Intro to EKG Flashcards
Where does the blood supply of the SA node come from?
right coronary artery (59% of people), left coronary artery (38% of people) or both (3% of people)
Where does the blood supply of the AV node come from?
always from the right coronary artery
What are the EKG distributions?
Anteroseptal: V1-V4. Anterior: V2–V4. Anterolateral: V4–V6, I, aVL. Lateral: I and aVL, V5, V6. Inferior: II, III, and aVF. Inferolateral: II, III, aVF, and V5 and V6
What is the normal range of the PR interval?
0.12 sec - 0.20 sec
What does the Q wave represent?
depolarization of the intraventricular septum .**When at least 1/3 as high as the R wave, considered to be indicative of a transmural MI
What is the normal range of the QRS interval?
0.04 to 0.12 sec. Anything >0.12 is considered a Bundle Branch Block or Interventricular conduction delay
What does the R wave represent?
the point when half of the ventricular myocardium has been depolarized
What causes a widened QRS complex?
A block in either the right or left bundle branch that delays depolarization of the ventricles
What does the ST segment represent?
Period from the end of ventricular depolarization to the beginning of ventricular repolarization. Elevation or depression is a hallmark sign of ischemia, CAD or impending MI (STEMI)
What is the normal range of the ST segment?
Norm 0.08 to 0.12 sec
When are prominent U waves observed?
seen in hypokalemia, but may be present in hypercalcemia, thyrotoxicosis, or exposure to digitalis, epinephrine
What is the normal range for the QT interval?
0.34 seconds to 0.43 second
What does the QT interval represent?
total duration of electrical activity of the ventricles.
What are two ways to calculate rhythm?
1) Count the # of R waves in a 6 second rhythm strip, then multiply by 10. 2) Find a R wave that lands on a bold line. Count the # of large boxes to the next R wave (300,150,100,75,60,50)
How do you determine regularity?
Look at the R-R distances using markings on a paper. Classify as regular, occasionally irregular, regularly irregular, or irregularly irregular
What can cause biphasic P waves?
Bifid = P mitrale (LA hypertrophy). Pointy = P pulmonale (RA hypertrophy)
What can cause a prolonged PR interval?
1st-3rd degree AV blocks.
Describe R wave progression
QRS complex should start out negative in lead V1 and end up positive by V6. The R wave will be tallest in lead V3 or V4.
What does a transition of R wave from negative to positive in V1 or V2 indicate?
is referred to as an early transition and can be indicative of a previous posterior wall MI.
What is the QRS axis?
Represents the overall direction of the heart’s activity. Axis of –30 to +90 degrees is normal
What EKG findings characterize a right bundle branch block?
wide bunny ears QRS in V1, V2 and sometimes inverted T waves
What is the EKG criteria for a LBBB?
QRS > 120 ms, Dominant S wave in V1, Broad R wave in leads I, AVL, V5-V6. Absent Q waves in leads I, V5, V6. ST and T waves normally opposite direction to QRS
What is the EKG criteria for a intraventricular conduction delay?
QRS duration >0.10s and criteria for specific bundle branch or fascicular blocks not met
What is the EKG criteria for a LVH?
The R wave in V5 plus the S wave in V1 exceeds 35 mm. Baseline ST depression in V5, V6
What might cause ST depression?
coronary ischemia, hypokalemia, digitalis toxicity
What is the criteria for ST elevation to indicated an MI?
An elevation of >1mm and longer than 80 milliseconds following the J-point
What EKG changes are seen with a NSTEMI?
during ischemia and infarction ST depression and T wave inversion. Afterwards ST returns to baseline but T wave inversion persists
What EKG changes are seen with a a STEMI?
during ischemia ST depression, peaked T waves then T wave inversion. during infarction ST elevation and appearance of Q waves. Afterwards ST segments and T waves return to normal but Q waves may persist
What is a lengthened QT interval a biomarker for?
ventricular tachyarrhythmias like torsades de pointes and sudden death.
What is the QT interval dependent on?
the heart rate (the faster the heart rate the shorter the QT interval) and may be adjusted to improve the detection of patients at increased risk of ventricular arrhythmia.
What could cause QT prolongation?
Na channel blockers, hypoelectrolytes, hypothermia, AMI, increased ICP
