2 Section 2 Selected Diseases and Disorders of the Cardiovascular System

Diagnostic Tests for Cardiovascular Function

In this section, diagnostic tests will be described.  Fortunately, tests used in cardiovascular diagnostics are often non-invasive meaning they don’t require surgical interventions to use. Electrocardiogram (ECG) are used to assess cardiovascular conduction pathways and involve monitoring the amplitude, duration and timing of P, QS and T waves. ECG is a great tool to diagnose dysrhythmias, which could be a sign of many negative factors affecting heart function, including myocardial infarction. ECGs can also indicate anatomical changes within the heart including signs of Pathologic Hypertrophy. Pathologic Hypertrophy is where the heart walls thickens and the heart grows into a spherical shape. Hypertrophy is misleading because the growth of heart muscle seems like a good thing but it is actually growing due to overcompensation. The further this progresses the less effective the heart becomes.  The stroke volume progressively diminishes and eventually signs and symptoms of congestive heart failure occur. Changes in ECGs can also reflect infections, including pericarditis, which is inflammation of the pericardial cavity or membranes. If a patient comes in with complaints of intermittent cardiac events that occur during certain activities or different times during the day doctors can utilize a Holter monitor. A Holter monitor can be taken home by the patient and constantly monitors their cardiac activity and sends the information to the doctor.

Auscultation, listening to the heart, is a useful tool to look for abnormalities particularly with the valves of the heart. If the valves aren’t working properly it can cause a regurgitation of blood as known as a murmur. Auscultation can also indicate a shunt, which is a hole in the interventricular septum that is allowing blood to pass through.

There is also a cardiac ultrasound known as an Echocardiograph. This tool allows you to visualize the valves and the walls of the heart to make sure everything is moving properly. You can detect damage to the heart wall caused by a variety of things including myocardial infarction or infection. You can spot damage on an echocardiogram by noticing when a portion of the wall isn’t contracting properly. Cardiac output, stroke volume and level of inflammation or fluid in the pericardial sac can also be assessed using this tool.  Computers can use echocardiograms to make a 3D image of the heart called a 3D echocardiogram.

An exercise stress test is where the doctor asks the patient to use a treadmill or stationary bike and measures their cardiac activity. This allows the doctor to monitor the patient’s cardiac activity at rest and also up to 80% max heart rate. This can allow the doctor to notice abnormalities or insufficiencies.

Radio Imaging techniques can be used for visualizing the heart as well. X-rays are not very good at visualizing soft tissue but it can be enhanced by injecting a radiodense dye such as iodine. Radioisotopes, such as Thallium can also be used, including with SPECT (single photon emission CT) scan if a 3D image is desired. It is important to use a radioisotope that decays quickly so as to not expose the patient to radiation for too long. Imaging can help find blockages and see where blood is perfusing and where it is not. Using the X-ray you can also look for hypertrophy of the heart. The heart is normally one third the width of the diaphragm, anything more than that can be indicative of a larger issue.

Another tool used in regards to the cardiovascular system is a catheter. Catheters can be used to measure blood pressure in a specific area such as pulmonary capillary wedge pressure or central venous pressure. They can also be used to inject dyes into specific areas for better visualization when using radioimaging techniques. A catheter can be inserted into multiple different areas in the body. If you want to access the right side of the heart, the catheter must enter the body via a vein, likely the basilic or femoral. Whereas, if you want to enter the left side of the heart then an artery would be a better route. Catheters can also be used to deliver Thrombolytic agents which are medications capable of breaking up Thrombocyte clots in blood vessels that can limit blood flow to certain areas. This route of administration allows a smaller dosage to be directly administered where the clot is, increasing efficiency. Catheters can also contain balloons that can expand in the blood vessel to aid in blood flow. Using a catheter to inject dye into the heart can allow you to visualize the ventricles and this is called a ventriculogram. Using ventriculograms, you can calculate the volume of the ventricle, if it generates sufficient pressure and stroke volume with minimum invasiveness.

There is a specialized form of an ultrasound called a Doppler that can monitor the heart in 4D and monitors direction and velocity of blood flow. This can be used to diagnose leaky valves and irregularities in the cardiac septum.

Another indicator of heart disease is blood composition. A high level of triglycerides can be indicative of developing fatty atherosclerotic plaques. Unbalanced electrolytes can lead to dysrhythmias because cardiac myocytes require specific levels of sodium, potassium and calcium in order to function properly. The red blood cell count is indicative of oxygenation of all tissues of the body including the heart. Low red blood cell count means there is less circulating hemoglobin and the heart might not be getting the oxygen it needs. It is also important to check white blood cell count to assess the presence of an infection, high white blood cell count would be indicative of this. Some other important indicators to look for in the blood is oxygenation of arterial blood, bicarbonate, oxygenated hemoglobin, carboxyhemoglobin, pH, lactic acid and carbon monoxide.

You can also get a rough estimation of blood oxygenation using a pulse oximeter, which uses two red wavelengths of light flashed through the skin. Oxygenated hemoglobin absorbs this red light differently than carboxyhemoglobin, so the pulse oximeter measures the ratio of different absorbance to calculated oxygen saturation. This tool also displays heart rate, which is beneficial to know in any scenario.

