization Acute pericarditis LBBB Prinzmetals angina Hyperkalemia Hypothermia LVH Persistent = ventricular aneurysm at site of infarct
What is the pathophysiology of st elevation?
Leakage of potassium from damaged tissue lowers electrical baseline and gives appearance of elevation since depolarization and repolarization less dependent on ratio of potassium
What does a q wave indicate?
Muscle death from lack of blood supply
Dead muscle cannot repolarize
Pathologic if 1 small box wide and deeper than 25% of r wave
What is the anatomy of blood supply to the heart?
LAD supplies anterior
Circumflex supplies lateral
RCA supplies inferior
PDA supplies posterior (from RCA in most, from circumflex in some)
What leads look at the anterior part of the heart?
V1-v2
Entire septum involved: v1-v4
What leads look at the inferior part of the heart?
II, III, and aVF
What EKG findings indicate posterior MI?
Tall r wave in v1 with concurrent st depression in v1-v2 or II, III, and aVF
Which leads look at the lateral part of the heart?
I, aVL
How can you look specifically at the right ventricle on an EKG?
Precordial leads placed opposite direction
Look at v4r to indicate MI
What should one suspect if no r wave in v1 or v2?
Old anterior MI
What is early repolarization and what does it look like on EKG?
Common finding in healthy young individuals
T wave begins during st segment and makes it appear mildly elevated
Commonly seen in v2 and v3 up to 1-3 mm
What does hypokalemia look like on EKG?
U wave due to delayed repolarization of ventricles
Seen in a few leads, not all
What does hyperkalemia look like on EKG?
*peaked t waves
Followed by short QTc, wide QRS, and flat to absent p waves
Resembles sine wave when k reaches critical levels
What does a PE look like on EKG?
Sinus tachycardia
Can show broad S wave in lead I followed by q and inverted t in lead III
Right heart strain gives RB pattern in lead I and the other effects since lead III is over RV
What does pericarditis look like on EKG?
Diffuse st elevation and pr depression - both ventricles and atria are injured and alter baseline
What does hypothermia appear like on an EKG?
Osborne wave - upward deflection of second half of QRS complex
