Heart cardiogram: what kind of test is it and what does it show

A cardiogram, or electrocardiogram, is a recording of the electrical signals that arise when the heart works. The test takes a few minutes, does not require puncturing the skin, and does not pass current through the body. From this recording, the doctor judges the rate and rhythm of contractions and the signs of damage to the heart muscle.

What a cardiogram and an electrocardiogram are

Electrocardiography is a method of recording the electrical fields that form when the heart works; its result is called an electrocardiogram. The method is considered one of the inexpensive but valuable methods of instrumental diagnostics in cardiology. In conversation, different names are used — heart cardiogram, heart ECG, electrocardiogram — but they refer to the same test. The signals are recorded on paper or in an electronic file.

How an ECG works and how the test is performed

The heart is a pump, but it is started by an electrical signal, similar to a command from a control panel. Electrodes on the skin read this signal, and the device turns it into curved lines. There are three options: a resting recording, a portable recording for a day or longer, and a stress test.

Before the procedure, the skin is cleaned, sometimes hair on the chest is shaved, and a conductive gel is applied. At rest, you need to lie still for several minutes, sometimes hold your breath: movement and shivering distort the result. The sensations are coolness from the electrodes and slight discomfort when they are removed. The portable recorder is worn for 24–48 hours, sometimes up to 7 days; during this time you cannot take a bath or shower. The stress test takes place in a hospital: a treadmill or exercise bike, 40–60 minutes, stopping if symptoms or fatigue appear; if exercise is impossible, a drug that raises the heart rate is administered. Preparation: clothes that are easy to remove, no lotions on the skin, and before the stress test — no heavy food or caffeine.

What a heart cardiogram shows

A rate of 60 to 100 beats per minute and an even, sequential rhythm are considered normal. An ECG often becomes the first test when heart disease is suspected. The recording provides information about:

• the rate, rhythm, and regularity of contractions, including premature contractions and dropped beats;
• signs of acute or previous myocardial damage — infarction and ischemia;
• disturbances of intracardiac conduction and left ventricular hypertrophy;
• shifts in the levels of potassium, calcium, magnesium, and other electrolytes;
• the effects of medications and implanted devices, and the size and position of the heart chambers.

What the waves and intervals on an ECG mean

The recording shows five waves — P, Q, R, S, T; sometimes a subtle U wave is visible. The P wave reflects depolarization of the atria, the QRS complex reflects depolarization of the ventricles, and the ST segment and T wave reflect recovery processes in the ventricular myocardium. The doctor assesses the heart axis, the rate and regularity of the waves, the amplitude and duration of the intervals, including PQ, QRS, and ST. A deviation from the usual picture is not a diagnosis in itself: it is compared with symptoms and other data.

What disorders can be seen on a cardiogram

Changes can be a sign of damage to the heart muscle, a shift in electrolyte levels, a congenital defect, an enlarged heart, fluid in the pericardial cavity, myocardial inflammation, previous or current infarction, insufficient blood supply to the arteries, and rhythm disturbances. Characteristic changes are produced by atrial fibrillation and atrial flutter, heart failure, paroxysmal supraventricular tachycardia, sick sinus syndrome, and Wolff–Parkinson–White syndrome. The method also helps to suspect noncardiac problems, such as pulmonary embolism.

A referral for a cardiogram is not in itself a reason to call an ambulance; 103/112 — for signs of infarction, that is, a life-threatening heart condition.

When an ECG is prescribed and what it does not show

A referral is given for chest pain and palpitations, when infarction, ischemic heart disease, or arrhythmia is suspected, before surgery, with a history of heart problems, and with a pronounced family history of heart disease. The recording is also made for those who already have heart disease or another condition affecting its work — including before and during the use of certain medications; the method is part of routine health screening. Accuracy depends on what exactly is being looked for: some heart problems do not show up on an ECG, and some conditions do not produce specific changes. The result may be ready on the day of the test or after several weeks; if there is no response, contact the doctor who referred you for the recording.

It is not possible to understand your own tracing from an article: interpreting the recording is the doctor's job. The material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer