Current and novel imaging techniques to evaluate myocardial dysfunction during hemodialysis.

PURPOSE OF REVIEW: Patients on hemodialysis have significantly higher rates of cardiovascular mortality resulting from a multitude of myocardial dysfunctions. Current imaging modalities allow independent assessment of cardiac morphology, contractile function, coronary arteries and cardiac perfusion. Techniques such as cardiac computed tomography (CT) imaging have been available for some time, but have not yet had widespread adoption because of technical limitations related to cardiac motion, radiation exposure and safety of contrast agents in kidney disease. RECENT FINDINGS: Novel dynamic contrast-enhanced (DCE) CT imaging can be used to acquire high-resolution cardiac images, which simultaneously allow the assessment of coronary arteries and the quantitative measurement of myocardial perfusion. The advancement of recent CT scanners and cardiac protocols have allowed noninvasive imaging of the whole heart in a single imaging session with minimal cardiac motion artefact and exposure to radiation. SUMMARY: DCE-CT imaging in clinical practice would allow comprehensive evaluation of the structure, function, and hemodynamics of the heart in a short, well tolerated scanning session. It is an imaging tool enabling the study of myocardial dysfunction in dialysis patients, who have greater cardiovascular risk than nonrenal cardiovascular disease populations, both at rest and under cardiac stress associated with hemodialysis itself.

Tissue sodium concentrations in chronic kidney disease and dialysis patients by lower leg sodium-23 magnetic resonance imaging.

BACKGROUND: Sodium-23 magnetic resonance imaging (23Na MRI) allows direct measurement of tissue sodium concentrations. Current knowledge of skin, muscle and bone sodium concentrations in chronic kidney disease (CKD) and renal replacement therapy patients is limited. In this study we measured the tissue sodium concentrations in CKD, hemodialysis (HD) and peritoneal dialysis (PD) patients with 23Na MRI of the lower leg and explored their correlations with established clinical biomarkers. METHODS: Ten healthy controls, 12 CKD Stages 3-5, 13 HD and 10 PD patients underwent proton and 23Na MRI of the leg. The skin, soleus and tibia were segmented manually and tissue sodium concentrations were measured. Plasma and serum samples were collected from each subject and analyzed for routine clinical biomarkers. Tissue sodium concentrations were compared between groups and correlations with blood-based biomarkers were explored. RESULTS: Tissue sodium concentrations in the skin, soleus and tibia were higher in HD and PD patients compared with controls. Serum albumin showed a strong, negative correlation with soleus sodium concentrations in HD patients (r = -0.81, P < 0.01). Estimated glomerular filtration rate showed a negative correlation with tissue sodium concentrations (soleus: r = -0.58, P < 0.01; tibia: r = -0.53, P = 0.01) in merged control-CKD patients. Hemoglobin was negatively correlated with tissue sodium concentrations in CKD (soleus: r = -0.65, P = 0.02; tibia: r = -0.73, P < 0.01) and HD (skin: r = -0.60, P = 0.04; tibia: r = -0.76, P < 0.01). CONCLUSION: Tissue sodium concentrations, measured by 23Na MRI, increase in HD and PD patients and may be associated with adverse metabolic effects in CKD and dialysis.

Defining CT Perfusion Thresholds for Infarction in the Golden Hour and With Ultra-Early Reperfusion.

In this brief report, computed tomography perfusion (CTP) thresholds predicting follow-up infarction in patients presenting 20 to 23 seconds and cerebral blood flow <5 to 7 ml/min-1/(100 g)-1 or relative cerebral blood flow <0.14 to 0.20 optimally predicted the final infarct. These thresholds are stricter than published thresholds.

Use of Noncontrast Computed Tomography and Computed Tomographic Perfusion in Predicting Intracerebral Hemorrhage After Intravenous Alteplase Therapy.

BACKGROUND AND PURPOSE: Intracerebral hemorrhage is a feared complication of intravenous alteplase therapy in patients with acute ischemic stroke. We explore the use of multimodal computed tomography in predicting this complication. METHODS: All patients were administered intravenous alteplase with/without intra-arterial therapy. An age- and sex-matched case-control design with classic and conditional logistic regression techniques was chosen for analyses. Outcome was parenchymal hemorrhage on 24- to 48-hour imaging. Exposure variables were imaging (noncontrast computed tomography hypoattenuation degree, relative volume of very low cerebral blood volume, relative volume of cerebral blood flow ≤7 mL/min·per 100 g, relative volume of Tmax ≥16 s with all volumes standardized to z axis coverage, mean permeability surface area product values within Tmax ≥8 s volume, and mean permeability surface area product values within ipsilesional hemisphere) and clinical variables (NIHSS [National Institutes of Health Stroke Scale], onset to imaging time, baseline systolic blood pressure, blood glucose, serum creatinine, treatment type, and reperfusion status). RESULTS: One-hundred eighteen subjects (22 patients with parenchymal hemorrhage versus 96 without, median baseline NIHSS score of 15) were included in the final analysis. In multivariable regression, noncontrast computed tomography hypoattenuation grade (P<0.006) and computerized tomography perfusion white matter relative volume of very low cerebral blood volume (P=0.04) were the only significant variables associated with parenchymal hemorrhage on follow-up imaging (area under the curve, 0.73; 95% confidence interval, 0.63-0.83). Interrater reliability for noncontrast computed tomography hypoattenuation grade was moderate (κ=0.6). CONCLUSIONS: Baseline hypoattenuation on noncontrast computed tomography and very low cerebral blood volume on computerized tomography perfusion are associated with development of parenchymal hemorrhage in patients with acute ischemic stroke receiving intravenous alteplase.

