Compare the Old and New ECG

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«Step 7: ST morphology Step 7+2: Conclusion»

Author(s) J.S.S.G. de Jong, MD
Moderator J.S.S.G. de Jong, MD
some notes about authorship

An abnormal ECG does not prove acute cardiac disease. And a normal ECG does not exclude cardiac disease. It is necessary therefore to compare new ECG with ECG's made in the past.

Hallmarks are:

So, one has to check for changes in all 7 steps.

Change in rhythm

Example: New atrial fibrillation. Atrial fibrillation occurs in ten percent of elderly people (>70 year) without clinical symptoms. Therefore atrial fibrillation in acute dyspneic patients does not prove atrial fibrillation-induced cardiac decompensation. Also other causes (e.g. cardiac ischemia, pneumonia) should be considered. Previous ECGs could provide additional information.


Example: Bradycardia. New sinus bradycardia of 50 beats per minute (bpm) may cause dizziness; however, long-existing bradycardias are often without symptoms. Therefore it is important to know the patient's normal frequency.

Conduction time

An increase in PQ time may be seen in elderly patients, but may also be caused by the use of medication or by ischemia. Broadening of the QRS complex may also be caused by medication or ischemia. An increase in QTc time may be caused by medication, but may also be hereditary. Comparison of a previous ECG with new ECG may provide the clue.

Heart axis

Ischemia may cause a change in the heart axis; on the other hand, a deviated heart axis caused by left anterior fascicular block may have already been present for years at the time the ECG was made (and would remain for life). Again, a previous ECG differentiates between old and new changes.

Pathological Q's

Hallmark of the comparison between old and new ECG are pathological Q's. New pathological Q's provide evidence for the occurrence of a myocardial infarction.

Increase R wave

Decrease of the R wave may be a sign of an infarction. Tamponade, cardiomyopathy and increased body size also decrease the R wave.

Increase of the R wave indicates hypertrophy of the left ventricle (leads V5-V6), or a posterior infarction (V2-V3) or a loss of body weight.

the ST segment

New elevation of the ST segment indicates an acute myocardial infarction. Chronic elevation of the ST segment may be caused by cardiac aneurysms or long-standing (several weeks) pericarditis.

T wave

T wave inversion can be caused by ischemia, disturbances in electrolytes or stress. Often no distinction can be made between these causes. T wave inversion indicates that something is possibly wrong and further investigation is needed.