Diagnostic, prognostic, and therapeutic implications of brain natriuretic peptide in dialysis and nondialysis-dependent chronic renal failure

Premature cardiovascular disease is the leading cause of morbidity and mortality in patients with end-stage renal failure. Natriuretic peptides, specifically brain natriuretic peptide, are released from the heart in response to chamber distension and thus increased in the presence of volume expansion and cardiac overload. Their physiological role is to cause vasodilatation and promote natriuresis to maintain volume homeostasis. Increasingly serum levels of brain natriuretic peptide are used to both diagnose and manage cardiovascular disorders. Furthermore, augmenting the beneficial hemodynamic actions of brain natriuretic peptide may have a therapeutic role in decompensated heart failure. However, the diagnostic role of serum brain natriuretic peptide levels in patients with advanced renal dysfunction remains to be defined. These patients have a high prevalence of left ventricular disorders, specifically left ventricular hypertrophy, which may reduce the diagnostic utility of brain natriuretic peptide. In addition, ventricular stretch may be determined by intravascular volume status rather than by cardiac dysfunction. Nonetheless, as the prognosis of patients with end-stage renal failure and co-existing heart failure is so poor, the availability of a further marker of cardiac ''distress'' may in the future become a useful diagnostic tool and in due course may become a primary goal for titration and tailoring of therapy.

NT-proBNP can be used to detect right ventricular systolic dysfunction in pulmonary hypertension

Right ventricular systolic dysfunction (RVSD) at baseline (pre-treatment) predicts early death in patients with pulmonary hypertension (PH). However, RVSD can only be detected reliably by prohibitively invasive or expensive techniques. N-terminal B-type natriuretic peptide concentration ([NT-proBNP]) correlates with RV function in PH; however, an [NT-proBNP] threshold that indicates RVSD in individual patients has not previously been determined. Twenty-five patients with PH (pulmonary arterial hypertension (n = 19) or chronic thromboembolic PH (n = 6)) underwent cardiovascular magnetic resonance (CMR) imaging and NT-proBNP measurement at baseline. [NT-proBNP] was correlated against RV dimensions and ejection fraction (RVEF) measured directly by CMR imaging. The ability of NT-proBNP to detect RVSD (defined as a CMR-derived RVEF >2 SDS below control values) was tested and predictors of [NT-proBNP] identified. [NT-proBNP] correlated negatively with RVEF. RVSD was present in nine out of 25 patients. An [NT-proBNP] threshold of 1,685 pg.mL(-1) was sensitive (100%) and specific (94%) in detecting RVSD. RVEF and RV mass index independently predicted [NT-proBNP]. In pulmonary hypertension, a baseline N-terminal B-type natriuretic peptide concentration of >1,685 ng.L(-1) suggests right ventricular systolic dysfunction, and thus an increased risk of early death. N-terminal B-type natriuretic peptide could prove useful as an objective, noninvasive means of identifying patients with pulmonary hypertension who have right ventricular systolic dysfunction at presentation.

Vascular function in patients with end-stage renal disease and/or coronary artery disease: A cardiac magnetic resonance imaging study

Decreased arterial compliance in end-stage renal disease (ESRD) is associated with increased cardiovascular risk. Our aim was to examine aortic compliance in patients with ESRD using cardiac magnetic resonance imaging (MRI) and to compare these with patients with advanced atherosclerotic disease who are known to be at high cardiovascular risk. We examined a total of 83 subjects matched for age: 24 had ESRD and were on dialysis therapy for 3+/-6 years, 24 had severe coronary artery disease (CAD), 11 had both ESRD and CAD (4+/-5 years on dialysis therapy), and 24 healthy subjects with no evidence of CAD. Vascular and cardiac function was assessed using cardiac MRI. Aortic compliance was significantly reduced in patients with CAD compared to control subjects (11.3+/-6.3 ml x 10(-3)/mm Hg vs 15.6+/-6.0 ml x 10(-3)/mm Hg, P=0.009). Patients with ESRD also exhibited significantly reduced aortic compliance compared to healthy controls (12.4+/-5.8 ml x 10(-3)/mm Hg vs 15.6+/-6.0 ml 10(-3)/mm Hg, P=0.012), whereas there was no significant difference in aortic compliance between patients with CAD and ESRD. Even in the absence of symptomatic CAD, patients with ESRD have significantly reduced aortic compliance compared to normal subjects. Patients with ESRD have equivalent aortic compliance to patients with advanced CAD. These findings suggest that a significantly reduced aortic compliance is one of many mechanisms promoting premature cardiovascular events in patients with ESRD compared to age-matched controls from the general population.

