Electrocardiogram
A recording of the heart's electrical activity at rest. It is the first test for chest pain, palpitations, or unexplained fainting.
What it measures
- What it measures
- Records the heart's electrical activity at rest: rhythm, rate, and how the impulse travels from the atria to the ventricles. It detects arrhythmias present at that moment, signs of ischemia, and evidence of a prior heart attack.
- Duration
- About 5 minutes
- Preparation
- No fasting. Bring any previous test results and the list of medicines you take.
- What it feels like
- You feel nothing. Adhesive electrodes are placed on the chest, arms, and legs, and the machine only listens - it sends no current into the body.
- Referral from another doctor
- No
- Results
- Same day
- Where it is done
- In the office
What it shows
Front view: the patient right side is on the left of the drawing. The ribs are numbered so the spaces can be counted. The diagram is not to scale and declares no measurement.
The six on the chest
- V1
- Fourth intercostal space, right sternal border
- V2
- Fourth intercostal space, left sternal border
- V3
- Midway between V2 and V4
- V4
- Fifth intercostal space, midclavicular line
- V5
- At the level of V4, anterior axillary line
- V6
- At the level of V4, midaxillary line
The four on the limbs
- RA
- Right wrist
- LA
- Left wrist
- RL
- Right ankle. It is the ground: it produces no lead
- LL
- Left ankle
Ten electrodes give twelve leads: the six on the chest, plus six more the machine computes by combining the limb electrodes in pairs.
The electrocardiogram is the starting point of almost any cardiac evaluation. It is fast, non-invasive, and gives something no other test delivers as immediately: how the electrical impulse is travelling right now.
That is also its limit - the present moment. A normal electrocardiogram does not rule out an arrhythmia that comes and goes: when symptoms are intermittent, the right test is a 24 or 48-hour Holter monitor. And if pain appears only with exertion, a resting tracing can look clean; that is where the stress test comes in.
This is why the electrocardiogram is rarely the only test. It is the one that points to the next.