The Heart

Atrial systole

Contract. Most blood has already flowed passively to the ventricles, atria both contract to force the last of the blood out into ventricles

isovolumetric relaxation

a brief interval during ventricular diastole when ventricular blood volume does not change because all four valves are closed

PR interval

atrial depolarization and the beginning of ventricular depolarization. Typically 0.17 seconds in length. A longer length seen in some types of AV heart block.

Q-T interval

duration of ventricular depolarization and repolarization; varies with rapid heart rates. Period includes ventricular contraction.

QRS complex

produced by the depolarization of the ventricles. The action potential from the SA node reaches the AV node and after a delay, it continues down the ventricular conduction pathway (His bundle, bundle branches, terminal Purkinje fibers) resulting in ventricular depolarization that is then followed by contraction. Typically 0.08 seconds in length.

P wave

produced by the firing of the SA node and the wave of depolarization that sweeps over the atria. The wave represents atrial depolarization that is quickly followed by atrial contraction.

T wave

produced by the repolarization of the ventricles (final phase). Cardiac ischemia may result in an inverted T wave.

PQ interval

represents the period between SA node firing and the beginning of ventricular depolarization.

Ventricular systole

the contraction of both right and left ventricles, lasting for 0.3 sec

S wave

the downward deflection seen following an R wave.

Q wave

the first downward deflection seen in a QRS complex. (This wave is often not present, depending on the particular lead being observed).

R wave

the upward deflection seen in a QRS complex.

Aortic valve

the valve located between the left ventricle and the aorta.

Pulmonary valve

the valve located between the right ventricle and the pulmonary trunk.

Semilunar valves

the valves located between the ventricles and the major blood vessel leading from the heart. They include the pulmonary and aortic valve.

stroke volume

the volume of blood pumped out by a ventricle with each heartbeat

Segments

tracing between waves; baselines on the ECG

S-T interval

tracing following ventricular depolarization that includes ventricular repolarization.

Intervals

tracings that include a wave

Bicuspid (mitral) valve

valve located between the left atrium and ventricle. During ventricular contraction, the valve prevents the backflow of blood from the left ventricle into the left atrium.

Tricuspid valve

valve located between the right atrium and ventricle. During ventricular contraction, the valve prevents the backflow of blood from the right ventricle into the right atrium.

Atrioventricular valves

valves located between the atria and ventricles including the tricuspid and bicuspid (mitral) valves.

PQ segment

when atrial contraction (atrial systole) occurs

List the electrical impulses as they travel through the heart.

1.) SA node discharges impulse, atrial excitation begins. 2.) Depolarization delayed at AV node. 3.) Depolarization passes to heart apex, ventricular excitation begins. 4.) Ventricular depolarization complete.

S-T segment

includes ventricular contraction (systole) and the initial phase of ventricular repolarization. ◦This segment can be elevated with an acute (recent onset) cardiac infarct or depressed due to a subendocardial infarction.