CHI335 Cardiovascular System Lecture I PDF

CHI335 Diagnosis I Cardiovascular System Lecture I  Identify the location, chambers, valves, and layers of the heart and some disorders that affect them Interpret the cardiac cycle Relate the major heart sounds to their significance Discuss how cardiac output is determined Explai...

CHI335 Diagnosis I Cardiovascular System Lecture I  Identify the location, chambers, valves, and layers of the heart and some disorders that affect them Interpret the cardiac cycle Relate the major heart sounds to their significance Discuss how cardiac output is determined Explain the components of the heart conduction system, the electrical events in the heart, and its abnormalities Discuss mechanisms of controlling blood pressure and the causes and classification of hypertension Explain some common cardiac-related physical examination findings in relation to noncardiac-related ones Explain some common cardiac diagnostic tests currently available  Cardiovascular system ▪ Heart (a pump) ▪ Vascular system (a collection of pipes making up a plumbing system) Main function ▪ Circulates blood in order to: ▪ Supply oxygen and nutrients to the tissues ▪ Help remove carbon dioxide and waste products from tissues  Pulmonary ▪ Circulation through lungs provides ability to transfer oxygen from atmosphere into body Systemic ▪ Oxygen and nutrients are distributed to body ▪ Carbon dioxide are returned to the heart to enter the pulmonary circulation Coronary ▪ Blood flow to heart muscle supports heart’s work in pumping oxygenated blood to body  Two atria that sit on two ventricles Atria are separated by a septum or wall called the interatrial septum Ventricles are separated by a wall called the interventricular septum Septum that separates the atria from the ventricles, the atrioventricular septum  Right atrium ▪ Receives blood that is returning from the body to the heart and blood from the coronary sinus Right ventricle ▪ Receives blood from the right atrium Left atrium ▪ Four pulmonary veins carrying oxygenated blood enter the left atrium Left ventricle ▪ Receives blood from the left atrium ▪ Works harder than any other chamber (why?)  Semilunar valves ▪ Pulmonary ▪ Between the right ventricle and the trunk of the pulmonary arteries ▪ Aortic ▪ Between the left ventricle and the aorta Atrioventricular (AV) ▪ Bicuspid (Mitral) ▪ Between the left atrium and the left ventricle ▪ Its 2 cusps are anchored by cordlike structures called chordae tendinae to specialized cardiac muscles called papillary muscles ▪ Tricuspid ▪ Between the right atrium & right ventricle, ▪ It has 3 cusps that also have chordae tendinae attached to papillary muscles  Heard through auscultation with a stethoscope ▪ Caused by the closure of the valves First heart sound (S1) ▪ Described as lub ▪ Closure of the tricuspid and bicuspid valves when the ventricles contract Second heart sound (S2) ▪ Described as dub ▪ Pulmonary and aortic semilunar valves closure when ventricles relax  Innermost layer is called the endocardium ▪ Very thin and lined with endothelium Middle layer is the muscular myocardium ▪ Cardiac muscle ▪ Pumping action of the heart Outermost layer is the Pericardium ▪ The entire membrane around the heart is called the pericardium ▪ Its inner layer called the epicardium or visceral pericardium ▪ Its outer fibrous layer called the parietal pericardium ▪ Cushions the heart if the chest experiences blunt trauma  Events from one heartbeat to the next First, simultaneously, two atria contract (atrial systole) and relax (atrial diastole) ▪ When the atria contract ▪ Tricuspid and bicuspid valves open → blood enters the ventricles Then, simultaneously, two ventricles contract (ventricular systole) and relax (ventricular diastole) ▪ When ventricles contract ▪ Tricuspid and bicuspid valves close (S1) ▪ Aortic and pulmonary valves open → blood leaves the heart ▪ When ventricles relax ▪ Aortic and pulmonary valves close (S2)  Electrical activity of the heart that is responsible for the contraction of the atria and ventricles The cardiac conduction system is regulated by ANS ▪ Heart muscle has an inherent rhythmic activity ▪ Aka self-excitability or autorhythmicity  