Current treatments and novel pharmacologic treatments for hyponatremia in congestive heart failure

Syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuresis is the most common cause of euvolemic hyponatremia and complicates a wide spectrum of diseases and neurosurgical conditions. The syndrome is characterized by clinical euvolemia, dilute plasma osmolality and inappropriately concentrated urine, with normal renal, adrenal and thyroid function. Hyponatremia in syndrome of inappropriate antidiuresis represents an excess of plasma water, rather than sodium deficiency. The severity of hyponatremia is limited by renal escape from antidiuresis. Treatment varies according to symptoms, severity and speed of onset of hyponatremia. Acute, severe, symptomatic hyponatremia may require rapid treatment with hypertonic saline, with care to avoid central pontine myelinosis. Chronic hyponatremia is managed with fluid restriction and demeclocycline for unresponsive cases. Vasopressin antagonists represent a new option for chronic hyponatremia of syndrome of inappropriate antidiuresis.

Is there a cardiovascular rationale for the use of combined vasopressin V1a/V2 receptor antagonists?

Arginine vasopressin (AVP) signals predominantly through the V1a receptor, which subserves vasoconstriction in the peripheral circulation, and is linked directly to stimulation of myocardial hypertrophic growth factors, and the V2 receptor, the main function of which is to alter the expression of aquaporin channels in the renal collecting ducts, which leads to water retention. Agents that antagonize or block these receptors could be expected to reduce vascular tone (assuming sufficient V1a signaling is present to be causing an effect), reduce direct mitogenic signaling in the myocardium (again assuming sufficient V1a effect is present), and increase water excretion (assuming sufficient V2 signaling is present). The case for antagonizing both sets of receptors depends on the clinical situation. Pure V1a antagonists might be useful in treatment of hypertension or heart failure, but they are of little use in hyponatremia unless it is caused by heart failure. V2 antagonists would be useful in any euvolemic or hypervolemic condition associated with hyponatremia and may help produce an effective and safe diuresis independent of serum sodium when used in conjunction with loop diuretics in patients with heart failure. Selective blockade of either receptor could lead to increased signaling at the unblocked receptor sites, potentially a problematic result, especially in heart failure where disease progression is affected by increased afterload, preload, and the direct myocardial effects of neurohormonal imbalance. Therefore, a strong rationale exists for the use of combined vasopressin antagonists in patients with heart failure, particularly if the agents are used on a chronic basis.

Conivaptan

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Contemporary Issues in the Pharmacologic Management of Acute Heart Failure

Acute heart failure is an evolving syndrome that continues to be defined by ongoing studies and registries. It is associated with significant morbidity and mortality and places a huge economic burden on health care systems. Improved understanding of the underlying pathophysiologic processes has prompted interest into understanding the implications of current and future pharmacologic management strategies beyond hemodynamics. Diuretics, vasodilators, and inotropes remain the mainstays of therapy with several new classes of agents on the horizon. Clinicians should understand the rationale for use and limitations of each therapy to maximize benefit and cost-effectiveness, while minimizing the potential for adverse outcomes.

Vasopressin-2-receptor antagonism augments water excretion without changes in renal hemodynamics or sodium and potassium excretion in human heart failure

Diuretics are frequently required to treat fluid retention in patients with congestive heart failure (CHF). Unfortunately, they can lead to a decline in renal function, electrolyte depletion, and neurohumoral activation. Arginine vasopressin (AVP) promotes renal water reabsorption via the V2 receptor, and its levels are increased in CHF. This study was designed to assess the effects of a single oral dose of tolvaptan, a selective V2-receptor blocker, in the absence of other medications, on renal function in human CHF and to compare this to the effects of a single oral dose of furosemide. We hypothesized that V2-receptor antagonism would yield a diuresis comparable to furosemide but would not adversely affect renal hemodynamics, plasma electrolyte concentration, or neurohumoral activation in stable human CHF. Renal and neurohumoral effects of tolvaptan and furosemide were assessed in an open-label, randomized, placebo-controlled crossover study in 14 patients with NYHA II-III CHF. Patients received placebo or 30 mg of tolvaptan on day 1 and were crossed over to the other medication on day 3. On day 5, all subjects received 80 mg of furosemide. Tolvaptan and furosemide induced similar diuretic responses. Unlike tolvaptan, furosemide increased urinary sodium and potassium excretion and decreased renal blood flow. Tolvaptan, furosemide, and placebo did not differ with respect to mean arterial pressure, glomerular filtration rate, or serum sodium and potassium. We conclude that tolvaptan is an effective aquaretic with no adverse effects on renal hemodynamics or serum electrolytes in patients with mild to moderate heart failure.