Published on December 2, 2021 by AliveCor India

What are the 4 lines on an ECG?

An ECG heart monitor is a common diagnostic tool used to assess the electrical and muscle functions of the heart.Although this is a simple test to perform, there is a lot of training involved in interpreting the ECG trace.

  • The heart is a dual-stage electric pump and the electrical activity of the core can be measured by electrodes placed on the skin.

  • The electrocardiogram measures the frequency and rate of heartbeats and also provides indirect evidence of blood circulation in the heart muscle.

  • There is a standardised ECG heart monitor system that has been developed to position the electrodes for our routine ECG.

What Does the Heart Look Like and How Does It Work?

Our heart has four chambers - right and left atria & right and left ventricles.Blood for our body is collected from the right side and then pumps it to the lungs and the left side of our heart receives blood from the lung to pump it to the body.Blood flows in our body:

  • Through the left atrium, oxygen-rich blood from the lungs enters the pulmonary veins.

  • Then that blood flows in the left ventricle and is pumped into the aorta to the rest of the body.

  • When the blood returns, it is depleted of oxygen by carrying carbon dioxide, a waste product of metabolism. And so the blood enters the right atrium through the vena cava to get pumped into the right ventricle.

  • Then the right ventricle pumps blood through the pulmonary artery to the lungs and here the carbon dioxide is left off replacing oxygen and so the cycle continues.

How is ECG Used to Evaluate Heart Function?

This electrode leads on the chest by ECG heart monitor can monitor electric pulses produced by the heart. Several leads provide for a variety of electrical observations of the heart. The doctor can understand well about heart rate and rhythm, and also blood circulation to the ventricles, by analyzing the recording.

The SA node normally generates an electrical impulse 50-100 times each minute. A heart rate of fewer than 50 beats per minute is referred to as bradycardia. Tachycardia is defined as a heart rate that is quicker than 100 beats per minute.

The heart typically beats in a sinus rhythm, with each nerve signal produced by the SA node resulting in a contraction of the ventricles, or beat. There are also several types of irregular electric pulses, some of which are natural variations and others of which are highly dangerous. Some electric pulses do not produce a beat and are responsible for abrupt death.

There can be many hurdles in the transmission of electrical pulse in the system that includes the Atria, SA Node, AV Node or the Ventricles. Few impulses can produce typical variations in cardiac rhythm, while others are potentially dangerous.

What are the 4 lines in an ECG?

The reading of the ECG Heart Monitor is essentially a pattern matching process. It is helpful to grasp the theory of what ECGs indicate in order to understand the patterns discovered.Normal beat generates four entities, each with a distinct pattern: P wave, QRS complex, T wave, and a U wave.

P Wave: The presence of a P wave suggests atrial depolarization. When the sinus node, also called the sinoatrial node, produces a nerve impulse that depolarizes the atria, the P wave develops.

If the action potential is coming from the SA node, the P wave in lead II should be vertical. In this context, the ECG is said to show a normal sinus rhythm. Each P wave should be followed by a QRS complex as long as atrial depolarization may propagate through the atrioventricular (AV) node to the ventricles.

Atrial enlargements can broaden or increase the amplitude of the P wave. Ectopic atrial beats can cause P wave shape to change. Many cardiac rhythms, including atrial fibrillation and possibly junctional beats, do not have identifiable P waves.

QRS Complex Wave: The “QRS complex,” which is a mix of the Q, R, and S waves, reflects ventricular depolarization. This word can be puzzling since not all ECG leads have all three of such waves; but, a “QRS complex” is claimed to continue regardless.

The QRS complex has an interval of 0.08 to 0.10 seconds or 80 to 100 milliseconds. It is moderate when the duration is between 0.10 and 0.12 seconds. QRS duration of more than 0.12 seconds is regarded as abnormal.

When electrical impulses take a while to propagate across the ventricular myocardium, the QRS duration increases. The His-Purkinje system, which contains cells that can conduct electricity very quickly, is the usual conduction system in the ventricles.

T Wave: The T wave follows the QRS complex and is triggered by ventricular repolarization.

T waves in most leads should be vertical; the exemptions are aVR and V1. T waves should also be uneven in structure. When compared to the inclination of the first section of the T wave, the second half should have a greater descent. If the T wave seems symmetrical, there may be heart disease present, such as ischemia.

U Wave: It occurs after the T wave of ventricular repolarization and, because of its compact size, it is not always visible. ‘U’ waves are supposed to reflect Purkinje fibre repolarization. However, the precise source of the U wave is unknown. The below are the most popular origin theories:

– Purkinje fibre repolarization is delayed.

– Prolonged repolarization of M-cells in the mid-myocardium

– Mechanical forces in the ventricular wall cause afterpotentials.

– The papillary muscle repolarization.

According to the study, U waves are commonly detected in all leads but V6, more often in V2 and V3, when the heart rate exceeds 96 beats per minute.

An inverse U wave might indicate myocardial ischemia or a left ventricular volume overflow.

A U-wave can be noticed in typical, younger, active people. Adults who are older and less athletic have an increase in the U-wave.

AliveCor brings out KardiaMobile 6L, a mobile ECG device to simplify our lives. This handheld ECG monitor helps to record our ECG in just 30 seconds that saves time & money.



P Wave | Learn the Heart (

QRS Complex | Learn the Heart (

T Wave | Learn the Heart (

U wave - Wikipedia

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