EKG I & II Flashcards
In a 3 lead EKG, what does lead I measure?
Lead I measures electrical potential between left arm (+) and right arm (-)
In a 3 lead EKG, what does lead II measure?
Lead II measures electrical potential between left leg (+) and right arm (-)
In a 3 lead EKG, what does lead III measure?
Lead III measures electrical potential between left leg (+) and left arm (-)
What 3 pieces of information can you get from a 3 lead EKG?
- HR
- Regularity of heart beat
- Length of conduction in different parts of the heart *May fail to reveal various abnormalities (12 lead EKG is now standard of care)
Name all of the leads included in a 12 lead EKG
- Limb leads I, II, and III
- Augmented leads aVR, aVL, and aVF
- Precordial or chest leads V1-V6.
In the X-axis, each small box is ____mm and represents ____sec.
Each large box is 5 small boxes and represents ____sec.
5 large squares equals ____sec.
In the X-axis, each small box is 1 mm and represents 0.04 sec.
Each large box is 5 small boxes and represents 0.20 sec.
5 large sqaures equals 1 sec.
In the Y-axis, each small box represents ____mV and each large square represents ____mV
In the Y-axis, each small box represents 0.1 mV and each large square represents 0.5 mV.
What is the primary pacemaker of the heart, located in the upper right atrium?
Sinoatrial node (SA node).
- Intrinsic rate 60-100 bpm
This structure slows impulses and backs up the pacemaker (i.e. if SA node stops working), and is located in the lower right atrium. AKA “gatekeeper”
Atrioventricular node (AV node)
- Intrinsic rate 40-60 bpm
Which structure spans from the AV node through the top portion of the ventricular septum and has an intrinsic rate of 20-40 bpm?
Bundle of his
The intrinsic rate of the left and right bundle branches is ______bpm
20-40 bpm
The intrinsice rate of Purkinje fibers is _____bpm
10-30 bpm
What does the P-wave represent?
- Depolarization of atria in response to SA node triggering.
- A normal P wave means the SA node is properly initiating the beat
What does the PR interval represent?
- Atrial depolarization through the onset of ventricular depolarization (delay of AV node to allow filling of ventricles).
- Used to measure the regularity of the rhythm (if R-R distance is the same throughout, you have a regular rhythm)
What does the QRS complex represent?
Ventricular depolarization - time from the AV node through the Purkinje fibers
What does the ST segment represent?
Beginning of ventricle repolarization (the time between ventricular depolarization to repolarization)
What does the T-wave represent?
Ventricular repolarization/relaxation
Dimentions of a normal P-wave:
- Normally (upright/inverted), but may be (upright/inverted) in aVR and V1.
- Up to _____mm in amplitude
- Less than _____ sec (or less than _____ small boxes)
- Normally upright, but may be inverted in aVR and V1.
- Up to 2.5 mm in amplitude
- Less than 0.12 sec or less than 3 small boxes
What does “sinus” mean?
Sinus only means SA node is pacing. It does not necessarily mean nl EKG.
The presence of broad, notched (bifid) P waves in lead II or V1 is a sign of ____________________.
The presence of broad, notched (bifid) P waves in lead II or V1 is a sign of left atrial enlargement.
- Causes: HTN, aortic stenosis, HOCM if seen in combination with LVH
The presence of peaked P waves (high amplitude) in leads II and V1 is indicative of _______________.
The presence of peaked P waves (high amplitude) in leads II and V1 is indicative of right atrial enlargement.
- Causes: pulmonary hypertension, chronic lung disease, TS
What are ectopic P waves? Are they upright or inverted?
- Waves that do not originate from the SA node.
- Upright if coming from high in atria
- Inverted if coming from lower or from AV node
- How is the PR interval measured?
- What is the nl duration (sec)?
- Measured from beginning of P wave to onset of QRS complex
- Normal duration <0.20 sec (1 large box)
***You need to measure multiple PR intervals!!! It can vary and can indicate AV blocks
- How is the QRS complex measured?
- Begins where the first wave complex deviates from baseline and ends where last wave of complex flattens at, above, or below the baseline.
What are the normal dimensions of the QRS complex?
- Less than 0.12 sec (3 small boxes)
- Amplitude varies from <5 mm to >15 mm.
- If QRS complexes are large enough to touch each other = LVH
What are the normal dimensions of a Q wave?
Should be less than 2 boxes in amplitude and 1 box in duration
What does a pathological Q wave look like and what does it mean?
A Q wave can be pathological if it is:
- Deeper than 2 small squares (0.2 mV) and/or
- Wider than 1 small square (0.04 s)
It’s ok to not see a QW, but large QW can indicate current MI or prior MI.
