Intro to the CVS PDF

Cardiovascular System Introduction to the CVS Welcome to the 2nd lecture in the series on the anatomy of the thorax. We turn our attention now to the cardiovascular system. This lecture is an introduction to that system, and it is divided into two parts.  Car...

Cardiovascular System Introduction to the CVS Welcome to the 2nd lecture in the series on the anatomy of the thorax. We turn our attention now to the cardiovascular system. This lecture is an introduction to that system, and it is divided into two parts.  Cardiovascular System Introduction to the CVS Part 1: Heart and Pericardium In this first part we will consider some general principles of the heart and its covering the pericardium.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the surface anatomy relating to the heart and great vessels ▪ List the layers of the pericardium and heart wall ▪ Describe the orientation of the heart and be able to recognise the position of each of the chambers ▪ Know the position and function of the cardiac skeleton These are the learning outcomes for the entire lecture.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the surface anatomy relating to the heart and great vessels ▪ List the layers of the pericardium and heart wall ▪ Describe the orientation of the heart and be able to recognise the position of each of the chambers ▪ Know the position and function of the cardiac skeleton However, the learning outcomes for this first part of the lecture are that afterwards you should be able to: Give an account of the surface anatomy relating to the heart and great vessels List the layers of the pericardium and heart wall The remaining outcomes will be given in the subsequent parts of the lecture.  Cardiorespiratory Systems The cardiovascular system is utterly incredible. At the centre of it all is the heart which is an elaborate muscular pump. We assume it will keep going hour after hour, day after day, year by year. And it never seems to need a service. Just think about it for a minute….. If it beats at 70 times a minute (which is just an average), that’s well over 4,000 beats every hour and over 100,000 beats every day. If I live until I’m 70, that will be over 2.5 billion beats, and that is assuming that I haven’t taken any exercise, seen a good movie, listened to an exciting piece of music, or met the love of my life. And I’ve done all of those things and more. Yet, I think I can rely on it to carry on for a few more years yet. It pumps blood into more than 60,000 miles of blood vessels which carry all of the nutrients and gases that I need to survive. But not everyone is so lucky.  Top 10 Global Causes of Death If you look at the most common causes of death, ischaemic heart disease is in top position across the world. It has been for as long as I can remember. This is caused largely by a reduction in the supply of oxygen and nutrients to the heart muscle. 2 nd on the list is stroke which is another cardiovascular problem, where there is a blockage of the blood vessels supplying the brain. So that gives us sufficient motivation to get to know this system well. Whilst this list is still showing however, note that 4 of the other main causes of death involve the respiratory system, giving us the motivation to learn about that system as well. However, we’ll take it step by step.  The Normal Heart So let’s start with the heart. The size of a person’s heart is roughly the size of their clenched fist.  The Pathological Heart Diseased hearts though or a diseased cardiovascular system mean that the heart has to work harder to overcome the pathology. When the heart contracts more it enlarges, much like any other muscle that we push to the limit.  Cardiac Percussion One can determine the actual size of a patient’s heart by percussion. This involves the examiner tapping his or her distal finger joints onto the patient’s chest wall to listen for a dull echo. The tap is started in the 5th intercostal space in the midaxillary line. The tap is progressed medially until the sound changes from resonant to dull. This marks the left border of the heart. Resonance is heard over lung tissue, and dullness over the heart.  Surface Anatomy of the Heart It is useful to be able to map out the position of the heart against the chest wall. The apex of the heart is first determined, either by its pulsation (apex beat) or by percussion. Because the heart is tilted and the apex lies forwards, it can be felt pounding against the chest wall as it relaxes. This is the apex beat. It Iies somewhere in the fifth intercostal space, 6- 9 cm to the left of the midsternal line. It is normally medial to the midclavicular line. Its actual position will be dependent upon both the size and shape of the patient, and their degree of pathology. The lower right border of the heart is located at the 5th or 6th right costal cartilage parasternally. The base of the heart runs from a point on the third right costal cartilage 1 cm from the sternum to a point in the second intercostal space 1-2 cm from the sternum. One can then map out the outline of the heart by joining the dots together with curved lines.  