Tips for reading ECGs

An ECG is a recording of the heart’s electrical activity.
Electrical current moving toward the positive electrode causes positive deflection.
Electrical current moving away from the positive electrode causes negative deflection.
The stronger the current, the stronger the deflection.
All 12-lead ECGs are 10 second strips.
The amplitude (vertical distance) of the deflection tells you the voltage (mV).
Length (horizontal distance) is a function of time: Wider = the longer time period.

When there are changes in these leads (particularly ischemic changes):

- Consider right ventricular infarction.
  - Beware of using agents that reduce preload (e.g., nitroglycerin).
  - Hypotension is a risk—consider fluid resuscitation.
- Consider the risk of ventricular dysrhythmias.

When there are changes in these leads (particularly ischemic changes):

- Consider ventricular dysrhythmias.
  - Particularly ventricular fibrillation
- High probability this patient needs percutaneous coronary intervention (angioplasty or stent placement).

ECGs collected and scanned by Dr. Kevin Hodges.

Emergent ECG?

Is it a STEMI?
Is there a serious rate problem?
Check each of these facets to inform your diagnosis.

Rate

Rhythm

(Pacemaker)

Ectopy

Intervals

Axis

Ischemia/
Infarct

Technique

Interpretation

Pull all of your investigations together to determine next steps.

Q waves can occur normally in several leads. If normal, these Q waves are called physiologic Q waves.
Physiologic Q waves normally do not exceed 30ms.
Pathology (especially myocardial infarction) can place a Q wave in any lead.
It is possible to examine the Q wave and, based upon its width, speculate whether it is pathologic or physiologic.