The role and assessment of ventricular peptides in heart failure

Plasma Clearance of B-Type Natriuretic Peptide (BNP) before and after Bariatric Surgery for Morbid Obesity

BACKGROUND

Obese patients have lower plasma concentrations of the cardiac natriuretic peptides (NPs) than their age- and sex-matched counterparts. This may reflect lower production and/or increased peptide clearance. It is unclear whether NP bioactivity is affected by obesity.

METHODS

We studied the effects of obesity on B-type natriuretic peptide (BNP) clearance and bioactivity by comparing results from standardized intravenous infusions of BNP administered 2 weeks before and 6 months after bariatric surgery in 12 consecutive patients with morbid obesity (body mass index, BMI > 35 kg/m2). Anthropometric, clinical, neurohormonal, renal, and echocardiographic variables were obtained pre- and postsurgery. Pre- vs postsurgery calculated intrainfusion peptide clearances were compared.

RESULTS

BMI (44.3 ± 5.0 vs 33.9 ± 5.2 kg/m2, P < 0.001) and waist circumference (130.3 ± 11.9 vs 107.5 ± 14.7 cm, P < 0.001) decreased substantially after bariatric surgery. Calculated plasma clearance of BNP was reduced (approximately 30%) after surgery. Though not controlled for, sodium intake was presumably lower after bariatric surgery. Despite this, preinfusion endogenous plasma NP concentrations did not significantly differ between pre- and postsurgery studies. The ratio of plasma N-terminal (NT)-proBNP to 24 h urine sodium excretion was higher postsurgery (P = 0.046; with similar nonsignificant findings for BNP, atrial NP (ANP) and NT-proANP), indicating increased circulating NPs for a given sodium status. Mean plasma NP concentrations for given calculated end-systolic wall stress and cardiac filling pressures (as assessed by echocardiographic E/e') rose slightly, but not significantly postsurgery. Second messenger, hemodynamic, renal, and neurohormonal responses to BNP were not altered between studies.

CONCLUSION

Obesity is associated with increased clearance, but preserved bioactivity, of BNP.

Laboratory and diagnostic testing: a perioperative update

Perioperative nurses are challenged to stay informed about the rapidly changing field of diagnostic and laboratory testing. The brain natriuretic peptide test primarily is used to differentiate dyspnea caused by heart failure from dyspnea that results from other causes. Virtual colonoscopy is a promising new alternative for detecting colorectal polyps and cancers. The microalbumin urine test provides an early indication of the development of diabetic complications. This update of relatively new laboratory tests and diagnostic studies also provides implications for perioperative nurses.

B-type natriuretic peptide and N-terminal pro B-type natriuretic peptide are depressed in obesity despite higher left ventricular end diastolic pressures

BACKGROUND

B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are frequently used in diagnosing and monitoring patients with heart failure. Recent studies have demonstrated that concentrations of these peptides are decreased in obese patients, but whether lower natriuretic peptide concentrations are really due to different hemodynamics is unknown. The relationship between these markers and left ventricular end diastolic pressure (LVEDP) in obesity has not been elucidated.

METHODS

We examined patients undergoing cardiac catheterization who had creatinine of < 2.0, no evidence of myocardial infarction or pulmonary embolism, and no cardiac transplant. Body mass index and LVEDP were determined, and BNP and NT-proBNP obtained at the start of each case. Obesity was defined as body mass index of > or = 30 kg/m2.

RESULTS

Of 203 patients enrolled, 101 were obese. The groups were similar in respect to race, creatinine, cholesterol, and history of dyslipidemia and cardiomyopathy. The obese patients tended to be younger, were more likely to have diabetes and hypertension, and were less likely to have coronary artery disease. The obese patients had higher LVEDP but reduced BNP and NT-pro-BNP. The relationship between the natriuretic peptides and LVEDP was poor, with r values of < 0.1.

CONCLUSIONS

Obese patients have reduced concentrations of BNP and NT-proBNP compared to nonobese patients despite having elevated LVEDP. This suggests that factors other than cardiac status impact on BNP and NT-proBNP concentrations. The poor relationship between natriuretic peptide concentrations and LVEDP also suggests that these concentrations should not be considered surrogates for cardiac filling pressures or volumes.

Negative inotropic effects of C-type natriuretic peptide are attenuated in hypertrophied ventricular myocytes associated with reduced cyclic GMP production

BACKGROUND

We tested the hypothesis that the negative inotropic effects of C-type natriuretic peptide (CNP) would be diminished in renal hypertensive (one-kidney-one-clip, 1K1C) hypertrophic rabbit hearts and that this attenuated effect would be due either to decreased cyclic GMP production or to reduced signaling.

