What is an electrocardiogram and why do you need one?

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What is an electrocardiogram and why do you need one?

Ernest Madu and Paul Edwards

Sunday, November 29, 2020

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AN electrocardiogram (often referred to as ECG or EKG) is the most-ordered heart test.

An ECG is required for virtually every patient being evaluated for a heart-related issue or heart-related symptom. It is a non-invasive test that can be easily performed within minutes and with no known adverse effects. It is usually performed by placing 10 small sticky pads (electrodes) on various places on the chest wall and patients' limbs, with wires connected to the electrodes leading to the ECG machine.

These wires transmit information on the electrical activity of the heart from the electrodes. The information is represented as tracings on the ECG paper. In individuals with significant amount of chest hair it may be necessary to shave the hair before putting the sticky pads in place to improve contact and conduction of the heart's electrical activity, so as to ensure a good tracing on the ECG paper.

In a conventional 12-lead ECG the overall magnitude of the heart's electrical activity is measured from 12 different angles and recorded over a brief period, usually 10 seconds. It is important to appreciate that the recording on the ECG paper is able to capture only an event that is present in that brief 10 seconds of recording, usually within one cardiac cycle (heartbeat) and so will miss any event that is intermittent or temporary. While a necessary screening tool, an ECG is, however, a limited tool for definitive assessment of the condition of the heart.

During each heartbeat, electrical activity within a healthy heart follows an orderly progression starting from the upper chambers of the heart (atria) and traversing through a series of conducting fibers to the lower chambers of the heart (ventricles). The electrical system of the heart is essential for its proper performance. The organised transport of electrical activity produces the characteristic ECG pattern that is seen on the ECG paper, which often is a grid form paper.

Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including disturbances of heart rate and rhythm and inadequate coronary artery blood flow, such as happens in blockage of heart vessels leading to heart attacks or chest pain. Outside of heart rhythm disorders, abnormal heart tracings may be indicative of various disease states. Heart rhythm abnormalities may include fast heart rate referred to as tachycardia, slow heart rates referred to as bradycardia; heart blocks; and irregular heartbeats such as atrial fibrillation. It can provide clues regarding enlargement of heart chambers and heart muscle.

Doctors properly trained in ECG interpretation are able to glean a large amount of information from the ECG reflecting the state of the heart with respect to chamber sizes, thickness of the walls, structure and function of the heart and it's electrical system. An ECG is useful in measuring the rate and rhythm of heartbeats, determining the appropriateness of heart rate, the size and position of the heart chambers, the presence of any prior damage to the heart's muscle or conduction system. It is also useful in determining if a heart attack is in progress or has previously occurred.

If my ECG is normal, does it mean my heart is okay and I have no heart disease?

This is a question we get asked a lot and the short answer is no. A normal ECG does not exclude heart disease. As previously noted, an ECG is a good screening tool but severely limited in definitively excluding significant heart disease. It is important to keep in mind that an ECG records only what is happening within a brief 10 seconds, usually within one cardiac cycle or heartbeat. What this means is that an event that is intermittent or temporary will not be captured during this recording time. In that case, an ECG that is normal in a patient that has symptoms does not in itself mean that there is no heart problem. If there is existing damage to the heart or a constant anomaly, it would be captured by an ECG but otherwise, it may not be picked up.

My doctor said that my ECG is normal, why do I need an ECHO?

It is common for patients in Jamaica to confuse ECG with an echocardiogram (ECHO). Many times also patients are under the false impression that a normal ECG means that everything is normal with their hearts and so confused when their doctors also recommend that they perform an echocardiogram. The point must be emphasised that an ECG is different from an ECHO and both provide different sets of complementary information and so both are required for proper evaluation of a patient with suspected heart disease. The echocardiogram is also a very commonly used diagnostic tool but not as commonly used as the ECG. The ECG can be considered a basic screening test that is done in almost everyone that has a history and physical. The echocardiogram, on the other hand, is an ultrasound examination of the heart that provides moving pictures and more comprehensive information on the structure and function of the heart.

I did an ECG during my last consultation, why are you requesting another ECG?

