Ischemic EKG Changes Flashcards
15 Steps to Reading an EKG
Rate Rhythm Axis P wave PR interval Q waves QRS interval ST segment T waves U waves QT interval Hypertrophy Infract Alternans Old ECG
EKG Changes in Ischemic Conditions
Q waves ST segments T waves U waves Infarct Old EKG
ST Depression vs. Elevation
ST Depression:
Unstable angina (troponin negative)
Non-ST Elevation Myocardial Infarction (NSTEMI) (troponin positive)
ST Elevation: ST Elevation Myocardial Infarction (STEMI) (troponin negative)
> 0.5 mm of change from baseline should start to get your attention
1 mm ST segment deviation is abnormal (one small box)
Distribution of the Leads vs. Areas of the Heart
V1-6 = anterior
V5 and 6: low lateral
I and aVL = high lateral
II, III, and aVF = inferior
V1 and 2 = anterior septal/setpal area
V3 and 4 = anterior area
V5 and 6 = lateral area or anteriolateral area
aVL and I = lateral or high lateral area; signify circumflex distribution
II, III, and aVF = inferior distribution
V1-6 = LAD distribution
EKG Findings and Localization of Injury
Positive Predictive Value in Localizing Site of Injury: Q waves = 98% (good) ST Elevation = 91% (good) T Wave Inversion = 89% (good) ST Depression = 60% (bad)
Pathophysiology of ST Depression
In resting/repolarized state the ischemic area is depolarized and generates electrical currents towards the overlying leads
T-P and P-R segments are actually shifted “up” in resting state
Thus when entire ventricle is depolarized it appears that the ST segment is “depressed”
Pathophysiology of ST Elevation
In resting/repolarized state the ischemic area is depolarized and generates electrical currents away from the overlying leads
T-P and P-R segments are actually shifted “down” in resting state
Thus when entire ventricle is depolarized it appears that the ST segment is “elevated”
Types of ST Elevation
Sad = STEMI Happy = Consider pericarditis, early repolarization or other causes
Q Waves
Always normal: aVR, V1
Always abnormal: V2, V3
Pathological Q waves: two consecutive leads with a duration of 3/4 small box or more + depth of 1 small box
If pathological = Indicates infarction
No ST elevation = Age-indeterminate
ST elevations = Acute infarct
Pathological Q Wave Determination
Q wave becomes deep and wide
Days and weeks occur = ST elevation will go back to normal but Q wave stays
Therefore Q wave with no ST elevation, not acute occurrence but it happened sometime
If Q wave + ST elevations then acute
T Waves
T wave is ventricular repolarization and every lead, the QRS and T wave should go in the same direction
This occurs because repolarization occurs in opposite direction of depolarization
T wave inversions occur in lead when polarity between the two is not correlating
When associated with ischemia they:
Are usually inverted (symmetrically) or biphasic
May help with localization to a particular portion of the left ventricle (but not as predictive as Q waves and ST elevation)
U Waves
Occurs right after T Wave Best seen in V2 and V3 Rarely seen Often seen with bradycardia Pathological if: > 1.5 mm in height or Inverted (ischemia)
