Cardiac Function and Conduction - Pathophysiology

What does this refer to

• Pumps blood through the lungs (pulmonary circulation)

• Delivers blood to the lungs for oxygenation

• Is a low pressure system

Right heart function

What does this refer to

• Pumps oxygenated blood through the systemic circulation.

• Delivers metabolic waste products to the lungs, kidneys, and liver

• Is a high pressure system

Left heart function

What does this refer to

“Carry blood away from the heart”

Arteries

What does this refer to

“Exchange fluids between the blood and interstitial space”

Capillaries

What does this refer to

“Carry blood to the heart”

Veins

What does this refer to

• Double-walled membranous sac

• Parietal: surface layer

• Visceral: inner layer

Pericardium

What does this refer to

• Space between the parietal and visceral layers

• Contains pericardial fluid (20 mL)

Pericardial cavity

What does this refer to

• Area where the heart is located

• Area above the diaphragm and between the lungs

Mediastinum

Which heart wall is the outer smooth layer

Epicardium

What heart wall does this refer to

• thickest layer of cardiac muscle made up of myocytes (aka cardiocytes)

• short, thick, striated fibers

Myocardium

What layer of the heart wall is below

• smooth innermost layer

• continuous with blood vessels

Endocardium

What does this refer to

“Bring deoxygenated blood from the systemic circulation to the right atrium”

Superior and inferior venae cavae

What does this refer to

• Transport unoxygenated blood from the right heart to the right and left lungs

• Branch into pulmonary capillaries

Right and left pulmonary arteries

What does this refer to

“Carry oxygenated blood from the lungs to the left side of the heart”

Pulmonary veins

What does this refer to

“Delivers oxygenated blood to systemic vessels that supply the body”

Aorta

What does this refer to

• One-way flow of blood from the atria to the ventricles

• Tricuspid valve: three leaflets or cusps

• Bicuspid (mitral) valve: two leaflets or cusps

Atrioventricular valves (AVs)

What does this refer to

• One-way flow from the ventricles to either the pulmonary artery or to the aorta

• Pulmonic semilunar valve

• Aortic semilunar valve

Semilunar valves

What does this refer to

“Supplies oxygen and other nutrients to the myocardium”

Coronary circulation

What does this refer to

• Conus artery

• Right marginal branch

• Posterior descending branch

Right coronary artery

What does this refer to

• Left anterior descending artery

• Circumflex artery

Left coronary artery

What does this refer to

• Are connections, or anastomoses, between the branches of the coronary circulation

• Protects the heart from ischemia

• Are formed by arteriogenesis or angiogenesis

Collateral arteries

What does this refer to

“Where the exchange of oxygen and other nutrients takes place”

Coronary capillaries

What does this refer to

• Coronary sinus

• Great cardiac vein

• Posterior vein of the left ventricle

Coronary veins

What does this refer to

What does this refer to

• Atrial systole

• Atrial diastole

• Ventricular systole

• Ventricular diastole

• Quiescent period

Cardiac cycle

What phase of the cardiac cycle is below

“atrial systole or ventricular diastole”

Phase 1

What phase of the cardiac cycle is below

“isovolumetric ventricular systole”

Phase 2

What phase of the cardiac cycle is below

“ventricular ejection (semilunar valves open)”

Phase 3

What phase of the cardiac cycle is below

“isovolumetric ventricular relaxation (aortic valve closes”

Phase 4

What phase of the cardiac cycle is below

“passive ventricular filling (mitral and tricuspid valves open)”

Phase 5

What does this refer to

• One contraction and one relaxation

• Makes up one heartbeat

Cardiac cycle

What does this refer to

• Relaxation: ventricles fill

Diastole

What does this refer to

• Contraction: blood leaves the ventricles

Systole

What does this refer to

• Unoxygenated (venous) blood from systemic circulation enters the right atrium through the superior and inferior venae cavae.

• From the atrium, the blood passes through the right AV (tricuspid) valve into the right ventricle.