Redefinition of uremic cardiomyopathy by contrast-enhanced cardiac magnetic resonance imaging

Patients with end stage renal failure (ESRF) have an increased risk of premature cardiovascular disease. Left ventricular (LV) abnormalities, so called 'uremic cardiomyopathy', are associated with poorer outcome. Cardiac magnetic resonance imaging (CMR) accurately defines LV dimensions and identifies underlying myocardial pathology. We studied the relationship between LV function and myocardial pathology in ESRF patients with CMR. A total of 134 patients with ESRF underwent CMR. LV function was assessed with further images acquired after gadolinium-diethylentriaminepentaacetic acid (DTPA). The presence of myocardial fibrosis was indicated by late gadolinium enhancement (LGE). Two main myocardial pathologies were identified. A total of 19 patients (14.2%) displayed 'subendocardial LGE' representing myocardial infarction, which was associated with conventional cardiovascular risk factors including a history of ischemic heart disease (IHD) (P < 0.001), hypercholesterolemia (P < 0.05), and diabetes (P < 0.01). Patients with subendocardial LGE had greater LV mass (P < 0.05), LV dilation (P < 0.01), and LV systolic dysfunction (P < 0.001) compared to patients with no evidence of LGE. The second pattern, 'diffuse LGE', seen in 19 patients (14.2%) appeared to represent regional areas of diffuse myocardial fibrosis. Diffuse LGE was associated with greater LV mass compared to patients without LGE (P < 0.01) but not systolic dysfunction. In total, 28.4% of all patients exhibited evidence of myocardial fibrosis demonstrated by LGE. In contrast to published literature describing three forms of uremic cardiomyopathy - left ventricular hypertrophy (LVH), dilation, and systolic dysfunction, we have shown that LVH is the predominant cardiomyopathy specific to uremia, while LV dilation and systolic dysfunction are due to underlying (possibly silent) ischemic heart disease.

Statins inhibit NK cell cytotoxicity by membrane raft depletion rather than inhibition of isoprenylation

To investigate the potential determinants of the pleiotropic effects of statins, we measured NK cell cytotoxicity in samples from normal subjects and patients, including patients receiving statin therapy. In a multivariate analysis, NK cell cytotoxicity was related to total plasma cholesterol concentration rather than statin use. In vitro, we investigated the role of lipid modification, specifically the effects on membrane rafts and raft-dependent signal transduction. We demonstrate that statins reduce NK cell cytotoxicity and that membrane cholesterol depletion by cyclodextrins has a similar effect. In contrast, isoprenyl transferase inhibitors had little or no effect on NK cell function. We hypothesise that the pleiotropic effects of statins reflect changes in membrane cholesterol and, specifically, the density of membrane rafts. Moreover, there is likely to be a relationship between membrane cholesterol, membrane rafts and cell function that may be involved in the pathogenesis of cardiovascular and metabolic diseases.

