Introduction: Circadian rhytmus have long been recognized to occur in many biologic phenomena, including secretion of hormones as well as autonomic nervous system. There is increasing evidence that circadian rhythms have been also found in cardiovascular events, for example, myocardial infarction, sudden cardiac death as well as stroke have shown a circadian pattern of the distribution. The pathophysiology and the mechanism underlying these variations are the focus of much investigation, while i tis not full understood up to date. Heart rate, blood pressure, neurohumoral vasoactive factors, such as plasma norepinephrine levels and renin activity, and probably also contractility are increased in the morning hours.
The aim of our study: To evaluate the circadian variability of plasma big endothelin and NT-proBNP level in patients with severe heart failure.
Patients: 13 patients with severe heart failure, stable for at least one month, male/female--8/5, NYHA III/IV--11/2, mean left ventricle ejection fraction 23 +/- 5%, mean cardiothoracic ratio 59 +/- 7%, all treated with RAAS blocade (11 x ACE-I, 2x ARB), all treated with diuretics, 12 patients treated with beta-blockers, 7 with digoxin. The cause of heart failure was ischemic heart disease (9) or dilated cardiomyopathy (4).
Methods: Blood samples for big endothelin and NT-proBNP were taken every two hours during a standartised daily regime.
Results: Mean plasma level of big endothelin (ranging from 1.25 to 1.71 pmol/l) had significant diurnal variability (upper limit of normal values 0.7 pmol/l). Mean plasma level of NT-proBNP (ranging from 782 to 934 pmol/l) had no diurnal variability (upper limit of normal values of 350 pmo/l).
Summary: Plasma level of NT-proBNP is stable during 24 hours and shows no circadian variability. Plasma big endothelin showed a morning peak after a systematic increase during bed rest. NT-proBNP could be evaluated any time during the day, big endothelin sample should be taken during standartised condition.