EKG Flashcards
What is the P wave?
depolarization of the atria (first deflection on EKG)
What is the QRS?
depolarization of the ventricular muscles (therefore also repolarization of atria); Q: typically downward before upward reflection; R: upward deflection; S: downward
What is the T wave?
Repolarizaiton of the ventricles
How does conduction travel?
sinus beat starts in the SA node; depolarization spreads through the atria and reaches the AV node; epolarization continues to the bundle of His and bundle branches, Purkinje fibers, and ventricular myocardium; activation in the ventricles starts out on the left side of the IV septum and travels to the R
How many electrodes are used in EKG and where are they placed?
right arm, left arm, right leg (not used - grounds), left leg, V1-V6
Where are V1-V6 placed?
V1: 4th ICS, 2 cm to the right of sternum; V2: 4th ICS, 2cm to the left of sternum; V3 Midway between V2 and V4; V4 5th ICS, left midclavicular line; V5 5th ICS, left anterior axillary line; V6 5th ICS, left midaxillary line;
What are the direction of the different leads?
I: right arm to left arm; II: right arm to left leg; III: left arm to left leg; aVF: middle of body to left leg (down); aVL: middle of body to left arm; aVR: middle of body to right arm
In which directions should the EKG go?
If going towards a +, then up! If going away from a +, then down; if going towards a + and then past or away, then going up then down
What are the 8 most important things to look at in an EKG?
- Calibration;
- Heart Rate;
- Heart Rhythm;
- Intervals (PR, QRS,QT);
- Mean QRS Axis;
- Abnormalities of the P-wave;
- Abnormalities of the QRS (hypertrophy, bundle branch block, infarction);
- Abnormalities of the ST-segment/T-wave
What is important about calibration?
Standard calibration has a reference pulse of 1 mV (10 mm high) and a large box that represents 0.2 sec (200 ms)
How can you calculate heart rate from an EKG?
- 1,500/(# mm between beats) = HR;
- Count-off the # of large boxes between two QRS complexes: 300 – 150 – 100 – 75 – 60 – 50;
3.(Especially) for irregular rhythms such as atrial fibrillation:
Count the # of complexes during 6 sec of the recording and x by 10. ECGs often have time markers spaced 3 sec apart. If 3-second markers are not present, count out 15 big boxes: 15 boxes x 200 msec/box=3000 msec
What are the characteristics required for sinus heart rhythm?
1) Every P wave is followed by a QRS, &
2) Every QRS is preceded by a P wave, &
3) P-wave is upright in leads I, II, and III, &
4) The PR interval is greater than 0.12 sec (3 small boxes)
What is sinus bradycardia?
HR below 60 bpm
What is sinus tachycardia?
HR above 100 bpm
What is the corrected QT?
divide the measured QT/ square root of the R-R interval (in seconds); this is b/c QT interval should decrease as HR goes up
What is a normal PR?
120-200 msec (3-5 small boxes)
What does increased PR mean?
First-degree AV block
What does decreased PR mean?
Preexcitation/WPW, Junctional rhythm
What is normal QRS?
less than 100 msec (less than or equal to 2.5 small boxes)
What does increased QRS mean?
Bundle branch block, Ventricular ectopy, Drug effect (e.g., certain antiarrhythmic drugs), increased potassium
What is the normal range for QT corrected?
equal to or greater than 450m/460f msec
What does decreased QT corrected mean?
Short QT syndrome, elevated calcium
What does increased QT corrected mean?
decrease in K or Ca, Ischemia, Congenital, toxic drug effect (e.g., certain antiarrhythmic drugs); this is “long QT”
What is 1st degree AV block?
PR interval is more than 5 small boxes block slowing conduction down
What is 2nd Degree AV block Type I?