Endothelial Dysfunction in Renal Transplant Recipients

Endothelial dysfunction and damage are systemic processes that are recognised to play a central role in the pathogenesis of hypertension and atherosclerotic cardiovascular disease. Renal failure is associated with impaired endothelium dependent vasodilatation that is partly a consequence of increased circulating levels of asymmetric dimethyl arginine. Endothelial dysfunction persists, although it is improved, after renal transplantation. Statins appear to improve endothelial dysfunction, as does withdrawal of calcineurin inhibitors, although there is no evidence that these strategies improve patient or graft survival. The situation in transplant recipients is complicated by the fact that endothelial dysfunction (within the graft vasculature) may be a separate process contributing to chronic allograft nephropathy and to circulating levels of endothelial cells and their components, thus limiting the utility of circulating markers of endothelial damage in this population.

Diagnostic potential of circulating natriuretic peptides in chronic kidney disease

BACKGROUND

Measurement of natriuretic peptides, particularly brain natriuretic peptide (BNP) is an established method for the diagnosis of cardiovascular disorders, chiefly left ventricular (LV) dysfunction. The influence of renal function on the diagnostic utility of natriuretic peptides is unclear.

METHODS

We performed a cross-sectional study of 296 patients with renal disease but no history of cardiac disease using echocardiography to assess LV mass and function. Circulating levels of atrial natriuretic peptide (ANP) and BNP were also measured.

RESULTS

The incidence of LV hypertrophy increased with progressive renal dysfunction; from 39% in patients with near-normal renal function, to 80% in renal transplant patients. There was a negative correlation between both ANP and BNP, and glomerular filtration rate (GFR) (ANP: r = -0.28, P<0.001; BNP: r = -0.40, P<0.001). Serum ANP and BNP had sensitivity and specificity for LV hypertrophy of 39.9%, 87.4% (ANP) and 61.4%, 67.6% (BNP) respectively. Sensitivity and specificity for LV dysfunction was 77.2%, 32.4% (ANP) and 71.8%, 40.0% (BNP). Significant confounders in determining serum ANP were haemoglobin, beta blockade and albumin, while serum BNP levels were significantly confounded by GFR, albumin, haemoglobin, beta blockade and age.

CONCLUSIONS

Across a spectrum of renal dysfunction, GFR is a more important determinant of serum BNP than ventricular function, and several factors are predictors of natriuretic peptide levels. In chronic kidney disease, the use of natriuretic peptides to diagnose LV hypertrophy must be interpreted in light of these other factors. The use of these peptides in renal dysfunction to diagnose LV dysfunction may be of limited value.

Cardiomyopathy in Becker Muscular Dystrophy—Does Regional Fibrosis Mimic Infarction?

We present a case of a 39-year-old man with Becker muscular dystrophy and severe congestive cardiac failure. Cardiac magnetic resonance imaging revealed subendocardial late gadolinium enhancement, similar to that seen in myocardial infarction. He had no risk factors for atherosclerotic coronary artery disease and coronary angiography was normal. We propose that regional subendocardial myocardial fibrosis which has been described histologically in the cardiomyopathy associated with Becker muscular dystrophy may resemble previous infarction at contrast enhanced cardiac magnetic resonance imaging.

Random blood glucose measurements and survival in nondiabetic renal transplant recipients

New-onset diabetes after renal transplantation (PTDM), a common consequence of immunosuppression, is associated with reduced patient survival. However, we know little about the impact of less marked changes in glucose homeostasis. To investigate this problem, we used data on average random blood glucose values during the first, second, and third months posttransplantation, derived from a cohort of 1186 patients who received their first cadaveric or living-donor transplant between 1984 and 2002. We analyzed both patient and death-censored graft survivals, subgrouping recipients into those with end-stage renal failure due to diabetic nephropathy versus those with PTDM versus patients without diabetes. We confirmed that PTDM patients display reduced survival following transplantation, but a long-term survival similar to that of patients with diabetic nephropathy and end-stage renal disease. However, among patients without diabetes, random blood glucose was also a strong determinant of outcome, even when in the low normal range. In contrast, neither the presence of diabetes nor random glucose levels showed a significant impact on graft survival. PTDM is recognized to be an important, potentially modifiable, risk factor for cardiovascular disease in transplant recipients. Our data suggest that there is a gradation of increased risk associated with impaired glycemic control that affects patients who do not have diabetes. These data support the need for improved understanding of glycemic control in transplant recipients and for more detailed screening for impaired glucose tolerance in this population.

