131 ECG III

Question 1

ST depression vs ST elevation on ECG

Answer 1

• -Several processes may result in cellular depolarization in the ischemic area (such as loss of intracellular K and reduction of transmembrane gradient).
• -This may give rise to depolarized cells with a slow response AP
• -In chronic stable angina and NSTEMI, the ischemic area tends to be subendocardial
• -In STEMI it tends to be transmural
• ST depression (≥ 1mm) if it is subendocardial (typical in angina) and non-ST elevation MI (NSTEMI)
• ST elevation ≥1mm (≥ 0.5mm in V2-3) if it is transmural (as in a transmural MI or ST elevation MI, STEMI). The ST segment is often (not always) convex when viewed from above.

Question 2

T wave inversion

Answer 2

Could be from ischemia

APs 1 and 2 (normal): the first to depolarize is the last to repolarize ➞ upright T wave.

In ischemia, AP duration is altered and therefore this sequence may be abnormal. In APs 1-3, the first to depolarize is the first to repolarize ➞ inverted T wave.

Question 3

Criteria for an Abnormal Q-wave

Answer 3

• For a Q wave to appear there must be a substantial area of necrosis.
• In smaller MI’s, Q waves do not appear on the ECG.
• The diagnosis is made from the other ECG changes (ST segment shifts, T wave inversion), the clinical situation and cardiac enzyme
• Older terminology for non q-wave MI is non-transmural or subendocardial MI. These terms have been abandoned by many but you hear them occasionally
• Non-Q wave MI has a better short term prognosis than Q wave MI (because it’s usually smaller) but may imply a high risk for subsequent MI

Question 4

Ventricular blood supply sources and ECG leads that best show anterior wall of LV, lateral wall of LV, inferior wall of LV

Answer 4

Electrical activity in the anterior wall of the LV is best seen in leads V1-V4

Electrical activity in the lateral wall of the LV is best seen in leads I, aVL, V4-V6

Electrical activity in the inferior wall of the LV is best seen in leads II, III, aVF

Question 5

Other Causes of ST Elevation

Answer 5

Normal variant: “early repolarization” or “J-point elevation”

• –Seen especially in young people
• –ST segment is usually elevated in multiple leads (instead of in leads that localize the changes to a specific region)
• –ST segment is usually concave (viewed from above)

Ventricular aneurysm

• –Persistent ST elevation after an MI suggests the presence of an aneurysm (an area of scar that bulges out during systole…also called a dyskinetic area)

Pericarditis

• –ST segment is usually elevated in multiple leads
• –Associated with clinical picture of pericarditis instead of that of MI
• –Sometimes associated with PR segment depression
• –Sequential ECG changes differs from those of MI

Question 6

Left or right Atrial Abnormality (Enlargement): Criteria

Answer 6

Question 7

QRS changes in eventricular enlargement

Answer 7

Question 8

RVH criteria

Answer 8

•V1: R wave is larger than S wave and/or

•V6: S wave is larger than R wave

•Limb leads: Right axis deviation (axis between 90º and 180º)

•Usually, right atrial p-wave abnormality is present

Question 9

LVH Criteria

Answer 9

•S-wave in V1 + R-wave in V5 or V6 ≥ 35 mm

•R in I + S in III ≥ 25

•R in aVL ≥ 12 mm

• S in aVR ≥ 15 mm
• R-wave V5 or V6 ≥ 25 mm
• In the precordial leads: any R + any S ≥ 45 mm
• R in aVF ≥ 20 mm
• S in V3 + R in aVL ≥20 for female, ≥28 for male (Cornell criteria)