MATERIAL AND METHODS

Using isolated control and 1K1C ventricular myocytes, cell shortening data (video edge detection) were collected: (1) at baseline and after CNP 10(-8,-7) M, followed by KT5823 (KT), a cyclic GMP-dependent protein kinase inhibitor; or (2) at baseline, following KT pre-treatment and subsequent CNP 10(-8,-7) M. In addition, cyclic GMP levels were determined by radioimmunoassay at baseline and CNP 10(-7) M.

RESULTS

In control myocytes, CNP decreased percent shortening (5.7 +/- 0.4 versus 4.0 +/- 0.4% at 10(-7) M), maximal rate of shortening (58.7 +/- 5.1 versus 45.2 +/- 3.6 microm/sec) and maximal rate of relaxation (57.1 +/- 4.9 versus 44.1 +/- 3.4 microm/sec) in a concentration-dependent manner. These effects were attenuated by subsequent KT administration. CNP failed to produce these negative functional effects in 1K1C myocytes. When pre-treated with KT, CNP had no negative functional effect in either normal and 1K1C myocytes. Basal levels of cyclic GMP were similar in control versus 1K1C myocytes; however, CNP produced a significant rise in cyclic GMP level in control (63.6 +/- 7.8 versus 83.5 +/- 11.3 pmol/10(5) myocytes) but not in 1K1C (49.2 +/- 2.6 versus 52.7 +/- 5.6) myocytes.

CONCLUSIONS

Thus, CNP acted through the cyclic GMP protein kinase in control myocytes. We conclude that in hypertrophic cardiac myocytes, the decreased effect of CNP was because of decreased production of cyclic GMP.

Utility of N-terminal brain natriuretic peptide plasma concentrations in comparison to lactate and troponin in children with congenital heart disease following open-heart surgery

We conducted a prospective study in a pediatric cardiac intensive care unit in order to determine the diagnostic value of N-terminal brain natriuretic peptide (N-BNP) plasma concentration in the perioperative care of children with congenital heart disease (CHD). N-BNP plasma concentrations were determined by using a validated enzyme immunoassay. We measured N-BNP the day before surgery and up to 15 days postoperatively in 23 children (age range, 0.25-11 years) undergoing cardiac surgery due to various CHDs. Supply and duration of catecholamines, vasodilators, and respiratory therapy were determined and correlated to N-BNP. In addition, troponin T (TnT) and arterial Lactat (aL) concentrations were measured simultaneously. We found a significant correlation between preoperative and maximal N-BNP levels and dosage of vasodilators (r = 0.41, p < 0.02 and r = 0.83, p < 0.01, respectively). Maximal TnT and aL levels were not correlated to dosage of vasodilators. The dosage and duration of catecholamines, the duration of respiratory therapy, and the plasma concentration of TnT and aL were not correlated to pre- or perioperative N-BNP. Maximal TnT and aL levels were correlated to duration (r = 0.53, p < 0.01 and r = 0.48, p < 0.02) and dosage (r = 0.52, p < 0.02 and r = 0.60, p < 0.01) of catecholamines and duration of respiratory therapy (r = 0.57, p < 0.01 and r = 0.50, p < 0.02). As recent studies show, N-BNP appears to be a powerful neurohumoral indicator of ventricular function and prognosis for guiding therapy in the outpatient department or for discriminating cardiac from noncardiac symptoms. In contrast, the value of N-BNP for guiding perioperative therapy in pediatric cardiac intensive care units is limited.

Atrial natriuretic peptide reverses the negative functional effects of stunning in rabbit myocardium

We tested the hypothesis that atrial natriuretic peptide (ANP) would decrease both the effects of myocardial stunning and oxygen consumption in rabbit hearts. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by two 15 min occlusions of the left anterior descending (LAD) artery separated by 15 min of reperfusion. Either ANP (0.2 mg) or vehicle (lactated Ringers) was then injected into the affected area of the left ventricle. In a third group, ANP was injected into the LAD region of non-stunned rabbits. Hemodynamic (heart rate, aortic and left ventricular pressures) and functional (wall thickening (WT), delay of onset of WT, and rate of WT) parameters were measured. Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) were used to determine myocardial O2 consumption. Stunning was demonstrated by an increase in the time delay to contraction and depressed WT. In the control group, baseline delay to contraction was 25+/-7 ms, and this increased to 84+/-16 following stunning and vehicle administration. In the ANP group, baseline delay was 20+/-6 at baseline and after stunning and ANP administration it was 30+/-7. Wall thickening decreased by approximately 30% with stunning and vehicle but only 8% in the ANP treated hearts. Stunning did not affect regional O2 consumption (6.0+/-1.1 stunned vs. 7.4+/-1.2 mlO2/min/100g non-stunned). ANP administration did not affect O2 consumption (7.3+/-1.7 stunned vs. 6.4+/-1.0 non-stunned). We therefore concluded that ANP administration reversed the effects of stunning without alteration in local O2 consumption in stunned myocardium.