Week 2 - Basic EKG Flashcards
The resting cardiac cell myocyte has a membrane potential of __________ mV
-90
inside is negative relative to outside
When the cardiac cell is depolarized, what occurs?
Influx of positive ions come into the cardiac cell (Ca++ for nodal and Na+ for cardiac myocytes) - making the inside positive compared to the negative outside
Once this action peaks, K+ is released from the cells driving the cell back to its resting state (-90 mV cardiac myocytes, -60 mV nodal cells)
What is the normal order for the cardiac conduction system
SA node –> AV node –> Bundle of His (left and right bundles) –> Purkinje fibers
The _____ ________ is electrically dominant
Left Ventricle
What are the normal interval lengths?
PR ______
QRS _______
QTc _______
PR: 0.12-0.20 seconds (120-200 msec) or 3-5 small boxes
QRS: 0.08-0.12 seconds (80-120 msec) or 2-3 small boxes
QTc: 0.35-0.44 seconds ish (350-440 msec)
Voltages can be represented as?
Vectors (direction and magnitude)
Is a normal T wave symmetrical or asymmetrical?
Asymmetrical
Slurred upstroke
What are the bipolar leads
Lead I, Lead II, Lead III
(limb leads)
Measures electrical differences between 2 electrodes. 1 positive, 1 negative
Where are the augmented leads placed?
aVR - Right arm, above wrist
aVL - Left arm, above wrist
aVF - Left foot, above ankle
How much time is represented by one little square on the ECG strip? One big square?
Little square - .04 seconds/40msec
Big square - .2 seconds/200msec
What are the waves of an ECG? What do they represent?
P wave - Atrial depolarization
QRS complex - Ventricular depolarization
T wave (and U wave) - Ventricular repolarization
A signal of 1 mV amplitude produces a ________ mm deflection
10
* 10 little boxes or 2 big boxes
Where is correct placement of the precordial leads?
V1 - 4th intercostal space, right of sternum
V2 - 4th intercostal space, left of sternum
V3 - midway between V2 & V4
V4 - 5th intercostal space, midclavicular line
V5 - anterior axillary line, same level as V4
V6 - midaxillary line, same level as V4, V5
What axis deviation would you suspect in a mainly negative deflection in lead I and a mainly positive deflection in an aVF lead sample
Right axis deviation
What axis deviation would you suspect in a mainly positive I lead and a mainly negative II lead sample
Left axis deviation
How would you describe the axis deviation if defletions were positive in lead I and II?
Normal axis deviation
The initial QRS vector is directed in which way?
To the right, anteriorly and slightly superiorly or inferiorly.
The main QRS vector is directed which way?
To the left, posteriorly and inferiorly. Represents R wave
The terminal QRS vector is directed which way?
Backwards and upwards, may go to the left or right. Represents S wave
depolarization of purkinje fibers
What are the precordial leads? Are they unipolar or bipolar?
V1-V6 (chest leads), unipolar
What parts of the heart can we visualize from the precordial/chest leads?
Anterior, septal, and lateral walls
What is the relationship of R and S waves in the precordial leads? Moving from right to left
rS —> Rs
R waves increase in size as S waves decrease in size
What is the transition zone?
Equal R and S waveform voltages. Usually occurs around V3-V4. Normal variant to have an early V2 or late V5 transition zone
In what lead is the R wave amplitude the greatest?
Usually lead V5, sometimes lead V4. V6 has a smaller R wave due to interference of the left lung
How long would a broadened P wave be (prolonged atrial activation time)?
> 0.11 seconds
What might be the cause of a prolonged p-wave (>0.11 seconds)?
- Inter atrial conduction delay
- Sick sinus syndrome
- Dual chamber pacemaker
P wave abnormalities in Right Atrial Enlargement
Normal conduction speed, increased p wave amplitude >2.5 mm
Lead II is best for p waveform
Associated with pulmonary valve stenosis, pulmonary hypertension, and cor pulmonale
Wandering atrial pacemaker characteristics
- Three different looking p waves (less than 100 bpm)
- Natural pacemaker cells move from SA node to distant cells within the SA node
- Caused by varying vagal tone (increased tone causes a decreased conduction speed within the SA node)
What could an accelerated idioventricular rhythm indicate?
Usually indicates reperfusion of the heart (short lived) after a cardiac event
How would you describe a 1st degree AV block?
