Heart

The heart is located in the chest cavity between the lungs in a region called the mediastinum (the mass of organs and tissues separating the lungs; in addition to the heart and its greater vessels, the mediastinum contains the trachea and the esophagus). Two thirds of the heart lies left of the midline. The wider base of the heart lies superior and beneath the second rib. The apex, or narrow part, of the heart lies inferiorly, slightly to the left between the fifth and sixth ribs near the diaphragm.

Blood vessels

Three main types of blood vessels are organized to carry blood to and from the heart. Capillaries (tiny blood vessels joining arterioles and venules) connect the arteries (large vessels carrying blood away from the heart) to the veins (vessels that convey blood from the capillaries and return it to the heart). The heart delivers the blood to the arteries, which branch into tiny vessels called arterioles (blood vessels of the smallest branch of the arterial circulation), which deliver the blood to the tissues. Within the tissues, microscopic vessels (capillaries) form an extensive (50,000 miles) network that allows exchanges of products and by-products between the tissues and blood. The capillaries then join with tiny veins, or venules, that link with the larger veins and return to the heart. The pattern is as follows:

Artery → arteriole → capillary → venule → vein

Coronary blood supply

Systemic circulation

Systemic circulation occurs when blood is pumped from the left ventricle of the heart through all parts of the body and returns to the right atrium. When the oxygenated blood leaves the left ventricle, it enters the largest artery (1 inch [2.5 cm] in diameter) of the body, the aorta. This is the main trunk of the systemic arterial circulation and is composed of four parts: the ascending aorta, the arch, the thoracic portion of the descending aorta, and the abdominal portion of the descending aorta. As the blood flows through the artery branches, the branches become smaller in diameter (arterioles). The blood continues to flow into the capillaries. The capillaries surround the cells and exchange oxygen, nutrients, carbon dioxide, and other waste products. The blood proceeds to the tiny venules, then to the larger veins, and finally returns to the right atrium via the largest vein, the vena cava (one of two large veins returning blood from the peripheral circulation to the right atrium of the heart).

Pulmonary circulation

The deoxygenated blood now passes through the pulmonary circulation to pick up the needed oxygen. Blood is pumped from the right atrium to the right ventricle, where it leaves the heart to travel via the pulmonary artery to the lungs. Once the blood reaches the lungs, it travels through arterioles to the capillaries. The microscopic capillaries surround the alveoli (air sacs), where oxygen diffuses into the bloodstream. The capillaries then connect with the venules and finally with the four pulmonary veins, which return the oxygenated blood to the left atrium of the heart. It is then pumped to the left ventricle and to the aorta, and systemic circulation is then repeated. The blood circulation pattern is as follows:

Superior or inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary artery → capillaries in the lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → aortic semilunar valve → aorta

Diagnostic imaging

Radiographic examination of the chest provides a film record of heart size, shape, and position and outline of shadows. Lung congestion is also shown, indicating heart failure (HF), perhaps in the earliest stages. Pleural effusion may be noted in left-sided HF.

Fluoroscopy, the action-picture radiograph, allows observation of movement. It is invaluable in pacemaker or intracardial catheter placement.

An angiogram is a series of radiographs taken after injection of a contrast medium into an artery or vein. Picturing the circulatory process aids in diagnosis of vessel occlusion, pooling in various heart chambers, and congenital anomalies. Angiography allows x-ray visualization of the heart, aorta, inferior vena cava, pulmonary artery and vein, and coronary arteries.

In an aortogram, the abdominal aorta and the major leg arteries are viewed by x-ray visualization after a contrast medium is injected through the femoral artery and into the aorta. Aneurysms and many other abnormalities can be diagnosed. Contrast media to visualize the aortic arch and branches may also be used.

Cardiac catheterization and angiography

Cardiac catheterization is an invasive procedure used to visualize the heart’s chambers, valves, great vessels, and coronary arteries. This procedure aids in diagnosis, in prevention of progression of cardiac conditions, and in accurate evaluation and treatment of the critically ill patient.

