Colin D. Chue

Arterial stiffness in chronic kidney disease: causes and consequences

Chronic kidney disease is associated with elevated cardiovascular risk, and heart failure and arrhythmias are the biggest causes of cardiovascular death in this population. Increased arterial stiffness is a hallmark of chronic kidney disease and is associated with adverse alterations in cardiac structure and function that may predispose to an increased risk of cardiovascular death. These changes are already apparent in early kidney disease, which is highly prevalent in the developed world. The mechanisms underlying increased arterial stiffness in chronic kidney disease are undoubtedly complex, but an understanding is paramount to enable the development of novel therapeutic strategies to prevent or reverse this pathophysiology and therefore reduce the cardiovascular disease burden in this high-risk cohort.

Arterial disease in chronic kidney disease

End stage renal disease is associated with a very high risk of premature cardiovascular death and morbidity. Early stage chronic kidney disease (CKD) is also associated with an increased frequency of cardiovascular events and is a common but poorly recognised and undertreated risk factor. Cardiovascular disease in CKD can be attributed to two distinct but overlapping pathological processes, namely atherosclerosis and arteriosclerosis. While the risk of athero-thrombotic events such as myocardial infarction is elevated, arteriosclerosis is the predominant pathophysiological process involving fibrosis and thickening of the medial arterial layer. This results in increased arterial stiffness causing left ventricular hypertrophy and fibrosis and the exposure of vulnerable vascular beds such as the brain and kidney to high pressure fluctuations causing small vessel disease. These pathophysiological features are manifest by a high risk of lethal arrhythmia, congestive heart failure, myocardial infarction and stroke. Recent work has highlighted the importance of aldosterone and disordered bone mineral metabolism.

Cardiovascular Effects of Sevelamer in Stage 3 CKD

Serum phosphate independently predicts cardiovascular mortality in the general population and CKD, even when levels are in the normal range. Associations between serum phosphate, arterial stiffness, and left ventricular (LV) mass suggest a possible pathophysiological mechanism, potentially mediated by the phosphaturic hormone fibroblast growth factor-23 (FGF-23). To what extent the phosphate binder sevelamer modulates these effects is not well understood. In this single-center, randomized, double-blind, placebo-controlled trial, we enrolled 120 patients with stage 3 nondiabetic CKD. After a 4-week open-label run-in period, during which time all patients received sevelamer carbonate, we randomly assigned 109 patients to sevelamer (n=55) or placebo (n=54) for an additional 36 weeks. We assessed LV mass and systolic and diastolic function with cardiovascular magnetic resonance imaging and echocardiography, and we assessed arterial stiffness by carotid-femoral pulse wave velocity. The mean age was 55 years, and the mean eGFR was 50 ml/min per 1.73 m(2). After 40 weeks, we found no statistically significant differences between sevelamer and placebo with regard to LV mass, systolic and diastolic function, or pulse wave velocity. Only 56% of subjects took ≥ 80% of prescribed therapy; in this compliant subgroup, treatment with sevelamer associated with lower urinary phosphate excretion and serum FGF-23 but not serum phosphate, klotho, vitamin D, or cardiovascular-related outcomes of interest. In conclusion, this study does not provide evidence that sevelamer carbonate improves LV mass, LV function, or arterial stiffness in stage 3 nondiabetic CKD.

Serum phosphate is associated with left ventricular mass in patients with chronic kidney disease: a cardiac magnetic resonance study.

