Cardiac Function and Conducting System

A set of vocabulary flashcards to help review key concepts of cardiac function and the conducting system.

Contractile Cells

99 percent of all cardiac muscle cells responsible for contraction.

Action Potential Duration

Cardiac contractile cell AP lasts 250–300 msec, longer than skeletal muscle AP which lasts 10 msec.

Plateau Phase

Due to sodium pumping out and calcium influx during the action potential.

Repolarization

Result of potassium efflux during the action potential.

Automaticity

The ability of cardiac muscles to contract without neural input.

SA Node

Sinoatrial node; primary pacemaker of the heart located in the posterior right atrium.

AV Node

Atrioventricular node; responsible for delaying the impulse to ensure atrial contraction before ventricular contraction.

Bradycardia

Defined as a heart rate slower than 60 bpm.

Tachycardia

Defined as a heart rate faster than 100 bpm.

P wave

Electrocardiogram wave indicating atrial depolarization.

QRS Complex

Electrocardiogram complex indicating ventricular depolarization and hidden atrial repolarization.

T wave

Electrocardiogram wave indicating ventricular repolarization.

Stroke Volume

Volume of blood ejected by a ventricle in one beat.

Cardiac Output

Volume of blood ejected from a ventricle in one minute.

Frank–Starling Principle

Increase in venous return leads to increased stretch on myocardial cells, improving contraction force.

Autonomic Innervation

The dual innervation of the heart by sympathetic and parasympathetic fibers, affecting heart rate and contraction.

Vagal Tone

The influence of the parasympathetic nervous system that slows heart rate.

Hormonal Effects on Heart Rate

Epinephrine and norepinephrine from the adrenal medulla increase heart rate and stroke volume.