The Pericardium The heart is enclosed in a fluid-filled sac, the pericardium. The outer layer of the pericardium is thick and tough, and provides a stable and protective cover for the heart. This is called the fibrous pericardium. It is attached inferiorly to the central tendon of the diaphragm, and anteriorly to the chest wall via the sternal cardiac ligament (although this is weak, and ill-defined). Superiorly and posteriorly, it blends into the adventitia (outer layer) of the great vessels as they enter and leave the heart. There are two further layers, both of which are serous membranes. The first is the parietal layer which is adherent to the inside of the fibrous layer. This is then reflected around the great vessels entering and leaving the heart where it then turns over onto the surface of the heart to become visceral pericardium. The space between parietal and visceral layers of pericardium is the pericardial cavity, which contains a small amount of fluid. There is between 10-50mL of fluid normally and this is produced by the serous layers. This pericardial fluid reduces the friction caused by the beating of the heart, and this is the principal function of the pericardia.  Pericardial Layers Fibrous pericardium Visceral pericardium Parietal pericardium Here is a dissection of the outer covering to show the relationship of these three layers to one another.  The Wall of the Heart Fibrous pericardium Parietal (serous) pericardium epicardium Visceral myocardium (serous) pericardium Endocardium Here is a schematic representation of the wall of the heart, with its outer fibrous layer and parietal pericardium immediately inside of that. Then there is the pericardial cavity, with the visceral pericardium sitting on the surface of the heart. Under the visceral pericardium is a layer of loose connective tissue called the epicardium, containing a variable amount of fat (epicardial fat). Beneath this is a thick layer of heart muscle, known as myocardium. The chambers of the heart are separated from this muscle by a thin layer of connective tissue and an epithelium (endothelium) which together are referred to as the endocardium. The endocardium is prone to infection by blood-borne bacteria, and this results in infective endocarditis. The latter often affects the endocardium around the heart valves, and can therefore lead to valve dysfunction.  Epicardial Fat Fat is particularly noticeable in the grooves between the chambers of the heart. This is also where blood vessels, lymphatics and nerves of the heart are located, and hence these tend to be covered in copious amounts of fat. The amount of epicardial fat is variable and is linked to the amount of general body fat. Too much fat has a negative impact on heart function, and there is a substantial amount of evidence linking epicardial fat to coronary artery disease. The coronary arteries are the arteries of the heart.  The Pericardial Sinuses Here is a sagittal view of the chest showing the heart in its pericardial cavity. Imagine dissecting the heart out by cutting opening the anterior wall of the pericardium and cutting through the vessels entering and leaving the heart. What would be left behind would be the posterior wall of the pericardium, and this is what you would see. There are 8 vessels connecting the heart – 2 arteries and 6 veins. The arteries are shown in red and purple above the yellow arrow. All of the others are the veins. Wrapped around these vessels are the reflections of the parietal pericardium as it then becomes visceral pericardium over the heart itself. The reflection around the arteries is separated from the venous reflection by a space; the transverse pericardial sinus. The reflections around the complex of veins give rise to another space, the oblique pericardial sinus. This space is blind-ended unlike the transverse sinus.  The Transverse Pericardial Sinus Here you can see a finger pushed into the transverse pericardial sinus. This space is often used by the heart surgeon during a transplant to tie off the arteries. A temporary ligature is pushed through the transverse sinus around the aorta and pulmonary trunk. The tubes of a heart-lung machine are inserted into these vessels and ligature is tightened to secure them in place.  