Methods of Increasing Cardiovascular Health

There are ways to improve your heart health without the use of medication. You can modify your diet and follow Health Canada’s plan to cut out fats, particularly saturated and trans fats and reduce salt intake to help reduce hypertension. You can follow an exercise plan, Health Canada recommends 3-5 times a week. Regular exercise lowers serum lipid levels which lowers your chance of developing atherosclerotic plaques. It also means your blood vessels will be more dilated, lowering peripheral resistance and consequently lowering the risk of hypertension. Exercise also increases the level of high density lipoproteins in the blood which work to remove lipids from the blood which also aid in decreasing your chance of atherosclerotic plaques. Reducing or stopping smoking is another thing that can be changed to increase heart health. Smoking causes vasoconstriction which causes an increase in peripheral resistance leading to high blood pressure. Stopping smoking can also decrease heart rate, lower serum lipid levels and reduce platelet adhesion ability. Smoking increases the likelihood of platelets adhering to each other which increases the risk of clots.

Medications

There are many classes of medications used to benefit cardiovascular health. Nitroglycerin is an example of a vasodilator. Nitroglycerin can be used to increase the diameter of coronary arteries to increase blood flow to the myocardium. This could help if someone has angina pectoris or myocardial infarction. This type of medication can also aid in the treatment of congestive heart failure by reducing the peripheral resistance and increasing the supply of oxygen to the myocardium. Vasodilators also work to reduce afterload, by dilating arteries including the aorta and consequently increasing stroke volume. Nitroglycerin is a synthetic version of the natural vasodilator Nitric Oxide which is produced by your blood vessels. The mechanism of these compounds is to dephosphorylate myosin heads, inactivating them meaning they are unable to contract, leading to a constant state of relaxation. Nitroglycerin is more formulated to target coronary vasodilation rather than systemic. Dosage is very important for these drugs because if a dosage is too high it can lead to a  bottoming out of blood pressure causing decreased oxygenation of the brain leading to dizziness, fatigue and anxiety. If the blood pressure drops too much the medulla will cause heart rate to increase to tachycardia to compensate for the low blood pressure. There are also medications called venodilators that can aid in decreasing preload to lower stress on the heart by dilating veins.

There are other medications called Beta-blockers that block Beta-1 adrenergic which normally bind epinephrine and norepinephrine released from the sympathetic nervous system and the cardiac accelerator nerve. These drugs decrease the workload on the heart by not allowing epinephrine or norepinephrine to increase heart rate and contractility.

Calcium channel blockers are medications also capable of causing vasodilation. Within the heart membrane there are calcium channels that shuttle calcium into the cell before each muscle contraction. Once calcium is in the cell it binds to troponin which is connected to the actin molecules. When calcium binds troponin it causes tropomyosin to shift and expose the actin binding sites on the myosin molecule leading to contraction. Blocking these calcium channels can lead to a decreased level of contraction and consequently easing the workload on the heart. There are types of calcium channel blockers that affect only cardiac muscle or only smooth muscle but they do not affect the contraction potential of skeletal muscle. The blocking of contraction in the smooth muscle of the arteries leads to vasodilation which also reduces the workload of the heart. These medications can help treat hypertension and angina pectoris. Patients who take calcium blockers become exercise intolerant as the heart is unable to speed up effectively enough to support increased physical activity.

Digoxin is a natural medicinal glycoside  found in the foxglove plant and is used to treat Dysrhythmias. Digoxin acts by blocking the sodium potassium pump in the heart muscle, increasing the level of sodium in the cell. This imbalance causes the sodium calcium pump to work preferentially bringing calcium into the cell. This increase in calcium will cause an increase in the strength of the contraction of the heart which will slow it down and allow a normal rhythm to resume.

Alpha-1 Adrenergic receptors in arteries receive epinephrine and norepinephrine from the sympathetic nervous system. There are medications that block these receptors called Alpha Blockers. When these receptors are blocked it stops the signal telling the arteries to vasoconstrict so consequently they vasodilate which reduces stress on the heart.

Another strategy is to block the endocrine control of blood pressure and heart rate. There is a class of drugs called ACE inhibitors which block the conversion of Angiotensin II leading to less vasoconstriction. Angiotensin II also stimulates the release of Aldosterone and ADH which work on your kidney to reduce urination. This keeps blood volume high but with a lack of Angiotensin II and furthermore Aldosterone and ADH then urination continues reducing blood volume.

Patients can also be prescribed a Diuretic also known as a water pill. These medications function to block the reabsorption of sodium and water into the blood, increasing urination. This is advantageous in certain situations as it works to reduce blood volume and consequently blood pressure. Secondly, reducing blood volume will reduce preload leading to reduced workload on the heart.