The passage of a catheter into the heart chambers through a peripheral vessel is used to measure (1) pressure within the heart and (2) blood-volume relationship to cardiac competence. Valvular defects, arterial occlusion, and congenital anomalies are determined. Blood samples are obtained. Contrast dye may be injected to allow better heart and vessel visualization (angiography). Cardiac catheterization is performed under sterile surgical conditions; its invasive nature requires a prior signed consent. Because iodine is in the contrast medium, determine sensitivity to iodine before injection to avoid an allergic reaction. After the procedure, assess circulation to the extremity used for catheter insertion. Check peripheral pulses, color, and sensation of the extremity every 15 minutes for 1 hour and then with decreasing frequency. Observe the puncture site for hematoma and bleeding. Monitor vital signs. Assess for abnormal heart rate, dysrhythmias, and signs of pulmonary emboli (respiratory difficulty). The patient lies supine for a designated period with a compression device over the pressure dressing at the insertion site to prevent hemorrhage.

Electrocardiography

The electrocardiogram (ECG, or EKG) is a graphic study of the electrical activities of the myocardium to determine transmission of cardiac impulses through the muscles and conduction tissue. Each ECG has three distinct waves, or deflections: the P wave, the QRS complex, and the T wave. When the heart contracts, the electrical activity is called depolarization. Repolarization is the relaxation phase. The P wave represents the depolarization of the atria. The QRS complex represents the depolarization of the ventricles. The T wave represents the repolarization of the ventricles. Atrial repolarization is not represented but does occur; it is covered by the large QRS complex and cannot be seen on the ECG tracing.

The ECG tracing is read or interpreted by a cardiac specialist (cardiologist) or by internal medicine specialists, family practitioners, pediatricians, and emergency department practitioners. The reading can also be displayed on the fluorescent screen (oscilloscope) of a cardiac monitor. A graphic tracing may be printed out by the monitor.

Ambulatory ECGs can be used to monitor heart rhythm over prolonged periods—12, 24, or 48 hours—and compared with various activities or symptoms recorded in a diary kept by the patient. A Holter monitor (small portable recorder) is attached to the patient by leads, with a 2-pound tape recorder carried on a belt or shoulder strap. The monitor operates continuously to record the patterns and rhythms of the patient’s heartbeat. In conjunction with the diary, the physician can note various events, times, and medication peaks that affect or precipitate dysrhythmias. An ambulatory ECG is particularly useful for patients whose clinical symptoms indicate heart disorders but who may have normal ECG tracings on a resting test.

Cardiac monitors

It is common practice to continuously assess the cardiac electrical activity of patients who are known or suspected to have dysrhythmias or who are prone to develop dysrhythmias or acute cardiovascular symptoms. A cardiac monitor displays information on the electrical activity of the heart transferred via conductive electrodes placed on the chest.

Most monitors provide a visual display of cardiac electrical activity and the correct heart rate. Preset alarms warn of heart rates that exceed or drop below limits considered acceptable for each patient and also warn of dysrhythmias.

Ambulatory patients are increasingly monitored by battery-powered ECG transmitters that do not directly connect the patient to the oscilloscope. This monitoring is called telemetry, which is the electronic transmission of data to a distant location. The electrodes placed on the patient’s chest are attached to a transmitter the patient carries in a pocket or pouch. The transmitter sends a radio signal to a receiver, usually located at the nurse’s station.

Patients need telemetry monitoring for various reasons, including a history of cardiac disease, angina pectoris, suspected dysrhythmias, a change in medications, an electrolyte abnormality, or unexplained syncope. Many of these patients are monitored in a centralized area such as an intermediate care or step-down unit (with monitors at the nurse’s station). Remote telemetry means the patient is on a medical-surgical unit and is monitored at a separate location, called the home unit, which is usually on a critical care unit. Remote telemetry patients are usually stable. But even a stable patient’s condition can change rapidly, and telemetry allows continuous heart monitoring to detect abnormalities.

Attachment to a cardiac monitor does not change a patient’s need for nursing interventions. Because the monitoring electrodes are on the anterior thorax (chest) rather than the extremities, the patient is relatively free to carry on usual activities. Pay special attention to the electrode site to ensure a constant tight seal between the electrode and the skin and to note the development of any skin impairment. The conduction gel dries out, even if the pad is sealed; changing electrodes regularly is recommended. Also check the telemetry pack for integrity of the lead wires and test the monitoring device’s battery with a battery tester. Inform the monitoring area whenever the patient is moved off the unit for a diagnostic test, since the patient may go outside the monitor’s range. Another important safety measure is to never remove the telemetry device and allow the patient to shower unless the physician has written the order to allow a shower. The patient could be subject to severe dysrhythmia, which would not be detected with the telemetry device removed.