Pericarditis Inflammation of the pericardium is called pericarditis. This is a painful condition, since the fibrous and parietal pericardial membranes are sensitive. The pericardium is supplied by the phrenic nerves (C3 to C5), and the irritation of the sensory receptors in the pericardium causes pain over the shoulder, since this is where the C3-5 dermatomes are found. The brain wrongly interprets the incoming signals to the C3-5 spinal cord as coming from skin. This is an example of referred pain. However, there are many other conditions which can cause stimulation of those nerves, and problems associated with the pericardium may easily be confused with other diseases of both the chest and abdomen.  Cardiac Tamponade Cardiac tamponade is a condition where the pericardial cavity fills with excessive amounts of fluid. This may be pericardial fluid if there is an irritation of the serous membranes, for example following an infection. The pericardial cavity can also fill with blood if there is a leak in the heart wall and serous pericardium. This is the case with the patient seen here on the right. It will be fatal if left untreated. Excess fluid in the pericardial cavity puts a pressure on the heart, and it will be unable to expand sufficiently during the relaxation phase of the heart. This results in an elevated venous pressure and a reduced cardiac output, and this leads to circulatory shock. There is a lack of oxygen to body tissues and the skin will appear bluish in colour. There is also a reduction in blood to the coronary arteries, and heart ischaemia may lead to a heart attack. To treat this, the pericardial fluid may be drained off by a pericardial tap. This is performed by inserting a needle upwards and to the left, immediately adjacent to the xiphisternum, avoiding the internal thoracic artery. Such a procedure is extremely hazardous, and should be performed with caution.  Cardiovascular System Introduction to the CVS Part 2: The Position of the Heart Welcome to part 2 of this introductory lecture on the cardiovascular system. In this section we will look at the heart in situ.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the surface anatomy relating to the heart and great vessels ▪ List the layers of the pericardium and heart wall ▪ Describe the orientation of the heart and be able to recognise the position of each of the chambers ▪ Know the position and function of the cardiac skeleton The learning outcomes for this part of the lecture are that afterwards you should be able to: Describe the orientation of the heart and be able to recognise the position of each of the chambers Know the position and function of the cardiac skeleton The remaining outcome will be dealt with in part 3.  The Basic Structure of the Heart We are all familiar with the shape of the heart from a young age. I remember perhaps too vividly drawing these on the playground wall, only to watch the rain wash them away. I didn’t realise at the time what a metaphor that was.  Heart Shape When I started learning anatomy I expected the heart to be … well, heart-shaped. I soon realised though that the pointed end faces downwards and forwards by a 70 degree angle. This is the apex. The blunt end at the top is the base. It now faces backwards  Development of the Heart 1 Base R L Anterior Apex This change all happens early in development. The heart originally was positioned with the apex pointing downwards, and the base facing upwards. There was a right side, a left side and an anterior and posterior surface.  Development of the Heart 2 Then in the 4th week of intrauterine life, the heart rotates to the left and tilts upwards. The anterior surface is now really the superior surface, posterior surface is now inferior. In addition, the right side of the heart is now more anteriorly positioned, and the left side is more posterior. The strange thing is when giving names to the parts of the heart, we refer back to the fetal position of those structures. Hence the right coronary artery actually arises anteriorly, the posterior interventricular artery lies inferiorly.  A Heart Drawing I remember my daughter bringing me this artwork that she had made for me on Father’s day. I just looked at her for a while and then said “Do you remember those bedtime stories that I read to you night after night? I think it was Sadler’s Medical Embryology. Do you not remember that by day 28 the fetal heart rotates to the left? She was never very good at telling left from right.  The Four Chambered Heart There are four chambers in the heart. Two above which are the atria. These receive venous blood via the base. Blood then flows into the ventricles by contraction of the atria and by gravity, and then the ventricles pump blood out of the heart into the outflow tracts which are situated on the superior surface at the top of the ventricles.  The Four Chambered Heart2 We talk of a right heart and a left heart. The right heart, comprising right atrium and right ventricle, serve to pump the deoxygenated blood returning from the systems of the body to the lungs. The outflow is via the pulmonary trunk, since the term pulmona means lung in Latin. The left atrium receives the blood returning from the lungs, which is now oxygenated and the left ventricle pumps it out via the aorta.  