Heart Anatomy & Procedures

Transcription

1 Heart Anatomy & Procedures Anatomy & Blood Flow Electrical System Coronary Arteries, Fuel Lines of the Heart Cardiac Disease States Cardiac Procedures NOTES: 9

2 Anatomy & Blood Flow Your heart is a muscular organ about the size of your fist. It is located behind the lower part of your sternum (breast bone). With each beat of the heart, the heart muscle pumps and circulates blood through the body. The heart can be divided into two sides with a muscular wall separating them called the septum. Each side of the heart (R & L) have two chambers stacked on top of each other. The upper chambers are called atria and the lower chambers are called ventricles. Blood flow through the heart is a continuous action providing the body with oxygen rich blood. Every minute, at rest, the heart beats beats per minute and pumps approximately 5 liters of blood through the body. When exercising, the heart rate and the amount of blood pumped each minute increases (up to 35 liters) to meet the physical demand. The flow of blood follows a continuous loop to supply the body with needed nutrients. The valves in the heart ensure that the blood flows in one direction. Un-oxygenated blood enters the right atrium from the body through the large veins (vena cava). When the atrium contracts, blood is propelled into the right ventricle through the tricuspid valve. The ventricle contracts directly after, and the blood flows forward through the pulmonary valve to the lungs (air sacs). It is in the lungs that the blood picks up oxygen form the air sacs and releases carbon dioxide (waste). The oxygen rich blood then returns to the left atrium which contracts and propels the blood through the mitral valve to the left ventricle. As the left ventricle contracts, the blood is sent through the aortic valve to the whole body. Once you understand the blood flow one can see that the ventricles are the primary pumps of the heart. The left ventricle is the largest muscle chamber in the heart with the most workload placed upon it. 10

3 Electrical System of Heart In order for the heart muscle to contract it needs a stimulation to direct it. In a healthy heart, the normal electrical pathways occur along fixed lines of specialized cells that produce an even contraction when stimulated. Electrical stimulation starts in the top of the right atrium at the Sinus Atrial (SA) node, which normally has a resting rate of firings per minute. This node acts as a spark plug and fires a stimulation that travels through both atria resulting in contraction of the right and left atria at the same time, which pushes blood through the valves to fill the ventricles. This is the first part of the pumping contraction of the heart. The second part occurs immediately after when the electrical stimulation reaches the middle of the heart at the Atrioventricular (AV) node. This node is connected to a nerve pathway, the Bundle of HIS, which transmits the electrical signal to the ventricle muscle wall causing contraction that pushes blood out of the heart (to lungs & body). The electrical system in the heart relies on intact pathways. The system will normally increase its firing rate in response to increased demands during exercise, stress or illness. Disruption along the pathways of the conduction system can lead to irregular stimulations, which are called Arrhythmias. There are many different types of arrhythmia, too slow, too fast, irregular. Atrial Fibrillation is a more common arrhythmia resulting in fast, irregular pulse (see Cardiac Disease States, p. 12). Coronary Arteries- Fuel Lines of Heart The heart muscle cells that do the contracting also need oxygen and fuel to function normally and have their own circulatory system. Coronary arteries are blood vessels that branch off the aorta and surround your heart muscle to fuel it with oxygen rich blood. There are two main coronary arteries the left and the right. The left artery divides into two arteries the anterior descending branch (LAD), which supplies blood to most of the left side of the heart and also the septum. The other branch is called the circumflex and it provides blood to the outer left and back of the heart. The right coronary artery (RCA) supplies blood to the right side of the heart and in most people it supplies the blood to the SA and AV nodes. 11

