Electrocardiogram (ECG)

This set of vocabulary flashcards covers the foundational concepts, wave components, lead systems, and common abnormalities of an electrocardiogram (ECG) as discussed in the lecture.

Electrocardiography

The detection of electrical currents transmitted through the heart and spread throughout the body using a device called an electrocardiograph.

Electrocardiogram (ECG)

A graphical description of the electrical activity of the heart created by analyzing several electrodes.

Electrode

A conductive pad attached to the skin that enables the recording of an electrical current.

Willem Eindhoven

The Nobel Prize winner (1924) who improved electrocardiography methods to be reproducible and accurate, and after whom Eindhoven's triangle is named.

Standard 12-Lead ECG

An ECG obtained using 10 electrodes to produce 12 different tracings, consisting of six limb leads and six chest leads.

Limb Leads

A set of six leads including the bipolar limb leads (I, II, and III) and the augmented limb leads (aVR, aVL, and aVF).

Precordial Leads

Also known as chest leads ($V_1$ to $V_6$), these electrodes are positioned on the chest to record electrical potential in the transverse plane.

Depolarization

The electrical changes associated with the contraction of any muscle, where the negative potential inside the muscle reverses and becomes slightly positive.

Repolarization

The process where positivity returns to the outside of the cardiac muscle fiber as it returns to a resting electrical state.

Eindhoven's Triangle

An imaginary equilateral triangle drawn around the center of the heart with vertices at the right arm (RA), left arm (LA), and left leg (LL).

Eindhoven's Law

A principle stating that if ECGs are recorded simultaneously with the three limb leads, the sum of potentials in Lead I and Lead III equals Lead II ($Lead\,I + Lead\,III = Lead\,II$).

Augmented Limb Leads

Leads labeled aVR (right arm), aVL (left arm), and aVF (foot) that use a reference point based on the average of two limb electrodes.

P Wave

A small upward deflection representing atrial depolarization spreading from the SA node through the atria.

QRS Complex

A large ECG deflection representing rapid ventricular depolarization; its normal duration is about $0.12\,s$ or less.

T Wave

A dome-shaped upward reflection representing ventricular repolarization, which occurs as the ventricles start to relax.

PQ Interval

The conduction time from the beginning of atrial excitation to the beginning of ventricular excitation, normally about $0.16\,s$.

ST Segment

The period between the end of the S wave and the beginning of the T wave, representing when ventricular contractile fibers are depolarized during the plateau phase.

QT Interval

The time from the start of the QRS complex to the end of the T wave, representing the total time of ventricular depolarization and repolarization ($0.35\,s$).

U Wave

A rare wave sometimes seen in chest leads $V_2$ and $V_3$ that has the same polarity as the T wave; a change in its size or inversion can indicate heart disease.

Systole

The phase of muscle contraction in the cardiac cycle.

Diastole

The phase of muscle relaxation in the cardiac cycle.

ECG Horizontal Calibration

The standard arrangement where $10$ small divisions (millimeter squares) represent $1\,mV$ in the vertical direction.

Small Square (Time)

A single millimeter square on ECG paper representing $0.04\,s$ or $4\,ms$ at a paper speed of $25\,mm/s$.

Large Square (Time)

A grid unit consisting of five small squares, representing $0.2\,s$ or $200\,ms$.

Tachycardia

A very fast heart rate, defined in an adult as faster than $100\,bpm$.

Bradycardia

A heart rhythm defined as being under $60\,bpm$ in an adult.

Atrial Fibrillation (AF)

A rhythm characterized by chaotic atrial activity with no P waves and normal but irregular QRS complexes.

Ventricular Fibrillation (VF)

The most serious cardiac arrhythmia characterized by totally chaotic, irregular ECG deflections and no effective heart pumping.