Objective To explore the relationship between serum phosphate, arterial stiffness and left ventricular mass (LVM) in patients with early-stage chronic kidney disease (CKD). Design A cross-sectional observational study. Setting Single centre. Patients 208 patients with stage 2 to stage 4 non-diabetic CKD. Interventions Arterial stiffness was determined through measurement of aortic pulse wave velocity (PWV). Cardiac magnetic resonance was used to determine LVM. Main outcome measure Relationship between serum phosphate, aortic PWV and LVM. Results Mean age was 54±13 years, mean glomerular filtration rate was 50±15 ml/min/1.73 m2, mean serum phosphate was 1.11±0.21 mmol/l and mean PWV was 8.6±2.1 m/s. When the cohort was divided into quartiles according to serum phosphate, LVM increased across quartiles (p=0.04), with no significant differences in age, kidney function, blood pressure or PWV. Serum phosphate correlated with LVM (r=0.173; p=0.01), but PWV did not (p=0.2). In a regression model containing gender, serum phosphate, office systolic blood pressure, albumin/creatinine ratio and haemoglobin, 30% of the variation in LVM was explained (p<0.0005), with serum phosphate accounting for 5% of the variance. Conclusion Serum phosphate is independently associated with LVM in patients with CKD. Interventional studies are required to determine whether this association is causative and whether reducing phosphate exposure reduces LVM in this population.

Comparison of magnetic resonance feature tracking for systolic and diastolic strain and strain rate calculation with spatial modulation of magnetization imaging analysis

To compare cardiovascular magnetic resonance‐feature tracking (CMR‐FT) with spatial modulation of magnetization (SPAMM) tagged imaging for the calculation of short and long axis Lagrangian strain measures in systole and diastole.

Impact of renal function on survival after transcatheter aortic valve implantation (TAVI): an analysis of the UK TAVI registry

Objective To determine the nature of the association between renal dysfunction and outcomes following transcatheter aortic valve implantation (TAVI) in all cases performed in the UK between 2007 and 2012. Methods The UK TAVI registry was established to report outcomes on all TAVI procedures performed within the UK. Data were collected prospectively on 3980 patients from 1 January 2007 until 31 December 2012. Results In total, 205 patients (5.5%) died during their admission. Moderate to advanced chronic kidney disease (CKD) (estimated glomerular filtration rate (eGFR) <45 mL/min/1.73 m2) was significantly associated with increased mortality, even after adjustment for risk factors (OR 1.45, 95% CI 1.03 to 2.05; p=0.04). For every 10 mL/min/1.73 m2 decrease in eGFR, in-hospital mortality increased by 8.2% (95% CI 1.1% to 14.7%; p=0.03). In total 1119 patients (30.2%) died during the follow-up period (median 543 days). Moderate to advanced CKD (eGFR <45 mL/min/1.73 m2) was significantly associated with increased mortality, even after adjustment for risk factors (OR 1.36, 95% CI 1.17 to 1.58; p<0.001). For every 10 mL/min/1.73 m2 decrease in eGFR, cumulative mortality increased by 4.4% (95% CI 1.2% to 7.5%; p=0.007). Preoperative kidney function and the need for preoperative dialysis treatment discriminated between patients who died and survived. However, predictive power was poor with none of the c-statistics being >0.6. Conclusions Pre-procedural renal dysfunction is associated, in a graded fashion independently of dialysis status, with worse outcomes, including mortality in patients undergoing TAVI.

The role of echocardiography in percutaneous left atrial appendage occlusion

Percutaneous device closure of the left atrial appendage (LAA) has been introduced in the last decade as a minimally invasive alternative treatment to long-term anticoagulation to reduce the risk of thrombo-embolism in patients with atrial fibrillation. Echocardiography is an essential tool at all stages of the procedure. Pre-procedural echocardiography is used to screen suitable candidates and to define LAA morphology and dimension; peri-procedural transoesophageal or intracardiac echocardiography has a major role in guiding, delivery, and deployment of the device, for screening of procedural complications and for assessing procedural success; and post-procedural echocardiography is important in the surveillance and monitoring of long-term outcome. This article aims to outline the role of echocardiography at each stage of LAA occlusion.