A node is a collection of specialized cardiac muscle fibres that have a certain rate of activity SA node is located in the posterior wall of the right atrium It is the heart’s primary or natural pacemaker ▪ Responsible for setting the heart rate Controlled by the autonomic nervous system (ANS) ▪ Innervated by both the sympathetic and parasympathetic division ▪ Electrical impulse travels from the SA node to the muscle fibres of both the right and left atria, causing them to contract, and to the AV node…  Located in the lower interatrial septum Electrical impulses that leave the SA node travel to the AV node ▪ Restrained for a very brief period of time before it is allowed to go forward It is considered as the heart’s secondary pacemaker ▪ If something happens to the SA node, the AV node takes over ▪ However, it can only cause contraction of ventricles Like the SA node, the AV node also receives sympathetic and parasympathetic innervation  AV bundle ▪ Aka atrioventricular bundle or bundle of His ▪ Located in the interventricular septum, splits into left and right bundle branches ▪ Electrical impulse travels from the AV node to both the right and left bundle branches Purkinje Fibers ▪ Fibers at the very end of bundle branches in the walls of ventricles ▪ Impulses flow through the Purkinje fibres, stimulating the ventricular muscles, causing them to contract  The volume of blood that is pumped out of the left or right ventricle each minute: CO = SV × HR Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR) Resting stroke volume of 74 mL (aver) Resting heart rate of 72 bpm (aver) 74 mL x 72 bpm = 5,328 mL/min  Factors that influence SV ▪ Amount of blood returning to the heart (i.e. preload) ▪ Contractility or strength of contraction of the heart (i.e. inotropy) ▪ Force that resists ejection of blood from the ventricles (i.e. afterload) Factors that influence HR ▪ Mostly via ANS regulation (SNS vs PNS) ▪ Hormones such as epinephrine ▪ Exercise ▪ Body temperature ▪ Changes in BP ▪ Age ▪ Sex ▪ Concentration of K+ and Ca2+  Pericarditis ▪ Characterized by inflammation of the sac surrounding the heart ▪ Sharp and localized pain in the chest ▪ Not immediately life-threatening, but should be treated Stable, unstable, and variant angina pectoris ▪ Caused by a narrowing or spasm of coronary arteries ▪ Pain is usually described as a tight feeling in the chest ▪ When it is brought about by stress or physical activity and goes away with rest, is called stable angina ▪ Unstable angina lasts longer, might occur during rest, and does not usually subside by rest  Myocardial infarction (MI) or heart attack ▪ Caused by a complete blockage of one or more coronary arteries ▪ Sometimes fatal ▪ Pain is often described as pressure or fullness in the chest ▪ Pain also frequently radiates to the back, neck, face, left shoulder, or arm ▪ Other signs and symptoms may include shortness of breath, profuse sweating, nausea, dizziness, and shock  Clubbing is an increase in the soft tissue of the distal part of the fingers or toes One current theory is that platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) from peripheral megakaryocytes lead to fibrovascular proliferation in the nail beds CVS causes ▪ Cyanotic congenital heart disease ▪ Infective endocarditis ▪ Aneurysms  A blue discolouration of the skin and mucous membranes Indicates the increased level of deoxygenated haemoglobin in blood vessels ▪ > 50 g/L of deoxygenated haemoglobin Central (cardiac cause) ▪ Right-to-left cardiac shunt (e.g. cyanotic congenital heart disease) Peripheral ▪ Cases of central cyanosis will present with peripheral cyanosis ▪ Exposure to (extreme) cold ▪ Low cardiac output, such as heart failure or shock ▪ Venous stasis ▪ Vasoconstrictions  Oedema behind the medial malleolus of the tibia and the distal shaft of the tibia (confirmed by pressing the thumb over those areas) Cardiac causes make it bilateral and pitting, worse in the evenings ▪ Cardiac failure ▪ Constrictive pericarditis  The third heart sound (S3) ▪ A low-pitched early diastolic sound ▪ Indicates a reduced ventricular compliance (a filling sound) ▪ It is strongly associated with increased atrial and ventricular end-diastolic