NEUROENDOCRINE CHANGES IN HEART-FAILURE AND THEIR CLINICAL RELEVANCE

The pathophysiology of heart failure is closely associated with neuroendocrine changes. Activation of these humoral systems apparently serves as a compensatory mechanism for the failing circulation. However, overshoot of such mechanisms may further depress cardiac function by increasing afterload, resulting in a vicious cycle of reflex neuroendocrine activation. Corollary decreases in renal function activate the renin-angiotensin-aldosterone system as well, which further contributes to the cycle of downward-spiralling cardiac function. Many hormonal factors are increased in congestive heart failure. While some influences are vasodilatory, the net effect is marked vasoconstriction. The level of activation of these systems apparently corresponds to the severity of heart failure. Furthermore, elevated levels of these hormones, including norepinephrine, atrial natriuretic factor plasma renin, and plasma arginine vasopressin, may play a more direct role in worsening heart failure. In fact, elevated catecholamine levels are directly related to prognosis. Catecholamines increase myocardial oxygen demand and are also arrhythmogenic. Oral catecholamines and phosphodiesterase inhibitors, which work by similar mechanisms, have yielded increased mortality rates in heart failure trials. In contrast, mortality rates are reduced in patients treated with angiotensin converting enzyme inhibitors. Thus, it is clear that neuroendocrine changes are not only a marker of the severity of heart failure, but also directly worsen it. Interventions that antagonize or diminish these neuroendocrine changes apparently benefit patients with heart failure.