AV node struggling to keep up - PR int getting progressively longer until it gives up/cycles
What is 2nd Degree AV block Type II?
all or nothing - either works correctly or doesn’t work at all
What is 3rd Degree AV block?
more P waves than QRS complexes complete block b/w atria and ventricles (complete heart block)
What does long QT look like on an EKG?
Q to T interval longer than half of the overall interval
What is the mean QRS axis?
Represents the vector of QRS depolarization; Normal: -30° to +90°; More negative than -30° represents left axis deviation; More positive than +90° represents right axis deviation.
How can you determine QRS axis?
Look in leads I & II! - If both +, normal axis. -If I+/II-, leftward axis -If I-/II+, rightward axis
What does leftward axis deviation mean clinically?
- Left Ventricular Hypertrophy
- Left Anterior Fascicular Block
- Inferior MI
What does rightward axis deviation mean clinically?
- Right Ventricular Hypertrophy
- Left Posterior Fascicular Block
- Pulmonary embolus
How do you determine abnormalities in the P waves?
Look in leads II and V1; enlargement in II (more than 2.5 small boxes) high means problem with R and wide means problem with L; enlargement in V1 is greater than 1 box for either curve
How does left ventricular hypertrophy present on EKG?
larger-than-normal electrical forces are generated by the LV; Leads on the left side of the heart (i.e., V5, V6, I, aVL) have taller-than-normal R waves +/- T-inversions; Leads on the right side of the heart (i.e., V1 & V2) have the opposite: deeper-than-normal S wave
What is a bundle branch block?
May develop from ischemic or degenerative damage. Slow myocyte-to-myocyte spread of electrical activity. The delay prolongs depolarization/widens the QRS.
What does a QRS duration of 0.10-0.12 s (2.5-3 small boxes) mean?
incomplete bundle branch block
What does QRS duration of more than 0.12 s (more than 3 small boxes) mean?
complete bundle branch block
What is right branch block and how does it present on EKG?
Think right heart strain (e.g., pulmonary embolism, rate-related aberration); activation is normal, switches to L ventricle, but bundle branch finally lets electrical activity come through it after L ventricle does what it needs to do - R ventricle slowly depolarizes; RSR in V1 - S in V6 - Can interpret Q-wave changes!
What is left branch block and how does it present on EKG?
Think degenerative disease, cardiomyopathy, myocardial infarction; starts off strange - activation heads down R side of septum (activates toward the L side); then the R ventricle does depolarize some, then headed toward L ventricle again; - S in V1 - Broad R in V6 - Cannot interpret Q-waves or ST-T changes!
What are pathological Q waves?
Pathological if width is more than 1 small box wide & depth is more than 25% of the total QRS height. Represents absence of electrical forces from infarcted cells. If a Q wave appears in only a single ECG lead, it is not diagnostic of an infarction- need at least 2 consecutive leads.
What does abnormal Q wave in the II, II, aVf mean?
inferior MI caused by RCA
What does abnormal Q wave in the V1-V2 mean?
anteroseptal MI caused by LAD
What does abnormal Q wave in V3-V4 mean?
anteroapical MI caused by LAD (distal)
What does abnormal Q wave in V5-V6, I, aVL mean?
anterolateral MI caused by CFX
What does tall R wave in V1-V2 mean?
posterior MI caused by RCA
What does ST elevation indicate?
Myocardial infarction; this is because injured segment is partly depolarized away from electrode before rest of heart normally depolarizes, which causes downward shift in recording electrode; ECG is thinking that the baseline is @ usual point (manifests as ST elevation)
What are common causes of ST elevation?
Myocardial infarction, pericarditis, coronary vasospasm; could also be cerebrovascular accident, pulmonary embolism, hypothermia
What are some T wave abnormalities?
Long QT: Hypocalcemia, Genetic, Drugs Short QT: Hypercalcemia, hyperkalemia Inverted T-waves: ischemia, LVH, digoxin Peaked T-waves: Hyperkalemia Flat T-wave & U-waves: Hypo K+, Mg++