Oftentimes, patients assume that because an ECG was done during their prior visit with a cardiologist, they would not need to do another ECG for their follow-up visit. International best practice requires that an ECG at a minimum be performed during a proper cardiology consultation. Because an ECG is no more than a basic screening tool, it is an essential component of a routine cardiology consultation, just like checking blood pressure and heart rate. Furthermore, the data on an ECG reflects an event that occurred within one heartbeat and so may change rapidly. The ECG electrodes detect small electrical changes that are a consequence of electrical activities happening within the heart muscle during each heartbeat.

What are some of the common reasons for performing an ECG?

The main reason for obtaining an ECG is to gain information about the electrical function of the heart. This information is necessary in the evaluation of individuals at risk for heart disease or with symptoms suspicious for heart disease. For proper medical evaluation, information obtained from ECG is best used in conjunction with known medical history and other complementary information from other diagnostic tests like an echocardiogram that provide detailed information on structure and function of the heart.

Some key indications for an ECG would include the following:

(1) Risk factors for heart disease including family history, age, smoking, hypertension, diabetes

(2) Routine cardiac or physical examination

(3) Chest pain or suspected heart attack

(4) Shortness of breath

(5) Murmurs heard on auscultation during physical examination

(6) Fainting or dizziness

(7) Palpitations

(8) Fatigue

(9) Monitoring drug therapy

(10) Perioperative evaluation for patients scheduled for surgery

(11) Critical occupations like airline pilots

(12) Screening for athletes

ECG Interpretation: Who should interpret an ECG and how soon after?

Most modern ECG machines include automated interpretation algorithms. Unfortunately, many of these interpretations are often incomplete or inaccurate and so every ECG requires proper interpretation by a cardiologist or physician with proper training and experience in interpreting ECGs. Despite recent advances, computer misinterpretation remains a significant problem and can result in clinical mismanagement. We frequently see patients who present with an ECG strip with computer generated interpretation that was never verified by an expert interpreter. This is wrong and may potentially put patients at risk. The results from automated algorithms should at best be considered “preliminary” until confirmed or revised by expert interpretation.

Interpretation of the ECG requires a fundamental appreciation of the electrical conduction system of the heart. What is considered “Normal” must be in the context of expert interpretation of the ECG and not based on a computer-generated report.

Perhaps, the most worrisome observation we have encountered is delayed interpretation of ECGs or interpretations without recommendations or follow-up plans. We have seen patients with several ECGs over time with serious abnormal findings reported but with no patient counseling or further recommendations for either confirmatory diagnostics or treatment. For ECG to be useful as a diagnostic tool, the interpretation must be accurate and timely and proper recommendations and follow up diagnostic or treatment plans must be clearly documented. We have also noted that some facilities in Jamaica perform ECGs on patients and do not provide a physician's report for days and sometimes weeks after the ECG is performed. This is improper as ECGs are supposed to be snapshots in time and must be interpreted by a physician in a timely manner so as not to miss an acute or critical finding warranting an urgent attention. The practice of batching ECGs for interpretation over many days or weeks is not recommended and certainly not acceptable.

ECG Artifacts

An ECG tracing may be affected by extraneous factors resulting in appearance of apparent heart-related abnormality. Some of these include motion and shivering that may present an illusion of irregular heart rhythm and may be misread as such if proper care is not taken. Accurately recognising and differentiating the ECG artifact from the true ECG signal can have a significant impact on patient care.

Improper or poor ECG performance technique can also influence the quality of ECG recording and can lead to improper diagnosis and treatment. It is important, therefore, that anyone performing or interpreting an ECG be properly trained.

Otherwise, ECG is a safe, painless, and highly useful noninvasive diagnostic tool if properly done and properly interpreted in a timely fashion.

Dr Ernest Madu, MD, FACC and Dr Paul Edwards, MD, FACC are consultant cardiologists at Heart Institute of the Caribbean (HIC) and HIC Heart Hospital.

Dr Madu is a main TED Speaker whose TED talk has been translated into 19 languages, seen, and shared by more than 500,000 viewers. He has received the Distinguished Cardiologist Award, the highest award from the American College of Cardiology, and has been named among the 100 most influential people in health care and among the 30 most influential in public health. Dr Madu is also a recipient of the Global Health Champion Award from the University of Pennsylvania.

Correspondence to info@caribbeanheart.com or call 876-906-2107


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