Chapter 17 Cardiovascular Emergencies

OBJECTIVES To know the risk factors of cardiac diseases. To know the epidemiology of cardiac diseases. To know the anatomy of the heart. To know the heart pump.

Introduction Heart disease is the number one killer. – Kills 600,000 Americans each year About half in ED or before reaching a hospital During first minutes or hours

Epidemiology In 2007, heart disease contributed to about 34% of all US deaths.

Epidemiology Prevention strategies include education and early recognition.

Anatomy and Physiology Structure and function – Cardiovascular system Composed of heart and blood vessels Delivers oxygenated blood and nutrients to cells Transports waste products to disposal sites

The Heart Sits above diaphragm – Size of a fist – Circulates 7,000 to 9,000 L of blood daily

The Heart Three layers: – Epicardium: outmost layer – Myocardium: muscular middle layer of wall – Endocardium: lines inside of the heart’s cavities

The Heart

Pericardium: sac surrounding the heart – Protects the heart and provides lubrication Parietal pericardium (superficial layer) Visceral pericardium – Abnormal accumulation of fluid can occur. Pericardial effusion: Small accumulation Pericardial tamponade: Large accumulation

The Heart Coronary arteries – Left coronary artery supplies: Left ventricle Interventricular septum Part of right ventricle

The Heart Coronary arteries (cont’d) – Right coronary artery supplies: Right atrium Right ventricle Part of the left ventricle

The Heart

Coronary sulcus: groove separating atria from ventricles Venous blood empties into the coronary sinus.

The Heart Atria are separated from ventricles by atrioventricular (AV) valves: – Tricuspid valve – Mitral valve – Semilunar valves Pulmonary semilunar valve Aortic semilunar valve © Tony Wear/ShutterStock, Inc.

The Cardiac Cycle Represents complete depolarization and repolarization of the atria and ventricles – Diastole: atria or ventricles are resting – Systole: atria or ventricles contracting

The Cardiac Cycle Relaxation phase: left atrium fills with blood under venous pressure. Atrial contraction: blood in each atrium is squeezed into respective ventricle – Atrial kick: contribution made by contraction

The Cardiac Cycle As ventricular contraction begins: – Ventricles contract. – Semilunar valves are forced open. – Blood from the right ventricle is squeezed into the pulmonary arteries. – Left ventricle blood is pushed into the aorta.

Blood Flow Through the Heart The heart acts as two pumps, separated by an interventricular septum. – Right side: low-pressure pump Superior vena cava collects blood from upper body Inferior vena cava collects blood from lower body – Left side: high-pressure pump Pulmonary veins collect blood from the lungs.

Blood Flow Through the Heart

Preload: initial stretching of cardiac myocytes prior to left-sided contraction Afterload: blood is driven out of the heart against systemic arteries

Blood Flow Through the Heart Two circulations: – Systemic circulation All blood vessels between left ventricle and right atrium – Pulmonary circulation All blood vessels between right ventricle and left atrium

Blood Flow Through the Heart

Blood Vessels Types of blood vessels: – Veins – Arteries Common structures – Tunica adventitia – Tunica media – Tunica intima – Lumen

Blood Vessels Arteries carry oxygenated blood away from the heart. – Sensitive to autonomic nervous system stimulation – Blood pressure generated by repeated forceful left ventricle contractions

Blood Vessels Veins carry deoxygenated blood back to the heart. – Venules empty into larger and larger veins. – Contain valves to keep blood flowing forward Capillaries separate arteries and veins.

Blood Vessels

The Pump at Work Skeletal muscle and thorocoabdominal pumps aid venous blood return to the heart. Technical terms: – Cardiac output (CO): Amount of blood pumped by either ventricle – Stroke volume (SV): Amount of blood pumped by either ventricle in a single contraction

The Pump at Work Technical terms (cont’d): – Heart rate (HR): Number of contractions per minute (pulse rate) – Ejection fraction (EF): Percentage of blood leaving the heart on each contraction

The Pump at Work CO = SV × HR – Must increase output to meet changing demand – Increases output by: Increasing SV Increasing rate Both

The Pump at Work Heart increases SV in several ways: – Frank-Starling mechanism: when cardiac muscles is stretched, contracts with greater force – If HR is constant, any SV increase will increase overall CO and the HR.

The Pump at Work Preload is influenced by the blood volume returned to the heart. – More blood is returned when more oxygen is demanded.

The Pump at Work With a constant SV, CO can be increased by increasing number of contractions per minute Which is : Positive chronotropic effect.

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