Sulci of the Heart Crux of the Heart Anterior View Posterior View Deep to the visceral pericardium, the surface of the heart contains grooves (sulci) corresponding to the divisions of its four chambers. The sulci are most prominent between the atria and ventricles (shown in yellow), and between the two ventricles (shown in blue). The atrio-ventricular sulcus is more commonly referred to as the coronary sulcus. ‘Coronary’ means crown. If a crown were placed over an upturned heart, it would sit comfortably on the atrio-ventricular groove. Anatomists are nothing if not imaginative! I have tried to replicate that here. The grooves between the ventricles are the interventricular sulci, there is an anterior and posterior interventricular sulcus, although because the heart has rotated during development, these are actually located superiorly and inferiorly respectively. The sulci contain blood vessels. These are the coronary arteries and their branches, and the cardiac veins. These vessels are embedded in epicardial fat. At the back of the heart, there is the site of union of the sulci, and this is known as the crux of the heart. The word crux means cross in Latin.  Right Heart Anterior View Posterior View The right atrium does indeed lie on the right. The right ventricle though lies in front. Hence, most of the right side of the heart is seen from an anterior view.  Left Heart Anterior View Posterior View Correspondingly the left side of the heart is seen mostly from behind. The majority of the left ventricle is both to the left and behind, whilst the left atrium is almost entirely posterior with a small anterior portion called the left auricle. The apex of the heart is the anterior part of the left ventricle.  The Beating Heart The two atria lie above and the two ventricles lie below. The atria and ventricles contract at different times to each other, with the contractions occurring in different directions.  The Cardiac Skeleton The heart muscle fibres are attached to fibrous tissue called the cardiac skeleton. This skeleton lies between the two sets of muscles and surrounds the valves of the heart. The atrial muscle contracts downwards towards the skeleton, and the ventricular muscle contracts upwards towards it.  Ventricular Twist The muscle fibres of the ventricles are actually spiralled, so the ventricular chambers are ‘wrung-out’ upon contraction. This ensures complete (or near complete) emptying.  Heart Valves Pulmonary valve Right Atrioventricular valve The atrioventricular valves open when the ventricles are relaxed. This phase is known as ventricular diastole. Of course, the atria are in a state of contraction at this time, and this is atrial systole. Then the ventricles contract closing the AV-valves and opening the outflow valves. This of course is ventricular systole.  The Heart Valves Pulmonary (semilunar) valve Aortic (semilunar) valve Left Right Atrioventricular Atrioventricular (Mitral) (Tricuspid) valve valve Here we can see all of the valves in this view at the level of the cardiac skeleton. Note that when the AV-valves are open the outflow valves are closed and vice-versa. Heart Orientation and Surface Features The heart shape may be likened to a wedge. The apex is the left-hand side of the thin end of the wedge. This of course is the tip of the left ventricle. The remainder of the thin end of the wedge is the lower part of the right ventricle. This turns a sharp corner here as the heart sits on the diaphragm, and the posterior part of the right ventricle is in contact with the central tendon of the diaphragm here. The sharp turn is known as the acute margin of the heart. At the thick end of the wedge we have the base, which is where the atria receive their venous drainage. Leading from the thin edge to the thick edge are the anterior surface superiorly and posterior surface inferiorly. The posterior surface sits on the diaphragm and can hence be referred to as the diaphragmatic surface. The left and right sides of the wedge form the right and left borders of the heart. These are known as the pulmonary surfaces because they are adjacent to the lungs. On the right this is principally the right atrium, whilst on the left it is the left ventricle. The left ventricle is curved on its left side, and this presents a rounded surface heading upwards to the anterior surface. This margin of the heart is therefore referred to as the obtuse margin.  Respiratory System Introduction to the CVS And that is all for now. That is in fact the last part of this introductory lecture, but we’ll continue our discussion of the heart into the next couple of lectures as well.