Cardiac infections are severe, life-threatening infections in many cases. The heart valves (endocardium), myocardium, and pericardium can all be infected. In addition, infection of cardiac devices (pacemakers, defibrillators) is becoming more frequently diagnosed with their increase in use. Diagnosis of cardiac infection can be challenging and usually requires a combination of microbiologic testing and cardiac imaging. Treatment often requires antimicrobial therapy but may also require surgical management for cure.
DIAGNOSTIC TESTING FOR CARDIAC INFECTIONS
An electrocardiogram (ECG) measures electrical activity in the heart using noninvasive monitoring with leads attached to the skin. Cardiac infections can cause disease-specific ECG changes, which can assist in diagnosis.
Echocardiography uses Doppler ultrasound to visualize structures and flow of blood through the heart. The test is very helpful in diagnosing most types of cardiac infections. There are two types of echocardiograms, a transthoracic echocardiogram (TTE), where the probe is placed on the chest wall, and a transesophageal echocardiogram (TEE), where the probe is inserted into the esophagus. The TEE often produces higher-quality images, particularly of aortic and mitral valves, since the TEE probe is closer to the heart itself.
Endocarditis is an infection of the valves of the heart.
Infection of the heart valves is thought to result from the colonization of damaged valvular endothelium by circulating pathogens. Endothelial damage may result from turbulent blood flow around the valve (congenital or rheumatic heart disease), direct injury from foreign bodies (e.g., intravenous catheters), or repeated intravenous injections of particles in intravenous drug users. Deposition of platelets and fibrin forms a thrombus at the site of the damaged endothelium. This is called nonbacterial thrombotic endocarditis (NBTE).
Organisms enter the bloodstream most often through the mouth (i.e., dental disease or dental procedures) or skin (i.e., trauma, injection drug use). Adhesion of bacteria to the damaged endothelium is enhanced by their ability to produce a glycocalyx.
Once the infection has begun, a combination of organisms and thrombus organize to form a vegetation (Figure 71–1). Destruction of the valve occurs at different rates depending on the virulence of the organism. As the valve is destroyed, symptoms of valvular regurgitation can develop. Organisms can spread to surrounding myocardium, resulting in abscess formation and destruction of the electrical conduction system.
Endocarditis. Note vegetations on mitral valve. Black arrows point to vegetations. (Reproduced with permission from Longo DL, Fauci AS, Kasper DL, et al. Harrison’s Principles of Internal Medicine. 18th ed. New York, NY: McGraw-Hill Education; 2012.)
As the vegetation on the valve enlarges, fragments can spread via the bloodstream (emboli), ...