3. Physiology
        3.2. Cardiovascular
            3.2.2. Heart
                3.2.2.2. Electrical activity
3.2.2.2.4. ECG

ECG

Normal ranges

PR - 0.12-20

QRS - 0.06-0.10

QT ~ 0.4

 

Changes in ECG in infarction

Initial change

Abnormally rapid repolarisation
* Due to accelerated K+ channel opening

--> ST segment elevation

Few minutes later

RMP decreases
Due to loss of intracellular K+

--> TQ segment depression (seen as ST segment elevation)

30 minutes later

Infarcted fibres begin to depolarise more slowly

--> ST segment elevation

Changes in ECG in electrolyte disturbance

High potassium (Hyperkalaemia)

Initial change:

Later (??> 8meq/L):

Eventually heart stops in diastole

NB:

[UTD]

Progressive slowing of impulses

Low potassium (Hypokalaemia)

Early:

Late:

NB:

[UTD]

High calcium (Hypercalcaemia)

But clinically rarely high enough to affect heart.

Low calcium (Hypocalcaemia)

Then

 

 

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Reviewed20050815


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