Electrocardiographic abnormalities and uremic cardiomyopathy

BACKGROUND

Progressive renal disease is associated with an increased risk of cardiovascular death, specifically sudden death. We investigated the link between uremic cardiomyopathy, QT interval and dispersal, and arrhythmias (by ambulatory ECG monitoring) in patients at different stages of progressive renal disease.

METHODS

In a cross-sectional study we investigated 296 patients with nondiabetic renal disease (53 transplant recipients, 55 hemodialysis patients, and 188 throughout the range of chronic renal failure). Patients underwent echocardiography, ECG, and ambulatory blood pressure and ECG monitoring.

RESULTS

Left ventricular mass was increased from the earliest stages of renal disease (near-normal renal function), the predominant pattern being eccentric left ventricular hypertrophy (LVH). There was a progressive increase in LVH with loss of renal function, so that more than 80% of patients on renal replacement therapy have LVH, the dominant pattern being concentric LVH. The prevalence of diastolic dysfunction increased in parallel with changes in left ventricular mass but systolic dysfunction and ventricular dilatation did not. Increased QT interval and QT dispersal were associated with poor renal function (maximal in dialysis patients), and were linked to LVH and other echocardiographic abnormalities. Arrhythmias were uncommon on ambulatory recording but were more common with poor renal function, in the presence of uremic cardiomyopathy, and increased QT interval and dispersal.

CONCLUSION

LVH is present from the earliest stages of progressive renal disease. This, and other forms of uremic cardiomyopathy, is linked to increased QT interval and dispersal, and with minor rhythm abnormalities, providing a link with the high risk of sudden death in this population.

Circulating Endothelial Cells in Renal Transplant Recipients

Circulating endothelial cells (CECs) are a marker of endothelial injury and endothelial dysfunction. We measured CECs in 95 patients with functioning renal transplants at risk of premature cardiovascular (CV) disease and in normal control subjects. We were unable to demonstrate consistent relationships between CEC levels and conventional CV risk factors in transplant recipients. However, CEC levels were increased in patients with a history of rejection. We conclude that CECs are of little use as a marker of CV risk in this population but may be a useful marker to monitor allograft rejection.

Contrast enhanced-cardiovascular magnetic resonance imaging in patients with pulmonary hypertension

AIMS

To determine the presence and extent of delayed contrast enhancement (DCE) in patients with pulmonary hypertension (PHT) using contrast enhanced-cardiovascular magnetic resonance imaging (ce-CMR).

METHODS AND RESULTS

Twenty-five patients with PHT underwent ce-CMR and right heart catheterization. Right ventricular (RV) and left ventricular (LV) volumes, ejection fraction, mass, and DCE mass were determined with ce-CMR. Mean pulmonary artery pressure (mean PAP) averaged 43 (12) mmHg and cardiac output 4.3 (1.2) L/min. DCE was demonstrated in 23 out of 25 patients. DCE was confined to the RV insertion points (RVIPs) in seven patients and extended into the interventricular septum (IVS) in the remaining 16 patients. In these 16 patients, septal contrast enhancement was associated with IVS bowing. The extent of contrast enhancement correlated positively with RV end-diastolic volume/body surface area, RV mass, mean PAP, and pulmonary vascular resistance and correlated inversely with RV ejection fraction.

CONCLUSION

DCE was present within the RVIPs and IVS of most patients with PHT studied. Extent of DCE correlated with RV function and pulmonary haemodynamics. DCE was associated with IVS bowing and may provide a novel marker for occult septal abnormalities directly relating to the haemodynamic stress experienced by these patients.

Hypertension, antihypertensive agents and outcomes following renal transplantation

Hypertension is common following renal transplantation and adversely affects graft and patient survival. However, strategies for antihypertensive drug therapy and target blood pressure have not been clearly defined.