4 The coronary arteries are susceptible to a build up of plaque inside their walls, which can lead to blocking the flow of blood to the heart muscle cells. This is known as Coronary Artery Disease (also know as Atherosclerosis). Risk factors for coronary disease can contribute to the build up of plaque in the artery (see Risk Factors section, p. 22). If the blockages are severe enough, at times of physical demands the heart muscle cells may not get enough blood flow and oxygen to function normally. In this case, symptoms such as a feeling of pressure or pain in the chest, neck or arm area may occur (Stable Angina) especially when activity is increased. If a blockage becomes unstable and ruptures, a blood clot can form over the rupture and this leads to sudden critical shortage of blood flow. This is the way most HEART ATTACKS occur (also known as Myocardial Infarction). It is important to seek medical attention quickly if you have new chest pains that last because there are treatments available to dissolve (clot busting medications) or remove the blockage (angioplasty) so that the damage to the heart muscle is minimal. Sometimes when a blockage of coronary artery is present and stable for a long time, Collateral blood vessels may develop to shunt blood around the blockage. These vessels increase the supply of blood through new pathways that branch off the main arteries. They develop in some people but not everyone. Cardiac Disease States Atherosclerosis Coronary arteries are particularly susceptible to atherosclerosis. In this condition, thickening of the vessel results from a build-up of plaque made up of fats, cholesterol, and other substances found in blood. The plaque causes narrowing of the vessel and can restrict blood flow. This process is known as Coronary Artery Disease (CAD). It is not usually until the diameter is decreased about 70% that flow is impaired and symptoms appear in the form of Angina or chest pain. In some cases, the plaque deposit in the coronary arteries can become unstable and rupture resulting in a rough area on the arterial wall. This process may attract the formation of a clot and the clot formation can create a critical blockage of the coronary artery so that the flow of oxygen rich blood to the heart muscle is blocked completely or near complete. The result is known as a Heart Attack or Myocardial Infarction (MI). Risk factors for coronary artery disease and heart attack include high blood pressure, smoking, diabetes, high cholesterol, stress, lack of exercise, overweight, age, gender and family history (see Risk Factors, p. 22). The cholesterol measured in your bloodstream (with a blood test) is not the only factor responsible for CAD, in fact blockages can occur with a normal blood cholesterol level if other risk factors are present. 12

5 Angina Angina is the medical term applied to lack of blood flow to the heart muscle (ischemia) causing pain or discomfort. It occurs when the heart muscle is not getting enough oxygen, usually when there is an increased demand for oxygen to the heart muscle cells during exercise, stress or illness. Coronary artery disease (blockages) is the primary cause of angina. The pain or discomfort felt usually is described as a sense of pressure or burning, squeezing, heaviness in chest area. However, angina can also feel like shortness of breath, indigestion or pain/discomfort radiating to neck, jaw, shoulders, back or arm. There are primarily two types of angina. Stable angina is the type that occurs from an increased demand for oxygen. It usually occurs consistently with a certain level of exertion and is relieved by rest and/or taking the medication nitroglycerine. Unstable angina is defined as chest pain/discomfort occurring at rest or if the pattern of angina changes. This is a more serious form of angina as it may indicate a more severe blockage in the coronary arteries. It can be due to coronary artery spasm or plaque rupture (unstable angina). Treatment for angina is primarily medical through the use of medications and can sometimes include intervention such as angioplasty, stents, or coronary artery bypass surgery. If you have experienced angina, where have you felt it? Mark where you have experienced angina symptoms on the diagram below: What are your symptoms of angina? Check all that apply. Chest pain Chest discomfort Chest pressure Nausea Fatigue Burning Weakness Feeling of indigestion Shortness of breath Sweating Light-headedness Other Chest pain or pressure radiating (moving) to your jaw or arms Squeezing/tightness in the chest Pain between the shoulder blades in the back 13

