Heart failure results when cardiac output is inadequate for the needs of the body. A defect in cardiac contractility is complicated by multiple compensatory processes that further weaken the failing heart. The drugs used in heart failure fall into 3 major groups with varying targets and actions.
|End-diastolic fiber length||The length of the ventricular fibers at the end of diastole; a determinant of the force of the following contraction|
|Heart failure||A condition in which the cardiac output is insufficient for the needs of the body. Low-output failure may be due to decreased stroke volume (systolic failure) or decreased filling (diastolic failure)|
|PDE inhibitor||Phosphodiesterase inhibitor; a drug that inhibits one or more enzymes that degrade cAMP (and other cyclic nucleotides). Examples: high concentrations of theophylline, inamrinone|
|Premature ventricular beat||An abnormal beat arising from a cell below the AV node—often from a Purkinje fiber, sometimes from a ventricular fiber|
|Sodium pump (Na+/K+ ATPase)||A transport molecule in the membranes of all vertebrate cells; responsible for the maintenance of normal low intracellular sodium and high intracellular potassium concentrations; it uses ATP to pump these ions against their concentration gradients|
|Sodium-calcium exchanger||A transport molecule in the membrane of many cells that pumps one calcium atom outward against its concentration gradient in exchange for three sodium ions moving inward down their concentration gradient|
|Ventricular function curve||The graph that relates cardiac output, stroke volume, etc, to filling pressure or end-diastolic fiber length; also known as the Frank-Starling curve|
|Ventricular tachycardia||An arrhythmia consisting entirely or largely of beats originating below the AV node|
Heart failure is an extremely serious cardiac condition associated with a high mortality rate. The fundamental physiologic defect in heart failure is a decrease in cardiac output relative to the needs of the body, and the major manifestations are dyspnea and fatigue. The causes of heart failure are still not completely understood. In some cases, it can be ascribed to simple loss of functional myocardium, as in myocardial infarction. It is frequently associated with chronic hypertension, valvular disease, coronary artery disease, and a variety of cardiomyopathies. About one third of cases are due to a reduction of cardiac contractile force and ejection fraction (systolic failure). Another third is caused by stiffening or other changes of the ventricles that prevent adequate filling during diastole; ejection fraction may be normal (diastolic failure). The remainder of cases can be attributed to a combination of systolic and diastolic dysfunction. The natural history of heart failure is characterized by a slow deterioration of cardiac function, punctuated by episodes of acute cardiac decompensation that are often associated with pulmonary or peripheral edema or both (congestion).
The reduction in cardiac output is best shown by the ventricular function curve (Frank-Starling curve; Figure 13–1). The changes in the ventricular function curve reflect some compensatory responses ...