ECG QRS transition


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ECG QRS transition

Cardiovascular system

Anatomy and physiology

Cardiovascular system anatomy and physiology

Lymphatic system anatomy and physiology

Coronary circulation


Blood pressure, blood flow, and resistance

Pressures in the cardiovascular system

Laminar flow and Reynolds number

Resistance to blood flow

Compliance of blood vessels

Control of blood flow circulation

Microcirculation and Starling forces

Cardiac output

Measuring cardiac output (Fick principle)

Stroke volume, ejection fraction, and cardiac output

Cardiac contractility

Frank-Starling relationship

Cardiac preload

Cardiac afterload

Law of Laplace

Cardiac and vascular function curves

Altering cardiac and vascular function curves

Cardiac cycle and pressure-volume loops

Cardiac cycle

Cardiac work

Pressure-volume loops

Changes in pressure-volume loops

Cardiovascular physiological responses

Physiological changes during exercise

Cardiovascular changes during hemorrhage

Cardiovascular changes during postural change

Auscultation of the heart

Normal heart sounds

Abnormal heart sounds

Myocyte electrophysiology

Action potentials in myocytes

Action potentials in pacemaker cells

Excitability and refractory periods

Cardiac excitation-contraction coupling


Electrical conduction in the heart

Cardiac conduction velocity

ECG basics

ECG normal sinus rhythm

ECG intervals

ECG QRS transition

ECG axis

ECG rate and rhythm

ECG cardiac infarction and ischemia

ECG cardiac hypertrophy and enlargement

Blood pressure regulation



Renin-angiotensin-aldosterone system


ECG QRS transition


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ECG QRS transition

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Content Reviewers

Rishi Desai, MD, MPH


Sam Gillespie, BSc

Tanner Marshall, MS

Charles Davis, MD

An electrocardiogram is also known as an ECG; the Dutch and German version of the word, elektrokardiogram, is shortened to EKG. It is a tool used to visualize, or “gram,” the electricity, or “electro,” that flows through the heart, or “cardio.” Specifically, an ECG tracing shows how the depolarization wave, which is a wave of positive charge, moves during each heartbeat by providing the perspectives of different sets of electrodes. This particular set of electrodes is called lead II; one electrode is placed on the right arm and the other on the left leg. Essentially, when the wave’s moving toward the left leg electrode, you get a positive deflection. This big, positive deflection corresponds to the wave moving down the septum. To read an ECG, there are a few key elements to keep in mind; one is to figure out the QRS transition.

The chest leads will have a mostly positive deflection, if a depolarization wave is moving towards them. The QRS transition zone refers to where the QRS complex switches from being mostly negative to mostly positive, from the point of view of the chest leads, V1 through V6, which “view” the heart through the horizontal plane. The QRS transition usually happens in lead V3 or V4, depending on factors such as chest lead placement and the exact anatomy of a person’s heart. So, the QRS transition tells us when the overall QRS vector is aligned in the direction of the chest leads; it’s a way of understanding what’s happening to the QRS axis in the horizontal plane.


The QRS transition in an ECG is the point at which the QRS complex changes from positive to negative or vice versa. This change reflects the depolarization of the ventricles, and is caused by the flow of current from the atria through to the ventricles. The QRS transition occurs when the ventricles reach their depolarization peak and is therefore a good measure of how well-paced the heartbeat is.


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  3. "Human Anatomy & Physiology" Pearson (2017)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "The principles of software QRS detection" IEEE Engineering in Medicine and Biology Magazine (2002)
  6. "A Real-Time QRS Detection Algorithm" IEEE Transactions on Biomedical Engineering (1985)

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