Exercise-stress ECG is another form of monitoring the heart’s capability, this time in a laboratory setting while the patient performs a prescribed exercise. Tasks include use of treadmills, stair climbing, and aerobic exercise. While being monitored carefully, the patient is coaxed to a limit of exertion to evaluate ischemia, dysrhythmia, and cardiac capability under extreme circumstances. Thus the test sets the limit of exercise tolerance in cardiac disease. If the patient is unable to tolerate activity, a stress test can be done by administering dipyridamole (Persantine) or adenosine (Adenocard), which mimics the patient’s heart under stress or activity.

Thallium scanning

Thallium 201 is an intracellular ion that is actively transported into normal cells. If the cell is ischemic or infarcted, the thallium will not be picked up. Because the thallium concentrates in tissue with normal blood flow, tissue with inadequate perfusion appears as dark areas on scanning—a “cold spot.” The radioisotope is injected intravenously while the patient exercises on a treadmill. Breast tissue in the female can produce artifact, leading to a false-positive result. Using technetium 99m sestamibi instead of thallium can help minimize artifact and thus improve accuracy. In patients who cannot tolerate physical exercise, dipyridamole is given before the thallium to physiologically simulate exercise-induced stress.

Echocardiography

Echocardiography uses high-frequency ultrasound directed at the heart. The echo, or reflected sound, is graphically recorded, outlining size, shape, and position of cardiac structures. This test is used to detect pericardial effusion (collection of blood or other fluid in the pericardial sac), ventricular function, cardiac chamber size and contents, ventricular muscle and septal motion and thickness, cardiac output (ejection fraction), cardiac tumors, valvular function, and congenital heart disorder.

Positron emission tomography

Positron emission tomography (PET) is a computerized radiographic technique that uses radioactive substances to examine the metabolic activity of various body structures. In PET studies the patient either inhales or is injected with a biochemical radioactive substance. Specific color-coded images reveal organs’ metabolic functions. Used to study dementia, stroke, epilepsy, and tumors, PET is proving its merit in the diagnosis and treatment of cardiac disease. PET’s ability to distinguish between viable and nonviable myocardial tissue allows physicians to identify the most appropriate candidates for bypass surgery or angioplasty. PET is also able to accurately detect coronary artery disease (CAD), noninvasively, in an asymptomatic patient, prompting early intervention that can salvage potentially ischemic myocardium.

Laboratory tests

The history, the physical examination, and blood studies aid the health care provider in diagnosing and monitoring the cardiovascular disease process. The nurse’s responsibility is to prepare the patient by explaining the tests and the preparation required for each test.

Blood cultures to detect growth of bacteria in the blood are crucial to the diagnosis of infective endocarditis.

A complete blood count (CBC) is a determination of the number of red and white blood cells per cubic millimeter, as well as the white blood cell differential, platelets, hemoglobin, and hematocrit. Low hemoglobin indicates decreased ability to carry oxygen to the cells and anemia; an elevated white blood cell (leukocyte) count indicates infection or inflammation; and an elevated red blood cell (erythrocyte) count indicates that the body is compensating for chronic hypoxemia (an abnormal deficiency of oxygen in the arterial blood) by stimulating red blood cell production by the bone marrow, leading to secondary polycythemia (abnormal increase in the number of red blood cells in the blood). Chronic hypoxemia is often noted in HF.

Coagulation studies are useful in monitoring the patient receiving anticoagulant drug therapy, which is prescribed for patients with myocardial infarction (MI). Coagulation studies are also important in patients who have chronic atrial fibrillation or patients with atrial fibrillation who are undergoing cardioversion (the restoration of the heart’s normal sinus rhythm by delivery of a synchronized electric shock through two metal paddles placed on the patient’s chest). Coagulation studies are needed if an MI is diagnosed in case fibrinolytics are needed to dissolve the thrombus. These studies include prothrombin time (PT), International Normalized Ratio (INR), and partial thromboplastin time (PTT).

Erythrocyte sedimentation rate (ESR) is used to monitor or rule out inflammatory infective conditions. The ESR is elevated with MI and infective endocarditis and decreases when healing begins. The ESR also indicates the extent of inflammation and infection in rheumatic fever.

Normal aging patterns

Risk factors

Research has identified risk factors that indicate predispositions to developing cardiovascular disease. The presence of more than one risk factor is associated with an increasing risk of developing cardiovascular disease. Risk factors are classified as those that are nonmodifiable and those that are modifiable.

Cardiac dysrhythmias