What can electrocardiograms spot? The conditions doctors can spot with the test
Q: Even though my doctor told me I am pretty healthy, she ordered an electrocardiogram (ECG) to be done right in her office. Besides a heart attack, what else can ECGs show?
A: Cardiac (heart) cells are not just muscle cells that squeeze to pump blood. They also participate in the transmission of the electrical signals of the heart. The heartbeat is controlled by these electrical signals in order to carefully coordinate the timing of the pumping action of the chambers of the heart, making the heart such a reliable and amazing organ.
An ECG measures the electrical activity of the heart, and the deflections on the ECG tracing (the up and down blips) are given simple names: P, Q, R, S, T and U waves.
Normally, the heart’s electrical signal begins in the area called the sinoatrial (SA) node, by the top of the heart. The electrical signal then propagates through the atria (the top smaller chambers of the heart, which squeeze blood to load the ventricles), and is represented in the P wave of the ECG.
Then, the electricity goes through the atrioventricular (AV) node and on to the ventricles (the big chambers of the heart; the right ventricle pumps blood to the lungs and the left ventricle pumps blood to the entire body), and is represented in the QRS wave group.
Finally, the electricity resets (represented by the T and U waves), so this normal sinus rhythm (NSR) can begin again.
A full 12-lead ECG looks at this electrical activity from multiple viewpoints. Findings can provide tremendous insight into many possible conditions. In addition, changes in an ECG over time can also give important information; hence, one reason your doctor may have ordered an ECG for you is to get a baseline now so there is something to compare it with in the future.
Some things that can be seen on an ECG include:
Rate, meaning the speed of your heartbeat, which if too slow or too fast can indicate certain cardiac conditions such as sick sinus syndrome, different types of tachycardias (for example, supraventricular tachycardia from Wolff Parkinson White Syndrome) and other abnormalities.
Rhythm, noting whether the electrical flow is following the NSR pathway (SA node to atria to AV node to the ventricles), or possibly showing atrial fibrillation, premature heartbeats (whether atrial or ventricular in origin) or other conditions.
Axis, indicating the overall "tilt" of someone’s heart. The heart is normally in the center of the chest, but it is usually not perfectly vertical; the base can be slightly angled toward the left.
Interval. Measuring the timing between the P, QRS, T and U waves can be indicative of conduction blocks (partial or complete) of the normal electrical flow pathway (for example, AV node blocks), might indicate certain electrolyte abnormalities and can give insight into many other conditions.
Duration: Measuring the amount of time it takes from the beginning of the deflection of each specific wave/wave group until the deflection returns to baseline can give insight to many possible conditions. For example, a widened/abnormally shaped QRS may indicate a block in the electricity as it goes through the ventricles.
Morphology. This refers to the specific shape of the P, Q, R, S, T and U waves, and may indicate hypertrophy (thick and/or muscular overgrowth) of a heart chamber, inflammation and even an acute heart attack.
Other things, such as findings indicative of certain electrolyte changes, certain specific conditions, chronic changes after a cardiac event and effects from medications.
An ECG, which is a non-invasive bedside test, gives a huge amount of information, with the potential to identify many possible heart issues and to guide many treatments. This is the reason ECGs are done so often, particularly in the emergency department when there is concern for many possible acute conditions and diseases.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.
This article originally appeared on MetroWest Daily News: ECGs measure electrical activity of heart, spot potential problems
