Electrocardiogram (ECG)

Introduction

The first electrocardiogram from the intact human heart was recorded with a mercury capillary electrometer by Augustus Waller in May 1887 at St. Mary’s Hospital, London.

An electrocardiogram (ECG or EKG) is a simple test that detects and records the heart’s electrical activity. An electrical impulse (or wave) travels through the heart with each heartbeat. ECG helps measure these impulses and produces a graphical representation known as an electrocardiograph. These graphs consist of spikes and downs known as waves, which helps assess the rhythm and rate of your heartbeat, which helps determine how healthy your heart is.

Process

•   Generally, these tests involve attaching small sticky sensors to your body, called electrodes, with wires attached to the ECG machine, which looks like a computer. The opposing end of the electrode is attached to the bottom of the heart and the positive end is attached to the apex of the heart
•   These electrodes detect the electric current under your skin, which arises because of the electrical impulse generated with each heartbeat and spreads under the skin
•   The ECG machine then shows a graphical representation of the activity of the patient’s heart and the doctor determines if there is something unusual with the heart

Types of ECG

Resting ECG

This is a simple, quick, and painless test that requires the patient to relax before attaching the electrodes to their body. This test usually takes about 5 to 10 minutes.

Stress Test

This test is typically done while exercising, making your heart work progressively harder since some heart problems only appear during exercise.

Holter Monitor

A Holter monitor is a device that measures the electrical activity in the patient’s heart for a period of 24 to 48 hours. In this test, electrodes attached to your chest record information on a portable battery-operated monitor, which you can carry in your pocket or strap to your shoulder. The patient needs to maintain a diary of their activities during the day to assist the doctor in identifying the cause of their symptoms. This test is also known as the ambulatory or 24hour ECG test.

Types of waves produced by ECG

An electrocardiogram (ECG or EKG) is a test that checks how your heart is functioning by measuring the heart’s electrical activity. An electrical impulse (or wave) travels through your heart with each heartbeat. This wave causes the muscle to squeeze and pump blood from the heart.

P wave (Atrial Depolarization)

Generally, the heart muscles or cells present in the heart muscles are in a polarized state. The ions start moving towards the positive electrode when the cells get depolarised. An electric impulse is generated, reflecting on the graph as a positive/ upward deflection, known as the P wave. The P wave represents atrial depolarization. The smaller muscle mass of the atria compared with the ventricles results in the P wave having a smaller amplitude than the QRS complex. In most cases, the P wave will be smooth and rounded, no more than 2.5 mm tall and no more than 0.11 seconds in duration. Atrial wave can be measured by determining the time interval between P waves

QRS Complex

•   As the name suggests, the QRS complex includes the Q-wave, R-wave and S-wave. These three waves occur in rapid succession. The QRS complex represents ventricular depolarization and its propagation. The standard QRS complex is <0.12
•   The wave of cardiac depolarization starts from the SA node and; spreads through the atria to the AV node; in the interventricular septum, as the wave of depolarization propagates towards the apex, cardiac myocytes depolarize from left to right; finally, the wave of depolarization spreads from the apex to the base of the ventricles
•   It is vital to recognize that not every QRS complex will contain Q, R and S waves. The convention is that the Q wave is always negative and that the R wave is the first positive wave of the complex. If the QRS complex only includes an upward (i.e. positive) deflection, it is an R wave. The S wave is the first negative deflection after an R wave
•   Under normal circumstances, the duration of the QRS complex in an adult patient will be between 0.06 and 0.10 seconds

T-wave

A T-wave follows the QRS complex and represents the repolarization of the ventricles. Unlike a P-wave, T-wave follows a slightly asymmetric pattern; the wave’s peak is somewhat closer to its end than to its beginning. A T-wave will typically follow the same direction as the QRS complex preceded by it. When a T-wave occurs in the opposite direction of the QRS complex, it generally indicates some cardiac pathology.

Normal and abnormal ECG readings

Normal ECG readings

•   Heart Rate- 60-100 bpm
•   PR Interval- 0.12-0.20 seconds
•   QRS Interval-0.06-0.10 seconds
•   QT Interval- Less than Half of the R-R Interval
•   ST-segment- 0.08 seconds

Abnormal ECG readings

•   A deflection from the normal ECG values lead to an abnormal ECG report
•   An abnormal ECG can mean many things. Sometimes, an ECG variation is a normal variation of the heart’s rhythm which is  not affecting your health
•   Other times, an abnormal ECG might signal a serious pathological condition, such as heart attack or arrhythmia

Medical Uses of ECG

•   Identifies rhythm disturbances, conduction abnormalities and electrolyte imbalances
•   Contributes information about the size of the heart and the relative position of the heart in   the chest
•   Document the diagnosis and progression of myocardial infarctions (MI)
•   Monitors recovery from MI
•   Monitors drug effects
•   ECG helps find cardiac arrhythmias (like Ventricular tachycardia, Heart Block)
•   Diagnosis of Myocarditis and Cardiomyopathy
•   Biotelemetry of the patient
•   Screening tool for ischemic heart disease during stress tests
•   To check the heart health in case of diabetes, high blood pressure, high cholesterol etc
•   Helpful with non-cardiac diseases (e.g. pulmonary embolism or hypothermia)
•   Pericardiocentesis
•   ECG helps the doctors to get a deeper insight into the causes of the patient’s symptoms by studying their ECG reports

When to use ECG

•   Usually, you do not need an ECG if you don’t have risk factors for heart disease or symptoms that suggest possible heart disease
•   One should probably get an ECG done if they have risk factors such as high blood pressure or symptoms of heart disease such as chest pain, shortness of breath, an irregular heart or heavy heartbeats

Conclusion

The electrocardiogram is a hugely beneficial invention in medicine and has assisted doctors with helpful information related to the patient’s heart. Doctors can monitor the electrical activity in the heart by studying the electrocardiograph, which in turn helps to determine any abnormal changes in the heart, which might lead to severe pathological conditions such as arrhythmia or heart attack. ECG can also help identify non-cardiac diseases, which might impact the electrical activity in the heart. Studying and interpreting the electrocardiograph helps the doctors to detect any changes in the heart on time, which might help save a patient’s life.