Cardiac Physiology and Electrical Activity Overview

P wave

Represents atrial depolarization before atrial systole.

Q wave

Small downward deflection indicating ventricular depolarization.

R wave

Very tall upward deflection indicating ventricular depolarization.

S wave

Medium downward deflection preceding ventricular systole.

T wave

Indicates ventricular repolarization before diastole.

Atrial repolarization

No distinct wave on ECG.

SA node

Pacemaker located in the right atrium. Contractile cells initiate stimulus.

Internodal pathway

Distributes electrical stimulus throughout the atria. Has conductile cells.

AV node

Junction of atria and ventricles; initiates stimulus if needed.

Atrioventricular bundle

Located in the interventricular septum. Conductile cells carry stimulus.

Left bundle branch

Conductile cells carry stimulus to the left ventricle.

Right bundle branch

Conductile cells carry stimulus to the right ventricle.

Purkinje fibers

Network of conductile cells that stimulates ventricular cardiac muscle.

Bradycardia

Heart rate less than 60 bpm with normal ECG.

Ventricular tachycardia

Characterized by absence of P and T waves.

Atrial flutter

Multiple small P waves before each QRS complex.

Ventricular fibrillation

Disorganized electrical activity in ventricles.

Electrocardiogram (ECG)

Measures electrical activity of the heart.

P-Q interval

Time for atrial depolarization on ECG.

Stroke volume

Volume of blood ejected from ventricles. Correlates with isovolumetric contraction-late

End diastolic volume (EDV)

Maximum blood volume in ventricles before contraction. Correlates with the end of atrial systole.

Lubb and Dubb

Sounds from AV and semilunar valve closure.

cardiac excitation sequence

SA node, internodal pathways, AV node, Bundle of His, right and left bundle branches, Purkinje fibers

Bundle of His location

interventricular septum

End Systolic Volume (ESV)

Amount of blood remaining in each ventricle at the end of systole (contraction). Correlate with isovolumetric relaxation-early.

atrial systole

Active filling, atrial contraction forces a small amount of additional blood into relaxed ventricles

Atrial systole ends, atrial diastole begins

Ventricles filled with blood

isovolumetric contraction-early ventricular systole

Ventricular contraction forces all valves closed, no blood flow occurs

isovolumetric contraction- late ventricular systole

As pressure in ventricles exceed that in the aorta, and pulmonary trunk, semilunar valves open. Blood flows out of ventricles

isovolumetric relaxation-early ventricular diastole

All valves closed, so no blood flows into ventricles. As ventricles relax, pressure in ventricles drops, blood flows back against cups of semilunar valves and forces them closed. Blood flows into the relaxed atria

isovolumetric relaxation-late ventricular diastole

Passive filling as AV valves open, all chambers are relaxed. Ventricles fill passively.

All valves closed, no blood flow

Isovolumetric contraction-early

Isovolumetric relaxation-early