6 Aneurysm An aneurysm is a ballooning or bulging of a blood vessel (artery) due to weakening of the wall from disease, injury or an abnormality from birth. Often aneurysms occur due to high blood pressure placed on the weakened area. They can occur in many different vessels including those in and out of heart (Aorta), coronary arteries, and the arteries in the brain. Management includes blood pressure control or surgery to correct the aneurysm. Congestive Heart Failure (CHF) CHF occurs when the heart cannot beat strongly enough to meet the demands/needs of the body in everyday life. The weakening of the heart wall muscle may be a result of a heart attack, viral infection, alcohol, valve disease, hypertension or some other illness. Please see Heart Function section (PURPLE). Hypertension (High blood pressure) Blood pressure (BP) is the pressure (mmhg) exerted inside on the walls of the blood vessels and heart chambers. BP is dynamic meaning it changes all the time as your body reacts to normal cardiovascular stresses throughout the day such exercise, body position and stress. Keep in mind when determining risk for heart disease; it is most important to know your RESTING BP, that is, sitting comfortably resting for at least 5 minutes. An automated home blood pressure machine is a reliable way to take your BP reading. The systolic pressure or top number is the pressure when your heart contracts and pushes out the blood from the ventricles. The diastolic pressure or lower number is the pressure when your heart relaxes between beats. Ideal BP High BP 120/80 mmhg Greater than 135/85 mmhg High blood pressure or Hypertension is a rise in the RESTING blood pressure either systolic, diastolic or both over 135/85mmHg. Hypertension increases your risk of cardiac disease, heart attack, and stroke. Hypertension is one of the most controllable risk factors for coronary artery disease. Monitoring and management of high blood pressure is described in Risk Factors section. Myocardial Infarction or Heart Attack A myocardial infarction commonly known as a Heart Attack happens when the blockage of blood flow (oxygen) to the heart muscle is of sufficient intensity and duration to cause death (necrosis) to some of the heart muscle tissue. It is usually the result of a blocked coronary artery by a plaque or blood clot. An area of dead muscle surrounding the blockage cannot be regenerated and instead scar tissue forms in the area. This scar tissue takes a few weeks to form depending on the size of the damage (infarct) and is 14

7 non-functioning tissue. That means it cannot contract like other muscle fibers nor can it transmit the electrical impulses in the heart. The location & size of the infarct will determine how the heart functions after. If present, collateral circulation (newly formed arteries) may help to decrease the amount of damage done and help in the healing process. Early recognition and prompt treatment of heart attack is very important to minimize damage to heart muscle. Learn the Signs of Heart Attack Chest discomfort (Pressure, squeezing, fullness or pain, burning or heaviness) Sweating Upper body discomfort (Neck, jaw, shoulder, arms, back ) Nausea Shortness of breath Light-headedness If you are experiencing any of these signs: Call or have someone call for you. Stop all activity and sit or lie down. If you take nitroglycerin, take your normal dosage. Chew and swallow one 325 mg tablet or two 81mg tablets of ASA (Aspirin ), as long as you are not allergic. o Do not take other pain medications such as acetaminophen (Tylenol ), or ibuprofen (Advil ) instead of Aspirin. o Do not substitute Aspirin for medical care. Rest and wait for (EMS) Emergency Medical Services. Retrieved from: on March 20, 2018 Myocarditis Myocarditis is an rare condition due to inflammation of the myocardium, the middle layer of the heart wall., usually caused by a virus. Myocarditis can leave the heart muscle weakened requiring medical treatment. In some cases the heart will completely recover, in others permanent weakening persists. Pericarditis Pericarditis is swelling and irritation of the pericardium, the thin sac-like membrane surrounding your heart, usually caused by a virus. Symptoms include chest pain that varies with position and deep breathing. Your doctor may recommend medications to reduce the inflammation and swelling such as aspirin or ibuprofen (Advil, Motrin IB, others) are recommended. Symptoms often improve and settle within a few weeks. Rarely, fluid accumulates around the heart needing medical attention. A short period of reduced activity is advised. 15

