The pathogenesis and treatment of hyponatremia in congestive heart failure

Novel Use of Tolvaptan in a Pediatric Patient With Congestive Heart Failure Due to Duchenne Muscular Dystrophy and Congenital Adrenal Hyperplasia

Successful management of hyponatremia in heart failure patients requires a multifaceted approach in order to preserve end-organ function. We describe the novel use of a selective vasopressin receptor antagonist, tolvaptan, for management of hyponatremia in a 17-year-old Caucasian male with severe Duchenne muscular dystrophy, congestive heart failure (CHF), and congenital adrenal hyperplasia. The medical history was significant for recurrent admissions for hyponatremia secondary to adrenal crises, which was also exacerbated by his CHF. After initiation of tolvaptan and its extended administration, he had no further hyponatremia-related admissions and no adverse reactions. The complexity of this combination of conditions is presented, and the efficacy of the drug and the rationale behind the treatment approach is discussed.

The critical link of hypervolemia and hyponatremia in heart failure and the potential role of arginine vasopressin antagonists

BACKGROUND

Hypervolemia and hyponatremia resulting from activation of the neurohormonal system and impairment of renal function are prominent features of decompensated heart failure. Both conditions share many pathophysiologic and prognostic features and each has been associated with increased morbidity and mortality. When both conditions coexist, therapeutic options are limited.

METHODS AND RESULTS

This review presents a concise digest of the pathophysiology, clinical significance, and pharmacological therapy of hyponatremia complicating heart failure with a special emphasis on vasopressin antagonists and their aquaretic effects in the absence of neurohormonal activation along with their ability to correct hyponatremia.

CONCLUSIONS

Hypervolemia and hyponatremia share many pathophysiologic and prognostic features in heart failure. Vasopressin antagonists provide a viable option for their management and a potentially unique role when both conditions coexists.

Conivaptan and its role in the treatment of hyponatremia

Hyponatremia is the most common electrolyte abnormality in hospitalized patients and is associated with increased morbidity and mortality. The recognition of the central role that arginin vasopressin plays in the pathogenesis of hyponatremia and the discovery that its actions are mediated by stimulation of V(1A) and V(2) receptors have led to the development of a new class of drugs, the arginin vasopressin antagonists. Conivaptan is a nonselective V(1A) and V(2) receptors antagonist that was the first of this class to be approved by the FDA for the management of euvolemic and hypervolemic hyponatremia. Its short-term safety and efficacy for the correction of hyponatremia have been established by multiple double-blind, randomized, controlled studies. Blocking the effects of arginin vasopressin on V(2) receptors produces aquaresis--the electrolyte-sparing excretion of water--an ideal approach to correct hypervolemic hyponatremia. The nonselectivity of conivaptan offers a theoretical advantage for its use in heart failure that may merit further exploration.

Treatment of dilutional hyponatremia in congestive heart failure

Water restriction is a slow and difficult way to treat dilutional hyponatremia during diuretic therapy of congestive heart failure. An i.v. infusion of 400-1 400 mmol hypertonic saline combined with repeated i.v. injections of loop diuretics was used instead in 9 cases (6 patients). In 4 cases with dominating left heart failure the serum sodium concentration increased and the heart failure was not aggravated as judged from pulmonary rales and body weight. Two of the five cases with dominating right heart failure responded in the same favourable way, but body weight increased 1-2 kg and hyponatremia reappeared in three. The only difference observed between responders and non-responders was that the responders were free from leg edema. This treatment of dilutional hyponatremia seems worth further cautious use in situations in which water restriction is troublesome, but it should probably be reserved for patients without severe right heart failure.

Treatment of hyponatremia

Hyponatremia is an electrolyte disorder that is defined by a serum sodium concentration of less than 136 mmol/L. Hyponatremia occurs at a high incidence. It is commonly associated with mild to moderate mental impairment. Hypoosmolar hyponatremia occurs in the setting of plasma volume deficiency ("hypovolemia", e. g. after gastrointestinal fluid loss), liver cirrhosis and cardiac failure ("hypervolemic" hyponatremia) and syndrome of inappropriate antidiuretic hormone secretion ("euvolemic" hyponatremia). Excessive antidiuretic hormone and continued fluid intake are the pathogenetic causes of these hyponatremias. Whereas hypovolemic hyponatremia is best corrected by isotonic saline, conventional proposals for euvolemic and hypervolemic hyponatremia consist of the following: fluid restriction, lithium carbonate, demeclocycline, urea and loop diuretic. None of these nonspecific treatments is entirely satisfactory. Recently a new class of pharmacological agents -orally available vasopressin antagonists, collectively called vaptans- have been described. A number of clinical trials using vaptans have been performed already. They showed vaptans to be effective, specific and safe in the treatment of euvolemic and hypervolemic hyponatremia.

Vaptans and the treatment of water-retaining disorders

Hyponatremia is a frequent and symptomatic electrolyte disorder for which specific treatments have been lacking. Hyponatremia is attributable to nonosmotic vasopressin stimulation and continued increased fluid intake. In the past, peptidic derivatives of arginine vasopressin proved that blockade of vasopressin V-2 receptors served to improve hyponatremia, however, these antagonists had intrinsic agonistic activity, too. In the past decade, random screening of molecules uncovered nonpeptide, orally available vasopressin antagonists without agonistic properties. The agents show competitive binding to the vasopressin V-2 receptor at an affinity comparable with that of arginine vasopressin. Four antagonists have undergone extensive study. Three of these agents--lixivaptan or VPA 985; SR 121 463 B; tolvaptan or OPC 41,061--are specific V-2 antagonists whereas conivaptan or YM 087 is a V-1/V-2 mixed antagonist. In animal and clinical studies all of the agents were able to correct water retention and hyponatremia in a dose-dependent manner. There was no tachyphylaxis, even when the agents were given over many weeks. It is expected that the clinical use of the agents will lead to a major improvement in the treatment of hyponatremia.

Clinical relevance and management of the major electrolyte abnormalities in congestive heart failure: hyponatremia, hypokalemia, and hypomagnesemia

Electrolyte disturbances are a common complication of CHF. CHF provides a perfect milieu for the development of these disturbances; renal dysfunction, elevation of neurohormonal substances, activation of the renin-angiotensin-aldosterone axis, and diuretic therapy represent the major contributory factors. Hyponatremia is closely aligned with an unfavorable clinical course. Hypokalemia is associated with increased ventricular dysrhythmias. Hypomagnesemia noted in advanced CHF can be accompanied by arrhythmias and refractory hypokalemia. CHF also offers the ideal milieu (diseased, ischemic, and arrhythmogenic myocardium; elevated catecholamines; and arrhythmogenic drugs) for the threatening clinical consequences (clinical deterioration, dysrhythmias, or death) of these disturbances. These consequences underscore the importance of the recognition, appreciation, and management of these electrolyte abnormalities.