EKG Training Notes 1

Anatomy of the Heart

Anatomy of the Heart

Located in the Mediastinum

Heart is composed of cardiac muscle tissue

Upper - Atrial (Thin)

Lower - Ventricle (Thick)

Layers of the Heart

Pericardium

Two layers of sac with scant fluid (lubricates and reduces friction)

Heart Wall Layers

Epicardium - Smooth Outer (Main Coronary Arteries)

Myocardium - Thick Middle Layer (Cardiac Muscle Cells Contractions)

Endocardium - Innermost Layer (Thin Connective & Oxygen Needed)

Valves of the Heart

Tricuspid Valve

Pulmonary Valve

Mitral Valve

Aortic Valve

Arteries

Thick walled and muscular blood vessels

Oxygenated blood that is taken away from the heart

Decrease in size becomes arterioles

Two main arteries (right and left) - Arise from aorta and carry oxygenated blood away from the heart & supply blood to the heart itself

Veins

Blood vessels that carry blood back to the heart

Venules (smaller veins) and operate under low pressure

Superior vena cava and inferior vena cava

Capillaries

Tiny blood vessels with extremely thin walls

Gaseous exchange

Pulmonary Circulation

Blood flow between the heart and the lungs

Right ventricle to lungs back to the heart

Systemic Circulation

Blood flow between the heart and the body (SYSTEM)

Left ventricle to the body and back to the heart

Blood Flow 1

Deoxygenated blood

Vena cava ‐> Right atrium ‐> Tricuspid valve ‐> Right Ventricle ‐> Pulmonic valve ‐> Pulmonary artery ‐> Lungs

Blood Flow 2

Oxygenated blood

Pulmonary vein ‐> left atrium ‐> mitral/bicuspid valve ‐> left ventricle ‐> aortic valve ‐> body

Lub-dub

The heart beats by both atrial contracting followed by the ventricles contracting

Cardiac Cycle

Represents the time sequence between the ventricular contractions and the ventricular relaxations

Systole

Contraction of the ventricles (Top)

Diastole

Relaxation of the ventricles (Bottom)

Stroke Volume

The volume of blood pumped out of one ventricle in a single beat \n Roughly 70 cc per beat

Heart Rate

The total contractions of the heart per min

Average 60‐100 bpm

Cardiac Output

The amount of blood pumped out of the left ventricle per min

HR x SV = cardiac output

Inadequate Q

Lead to congestive heart failure or myocardial infarction

Symptoms: Shortness of breath, Dizziness, Decreased bp, Chest pains, and Cool clammy skin

Abnormal Cardiac Output

Raise either SV or HR or lower it

Preload

Pressure in the ventricles at the end of diastole \n Affected by the exact volume of blood that returns to the right atrium and can be decreased

Afterload

The resistance against what the heart must pump

Affects SV and Q

Starling’s Law of the Heart

The more the heart is stretch, the more forceful the contraction will be (think RUBBER BAND)

Peripheral Vascular Resistance

The amount of opposition to blow flow offered by the arterioles

This can change blood pressure, the more resistance, the higher the blood pressure

Autonomic Nervous System

The part of the nervous system that controls involuntary actions

Sympathetic Nervous System

Responsible for fight or flight

Releases norepinephrine which can increase the HR and contractile force of the heart

Parasympathetic Nervous System

Controls rest and digestion

Acetylcholine is the chemical neurotransmitter that when released can slow the heart rate

Four Heart Properties

Automaticity

Excitability

Conductivity

Contractibility

Automaticity

• The ability of cardiac pacemaker cells to generate their own electrical impulses without external stimulation \n • The intrinsic spontaneous depolarization produced the contraction \n • This is specific to the pacemaker cell site (the SA node, AV junction, and Purkinje fibers)

Excitability

• The ability off cardiac cells to respond to an electrical stimulus \n • Shared by all cardiac cells \n • When the cells are highly stimulated, a weaker stimulus can cause a contraction

Conductivity

• The ability of cardiac cells to receive an electrical stimulus and then transmit it to other cardiac cells \n • This allows for the heart to function as a unit when the cells are connected together

Contractility

• Also known as rhythmicity, the ability of cardiac cells to shorten and cause cardiac muscle contraction in response to electrical stimulus

• This allows for the body to produce a regular heartbeat

Sino Atrial Node

Pacemaker of the heart (60 - 100 bpm)

Atrioventricular Node

Collects impulse and pauses the transmission of the impulse, allowing the heart to fully contract

Bundle of His

Travels to the ventricles through bundle branches (slower impulse firing rate of 40 - 60 bpm)

Purkinje Fibers

Allows for the impulse to contract the ventricles (slowest intrinsic firing rate of 20 - 40 bpm)