Anticoagulants are medications that can reduce the adhering ability of platelets to reduce the chances of blood clots. This is why these medications, such as warfarin or heparin, are also referred to as blood thinners. This can be dangerous because it also limits the ability for the blood to coagulate when it is necessary. If someone is on an anticoagulant and gets injured they are at risk of severe bleeding that could need medical intervention. Vitamin K can act as an antidote for anticoagulants, such as Warfarin, to help the blood clot.

Another class of drug that can aid in cardiovascular health is cholesterol or lipid lowering drugs, such as statins or Lipitor. The goal of these drugs is to block the synthesis of low density lipoprotein or Cholesterol which occurs in the liver. Low density Lipoproteins (LDLs) travel through the blood and are “sloppy” meaning they can lead to the development of Atheromas or Atherosclerotic plaques therefore lowering the amount of them in the blood is beneficial.

Coronary Artery Disease

Coronary Artery Disease (CAD) or Ischemic Heart Disease is a disease of the arteries that feed the heart muscle itself. This disease can be separated into two main diseases, Angina Pectoris and Myocardial Infarction. Both these diseases can cause damage to the heart including to the conduction pathway that can lead to dysrhythmias which can be fatal. Physical risk factors for this disease include hypertension, being male and being Caucasian. There are also genetic and lifestyle risk factors that can contribute.

An important term related to CAD is Atherosclerosis. Atherosclerosis arterial refers to the hardening of the arteries, we all will experience atherosclerosis if we live long enough. Over time, the cells in the arteries become less efficient at regenerating themselves and the elastic fibers in the walls lose their elasticity causing stiffness. This stiffness leads to a narrowing of the arterial lumen which is known to increase blood pressure. Once you are over the age of 50 it is common to see your blood pressure slowly increase due to atherosclerosis. The narrowing of these arterial lumens can lead to a depletion of oxygen reaching vital tissues such as the kidneys, brain and heart. Since these tissues are very sensitive to low oxygen they start to become dysfunctional, some parts even die. Atherosclerosis specifically refers to a disease including the formation of atheromas and atherosclerotic plaques. These plaques consist of fat, calcium, thrombocytes, fibrin, cellular debris, erythrocytes and leukocytes. The areas most susceptible to these plaques are larger arteries such as the aorta, iliac, coronary and carotid arteries. Another area that commonly experiences these plaques is any point of bifurcation. Bifurcation is a fork in a blood vessel which produces turbulence in the blood that causes stress on the wall of the blood vessel. This stress can set the stage for the development of an atheroma. Diet and lifestyle play a large part in the development of these plaques including fat and salt intake and chronic stress. The removal of plaques at this bifurcation point is called endarterectomy.

LDLs are loosely packaged and known to bring the lipids present in these plaques to the area. The liver has a way to counteract this by releasing High Density Lipoproteins (HDLs) which act as scavengers and collect the lipids left in the blood and return them to the liver to make bile. The difference between LDLs and HDLs is their makeup, HDLs are 50% lipid while LDLs are over 75% which is responsible for the “sloppy” nature of LDLs.

These plaques can lead to a lot of health issues. The formation of plaques in a blood vessel increases rigidity of the blood vessel which can leave the vessel wall susceptible to bulging leading to an aneurysm. There is also a chance of a piece of the plaque falling off and traveling through the blood called an embolus. If the embolus is part of the thrombus it is called a thromboembolism. These can clog blood vessels causing certain tissues downstream to become hypoxic. This could be deadly if the embolus lodges in the brain or the heart. Once the plaque starts forming on the blood vessel wall, further damage will be done by the immune system. Platelets will create more material in the plaque as they accumulate in the area and the smooth muscle will start proliferating. The fibroblasts start producing collagen which creates a cap over the thrombus. This cap tends not to be stable and there is a risk of embolism.

Lifestyle changes for Coronary Artery Disease

Obesity is a risk factor for CAD and can be remedied with better diet and exercise. Smoking is also a risk factor because it reduces the levels of HDLs in the blood stream therefore reducing the amount of lipids scavenged from the LDLs, It also increases the level of LDLs. Smoking also increases heart rate and vasoconstriction which in turn increases blood pressure which is a risk factor for CAD. There is an increased level of fibrin and platelets associated with smoking which increases your chance of a thrombus if you are sedentary. This is another reason exercise is strongly recommended as it reduces blood pressure, stress, LDLs and serum cholesterol levels while increasing HDLs. This risk is also increased if you are smoking and taking the birth control pill as both increase the chance of platelet adhesion.

Diabetes is also a risk factor for CAD due to the presence of high serum glucose and lipid levels. Metabolic Syndrome is a cluster of four things, high blood pressure, high blood glucose, high cholesterol and being overweight. All of these conditions are risk factors for CAD.

Diagnostic Tests and Treatment for Coronary Artery Disease

To diagnose CAD a good first step is blood tests to assess lipid levels and C- reactive proteins. A Doppler ultrasound device can be used to see blockages and measure blood velocity. It is also good to take blood pressure readings on limbs that are suspected to contain plaques.

Anti-lipidemic and anticoagulant drugs can be prescribed to help with CAD. If the blockage is located in the coronary artery then bypass grafts can be put in an angioplasty with a balloon and laying a stent could also be useful.