Cardiology

Anatomy, histology and physiology

Pathology

Ischemic heart disease

Is a condition characterized by reduced blood flow to the heart muscle (myocardium) due to narrowing or blockage of the coronary arteries. This can lead to chest pain (angina), shortness of breath, and other symptoms. If left untreated, ischemic heart disease can lead to heart attacks and heart failure.
The most common cause of ischemic heart disease is atherosclerosis, a condition in which fatty deposits (plaques) build up in the walls of the coronary arteries, leading to narrowing and reduced blood flow. Other risk factors for ischemic heart disease include high blood pressure, smoking, diabetes, obesity, and a family history of heart disease.

Clinical features

• Stable angina: is characterized by chest pain or discomfort that occurs with exertion or emotional stress and is relieved by rest or nitroglycerin. The pain is usually described as a pressure or tightness in the chest and may radiate to the arms, neck, jaw, or back. Stable angina is typically caused by atherosclerosis and is a warning sign of underlying coronary artery disease.
• Unstable angina: is characterized by chest pain or discomfort that occurs at rest or with minimal exertion and is not relieved by rest or nitroglycerin. The pain may be more severe and prolonged than stable angina and may be associated with other symptoms such as shortness of breath, sweating, nausea, or lightheadedness. Unstable angina is a medical emergency and requires immediate evaluation and treatment.
• Myocardial infarction (heart attack): occurs when a coronary artery is completely blocked, leading to death of the affected area of the myocardium. Symptoms of a heart attack may include chest pain or discomfort that lasts for more than a few minutes, shortness of breath, sweating, nausea, or lightheadedness. A heart attack is a medical emergency and requires immediate evaluation and treatment.

Diagnosis

The diagnosis of ischemic heart disease is based on a combination of clinical history, physical examination, and diagnostic tests. Common diagnostic tests include:

• Electrocardiogram (ECG or EKG): can detect changes in the heart's electrical activity that may indicate ischemia or infarction.
  ST elevation: indicates myocardial injury, often due to acute myocardial infarction (heart attack).
  ST depression: indicates myocardial ischemia, which can be caused by conditions such as angina or coronary artery disease.
  Other signs include T-wave flattening or inversion. T-wave inversions can indicate ischemia and T-wave flattening can be a sign of ischemia as well, but is less specific. Pathological Q waves, for example wide and deep Q wave, can indicate a previous myocardial infarction, but can also indicate other conditions such as cardiomyopathy or conduction abnormalities, pregnancy, or just misplaced electrodes.
• Stress testing: involves exercising on a treadmill or bike while monitoring the heart's response. This can help identify areas of the heart that are not receiving enough blood flow.
• Echocardiography: uses sound waves to create images of the heart and can help assess the heart's function and identify areas of damage.
• Coronary angiography: involves injecting a contrast dye into the coronary arteries and taking X-ray images to visualize any blockages or narrowing.
• Blood tests: can measure levels of certain enzymes and proteins that may indicate damage to the heart muscle, like for example troponin, that is released when the heart muscle is damaged. BNP (B-type natriuretic peptide) can also be measured, as it is released in response to increased pressure in the heart and can be elevated in heart failure.

Treatment

Treatment for ischemic heart disease may include:

Life style changes: such as diet (to lower cholesterol levels), smoking cessation, weight loss and exercise (to improve cardiovascular health).
Medications: such as aspirin (to reduce blood clotting) , beta-blockers (to reduce heart rate and blood pressure) , and statins ( to lower cholesterol levels in the blood).
Procedures: such as angioplasty and stenting (to open up blocked arteries) or coronary artery bypass surgery (to create a new route for blood flow around blocked arteries).

Complications

Complications of ischemic heart disease may include heart failure, arrhythmias, and sudden cardiac death. If the infarct is big enough, it can lead to cardiogenic shock, which is a state of inadequate tissue perfusion due to the heart's inability to pump enough blood to meet the body's needs. This can lead to organ failure and death if not treated promptly. Also mechanical complications can occur, such as ventricular free wall rupture, interventricular septal rupture, and papillary muscle rupture, which can lead to acute mitral regurgitation. These complications are more likely to occur in the first week after a myocardial infarction, when the infarcted tissue is still weak, as scar tissue has not formed yet, and therefore the affected area is vulnerable to rupture. If a rupture occurs, it can lead to sudden death due to cardiac tamponade (blood leaks into and fills the pericardial sac that surrounds the heart, so the heart no longer has space to function) or severe mitral regurgitation.

Histology

• Atherosclerosis: is characterized by the presence of fatty plaques in the walls of the coronary arteries. These plaques are made up of cholesterol, inflammatory cells, and other substances. The plaques can cause narrowing of the arteries, leading to reduced blood flow to the myocardium.
• Myocardial ischemia: is characterized by the presence of areas of the myocardium that are deprived of oxygen and nutrients due to reduced blood flow. This can lead to myocyte injury and death, as well as inflammation and fibrosis in the affected areas.
• Myocardial infarction: is characterized by the presence of areas of the myocardium that have undergone necrosis (cell death) due to prolonged ischemia. This can lead to the formation of scar tissue in the affected areas, which can impair the function of the heart.

