Cardiac Electrophysiology and Hemodynamics: ECG, Heart Function, and Regulation

Sinoatrial node (SA node)

Pacemaker, initiates depolarization

Atrioventricular node (AV node)

Passes depolarization to ventricles; only way of passing on the wave of depolarization from the atria to the ventricles with a brief delay to allow for ventricular filling

Bundle Branches

To left and right ventricle

Purkinje fibers

Throughout ventricles

Amplitude

Measurement of the height of the electrocardiogram waveforms

Duration

Measurement of the time interval of the electrocardiogram waveforms

P Wave

Atrial depolarization (contraction)

PR Interval

Time from the beginning of atrial depolarization to the beginning of ventricular depolarization

QRS Complex

Ventricular depolarization (contraction)

ST Segment

Period between ventricular depolarization and repolarization

T Wave

Ventricular repolarization (relaxation)

Electrical disturbances

Abnormalities in the heart's electrical activity

Coronary vessel occlusion

Blockage of blood flow in the coronary arteries

ST Depression

Indication of ischemia or reduced blood flow to the heart

ST Elevation

Indication of myocardial infarction or heart attack

Parasympathetic nervous system

Part of the autonomic nervous system that slows heart rate

Sympathetic nervous system

Part of the autonomic nervous system that increases heart rate

End-diastolic volume (EDV)

Preload; volume of blood in the ventricles at the end of diastole

Average aortic blood pressure

Afterload; pressure the heart must work against to eject blood

Strength of the ventricular contraction

Contractility; forcefulness of the heart's contraction

Factors affecting stroke volume

Alterations to the Ventricular Pressure Volume Loop

U wave

During a normal Cardiac Cycle, the U wave is "hidden" by the QRS Complex.

Graded exercise test

A test to evaluate cardiac function by observing ECG during exercise and changes in blood pressure.

Atherosclerosis

Fatty plaque that narrows coronary arteries and reduces blood flow to myocardium.

Myocardial ischemia

A condition characterized by reduced blood flow to the heart muscle.

S-T segment depression

Suggests myocardial ischemia.

S-T segment elevation

Suggests acute myocardial infarction.

Cardiac Output

The amount of blood pumped by the heart each minute, calculated as Q = HR x SV.

Heart rate

The number of beats per minute.

Stroke volume

The amount of blood ejected in each beat.

Mean arterial pressure

The average pressure in a person's arteries during one cardiac cycle.

Strength of ventricular contraction (Contractility)

Enhanced by circulating epinephrine and norepinephrine and direct sympathetic stimulation of heart.

Frank-Starling mechanism

Greater EDV results in a more forceful contraction due to stretch of ventricles.

Venous return

Increased by venoconstriction, skeletal muscle pump, and respiratory pump.

Aortic pressure

Inversely related to stroke volume; high afterload results in decreased stroke volume.

Ventricular contractility

Increased contractility results in higher stroke volume.

Factors that regulate cardiac output

Include parasympathetic nerves, mean arterial pressure, EDV, and contraction strength.

Preload

The initial stretching of the cardiac myocytes prior to contraction.

Afterload

The pressure the heart must work against to eject blood.

Contractility

The intrinsic ability of cardiac muscle to contract.