Non-invasive intradialytic percutaneous perfusion monitoring: a view to the heart through the skin.

Introduction: The life-sustaining treatment of hemodialysis (HD) induces recurrent and cumulative systemic circulatory stress resulting in cardiovascular injury. These recurrent insults compound preexisting cardiovascular sequalae leading to the development of myocardial injury and resulting in extremely high morbidity/mortality. This is largely a consequence of challenged microcirculatory flow within the myocardium (evidenced by detailed imaging-based studies). Currently, monitoring during HD is performed at the macrovascular level. Non-invasive monitoring of organ perfusion would allow the detection and therapeutic amelioration of this pathophysiological response to HD. Non-invasive percutaneous perfusion monitoring of the skin (using photoplethysmography-PPG) has been shown to be predictive of HD-induced myocardial stunning (a consequence of segmental ischemia). In this study, we extended these observations to include a dynamic assessment of skin perfusion during HD compared with directly measured myocardial perfusion during dialysis and cardiac contractile function. Methods: We evaluated the intradialytic microcirculatory response in 12 patients receiving conventional HD treatments using continuous percutaneous perfusion monitoring throughout HD. Cardiac echocardiography was performed prior to the initiation of HD, and again at peak-HD stress, to assess the development of regional wall motion abnormalities (RWMAs). Myocardial perfusion imaging was obtained at the same timepoints (pre-HD and peak-HD stress), utilizing intravenous administered contrast and a computerized tomography (CT)-based method. Intradialytic changes in pulse strength (derived from PPG) were compared with the development of HD-induced RWMAs (indicative of myocardial stunning) and changes in myocardial perfusion. Results: We found an association between the lowest pulse strength reduction (PPG) and the development of RWMAs (p = 0.03) and also with changes in global myocardial perfusion (CT) (p = 0.05). Ultrafiltration rate (mL/kg/hour) was a significant driver of HD-induced circulatory stress [(associated with the greatest pulse strength reduction (p = 0.01), a reduction in global myocardial perfusion (p = 0.001), and the development of RWMAs (p = 0.03)]. Discussion: Percutaneous perfusion monitoring using PPG is a useful method of assessing intradialytic hemodynamic stability and HD-induced circulatory stress. The information generated at the microcirculatory level of the skin is reflective of direct measures of myocardial perfusion and the development of HD-induced myocardial stunning. This approach for the detection and management of HD-induced cardiac injury warrants additional evaluation.

Therapeutic Hypothermia Reduces Peritoneal Dialysis Induced Myocardial Blood Flow Heterogeneity and Arrhythmia.

Background: Moderate therapeutic hypothermia (TH) is a well-recognized cardio-protective strategy. The instillation of fluid into the peritoneum provides an opportunity to deliver moderate hypothermia as primary prevention against cardiovascular events. We aimed to to investigate both cardiac perfusion consequences (overall blood flow and detailed assessment of perfusion heterogeneity) and subsequently simulate the associated arrhythmic risk for patients undergoing peritoneal dialysis (PD) induced TH. Methods: Patients underwent high resolution myocardial perfusion scanning using high resolution 256 slice CT scanning, at rest and with adenosine stress. The first visit using the patient's usual PD regimen, on the second visit the same regime was utilized but with cooled peritoneal dialysate at 32°C. Myocardial blood flow (MBF) was quantified from generated perfusion maps, reconstructed in 3D. MBF heterogeneity was assessed by fractal dimension (FD) measurement on the 3D left ventricular reconstruction. Arrhythmogenicity was quantified from a sophisticated computational simulation using a multi-scale human 3D ventricle wedge electrophysiological computational model. Results: We studied 7 PD patients, mean age of 60 ± 7 and mean vintage dialysis of 23.6 ± 17.6 months. There were no significant different in overall segmental MBF between normothermic condition (NT) and TH. MBF heterogeneity was significantly decreased (-14%, p = 0.03) at rest and after stress (-14%, p = 0.03) when cooling was applied. Computational simulation showed that TH allowed a normalization of action potential, QT duration and T wave. Conclusion: TH-PD results in moderate hypothermia leading to a reduction in perfusion heterogeneity and simulated risk of non-terminating malignant ventricular arrhythmias.