Heart failure

Is a condition in which the heart is unable to pump enough blood to meet the body's needs. This can lead to symptoms such as shortness of breath, fatigue, and swelling in the legs and ankles. Heart failure can be caused by a variety of factors, including coronary artery disease, high blood pressure, and cardiomyopathy.
There are two main types of heart failure based on ejection fraction, which is a measure of how much blood the left ventricle pumps out with each contraction (compared to how much blood was in the ventricle before the contraction):

• Heart failure with reduced ejection fraction (HFrEF): also known as systolic heart failure, occurs when the heart's ability to contract and pump blood is impaired. This is typically defined as a left ventricular ejection fraction (LVEF) of less than 40%.
• Heart failure with preserved ejection fraction (HFpEF): also known as diastolic heart failure, occurs when the heart's ability to relax and fill with blood is impaired. This is typically defined as a left ventricular ejection fraction (LVEF) of 50% or higher, along with evidence of diastolic dysfunction.

Histology

• HFrEF: myocytes tend to have increased length with enlarged nuclei (hypertrophy). Focal myocyte death leads to fibrosis. This can lead to increased inflammation in the interstitium.
• HFpEF: myocytes tend to have increased width with enlarged nuclei (hypertrophy). There is often interstitial fibrosis present, which can lead to stiffening of the myocardium and impaired relaxation. There may also be evidence of microvascular disease, which can contribute to ischemia and myocyte injury.

Causes

Common causes of heart failure include coronary artery disease, hypertension, cardiomyopathy, valvular heart disease, and arrhythmias. Other factors that can contribute to heart failure include diabetes, obesity, and smoking.

Diagnosis

The diagnosis of heart failure is based on a combination of clinical history, physical examination, and diagnostic tests. Common diagnostic tests include:

• Electrocardiogram (ECG or EKG): can detect changes in the heart's electrical activity that may indicate underlying heart disease.
• Echocardiography: uses sound waves to create images of the heart and can help assess the heart's function and identify areas of damage.
• Chest X-ray: can help identify signs of heart failure, such as an enlarged heart or fluid in the lungs.
• Blood tests: can measure levels of certain enzymes and proteins that may indicate damage to the heart muscle, like for example troponin, that is released when the heart muscle is damaged. BNP (B-type natriuretic peptide) can also be measured, as it is released in response to increased pressure in the heart and can be elevated in heart failure.

Treatment

Treatment for heart failure may include:

Life style changes: such as fluid restriction (to decrease preload), low salt diet (to decrease fluid retention), exercise (to improve cardiovascular fitness and overall health).
Medications:
ACE and ARB inhibitors, such as enalapril, ramipril, candesartan, losartan, valsartan (to reduce blood pressure and decrease afterload),
Beta-blockers, such as metaprolol, atenolol, propranolol, sotalol, carvedilol (to reduce heart rate and myocardial oxygen demand),
Diuretics (to reduce fluid retention)
Thiazide diuretics, such as hydrochlorothiazide, chlorthalidone
Loop diuretics, such as furosemide, bumetanide
Potassium-sparing diuretics (aldosterone antagonists or sodium channel blockers) , such as spironolactone, eplerenone, amiloride
Vasodilators (to reduce afterload), such as nitrates (nitroglycerin and isosorbide mononitrate) and hydralazine
Nitrates: work mainly on veins (venodilators) to reduce preload and on coronary arteries to improve blood flow to the myocardium.
Hydralazine: works mainly on arterioles (arteriodilator) to reduce afterload.
Inotropes (to increase contractility), such as digoxin (a sodium- potassium ATPase inhibitor ), dobutamine (a beta-1 agonist), and milrinone (a phosphodiesterase-3 inhibitor ).
Procedures: really depends on the underlying cause of the heart failure, but can include procedures such as implantable devices (like pacemakers and defibrillators), heart pumps (LVADs), and heart transplantation to improve heart function and manage symptoms.

Hypertrophic cardiomyopathy

Is when the heart muscle or the myocardium becomes thickened (hypertrophied). This can lead to diastolic dysfunction (the heart cannot relax normally), valves might not be able to close normally leading to regurgitation and even myocardial ischemia as the abnormal myocytes can compress small arteries in the heart. Hypertrophic cardiomyopathy can either be aquired or genetic. The acquired causes include hypertension and aortic stenosis, which both increase the pressure tension in the heart.
Genetic causes include mutations in genes that encode sarcomere-associated proteins, like beta-myosin heavy chain and myosin binding protein C.
To be diagnosed with hypertrophic cardiomyopathy as an adults the left ventricular end diastolic wall thickness should be >13 mm or > 15 mm (on imaging) depending on criteria used.
Histology

Myocytes are large and have large, often box-like, nuclei (hypertrophy of myocytes). The enlarged myocytes then can cause local ischemia and death of surrounding myocytes by compressing arteries within the myocardium. This eventually causes replacement fibrosis, as the dead myocytes are replaced by fibrosis (scarring). The scarred myocardium then affects the myocytes parallel alignment, leading to fiber disarray.

Dilated cardiomyopathy

Is when the heart ventricles, one or both, have enlarged, and the myocardium stretched and thinned, leading to impaired contraction (left ventricular ejection fraction, LVEF, under 40%).
Histology

Myocytes tend to have increased length with enlarged nuclei (hypertrophy). Focal myocyte death leads to fibrosis. This can lead to increased inflammation in the interstitium.