Intro to EKG Flashcards
P wave
atrial depolarization
QRS
ventricular depolarization
T wave
ventricular repolarization
U waves
inconsistent
PR interval
From onset of P wave to onset of QRS is measure of AV node conduction time. Normal is 0.12-0.20 seconds
QT interval
From onset of Q to end of T, represents total duration of depolarization and repolarization
How to calculate HR from EKG
HR= 300/ # heavy lines btw QRS’s OR HR= 1500/ #mm btw QRS’s
What are EKG leads
Electrodes that measure the difference in electrical potential btw: two different points (bipolary leads) on the body or one point on th body and a virtual reference point with zero electrical potential located in center of heart (unipolar leads)
Describe polarity on EKG. Which direction will QRS be in left, lateral and right sided leads?
Depolarization moving toward a positive electrode produces a positive deflection. QRS is + in left and lateral, and - in right leads
Describe placement of bipolar limb leads
lead I (+ on one handt, - on other hand), lead II (- on hand, + on foot), lead III (+ on foot and - on hand)
Describe placement of augmented limb leads
Unipolar leads. aVL (+ on left wrist), aVR (+ on right wrist), aVF (+ on ankle)
What are lateral leads
lead I and aVL : reflect lateral wall changes
What are inferior leads:
lead II, III and aVF: reflect inferior wall changes
What do the right chest and left chest leads measure
Right chest leads (V1 and V2) moniter RV. Left chest leads (V5 and V6) monitor LV
EKG of ventricular hypertrophy
more muscle= more volts= greater amplitude. Left ventricle hypertrophy shows big R waves in left sided leads (I, aVL, V5, V6). Right ventricle hypertrophy shows big R waves in right sided leads (V1, V2)
EKG of ischemic changes in heart
ischemia alters ventricular repolarization. Ischemia due to sudden high oxygen demand in the presence of fixed coronary obstruction causes depression of the ST segment. Ischemia due to acute coronary artery obstruction during low oxygen demand causes T wave inversion
ischemia alters ventricular repolarization. Ischemia due to sudden high oxygen demand in the presence of fixed coronary obstruction causes depression of the ST segment. Ischemia due to acute coronary artery obstruction during low oxygen demand causes T wave inversion
EKG in transmural injury
Transmural injury in acute coronary syndrome, usually with clot due to platelet aggregation in coronary artery, results in ST elevation
EKG in transmural infarct/necrosis
Sizeable Q wave. Infarcts usually only develop in left ventricle. Q waves in inferior leads (II, III, aVF) are due to inferior infarcts. Q waves in V1-V4 are due to anterior wall infarcts. Lead I, aVL and V5,V6 are due to lateral wall infarcts
What criteria are required for a ‘sizeable’ Q wave
> 1/4 the amplitude of R wave, > one small box wide, present in at least 2 leads reflecting same region of left ventricle
Describe EKG changes that occur over time in an evolving transmural MI
Hyperactute T waves, T-wave inversion (ischemia), ST elevation (current of injury), Q waves +/- T wave inversion and ST elevation
Compare Transmural to subendocardial MI
Transmural: ST elevation with Q waves. Subendochondral: ST depression no Q wave
Leads and associated infarct locations
V1-V2: anteroseptal wall. V3-V4: anterior wall. V5-V6: anterolateral wall. II, III, aVF: inferior wall. I, aVL: high lateral wall
Prolonged QT definition
QT interval is more than half the RR interval
Causes of prolonged QT interval
hypcalcemia, hypokalemia, hypomagnesemia, Class1A or 3 anti-arrhythmic drugs, hypothermia, long QT syndrome
Hypercalcemia vs hypocalcemia on EKG
Hyper: shortened QT. Hypo: prolonged QT. Both can predispose to arrhythmia
Hypokalemia EKG
Prolonged QT, prominent U waves, inverted T waves
Hyperkalemia EKG
mild: Tall T waves makes peaked and symmetrical EKG. Moderate: P + R waves flatten, QRS + T broaden, big S waves. Severe: P+ R waves gone, S and T waves broaden, sine wave pattern
How do drugs, electrolytes, etc lead to arrhythmias?
abnormal QT interval and T wave are altered due to alterations in repolarization