8 Spontaneous Coronary Artery Dissection (SCAD) Spontaneous Coronary Artery Dissection (SCAD) is a rare cardiac event when a tear forms in the inner lining of one of the blood vessels of the heart. The tear can cause blood to build up between the layers of the blood vessel, narrowing the vessel enough to limit blood to the heart muscle and in some cases cause a heart attack/damage. SCAD is more common in women. The signs and symptoms of SCAD are the same as those for a heart attack; chest, arm, shoulder, or jaw pain, shortness of breath, sweating, nausea, dizziness. If SCAD is suspected, your doctor may do tests similar to those for a heart attack, such as blood tests and an EKG. A coronary angiogram or CT angiogram may be performed for a closer look at your coronary arteries. In the majority of cases, the coronary blockage will recover and repair without needing bypass or stenting. Arrhythmias An arrhythmia is an abnormal rate or rhythm in the heart and can cause symptoms such as palpitations, dizziness, or fainting. Treatment can be through medications, surgery, and the use of pacemakers. Types of arrhythmias include: Premature ventricular or atrial contractions (PVC s or PAC s) are extra beats that can originate either in the atria or ventricles. Generally these beats are not harmful and do not require treatment if they are not severely symptomatic. Bradycardia is defined as a heart rate below 60 beats per minute. Many healthy people will have slow heart rates at rest even below 50 beats per minute. Some degree of bradycardia in cardiac patients is acceptable, especially for patients with CAD. This may be related to medications, which purposely slow the heart to reduce cardiac stress. However, excess slowing or prolonged pauses especially with fainting or near fainting may require treatment including medication adjustments or surgical implantation of a pacemaker. Atrial Fibrillation (AFib) is the most common type of heartbeat disorder. It makes your heart beat irregularly and usually at a faster than normal rate. The normal natural SA node (pacemaker) of your heart no longer controls the heart rate, instead, many cells in the atria start to fire irregularly at a very fast rate. Some of these signals travel down to the ventricle to cause a contraction making your pulse rate fast and irregular. 16

9 AFib occurs in about 6% of individuals over 65 years of age and is more common in people who have these risk factors: high blood pressure abnormal heart valve congestive heart failure overactive thyroid gland obstructive sleep apnea excess alcohol consumption COPD/lung disease Some people may experience symptoms such as feeling your heart jumping or racing (often called palpitations), while others don t feel anything at all. In some individuals, AFib episodes can be triggered by: caffeine, stressful situations, ingesting cold drinks, alcohol, fatigue or illness, not doing a long warm up when exercising. Avoiding some of these triggers may help you manage your condition. Treatment for AFib is usually directed at slowing the heart rate so the heart can pump more efficiently or eliminating the fibrillation. This is done through medications, cardioversion, or catheter ablation procedure. Medications to lower heart rate Medications to control rhythm Electrical Cardioversion Catheter Ablation Slows heart rate but do not prevent AFib from occurring. Beta-blockers (Atenolol, Bisoprolol, Metoprolol, propranolol) Calcium channel blockers (Diltiazem, Verapamil) Digoxin Helps heart stay in normal rhythm or prevent AFib from occurring. Amiodarone, dronedarone, flecainide, propafenone, sotalol During a brief anesthetic, a defibrillator applies a shock to your heart to put it back into a normal rhythm. A simple and safe treatment but does not prevent future episodes of Afib. Surgical procedure via catheter that ablates heart cells that cause fibrillation. It is invasive and suitable for some people with AFib, but not everyone. AFib increases your risk of stroke since the uneven heartbeat can cause blood to pool in the heart chambers where blood clot can form. If these blood clots break loose and travel to the brain it can cause a stroke. Fortunately, there are blood thinner medications that can significantly lower the risk of stroke. Aspirin is generally ineffective in preventing strokes from atrial fibrillation. It is important for your health care provider to assess your personal risk of stroke. Lifestyle changes to support weight loss and increased exercise are important parts of treatment. Regular moderate exercise like walking has been shown to improve both severity and symptoms of AFib as well as improve the effectiveness of cardioversion and ablation procedures. In addition, a modest weight loss (10% body weight) if overweight has been shown to decrease the number, duration, and severity of AFib episodes and 17

