Ischemia and injury

Dr. Sarah SreekanthAssistant professor,

Dept of General Medicine, CHRI22.03.2015

Important to remember!

• ECG is not sufficiently specific or sensitive to be used without a patient's clinical history

Myocardial ischemia and injury

• Mismatch between perfusion and demand• Ischemic myocardium goes for anaerobic

metabolism to sustain itself• Can survive but cannot function• Remains in resting state and does not

participate in contraction• Reversible if blood supply is restored or

demand is lowered

• If blood flow is restored before glycogen gets depleted, cells resume contraction promptly (ischemia)

• If severe depletion of glycogen has occurred, it becomes stunned and recovery is delayed (injury)

• If complete depletion of glycogen occurs, necrosis of the cells results, leading to infarction

Why is it clinically important?

• When ECG changes occur in association with chest pain but without frank infarction, they confer prognostic significance.

• About 20% of patients with ST segment depression and 15% with T wave inversion will experience severe angina, myocardial infarction, or death within 12 months of their initial presentation.

ECG CHANGES IN ISCHEMIA

ECG effects of myocardial ischemia

• Manifest by changes in T waves

• T waves may become– Flattened– Inverted– Tall or– Biphasic

ECG effects of myocardial ischemia

• T waves that are deep and symmetrically inverted (arrowhead) strongly suggest myocardial ischaemia.

• At least 1 mm deep• Present in ≥ 2 continuous leads that have

dominant R waves (R/S ratio > 1)• Dynamic — not present on old ECG or

changing over time

T wave inversion

Widespread T wave inversion due to myocardial ischaemia

Point to note

• Inverted T waves are normal in leads III, aVR, and V1

• Associated with a predominantly negative QRS complex.

A – T wave in coronary insufficiencyB – T wave in LVH with strainC – T wave in digitalis effect

Other causes of T inversion

ECG CHANGES IN MYOCARDIAL INJURY

ECG effects of myocardial injury

• Deviation of the ST segment• ST segment deviated towards the surface of

the injured tissue• Patterns of deviation– ST depression– St elevation

Forms of ST depression

• Horizontality• Upward sloping ST depression• Downward sloping ST depression

ST depression• Horizontal or downsloping ST depression ≥ 0.5

mm at the J-point in ≥ 2 contiguous leads indicates myocardial ischaemia.

• ST depression ≥ 1 mm is more specific and conveys a worse prognosis.

• ST depression ≥ 2 mm in ≥ 3 leads is associated with a high probability of NSTEMI and predicts significant mortality (35% mortality at 30 days).

• Upsloping ST depression is non-specific for myocardial ischaemia.

Normal ST segmentHorizontality of ST segment

Plane ST segment Upwards sloping ST Downsloping ST segment

Horizontal ST segment depression

Upwards sloping ST depression in V2 – V5

Downsloping ST depression with T inversion in I, aVL, V5, V6

Other causes for ST depression

DEPRESSED ST ---> • D - Drooping valve (MV Prolapse) • E - Enlargement of the left ventricle • P - Potassium low • R - Reciprocal ST Depression (eg. Inferior MI) • E - Encephalon (Intracerebral) Haemorrhage • S - Subendocardial Infarct • S - Subendocardial Ischaemia • E - Embolism (Pulmonary) • D - Dilated Cardiomyopathy • S - Shock• T - Toxicity (Digitalis/Quinidine

ST

ST elevation

• Epicardial injury – ST deviated towards epicardial surface

• Leads oriented towards the epicardial surface eg Lead V6 will have a raised ST segment

• Leads oriented away will have a depressed ST segment eg aVR

Take home messages

• Ischaemia , injury and infarct are constituents of a contiguous spectrum caused due to decrease in perfusion to a given myocardial region

• Deep symmetrical arrow head T wave denotes ischaemia

• ST segment deviations (depression and elevation) reflect injury