PR intervals longer than .2 seconds
QRS complex for each p wave
* Slowing of conduction within the AV node
Which block consists of progressively longer PR intervals followed by a dropped QRS.
Second degree AV block Type 1 (Mobitz I or Wenckebach)
* “Longer, longer, longer drop, then you have a wenckebach”
Second degree Mobitz II AV block characteristics
- PR interval remains constant, can be normal or prolonged
- Intermittent QRS dropped
- Always INFRANODAL
- Usually an emergent scenario
- Usually wide QRS!
Every other P wave being conducted is an example of __________
2:1 AV block.
Unless there has been an MI, generally if it has a wide QRS complex it is occurring in the His/Purkinje system. This means a 2nd degree type 2 block! BAD, get pacing pads
Which AV block consists of P waves and QRS complexes occuring, but independent of each other?
3rd degree AV block (complete)
NEEDS A PACEMAKER
The frontal plane consists of leads:
I, II, III, aVR, aVL, aVF
(limb leads and augmented limb leads)
The horizontal plane consists of leads:
V1-V6
(precordial leads)
When a wave of depolarization spreads toward a lead’s positive pole, it causes a _________ deflection
positive (upward)
When a wave of depolarization spreads toward a lead’s negative pole, it causes a _________ deflection
negative (downward)
A biphasic deflection occurs when a wave of depolarization is moving _________
at a right angle to the lead
What two things determine the QRS Axis?
- Anatomical position of the heart
- Direction the stimulus spreads through the heart
What is a possible pathological cause of right axis deviation
- Right ventricular hypertrophy
- Lateral wall MI
- COPD
What is a possible pathological cause of left axis deviation?
- Left ventricular hypertrophy
True or false:
Palpitations are always an abnormal/pathological finding
False
* may occur with increased sympathetic stimulation (e.g. excitement, anxiety, exercise)
Treatment of sinus tachycardia associated with a pathologic cause must always be directed at ____________
the underlying cause (sepsis, fever, internal bleeding, etc.)
What is an escape beat or rhythm?
If a primary or “higher level” pacemaker (e.g. SA node) fails to fire or conduct, another pacemaker (e.g. AV node) may generate a “rescue” beat or rhythm, generally at a slower rate
What are the rates for the secondary pacemakers?
- Atrial cells: 60-80 bpm
- AV nodal/junctional: 40-60 bpm
- His/Purkinje: 20-40 bpm
- Ventricular myocytes: <20 bpm
In junctional escape rhythm, the atria are activiated in a retrograde fashion, producing ___________ p waves in leads II, III, aVF
negative
Idioventricular escape rhythms usually have ________ complex QRS and indicate a potentially life threatening situation
wide
* infranodal causes asynchronous depolarization of ventricles
In urgent situations, intravenous __________ can be adminstered to increase the rate of atrial or AV nodal pacemakers
atropine
__________ will may be effective for bradycardia resulting from infranodal escape rhythms - instead __________ agents should be adminstered
sympathomimetic (dopamine, isuprel)
The most common cause of short term sinus arrhythmia is _________
respiration
* inspiration increases sympathetic tone (increased RR)
* Expiration increases vagal tone (decreased RR)
What is the progression of treatment for acute PSVT?
- Vagal maneuvers
- IV adenosine
- Beta/Calcium channel blockers
- Cardioversion (rarely needed)
How does the ECG for A-flutter and A-fib differ?
- Flutter: regular interval, nearly identical saw-tooth waves (suggestive of single, stable reentrant pathway)
- Fib: “wavelets”, varying continuosly in amplitude and polarity (suggestive of multiple, unstable ectopic foci)
1:1 AV conduction of a-flutter is a medical emergency treated with _________
immediate synchronized cardioversion
Acute treatment of a-fib or a-flutter focuses on ________. This can be achieved with the use of __________
- rate control or rhythm control
- AV nodal blocking agents (beta blockers, calcium channel blockers
What is AVNRT?
Atrioventricular nodal reentry tachycardia. Most common reentry SVT (60%). More common in females
What are the characteristics of AVNRT?
A circuit is formed via 2 separate pathways. This generally creates a slower and faster pathway. The slower pathway (normal conduction) arrives to the ventricles later. The faster pathway activates the atria and ventricles simultaneously. Normal QRS waveform. Because circuit is within the AV node, the QRS looks “normal”
AVNRT and AVRT are _________ on AV nodal conduction.
dependent
What is AVRT?
