action potential – A change in the electrical potential of cells that passes an impulse along cell membranes

acute pericarditis – Sudden inflammation of the outer covering of the heart 

acquired long QT syndrome – Prolongation of the QT interval

adriablastin – A cancer drug that causes cardiotoxicity and low-voltage QRS

afterload – The force that the heart needs to exert against for optimal cardiac output

amyloidosis – A congenital disease that forms abnormal protein deposits known as amyloid throughout the body 

ÅQRSF – Mean frontal QRS axis

arrhythmia – A group of heart conditions that causes an irregular heart rhythm

arrhythmogenic – Tends to cause an arrhythmia

atrial flutter – An arrhythmia of the atrium with aberrant impulses generated outside the SA node

atrial fibrillation – A rapid rhythm generated outside the SA node in which the atrial depolarization is uncoordinated, the atria quiver, and blood is not moved to the ventricles

atrial infarction – Poor perfusion to the atrium causing necrosis of the heart tissues

AV block – The slow conduction of impulses from the atrium into the ventricle via the AV sinus 

Bazett formula – Calculates the time-corrected QT interval

BBB – Bundle branch block

biatrial enlargement – Hypertrophy and/or dilatation of the right and left atria 

bifidity – Two-lobed P wave

biventricular hypertrophy – Bilateral ventricular enlargement

bradycardia – Slow heart rate < 60 bpm

Cabrera circle – A hexaxial reference system that depicts the impulses detected by the limb and precordial leads

CAD – Coronary artery disease

cardiac axis – The average direction of the cardiac vector

circadian variations – ECG changes throughout a 24-hour cycle

conduction cell – Forms the circuit for impulse conduction of the heart

congenital long QT syndrome – A hereditary condition characterized by a prolonged QT interval

Cornell index – Recent indices for left ventricular hypertrophy

coronary artery disease – A condition in which there is narrowing and hardening of the coronary arteries due to plaque formation

CT angiography – A radiologic imaging modality used to visualize the arteries

cyanosis – Bluish skin discoloration

D-dimer test – A blood test that detects the presence of thrombus formation

Danon disease – A congenital disorder of glycogen storage

depolarization – A shift in the electrical distribution within the cell membranes that makes it less negative

dyspnea – Difficulty breathing

Ebstein anomaly – A congenital heart disease involving the tricuspid valve

ECG – Electrocardiogram

Einthoven triangle – An imaginary inverted equilateral triangle depicting the action potentials picked up by the limb leads of an ECG

electrocardiology – The study of the conduction system of the heart

escape beats – Delayed impulses from the sinus node cells forcing the conduction cells to produce an action potential

Fabry disease – Congenital disorder that causes a deficiency of alpha-galactosidase

false poling – Misplaced limb lead

fascicular blocks – The slowing of impulses in the infra-Hisian conduction system

frontal plane axis – Showcases the superior, inferior, right, and left sides of the heart 

funnel chest – Congenital deformity causing a concave anterior chest wall

hemochromatosis – A disorder of iron uptake by the intestines, in which too much iron is absorbed and deposited in the tissues

horizontal plane – Showcases the anterior, posterior, right, and left sides of the heart

hypercalcemia – Elevated serum calcium levels

hyperkalemia – An elevated serum potassium level

hypertrophy – Increased tissue mass, enlargement

hypokalemia – Low serum potassium levels

hypothermia – Low core temperature

idioventricular rhythm – Polonged QRS complex with normal rate

infarction – Dead tissue caused by an obstruction of its blood supply

infra-Hisian – Bundle of Purkinje fibers that allows synchronous atrial activation to stimulate ventricular contractions

iRBBB – Incomplete right bundle branch block

irregular rhythm – The R-R intervals are not equidistant to one another 

ischemia – A medical condition that obstructs normal blood perfusion to tissues

isoelectric line – Represents a straight line where there are no positive or negative deflections in ECG

J-point or junctional point – Demarcates the beginning of repolarization

LA – Left atrium

LAFB – Left anterior fascicular block

LBBB – Left bundle branch block 

Lenègre disease – A condition in which there is fibrosis of the infra-Hisian conduction system

LPFB – Left posterior fascicular block

MI – Myocardial infarction

myocardial infarction – Cessation of blood flow to a portion of the heart causing tissue necrosis and irreversible damage to heart muscles; a heart attack 

negative deflection – Downward projection of an ECG tracing

Osborn wave – A short positive deflection after the QRS complex and before the ST segment

P biatriale – Left and right atrial enlargement 

P mitrale – Left atrial enlargement

P pulmonale – Right atrial enlargement 

p-vector – The direction of the impulses that generate the P wave

pericarditis – Inflammation of the outer covering of the heart

precordial – Situated in front of the heart

premature ventricular contraction (PVC)- An action potential produced by a conduction cell ahead of the sinus node cell

Prinzmetal angina – Chest pains brought about by coronary artery spasm

pseudo-notching – Notching in the QRS complex without any associated pathological condition

pseudo-slurring – An insignificant notch of < 1 mm in the QRS complex that has no associated pathological condition

pulmonary embolism – A blood clot that has obstructed the blood flow in the pulmonary artery

R wave progression – The transition of the R wave from a negative deflection to a positive deflection in the precordial leads

RBBB – Right bundle branch block

regular rhythm – The R-R intervals are equidistant to one another

regurgitation – Backflow of blood due to the incomplete closure of valves

repolarization – A change in the cell membrane potential that turns it into a negative value

RVH – Right ventricular hypertrophy

sarcoidosis – An inflammatory disease that causes granulomas to form, especially in lymph and lung tissues

sensitivity – The probability that a test is truly negative

sinoatrial node – The main pacemaker of the heart

sinus node – The heart’s normal pacemaker site

sinus node cell – Cells from the main pacemaker of the heart, the sinoatrial node

sinus rhythm – A normal heartbeat

sinus tachycardia – Rapid heart rate > 100 beats per minute

Sokolow/Lyon – Old indices for left ventricular hypertrophy

specificity – The probability that a test is truly positive

stenosis – Narrowing in the vessel, causing resistance of blood flow 

tachypnea – Rapid breathing

thrombus – A blood clot 

tricuspid atresia – Abnormal narrowing of the tricuspid valve

trifascicular – Three branches

vagal stimulation – A medical procedure that brings electrical impulses to the vagus nerve

vectorcardiogram – A graph that plots the vectors of impulses within the heart

vectors – Directions of action potentials or impulses

ventilation-perfusion scan – A nuclear medicine procedure that diagnoses pulmonary embolism

ventricular escape rhythm – Ventricular conduction cells become the heart’s pacemaker with a rate of 15–40 bpm

ventricular tachycardia – Wide QRS complex tachyarrhythmia

working heart cell – Specialized cells that perform the mechanical function of cardiac output