The safety and tolerability of spironolactone in patients with mild to moderate chronic kidney disease

AIM Mineralocorticoid receptor blockade (MRBs) in combination with angiotensin converting enzyme (ACE) inhibitors and angiotensin-II receptor blockade (ARBs) improve prognostic markers of cardiovascular and renal disease in early stage chronic kidney disease (CKD). Concerns relating to the safety and tolerability of MRBs in CKD may limit their use in a non clinical trial setting. METHODS In the Chronic Renal Impairment in Birmingham II study, 115 patients with non-diabetic early stage CKD (eGFR 30-89ml/min/1.73m(2) ) received 25mg daily of spironolactone for 4 weeks before randomization to continuing treatment or placebo for a further 36 weeks. All patients were on ACE inhibitors and/or ARB therapy. Potassium and renal function were checked at weeks 1, 2, 4, 8, 16, 28 and 40. The incidence of hyperkalaemia, significant renal dysfunction (reduction eGFR ≥25%) and adverse effects was assessed. RESULTS After 40 weeks of treatment the incidence of serious hyperkalaemia (K(+) ≥6.0mmol/L) was <1%. A potassium 5.5-5.9mmol/L occurred on ≥1 occasion over follow-up in 11 patients (nine on spironolactone) and was predicted by baseline potassium ≥5.0mmol/L and eGFR ≤45 ml/min/1.73m(2) . Over follow-up, three patients experienced significant renal dysfunction but no patients withdrew due to intolerance or side effects. Changes in potassium, eGFR and systolic blood pressure were most apparent in the first 4 eeks. CONCLUSION Spironolactone was well tolerated in selected patients with early stage CKD. Strict monitoring over the first month of treatment followed by standard surveillance as for ACE inhibitors and ARBs is suggested.

Cardiovascular Effects of Unilateral Nephrectomy in Living Kidney Donors

Abstract—There is a robust inverse graded association between glomerular filtration rate (GFR) and cardiovascular risk, but proof of causality is lacking. Emerging data suggest living kidney donation may be associated with increased cardiovascular mortality although the mechanisms are unclear. We hypothesized that the reduction in GFR in living kidney donors is associated with increased left ventricular mass, impaired left ventricular function, and increased aortic stiffness. This was a multicenter, parallel group, blinded end point study of living kidney donors and healthy controls (n=124), conducted from March 2011 to August 2014. The primary outcome was a change in left ventricular mass assessed by magnetic resonance imaging (baseline to 12 months). At 12 months, the decrease in isotopic GFR in donors was −30±12 mL/min/1.73m2. In donors compared with controls, there were significant increases in left ventricular mass (+7±10 versus −3±8 g; P<0.001) and mass:volume ratio (+0.06±0.12 versus −0.01±0.09 g/mL; P<0.01), whereas aortic distensibility (−0.29±1.38 versus +0.28±0.79×10−3 mm Hg−1; P=0.03) and global circumferential strain decreased (−1.1±3.8 versus +0.4±2.4%; P=0.04). Donors had greater risks of developing detectable highly sensitive troponin T (odds ratio, 16.2 [95% confidence interval, 2.6–100.1]; P<0.01) and microalbuminuria (odds ratio, 3.8 [95% confidence interval, 1.1–12.8]; P=0.04). Serum uric acid, parathyroid hormone, fibroblast growth factor-23, and high-sensitivity C-reactive protein all increased significantly. There were no changes in ambulatory blood pressure. Change in GFR was independently associated with change in left ventricular mass (R2=0.28; P=0.01). These findings suggest that reduced GFR should be regarded as an independent causative cardiovascular risk factor. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT01028703.

Is lowering phosphate exposure the key to preventing arterial stiffening with age

Cardiovascular disease remains the leading cause of death world wide. Although atheroma is clearly important, the role of arteriosclerotic vascular disease is often overlooked. Arteriosclerosis causes increased arterial stiffness, with consequent systolic hypertension and left ventricular hypertrophy. Serum phosphate is increasingly being recognised as a cardiovascular risk factor and has been implicated in the development of arteriosclerosis and arterial calcification. Its determinants are unclear, but both diet and minor reductions in renal function may be important. Diets in affluent populations are high in phosphate because of increased consumption of animal protein and the use of phosphate-containing preservatives. This viewpoint suggests that the consumption of a phosphate-rich diet, exacerbated by the high prevalence of chronic kidney disease found in ageing populations, accelerates the development of arteriosclerosis. It is hypothesised that reducing phosphate intake will attenuate the progression of arterial stiffness with major beneficial effects upon cardiovascular mortality and morbidity.