AIM

To assess the influence of achieved blood pressure and antihypertension drug therapy on graft and patient survival with the aim of identifying targets and event rates for future intervention studies.

METHODS

We undertook a longitudinal follow up study of 634 renal transplant patients. Patients were surveyed in December 1994 and followed up after 102 months. Blood pressure (BP) was determined from the mean of three clinic readings and antihypertensive drug therapy recorded.

RESULTS

Complete follow up data were available for analysis on 622 patients (57.2% male; mean age: 45.2 +/- 13.0 yr. There were 158 (25.4%) deaths and 115 (18.5%) death-censored graft failures. Lower systolic and diastolic blood pressure were associated with better graft survival in the Kaplan-Meier analysis. Univariate analysis showed serum creatinine (HR 1.012, p < 0.001), duration of renal replacement therapy (HR 0.946, p = 0.012), age (HR 0.979, p = 0.014) and pulse pressure (HR 1.017, p = 0.044) to be predictors of graft survival with serum creatinine and duration of renal replacement therapy as the only significant factors in the multivariate analysis. Lower systolic and pulse pressure were associated with better patient survival in the Kaplan-Meier analysis. Age (HR) 1.062, p < 0.0001), serum creatinine (HR 1.002, p = 0.021), diabetes (HR 3.371, p < 0.0001), and pulse pressure (HR 1.013, p = 0.036) were significant predictors of patient survival in the univariate and multivariate analysis. Patient survival was reduced with increasing number of antihypertensives (p < 0.05), as was graft survival (p < 0.05). Reduced patient and graft survival were seen in patients prescribed calcium channel antagonists (p < 0.01). There was no increased patient mortality in those patients on beta-blockers or angiotensin converting enzyme (ACE) inhibitors.

CONCLUSION

Hypertension is a risk factor, which remains despite the use of anti-hypertensives, for reduced patient and graft survival. The risk was not significant when blood pressure was entered together with serum creatinine in the multivariate analysis. Beta-blockers may have a beneficial effect on cardiovascular mortality, and ACE inhibitors a beneficial effect on both patient and graft survival. There is a pressing need for interventional studies to assess the impact of blood pressure targets on patient and graft survival and the effect of individual agents on these outcomes.

Determinants of hypertension and left ventricular function in end stage renal failure: a pilot study using cardiovascular magnetic resonance imaging

Cardiovascular disease is the principal cause of mortality in patients with renal failure. Left ventricular (LV) abnormalities are adverse prognostic indicators for cardiovascular outcome. The aim of this study was to use cardiac magnetic resonance scanning (CMR) to define LV functional abnormalities in haemodialysis (HD) patients and clarify the determinants of blood pressure (BP) and the effect of anaemia in this population. We studied 44 HD patients and 11 controls with CMR performed following dialysis. Forty patients and 11 controls completed the study. LV mass (P<0.001) and estimated systemic vascular resistance (SVR) (P = 0.002) were significantly higher in the dialysis group compared to controls. LV ejection fraction (P = 0.002) and SV (P = 0.043) were lower than controls. In the HD patients, BP correlated significantly with cardiac output (CO; r = 0.569, P<0.001) and end diastolic volume (EDV; r = 0.565, P<0.001) but there was no correlation between BP and SVR (r = 0.201, P = 0.594). Haemoglobin was inversely correlated with both CO (r = -0.531, P<0.001) and EDV (r = -0.493, P = 0.001) and positively with SVR (r = 0.402, P = 0.009). HD patients had a higher LV mass and lower ejection fraction than controls. The relationship of BP with CO, but not SVR, supports the theory that a major determinant of BP is intravascular volume and CO rather than vascular resistance although there was a fixed increase in SVR in this population. Improved understanding of the mechanisms underlying increased SVR and improved control of CO and intravascular volume may allow better therapeutic strategies. CMR provides insights into the pathophysiology of hypertension and LV dysfunction in HD patients.