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Left ventricular outflow tract obstruction (LVOTO) refers to the limitation of blood flow out of the left ventricle. The level of obstruction can be valvular, sub-valvular, or supravalvular. It can include anatomic stenotic lesions anywhere from left ventricle (LV) outflow to descending aorta. Hemodynamically, LVOTO has been defined as a peak instantaneous gradient at LV outflow of at least 30 mmHg, either at rest or on provocation.  While traditionally defined in patients with hypertrophic cardiomyopathy, LVOTO is known to have several causes.  LVOTO constitutes 6% of congenital heart diseases and in most cases, the cause of LVOTO is congenital.  It can occur in isolation or accompany other congenital heart diseases.  Dynamic LVOTO can also be seen in critically ill patients, whereby the use of inotropes in patients with intravascular volume depletion results in hypovolemia.  In general, there is an obstruction to forward flow which increases afterload, and if untreated, can result in hypertrophy, dilatation, and eventual failure of the left ventricle.  , (Copyright © 2022, StatPearls Publishing LLC.)

Bacterial endocarditis refers to infection of the endocardial surface of the heart. It usually involves heart valves, but it can occur on the endocardium or intracardiac devices. There are two types: : Acute endocarditis is a febrile illness that rapidly damages cardiac structures and spreads hematogenously which can progress to death within weeks if not treated. . Subacute endocarditis has a slower disease process and may be present for weeks to months with gradual progression unless complicated by major embolic event or ruptured structure., (Copyright © 2022, StatPearls Publishing LLC.)

Ambulatory electrocardiogram (ECG) monitoring is an invaluable tool to assess and establish a diagnosis of a patient’s symptoms. There are a variety of possible ambulatory ECG monitors to choose from. Holter monitors are used to record 24 to 48 hours of activity. Event monitors can record 2 to 4 hours of activity. Implantable loop recorders can record for up to 3 years. The choice among these technologies is usually based on the suspected monitoring duration that will be required to capture a spontaneous event. Thus, if symptoms occur daily, a Holter monitor may be adequate. If symptoms occur weekly or monthly, an event monitor may be best. If symptoms occur less than monthly or even a few times per year, then an implantable loop recorder is likely the best option. Typical event recorders may not be useful at all if the patient collapses and cannot activate the device. Because of such, a device that can activate on its own and/or has memory to retain information for later download is preferred. This article will cover implantable loop recorders. The implantable loop recorder (ILR) is a subcutaneous monitoring device used to monitor electrical activity of the heart over an extended period, compared to the fixed picture of electrical activity that is seen with ECGs., (Copyright © 2022, StatPearls Publishing LLC.)

Treadmill stress testing is a form of cardiovascular stress testing that uses exercise with electrocardiography (ECG) and blood pressure monitoring. This form of stress testing is usually performed with exercise protocols using either a treadmill or bicycle. In addition, patients who are unable to exercise may benefit from the administration of a pharmacologic agent that stimulates the heart's activity, simulating exercise-induced changes. With treadmill stress testing, providers can determine a patient's functional capacity, assess the probability and extent of coronary artery disease (CAD), and assess the risks, prognosis, and effects of therapy. Observations from the Henry Ford exercise testing (FIT) study appear to suggest a graded and inverse correlation between cardiorespiratory fitness and incidental atrial fibrillation, especially for obese patients. Exercise Physiology Exercise is associated with sympathetic stimulation and changes in the coronary vasomotor tone, which affects coronary blood flow. Several studies have reported that the coronaries dilate during exercise. Some reported mechanisms contributing to this dilatation include the release of vasoactive substances from the endothelium due to increased myocardial oxygen consumption, passive relaxation due to the increase in coronary arterial pressure, and endothelium-mediated limitation of constrictor effects of catecholamine. During exercise, the increase in myocardial oxygen demand and coronary vasodilation allows for increased oxygen delivery which is crucial to myocardial perfusion, thereby preventing ischemia. Through this hyperemic effect, providers can identify ischemia, as stenotic vessels do not vasodilate as well as normal vessels. Due to sympathetic stimulation and vagal inhibition, an increase in stroke volume, heart rate, and cardiac output is noted. Alveolar ventilation and venous return also increase as a consequence of selective vasoconstriction. The hemodynamic response depends on the amount of muscle mass involved, exercise intensity, and overall conditioning. As exercise progresses, skeletal muscle blood flow increase and peripheral resistance decrease leading to a rise in systolic blood pressure (SBP), mean arterial pressure (MAP), and pulse pressure. Diastolic blood pressure (DBP) may remain unchanged, slightly increase, or slightly decrease. The age-predicted maximum heart rate is a useful measure for estimating the adequacy of stress on the heart to induce ischemia. The goal is usually 85% of the age-predicted maximum heart rate, calculated by subtracting the patient's age from 220., (Copyright © 2022, StatPearls Publishing LLC.)