Treatment of Heart Disease
Heart specialists employ medical and surgical approaches to the treatment of heart disease, often in combination.
One of the oldest drugs for heart treatment, and still the most important drug for many patients, is digitalis. This agent, which slows and strengthens heart muscle contractions, is obtained from the leaf of the foxglove, a plant originally found growing wild in many parts of Europe. Foxglove is now cultivated to ensure a steady supply of digitalis for medical purposes. Several forms of nitroglycerin are used to relieve angina pectoris. This drug dilates (widens) the vessels in the coronary circulation and improves the blood supply to the heart. Beta-adrenergic blocking agents (“beta-blockers”) control sympathetic stimulation of the heart. They reduce the rate and strength of heart contractions, thus reducing the heart’s oxygen demand. Propanolol is one example. Antiarrhythmic agents (e.g., quinidine) are used to regulate the rate and rhythm of the heartbeat. Slow calcium-channel blockers aid in the treatment of coronary heart disease and hypertension by several mechanisms. They may dilate vessels, control the force of heart contractions, or regulate conduction through the atrioventricular node. Their actions are based on the fact that calcium ions must enter muscle cells before contraction can occur. Anticoagulants are valuable drugs for some heart patients. They may be used to prevent clot formation in patients with damage to heart valves or blood vessels or in patients who have had a myocardial infarction. Aspirin, chemically known as acetylsalicylic acid (ASA), is an inexpensive and time-tested drug for pain and inflammation that reduces blood clotting by interfering with platelet activity. A small daily dose of aspirin is recommended for patients with angina pectoris, those who have suffered a myocardial infarction, and those who have undergone surgery to open or bypass narrowed coronary arteries. It is contraindicated for people with bleeding disorders or gastric ulcers, because aspirin irritates the lining of the stomach.
Correction of Arrhythmias
If the SA node fails to generate a normal heartbeat or there is some failure in the cardiac conduction system, an electric, battery-operated artificial pacemaker can be employed (Fig. 10-17). This device, implanted under the skin, supplies regular impulses to stimulate the heartbeat. The site of implantation is usually in the left chest area. A pacing wire (lead) from the pacemaker is then passed into the heart through a vessel and lodged in the heart. The lead may be fixed in an atrium or a ventricle (usually on the right side). A dual chamber pacemaker has a lead in each chamber to coordinate beats between the atrium and ventricle. Some pacemakers operate at a set rate; others can be set to stimulate a beat only when the heart fails to do so on its own. Another type of pacemaker adjusts its pacing rate in response to changing activity, as during exercise. This rather simple device has saved many people whose hearts cannot beat effectively alone. In an emergency, a similar stimulus can be supplied to the heart muscle through electrodes placed externally on the chest wall. In cases of chronic ventricular fibrillation, a batterypowered device can be implanted in the chest to restore a normal rhythm. The device detects a rapid abnormal rhythm and delivers a direct shock to the heart. The restoration of a normal heartbeat either by electric shock or drugs, is called cardioversion, and this device is known as an implantable cardioverter-defibrillator (ICD). A lead wire from the defibrillator is placed in the right ventricle through the pulmonary artery. In cases of severe tachycardia, tissue that is causing the disturbance can be destroyed by surgery or catheterization.
Figure 10-17 Placement of an artificial pacemaker. The lead is placed in an atrium or ventricle (usually on the right side). A dual chamber pacemaker has a lead in both chambers.
The heart-lung machine makes many operations on the heart and other thoracic organs possible. There are several types of machines in use, all of which serve as temporary substitutes for the patient’s heart and lungs. The machine siphons off the blood from the large vessels entering the heart on the right side, so that no blood passes through the heart and lungs. While in the machine, the blood is oxygenated, and carbon dioxide is removed chemically. The blood is also “defoamed,” or rid of air bubbles, which could fatally obstruct blood vessels. The machine then pumps the processed blood back into the general circulation through a large artery. Modern advances have enabled cardiac surgeons to perform certain procedures without bypassing the circulation, immobilizing part of the heart while it continues to beat.
Coronary artery bypass graft (CABG) to relieve obstruction in the coronary arteries is a common and often successful treatment (Fig. 10-18). While the damaged coronary arteries remain in place, healthy segments of blood vessels from other parts of the patient’s body are grafted onto the vessels to bypass any obstructions. Usually, parts of the saphenous vein (a superficial vein in the leg) or the mammary artery in the chest are used. Sometimes, as many as six or seven segments are required to establish an adequate blood supply. The mortality associated with this operation is low, and most patients are able to return to a nearly normal lifestyle after recovery from the surgery.
The effectiveness of this procedure diminishes over a period of years, however, owing to blockage of the replacement vessels. Less invasive surgical procedures include the technique of angioplasty, which is used to open restricted arteries in the heart and other areas of the body. In coronary angioplasty, a fluoroscope guides a catheter with a balloon to the affected area (Fig. 10-19). There, the balloon is inflated to break up the blockage in the coronary artery, thus restoring effective circulation to the heart muscle. To prevent repeated blockage, a small tube called a stent may be inserted in the vessel to keep it open (Fig. 10-20).
Figure 10-18 Coronary artery bypass graft (CABG) (A) This graft uses a segment of the saphenous vein to carry blood from the aorta to a part of the right coronary artery that is distal to the occlusion. (B) The mammary artery is grafted to bypass an obstruction in the left anterior descending (LAD) artery.
Figure 10-20 Intracoronary artery stent. (A) Stent closed, before the balloon is inflated. (B) The balloon is inflated to open the stent. The stent will remain expanded after the balloon is deflated and removed.
Figure 10-19 Coronary angioplasty (PTCA). (A) A guide catheter is threaded into the coronary artery. (B) A balloon catheter is inserted through the occlusion and inflated. (C) The balloon is inflated and deflated until plaque is flattened and the vessel is opened.
Diseased valves may become so deformed and scarred from endocarditis that they are ineffective and often obstructive. In most cases, there is so much damage that valve replacement is the best treatment. Substitute valves made of a variety of natural and artificial materials have been used successfully. The news media have given considerable attention to the surgical transplantation of human hearts and sometimes of lungs and hearts together. This surgery is done in specialized centers and is available to some patients with degenerative heart disease who are otherwise in good health. Tissues of the recently deceased donor and of the recipient must be as closely matched as possible to avoid rejection. Efforts to replace a damaged heart with a completely artificial heart have not met with long term success so far. There are devices available, however, to assist a damaged heart in pumping during recovery from heart attack or while a patient is awaiting a donor heart.