Cardiac Output and ECG
Stroke volume, heart rate and interpretation of the standard ECG waves. (Biology › Body Fluids and Circulation, NEET UG syllabus.)
What is Cardiac Output and ECG?
The volume of blood pumped by each ventricle of the heart per minute.
Key formula / rule: Cardiac Output
Key points
- Define cardiac output, stroke volume, and heart rate.
- State the formula for cardiac output and calculate it given stroke volume and heart rate.
- Describe the factors that can influence cardiac output.
- Explain the basic principle of electrocardiography.
Common exam trap
Confusing depolarization and repolarization with the mechanical events of contraction and relaxation directly, rather than the electrical events that precede them.
Definitions
- Term
Cardiac Output
- Meaning
The volume of blood pumped by each ventricle of the heart per minute.
- Term
Stroke Volume
- Meaning
The volume of blood pumped out by each ventricle during a single cardiac contraction (per beat).
- Term
Heart Rate
- Meaning
The number of × the heart beats per minute.
- Term
Electrocardiogram (ECG)
- Meaning
A graphical recording of the electrical activity of the heart during a cardiac cycle.
- Term
P-wave
- Meaning
The first small upward deflection on an ECG, representing atrial depolarization.
- Term
QRS complex
- Meaning
The large, sharp deflection on an ECG, representing ventricular depolarization.
- Term
T-wave
- Meaning
The upward rounded deflection on an ECG following the QRS complex, representing ventricular repolarization.
Learning objectives
Define cardiac output, stroke volume, and heart rate.
State the formula for cardiac output and calculate it given stroke volume and heart rate.
Describe the factors that can influence cardiac output.
Explain the basic principle of electrocardiography.
Identify and describe the P-wave, QRS complex, and T-wave in a standard ECG.
Correlate each ECG wave with its corresponding electrical event in the cardiac cycle.
Recognize the diagnostic significance and clinical applications of an ECG.
Formulae
- Name
Cardiac Output
- Note
Where CO is Cardiac Output, SV is Stroke Volume, and HR is Heart Rate.
- Expression
CO = SV × HR
Prerequisites
Basic knowledge of the structure of the human heart (chambers, valves, major blood vessels).
Understanding of the general pathway of blood circulation through the heart and body.
Fundamental concepts of nerve impulse generation and conduction.
Common mistakes
Confusing depolarization and repolarization with the mechanical events of contraction and relaxation directly, rather than the electrical events that precede them.
Forgetting that atrial repolarization occurs during the QRS complex but is obscured by the larger ventricular depolarization.
Not knowing the typical normal values for heart rate, stroke volume, and cardiac output.
Misinterpreting the sequence or significance of the P, QRS, and T waves on an ECG.
Believing that an ECG directly measures blood flow or pressure.
Keywords
Cardiac Output
Stroke Volume
Heart Rate
ECG
Electrocardiogram
P-wave
QRS complex
T-wave
Depolarization
Repolarization
Cardiac Cycle
Ventricle
Atrium
Practice preview
What is the formula for calculating cardiac output?…
easy
Which of the following correctly describes the sequence of electrical events represented by the P-wave, QRS complex, and T-wave in a standard ECG?…
medium
A prolonged PR interval on an ECG typically indicates a delay in the conduction of electrical impulses from the atria to the ventricles. This condition is most commonly associated with which of the following?…
hard