• In the ventricle, the blood flows from the inflow tract to the outflow tract and then through the pulmonic semilunar valve (pulmonary valve) into the pulmonary artery, which delivers it to lungs for oxygenation.

• Oxygenated blood from the lungs enters the left atrium through the four pulmonary veins (two from the left lung and two from the right).

• From the left atrium, the blood passes through the left AV valve (mitral valve) into the left ventricle.

• In the ventricle, the blood flows from the inflow tract to the outflow tract and then through the aortic semilunar valve (aortic valve) into the aorta, which delivers it to the entire body.

Blood Flow During the Cardiac Cycle

What does this refer to

• Atria contract

• Blood pressure in atria increases

• Blood forced into ventricles

Atrial systole

What does this refer to

• Ventricles contract

• Ventricular pressure increases

• AV valves close

• Heart sound S1

• No blood ejected yet

Isovolumetric contraction of cardiac cycle

What does this refer to

• Ventricular pressure exceeds arterial pressure

• Semilunar valves open

• Blood ejected into arteries

• Not all blood expelled

• Amount ejected = stroke volume

• % = Ejection fraction

Ventricular ejection of cardiac cycle

What does this refer to

• Early in ventricular diastole

• Blood briefly flows backwards

• Semilunar valves close

• Heart sound s2

• AV valves not yet open

• No blood taken in yet

Isovolumetric relaxation of the cardiac cycle

What does this refer to

• Ventricular pressure drops

• AV valves open

• Ventricles begin to fill

• (Completely filled by atrial systole)

Ventricular filling

What does this refer to

• Are connections, or anastomoses, between the branches of the coronary circulation

• Protects the heart from ischemia

• Are formed by arteriogenesis or angiogenesis

Collteral arteries (Structures That Support Cardiac Metabolism: Coronary Circulation)

What does this refer to

“Supplies oxygen and other nutrients to the myocardium”

Coronary circulation

What does this refer to

• Conus artery

• Right marginal branch

• Posterior descending branch

Right coronary artery

What does this refer to

• Left anterior descending artery

• Circumflex artery

Left coronary artery

What does this refer to

“Where the exchange of oxygen and other nutrients takes place”

Coronary capillaries

What does this refer to

• Coronary sinus

• Great cardiac vein

• Posterior vein of the left ventricle

Coronary veins

What does this refer to

Cardiac action potentials

• Transmission of electrical impulses

Conduction system

• Sinoatrial (SA) node

  • Pacemaker of the heart

  • Intranodal pathways

Atrioventricular (AV) node

Bundle of His (AV bundle)

Right and left bundle branches

Purkinje fibers

Ventricular myocardium

Structures That Control Heart Action

What does this refer to

• Autorhythmic

  • Spontaneous depolarization at regular intervals

• Some specialized to generate action potentials

  • “Cardiac conduction system”

  • Sinoatrial (SA) node

  • Atrioventricular (AV) node

Cardiac Myocytes

What does this refer to

• Myocytes in right atrium

• “Pacemaker”

• Initiates heartbeat

• Determines heart rate

• Firing rate is increased/decreased by nerves

• 70 – 80 beats per minute (bpm)

Sinoatrial (SA) Node

What does this refer to

• Near Right AV Valve

• Electrical Gateway To Ventricles

• Distributes Signal To Ventricular Myocardium

• AV Bundle

• Purkinje Fibers

Atrioventricular (AV) Node

What does this refer to

• Signal travels from AV node through ventricular myocardium

• Ventricles contract ~simultaneously

• Also depends on substances delivered to myocardium via coronary arteries

• Nutrients and Oxygen

• Hormones and Biochemicals

Cardiac rhythm

What does this refer to

• Electrical currents generated in the heart travel weakly through all body tissues

• These currents can be measured using electrodes applied to the skin

Electrocardiogram

What does this refer to

• Sum of all cardiac action potentials

• P wave: atrial depolarization

• PR interval: time from the onset of atrial activation to the onset of ventricular activation