10 improve quality of life. Combining both weight loss and increased exercise capacity has cumulative beneficial effects. Atrial flutter: This is a closely related cousin of atrial fibrillation. Atrial Flutter is often fast but usually a more regular rhythm than atrial fibrillation. Treatments are similar. Ventricular Tachycardia/Fibrillation: These are extremely rapid heart rates that can lead to fainting, cardiac arrest and sometimes death. More often, they occur in patients with severe heart muscle weakening. Prompt treatment with a defibrillator is required. Patients at higher risk for these events require medications and often an Implantable Cardiac Defibrillator (ICD). Obstructive Sleep Apnea (OSA) This is a medical condition that can cause your breathing to stop and start many times while you sleep. It is caused by the muscles at the back of the throat relaxing too much to allow normal breathing. There is a strong link between sleep apnea and high blood pressure and stroke. Even short pauses in breathing while you sleep are hard on the heart because they lower the amount of oxygen reaching the heart. Symptoms may include: Excessive daytime sleepiness Loud snoring, observed episodes of breathing stopping during sleep Abrupt awakenings with gasping or choking Difficulty concentrating during the day / headaches Experiencing mood changes, such as depression or irritability High blood pressure Risk factors for this condition include: Excess weight (fat deposits around the upper airway may obstruct breathing; however, thin people can develop the disorder, too) Narrowed airway (you may inherit naturally narrow airways or, your tonsils/adenoids may become enlarged, which can block your airway) High blood pressure Heavy alcohol consumption Smoking Diabetes Asthma (recent research has found an association between asthma and the risk of obstructive sleep apnea) Treatment: Continuous positive airway pressure (CPAP) machines with mask over mouth and nose are worn during sleep. They provide enough pressure to keep airway open during sleep and allow for normal oxygen and sleep cycle. If overweight, losing weight can also help to decrease symptoms of OSA. 18

11 Diagnostic Cardiac Procedures Electrocardiogram (ECG): This is a graphic record of the hearts electrical system. This provides important information about the rhythm, size and electrical abnormalities of the heart, such as previous heart attacks. Echocardiogram: This is an ultrasound of the heart commonly called an echo. This test allows the doctor to visualize the heart s muscle function, the chambers, and the valves in the heart on a screen in a non-invasive way. This helps in the diagnosis of a variety of cardiac abnormalities. The heart usually ejects 55 65% of the blood out of the bottom chambers with each beat (Ejection Fraction). This number can be reduced if heart muscle is damaged with a heart attack. Ejection fraction (heart strength) is commonly assessed after a heart attack using an echo machine. Cardiac Stress Testing: This is a test where patients exercise on a treadmill or bike while their ECG is continuously analyzed. Patients symptoms, heart rate, and blood pressure are recorded as the test proceeds and exercise intensity increases. Stress testing is used for: a) Diagnosis of coronary disease in patients with suspicious symptoms b) Assessing risk in patients with known coronary disease c) Assisting exercise recommendations Nuclear Medicine Testing: This involves the use of radioactive substances to help diagnose coronary artery disease and areas of injured heart muscle. These scans are done at rest and after exercise on the treadmill. The radioactive substance is injected intravenously and absorbed in the heart. If patients are unable to exercise on a treadmill, a medication (Persantine Cardiolite) is given to chemically stress your heart. Nuclear scans measure heart tissue that is abnormal; either dead/ scarred or severely deprived of blood. Angiogram An angiogram is a test that takes X-ray pictures of the coronary arteries and the vessels that supply blood to the heart. During the angiogram, a catheter is inserted into an artery in the arm or the groin and wound up towards the heart; there a special dye is injected into a catheter placed in the coronary arteries so that the blood vessels become visible. The dye is dense enough to allow the cardiologist to see if there are blockages in the coronary arteries and to determine their size. Therapeutic Cardiac Procedures Angioplasty An angioplasty is a procedure designed to dilate (widen or expand) narrowed coronary arteries, in order to restore normal blood flow to the heart. The procedure is very similar to an angiogram except the catheter used has a balloon on its tip, which is inflated and 19