pressure ▪ It can be physiological in children, pregnancy & elite athletes, and thyrotoxicosis The fourth heart sound (S4) ▪ A low-pitched late diastolic sound ▪ Indicates a forceful atrial contraction against a poorly compliant ventricle  Abnormal heart sounds ▪ Graded from 1 to 6, with 1 being barely audible and 6 being quite loud Signs and symptoms vary considerably depending on the cause and severity ▪ In mild severity, there may be no symptoms at all ▪ Often no treatment is required  Abnormal sounds heard over the big arteries Associated with turbulent blood flow and may occasionally be palpated as a thrill Causes ▪ Atherosclerotic partial occlusion ▪ Stenosis  Shortness of breath (SOB) is an awareness of breathing Cardiac dyspnoea is typically chronic and occurs with exertion because of failure of the left ventricular output to rise with exercise Orthopnoea is a dyspnoea that develops when a patient is supine; mainly due to pulmonary oedema  Syncope is a transient loss of consciousness resulting from cerebral hypoxia, usually due to inadequate blood flow Presyncope is a transient sensation of light- headedness/weakness without loss of consciousness Cardiac causes: ▪ Left heart outflow obstruction (e.g. AS) ▪ Some cardiac dysrhythmia ▪ Very low systolic BP  Fatigue is a common symptom of cardiac failure. It may be associated with reduced cardiac output and poor blood supply to the body  Rate: abnormally fast (tachy) or slow (brady) Rhythm: irregular rhythm Strength: weak, narrow Delay: radio-femoral or radio-radial delay  Increase or decrease in either or both ▪ Systolic BP ▪ Diastolic BP BP is affected by ▪ Cardiac output ▪ Peripheral vascular resistance ▪ Elasticity of arterial walls ▪ Volume of blood  Mechanisms regulating blood pressure ▪ Baroreceptors in brain & arteries ▪ Kidneys ▪ Renin-angiotensin system  Essential, idiopathic, or primary hypertension ▪ Over 90 % of the cases have no known cause Secondary hypertension ▪ Cause(s) has been identified ▪ Narrowing of the arteries, and cold medicines, kidney disease, endocrine disorders, pregnancy, drug use, sleep apnea, obesity, smoking, a high- sodium diet, excessive alcohol consumption, diabetes mellitus, oral contraceptives, and stress Note: Both essential and secondary hypertension can present as malignant hypertension (next lecture) The National Heart Foundation of Australia  Represents the electrical activity of the heart ▪ Correlates to the contraction and relaxation of the heart A basic ECG recording is made while the patient is at rest ▪ Six electrodes are attached to the chest plus four more, one to each extremity (a 10-lead ECG) Know the ECG, its components, and what they represent but its interpretation will not be examined  P wave ▪ The first (normally upward) wave, which represents depolarisation (contraction) of the atria QRS complex ▪ The second element consists of three waves (Q, R, and S) that represent ventricular depolarisation (contraction) T wave ▪ Third element is the T wave, and it represents the repolarization (relaxation) of the ventricles  P-R interval ▪ From the beginning of the P wave to the beginning of QRS complex S-T segment ▪ Begins at the end of the S wave and ends at the beginning of the T wave Q-T interval ▪ From the beginning of the QRS to the end of the T-wave  Stress tests ▪ ECGs performed while a patient is exercising or has been given drugs to increase the heart rate Cardiac enzymes in the blood ▪ When heart muscle is damaged, certain enzymes are released into the blood and can be measured ▪ Cardiac troponin (cT) & Creatine phosphokinase (CK-MB) Chest x-ray ▪ X-rays show the size and shape of the heart Nuclear scan ▪ Follows radioactive substances through the blood vessels of the heart to reveal narrow or obstructed arteries  Angiography & CT/MR angiography ▪ Much like a CT scan of the arteries, useful for finding narrowed arteries Echocardiogram ▪ Uses sound waves to visualise the size, shape, and defects of the heart as well as the movement of the blood inside Coronary catheterisation ▪ Using a contrast medium, a catheter is moved through a blood vessel to the heart in order to better diagnose heart conditions or manage obstructions