Atrioventricular reentry tachycardia
Second most common reentry tachycardia. Most common in males
How does AVRT work?
Conduction circuit involving the atria and ventricles. This causes the faster conduction pathway to hit the ventricles before the normal pathway does. The result is wide QRS complexes manifested by delta waves.
Short PR, delta waves, and wide QRS
Multifocal atrial tachycardia characteristics
Rate greater than 100
3 different looking p waves
Generally occurs in COPD patients
Sustained VT is defined as lasting longer than _______ _________
30 seconds
______ or more PVC’s is considered _________ ___________
3, ventricular tachycardia
What causes the wide QRS morphology in PVC’s
Impulse begins in one of the ventricles and they are simultaneously stimulated
PVC’s arising from the base of the heart have an inferior/rightward axis and are considered ___________, occuring in a structurally ____________ heart
- benign
- normal
During PVC’s, ST-T waves directed in the opposite direction of the QRS is a __________ finding, and ____________ myocardial ischemia
- common
- is not indicative
Polymorphic VT in the absence of QT prolongation most often indicates _________
ACUTE MYOCARDIAL ISCHEMIA
Accelerated idioventricular rhythm (AIVR) is particularly common in __________ and may be a sign of __________
- acute MI
- reperfusion
Determine which rhythm is pictured:
1st Degree AV block
Determine which rhythm is pictured:
2nd Degree AV block Type I - Wenkebach
Determine which rhythm is pictured:
2nd Degree AV block Type II
Determine which rhythm is pictured:
3rd Degree AV Block
Wolfe-Parkinson-White is characterized by ___________ of the ventricles
Pre-excitation
Describe the WPW triad. Why does this occur?
- Short PR interval, Wide QRS, delta wave
- Ventricles are stimulated early via an accesory conduction path
What ECG findings are consistent with hyperkalemia?
- peaked T waves in precordial leads, sometimes taller than R waves
- widened QRS
- small or indiscernible p waves
- 1st degree AV block
What ECG findings are consistent with hypokalemia?
- U wave prominence
- Increased P wave amplitude
ECG changes aren’t as dramatic and may be rare
QT prolongation may be a manifestation of what electrolyte abnormality? What is a possible complication?
- hypomagnesemia
- Torsades
Hypocalcemia may present with a _______ ST segment, while hypercalcemia may present with a _________ ST segment
- long
- short
True or false
Mechanical component of the heart is shown on an ECG
False
Which heart valves interact with deoxygenated blood?
Tricuspid and pulmonic valve
4 main ions responsible for electrical conduction within the heart?
Ca ++, Na +, K +, Cl-
Which heart pump is responsible for maintaining the resting potential of the heart?
Na+/K+ pump. 3 Na+ taken OUT of the cell, 2 K+ brought INTO the cell!
(-90 mV resting potential)
Changes in membrane potentials causing depolarization and repolarization cause ______________
Contraction and relaxation of the cardiac myocyte
Increased muscle thickness causes _________ conduction times
Increased
What ion is responsible for depolarization of SA nodal cells?
Calcium
(think about the effect of CALCIUM channel blockers on HR - they slow the SA node and subsequently the HR)
Funny channels allow Na+ to enter the cell first, than Ca+ is primarily responsible for depolarization via L type (Main) and T type channels
Which leads are best to visualize the p waves
II and V1
The P waves should always be positive (upward deflections) in normal conduction in which leads
II, III, aVF
Which arrhythmia has a shift of the natural pacemaker site from the head of the SA node to distant sites within the SA node
Wandering Pacemaker
3 different looking p waves
Rate less than 100
What is occuring during the plateau phase of myocyte action potentials?
There is an equal outflow of potassium (+) from the cell and inflow of calcium into the cell (+). The balance in charges causes a relatively flat morphology.
PVC’s are followed by a _________ ____________
Compensatory Pause
The following is a diagram of the action potential of which type of cardiac cell?
SA/AV Nodal
The following is a diagram of the action potential of which type of cardiac cell?
Cardaic Myocyte
* morphology for atrial vs ventricular is slightly different, but follow this general pattern
What does a negative delta wave in lead I suggest in WPW?
right sided accessory pathway
When would you likely see Osborn waves?
Hypercalcemia, hypothermia
Opposite of a normal T wave, quick upstroke slurred downstroke. Can look like an MI
