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 – prolonged 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