From the end of the QRS complex to the beginning of the T wave.
It’s important to determine if the ST segment is elevated or depressed by using the isoelectric line. Greater than ____small boxes may be pathologic. Use the _____ interval as reference to see if ST is elevated or depressed.
It’s important to determine if the ST segment is elevated or depressed by using the isoelectric line. Greater than 2 small boxes may be pathologic. Use the PR interval as reference to see if ST is elevated or depressed.
What does ST elevation represent?
- Infarction
- Pericarditis - diffuse elevation in all/most leads
- Early repolarization
What does ST depression represent?
- Ischemia
- After Digitalis administration (Digitalis is an inotropic medication that helps the heart squeeze harder, used with CHF)
What is the J point?
- The point at which the ST segment “takes off” from the QRS complex is called the J point. It represents the end of ventricular depolarization.
- May not be evident
- May indicate early repolarization, ischemia/infarction, or pericarditis
What can inverted T waves be indicative of?
- Cardiac ischemia
- Left ventricular hypertrophy
- CNS injury
- Digitalis administration
- Hypokalemia
T wave amplitude more than half the height of QRS complex (peaked T waves) may indicate __________ or __________.
T wave amplitude more than half the height of QRS complex (peaked T waves) may indicate myocardial ischemia or hyperkalemia
How is the QT interval measured?
Beginning of QRS complex to end of T wave
What does the QT interval represent?
Ventricular depolarization and repolarization (how quickly the ventricle contracts and relaxes)
- What is the normal duration of QT interval?
- 33 sec - 0.47 sec (>0.5 is abnormal!)
- As a rule of thumb, the QT interval should be half the R-R interval
- Most EKGs will provide a corrected QT (QTc)
Prolonged and shortened QT interval both increase risk of ____________.
Prolonged and shortened QT interval both increase risk of ventricular tachycardia - torsades.
- Prolonged QT can be genetic or caused by ________, __________, or ___________.
- Shortening can be due to __________.
- Prolonged QT can be genetic or caused by medications, hypothyroidism, or hypocalcemia.
- Shortening can be due to hypercalcemia
Where would you see a U wave and what would it represent?
- Thought to represent repolarization of the papillary muscles or Purkinje fibers
- If present, will follow the T waves (seen more often in young athletes and bradycardia)
- If large, may represent hypokalemia, thyroid disease, medication effect
What are the two most common ways to calculate rate on the EKG?
- Six-second method (simplest, quickest, andmost commonly used method - used to approximate rate in regular rhythms)
- Triplicate methods
How do you calculate HR using the 6-second method?
Count the # of QRS complexes in a 6 second interval and multiply # by 10.
How do you calculate HR using the triplicate method?
- Find an R wave that falls on a dark line
- Count out to the right each dark line as 300, 150, 100, 75, 60, 50 bpm.
- If irregular rhythm, report as range from smallest to biggest.
What can an indeterminate axis represent?
Emphysema, hyperkalemia, lead placement
What are the steps for EKG interpretation? (acronym)
Age of pt
Rate
Axis
Rhythm
Evaluate each EKG element as follows:
P wave (peaked or absent? PR interval short/prolonged?)
Q wave (deep Q wave? QT interval short/prolonged?)
R wave
ST segment (elevation/depression?)
T wave (peaked or inverted? U wave?)
What does axis represent?
- Refers to general direction of the heart’s depolarization
- Should be in the direction of the most muscle in the heart - usually the left ventricle
- Clinical relevance: hypertrophy, ischemia/infarction, blocks
Describe the thumb method of determining axis orientation
- Left thumb is Lead I and right thumb is aVF
- If QRS is predominantly positive, hold that thumb up, and if negative, down
- If Lead I and aVF are positive = both thumbs up = normal
- If Lead I positive and aVF negative = left thumb up, right thumb down = left axis deviation (LAD)
- If Lead I negative and aVF positive = left thumb down, right thumb up = right axis deviation (RAD)
- If both Lead I and aVF negative = both thumbs down = indeterminate: (if lead II positive = normal. If lead II negative = LAD)
What can a left axis deviation (LAD) represent?
- Left ventricular hypertrophy (LVH)
- Emphysema
- Hyperkalemia
- Atrial septal defect
- Obesity
What can a right axis deviation (RAD) indicate?
- Normal in kids and tall thin adults
- Right ventricular hypertrophy
- Chronic lung dz
- PE
What does regularly irregular mean?
- Patterned irregularity or “group beating”
What does irregularly irregular mean?