12 deflated a number of times to compress the plaque and enlarge the diameter of the coronary artery. Frequently a coronary stent is inserted during the procedure to prop open the coronary artery. It is made of a mesh-like metal material and remains in the coronary artery. Once properly placed, stents do not move (migrate). This procedure is also known as Percutaneous Coronary Intervention (PCI). Angioplasty can be life saving in the middle of a heart attack. In stable patients however, angioplasty is used to control symptoms (angina) and not for heart attack prevention. Coronary- Artery Bypass- Graft (CABG) Surgery The need for CABG is determined from diagnostic tests and assessment. If the results of an angiogram show multiple vessels are significantly blocked, bypass may be recommended. CABG or open-heart surgery is a surgical procedure where arteries or veins are taken from one part of the body and sutured around the blockage in the coronary artery to reroute blood flow. A portion of a vein from the leg, a forearm artery or the internal mammary artery from the chest is used. During surgery these vessels are connected directly to the coronary arteries on the surface of the heart beyond the blockages. This way, blood is rerouted around the blocked arteries. CABG will improve the blood flow to the heart. Exercise tolerance is improved and fatigue is reduced. Angina is often eliminated following CABG. Heart Valve Surgery: Heart valves may need repair due to birth defects, rheumatic fever, bacterial infections or age related wear and tear. Some valves become leaky (regurgitation) and some valves become stiff and restrictive (stenosis). Heart valve problems increase the workload of the heart. When the heart can no longer keep up, heart failure may result. Valves can be repaired or replaced through open-heart surgery and now sometimes via a catheter technique (TAVI). The best solution is chosen for each individual patient based on diagnostic tests. Transcatheter Aortic Valve Implantation (TAVI) TAVI is a less invasive procedure than traditional open-heart surgery that allows doctors to correct a severe narrowing (stenosis) in the aortic valve. Using a long catheter tube inserted through an artery in the groin, a new replacement valve is implanted. This procedure allows a quicker recovery (patients are discharged from hospital as early as 1-3 days after the procedure). It is currently offered to patients who are considered too sick or high risk for open-heart surgery. Aortic valve replacement via open-heart surgery is still considered the gold standard, with excellent outcomes that have been proven over long periods of follow-up. TAVI rates are increasing and more patients may be offered this therapy in the future. Pacemaker: This is a small battery operated device that produces the electrical impulse needed to keep the heart beating in a regular rhythm. The lead (a wire) is implanted in the wall of the heart. The pacemaker functions like a thermostat, if the pulse drops too slow the pacemaker will kick in. A pacemaker cannot remove extra beats or prevent fast rhythms and is used only for bradycardias (slow rhythms). It is usually implanted under the collarbone or in the abdomen. 20

13 Implantable Cardiac Defibrillator (ICD): This is a device slightly larger than a pacemaker that is inserted to treat dangerous heart rate irregularities. It is programmed to monitor the heart rhythm, detect dangerous rhythms and when necessary, give an electrical shock to restore a normal heart rate and rhythm. It is usually prescribed for people who have experienced a cardiac arrest in the past or who have a high risk for this to occur. Heart Transplant A heart transplant is when a person s sick heart is replaced with a healthy one from an organ donor (someone who has died and whose organs have been donated). Organ transplants are only possible because of the gift of an organ from a donor and their family. People who need a heart transplant have heart failure that is getting worse and no longer treatable in any other way. Potential candiates are referred to St Paul s Hospital Heart Transplant Program. Left Ventricular Assist Device (LVAD) A ventricular assist device (VAD) is a rarely used mechanical pump used to circulate blood when the heart fails. The primary reason for VADs is as a bridge to transplantation, allowing patients to wait at home and regain fitness while a donor heart is found. This internal pump is driven by a small motor and powered by batteries that are carried in a small purse, which is slung over the shoulders. Blood flows into the pump via a cannula (small tube) that is connected to the left ventricle and blood is ejected into a second cannula, which is connected to the ascending aorta. The patient and family are trained in the management of the pump. References Hypertension Guidelines Canada. Retrieved form: 2. American Heart Association Retrieved from: 3. Heart and Stroke Foundation of Canada. (2018). Retrieved from: 4. Stone, J.A., Arthur, H.M., & Suskin, N.G. (2009). Canadian Guidelines for Cardiac Rehabilitation and Cardiovascular Disease Prevention, 3rd ed. Winnipeg, Canada: Canadian Association of Cardiac Rehabilitation. 5. The Merck Manual. Sixteenth Edition. 25: , Merck Research Laboratories, Ventricular Assisting Device, Providence Heart and Lung Institute at St. Paul s Hospital (2012). 7. Pathak, RK et al. Long term effect of goal-directed weight management in an atrial fibrillation cohort; a long-term follow-up study (LEGACY). J Am Coll Cardiol 2010; 65: Mayo Clinic Patient care and health information 2018.Retrieved from: 21