  • Time necessary to travel from the sinus node through the atrium, AV node, and His-Purkinje system to activate ventricular myocardial cells

• QRS complex: sum of all ventricular depolarizations

• ST interval: ventricular myocardium depolarized

• QT interval: “electrical systole” of the ventricles

  • Varies inversely with the heart rate

Normal electrocardiogram (ECG)

What does this refer to

• Heart rate (HR) (beats/min)

  • ~75 bpm at rest

• Stroke volume (SV)

  • ~70 ml/beat at rest

• Cardiac output (CO)

  • Co = HR * SV

  • 75 * 70 = 5,000 ml/min at rest

  • Cardiac output is not constant

• Resting

  • ~5 liters/min resting (total volume)

• Vigorous exercise

  • ~21 liters/min in good condition

  • ~35 liters/min Olympic athlete

• CO = HR * SV,

  • CO Increased by HR or SV increase

Cardiac output

What does this refer to

• Is the amount of blood ejected per beat

• Normal is 66% for women and 58% for men.

• Is calculated by dividing the stroke volume by the end-diastolic volume

• Is an indicator of ventricular function

Ejection fraction (Factors affecting cardiac output)

What does this refer to

• Is the volume inside the ventricle at the end of diastole

• Is also called ventricular end-diastolic volume (VEDV) and ventricular end-diastolic pressure (VEDP)

  • Is determined by two primary factors

    • Amount of venous return to the ventricle

    • Blood left in the ventricle after systole or end-systolic volume

• When preload exceeds physiologic range, further muscle stretching causes a decline in cardiac output.

Factors Affecting Cardiac Output

What is this referring to

• Is the resistance to ejection during systole

• Aortic systolic pressure is a good index of afterload for the left ventricle.

• Decreased afterload: heart contracts more rapidly

• Increased afterload: slows contractions and increases work load

• Systemic vascular resistance (SVR)

• Total peripheral resistance (TPR)

Afterload (Factors Affecting Cardiac Output)

What does this refer to

• Is the volume of blood at the end of diastole

• Myocardial stretch determines the force of myocardial contraction.

  • More stretch = Increased force of contraction

• Is the major way that the right and left ventricles maintain equal minute outputs, despite stroke (beat) output variation

Frank-Starling law of the heart (factors affecting cardiac output)

What does this refer to

• Contractile force within a chamber depends on the radius of the chamber and the thickness of its wall.

  • Smaller chambers and thicker chamber walls equal increased contraction force.

  • In ventricular dilation, the force needed to maintain ventricular pressure lessens available contractile force.

Laplace’s law (factors affecting cardiac output)

What does this refer to

• Inotropic agents

  • Positive inotropic agents: increase the force of contraction

    • Norepinephrine

    • Epinephrine

  • Negative inotropic agents: decrease the force of contraction

    • Acetylcholine released from the vagus nerve

• Hypoxia: decreases contractility

Myocardial contractility (cont.) (factors affecting cardiac output)

What does this refer to

• Easily measured (pulse)

• 70 – 80 average resting rate

• Tachycardia: resting >100 bpm

• Bradycardia: resting <60 bpm

• Regulated by nervous system

• Cardiac accelerator nerves

• Secrete norepinephrine

• Binds to receptors in heart

• Increases heart rate

• Vagus nerves

• Secrete acetylcholine

• Send signals to AV and SA nodes

• Fire less frequently

Heart rate (cardiac output)

What does this refer to

• Governed by three factors

  • Preload

  • Contractility

  • Afterload

Stroke volume

What does this refer to

• Mean arterial pressure increases when there is an increase in cardiac output or when the diameter of the blood vessels (principally the arterioles) is decreased

• Flow in blood vessels is laminar and the flow is smooth, and no sound is generated

  • the radius of the vessel and the viscosity of the blood

Other concepts