Electrocardiogram (ECG): What It Is and How It Works

The electrocardiogram (ECG or EKG) is the most widely used cardiac study in the world. This quick, painless, and non-invasive test records the electrical activity of the heart and provides fundamental information about its rhythm, rate, and overall condition. At Dr. Elders Jimenez Iglesias's office in Hospital Galenia, Cancun, we perform 12-lead electrocardiograms with immediate interpretation by the specialist.

What is an electrocardiogram and what is it for

An electrocardiogram is a diagnostic test that records the electrical signals produced by the heart with each beat. Every time the heart beats, an electrical wave travels through it from top to bottom, causing the muscle to contract and pump blood. The ECG captures these waves through electrodes placed on the skin, generating a graphic tracing that the cardiologist interprets to evaluate heart health.

This study is the first line of evaluation in cardiology. It is so important that it forms part of any complete cardiac checkup, along with the echocardiogram and clinical assessment.

What does an electrocardiogram detect

A 12-lead ECG provides key information about multiple aspects of cardiac function:

• ●Cardiac arrhythmias: atrial fibrillation, tachycardias, bradycardias, heart blocks, and premature beats
• ●Myocardial infarction: signs of acute or old heart attack (pathological Q waves, ST segment elevation or depression)
• ●Ventricular hypertrophy: abnormal thickening of heart walls, common in chronic hypertension
• ●Conduction abnormalities: bundle branch blocks, Wolff-Parkinson-White syndrome, prolonged QT intervals
• ●Medication effects: some cardiac drugs modify the ECG tracing and require monitoring
• ●Electrolyte disturbances: potassium, calcium, or magnesium imbalances affecting heart rhythm
• ●Pericarditis: inflammation of the sac surrounding the heart
• ●Myocardial ischemia: insufficient blood supply to the heart muscle

How is an ECG performed step by step

The procedure is simple and takes between 5 and 10 minutes. It causes no pain or discomfort:

• ●You will be asked to lie on the examination table and expose your chest, wrists, and ankles
• ●The technician will clean the skin areas where electrodes will be placed to ensure good contact
• ●Ten adhesive electrodes are placed: 6 on the chest (precordial) and 4 on the limbs (one on each wrist and ankle)
• ●You will be asked to remain still and breathe normally for a few seconds
• ●The equipment records the electrical activity of the heart and generates the tracing on paper or digital screen
• ●The cardiologist interprets the results immediately

The 12-lead ECG explained

When we refer to a 12-lead ECG, we mean the study records the heart's electrical activity from 12 different angles. This provides a complete picture of the cardiac electrical function. The leads are divided into:

• ●Limb leads (I, II, III, aVR, aVL, aVF): evaluate the frontal plane of the heart, meaning the electrical activity as seen from the front
• ●Precordial leads (V1 through V6): evaluate the horizontal plane, providing information about the anterior, lateral, and septal walls of the heart

Each lead records the same electrical activity but from a different angle, similar to photographing an object from different positions. This allows precise localization of where an abnormality occurs.

When do you need an electrocardiogram

Your cardiologist may order an ECG in the following situations:

• ●Chest pain or discomfort of any kind
• ●Palpitations, rapid or irregular heartbeat
• ●Dizziness, fainting, or near-fainting episodes
• ●Unexplained shortness of breath, especially with exertion
• ●As part of a routine cardiac checkup starting at age 40
• ●Follow-up of hypertension, diabetes, or known coronary artery disease
• ●Preoperative evaluation before a scheduled surgery
• ●Monitoring of medications that may affect heart rhythm
• ●After a cardiac event such as heart attack or arrhythmia
• ●Athlete screening before starting intense physical activity

How to prepare for an ECG

Preparation is minimal and straightforward:

• ●No fasting or medication changes are required (unless specifically instructed by the cardiologist)
• ●Wear comfortable clothing that allows easy access to the chest, wrists, and ankles
• ●Avoid applying creams or lotions to the chest on the day of the study, as they may interfere with electrode adhesion
• ●Inform the doctor about all medications you take, including supplements
• ●If you have a lot of chest hair, a small area may need to be shaved for electrode placement

Basic interpretation of results

The ECG tracing shows characteristic waves that the cardiologist systematically analyzes:

• ●P wave: represents atrial activation (depolarization). Its shape and duration indicate whether the atria are functioning normally
• ●QRS complex: represents ventricular activation. Its amplitude and duration reflect the condition of the ventricular muscle
• ●T wave: represents ventricular recovery (repolarization). Alterations in its shape may indicate ischemia
• ●PR interval: time between atrial and ventricular activation. Prolongation suggests a conduction block
• ●ST segment: section between the QRS complex and T wave. Its elevation or depression is key in diagnosing infarction or ischemia

Advantages of the electrocardiogram

• ●Fast: the recording takes less than one minute once electrodes are placed
• ●Painless: causes no discomfort or side effects
• ●No radiation: completely safe, can be repeated as many times as needed
• ●Affordable: one of the most accessible cardiac studies
• ●Immediate results: the cardiologist can interpret the tracing instantly
• ●Portable: can be performed in the office, emergency room, or at the patient's bedside

ECG limitations and complementary studies

Although the electrocardiogram is essential, it has limitations. It records electrical activity at a single point in time, so some intermittent arrhythmias may not be detected. In such cases, the cardiologist may order a 24-hour Holter monitor for continuous recording. Additionally, the ECG does not directly evaluate heart structure or valve function; for that, it is complemented with an echocardiogram. If coronary artery disease is suspected, a stress test or nuclear cardiology studies may be indicated.

ECG in Cancun: where to get one

At Dr. Elders Jimenez Iglesias's office, located in Hospital Galenia, Office 403-A, Tower B, in Cancun's Hotel Zone, we have state-of-the-art digital electrocardiography equipment. The study is performed during the same cardiology consultation and results are interpreted immediately so you receive a diagnosis the same day.

If you need an electrocardiogram in Cancun or are experiencing any cardiac symptoms, do not wait. Schedule your appointment with Dr. Jimenez Iglesias by calling (998) 116-3657 or through our online form. Early detection of ECG abnormalities can prevent serious complications and save lives.

Dr. Elders Jimenez Iglesias

Cardiologist · Nuclear Cardiology

Professional License: 13819257 · Specialty: 12543211