Intradialytic Cardiac Magnetic Resonance Imaging to Assess Cardiovascular Responses in a Short-Term Trial of Hemodiafiltration and Hemodialysis

Abstract

Hemodynamic stress during hemodialysis (HD) results in recurrent segmental ischemic injury (myocardial stunning) that drives cumulative cardiac damage. We performed a fully comprehensive study of the cardiovascular effect of dialysis sessions using intradialytic cardiac magnetic resonance imaging (MRI) to examine the comparative acute effects of standard HD versus hemodiafiltration (HDF) in stable patients. We randomly allocated 12 patients on HD (ages 32-72 years old) to either HD or HDF. Patients were stabilized on a modality for 2 weeks before undergoing serial cardiac MRI assessment during dialysis. Patients then crossed over to the other modality and were rescanned after 2 weeks. Cardiac MRI measurements included cardiac index, stroke volume index, global and regional contractile function (myocardial strain), coronary artery flow, and myocardial perfusion. Patients had mean±SEM ultrafiltration rates of 3.8±2.9 ml/kg per hour during HD and 4.4±2.5 ml/kg per hour during HDF (P=0.29), and both modalities provided a similar degree of cooling. All measures of systolic contractile function fell during HD and HDF, with partial recovery after dialysis. All patients experienced some degree of segmental left ventricular dysfunction, with severity proportional to ultrafiltration rate and BP reduction. Myocardial perfusion decreased significantly during HD and HDF. Treatment modality did not influence any of the cardiovascular responses to dialysis. In conclusion, in this randomized, crossover study, there was no significant difference in the cardiovascular response to HDF or HD with cooled dialysate as assessed with intradialytic MRI.

Keywords: cardiac MRI; hemodiafiltration; hemodialysis; myocardial stunning; randomized controlled trials.

Figure 1.

BP and cardiovascular responses predialysis, during dialysis, and postdialysis for HD and HDF treatments. (A) SBP and diastolic BP (DBP) data. (B) SVI and CI measured using PC-MRI of aortic flow shows a significant decrease during dialysis, reaching a nadir after 230 minutes and partial recovery at 50 minutes postdialysis. (C) IVC flux shows a decrease during dialysis and recovery after treatment. Heart rate did not change significantly throughout either dialysis treatment. *However, at 240 minutes, it was significantly different between HD and HDF (P<0.05).

Figure 2.

HD and HDF result in cardiac stunning to the same degree. (A, i) Whole–wall short–axis circumferential strain and (A, ii) whole–wall longitudinal strain. Strain is seen to decrease (i.e., become less negative, indicating less strain) during dialysis and subsequently return to baseline 70 minutes postdialysis. (B, i) Number of dysfunctional segments in the short axis and (B, ii) number of dysfunctional segments in the long axis at time points during HD or HDF. Dysfunctional segments (>20% reduction in strain from baseline) are evident from 70 minutes and then, decrease but do not return to baseline after treatment. There were no differences in number of dysfunctional segments between HD and HDF at any time point (repeated measures ANOVA across the five time points and between treatments). However, on performing a paired t test, a significant difference was seen between the two treatments at 70 minutes postdialysis (P=0.01).*

Figure 3.

No differences in effect of HD or HDF on myocardial perfusion. Baseline perfusion and nadir perfusion during dialysis for both HD and HDF. Significant decrease in perfusion is seen for both treatment modalities.

Figure 4.

No significant differences in effect of HD or HDF on relationship between circulatory stress and cardiac response. (A, i) A positive correlation between number of dysfunctional LV segments in the long axis and UFV for HD (r=0.70, P=0.02) and HDF (r=0.59, P=0.05). (A, ii) A negative correlation between change in SVI during dialysis and UFV (r=−0.813, P=0.01 for HD and r=−0.838, P=0.01 for HDF). (A, iii) A negative correlation between change in CI during dialysis and UFV (r=−0.831, P<0.001 for HD and r=−0.845, P=0.01 for HDF). (B, i) A negative correlation between change in SVI during dialysis and number of dysfunctional LV segments (r=−0.720, P=0.01 for HD and r=−0.698, P=0.02 for HDF). (B, ii) A negative correlation between change in CI during dialysis and number of dysfunctional LV segments (r=−0.502, P>0.10 for HD and r=−0.716, P=0.02 for HDF). (B, iii) A negative correlation between minimum SBP and number of dysfunctional LV segments was found for HD (r=−0.8, P<0.001) but not HDF. LA, long axis; SA, short axis.

Figure 5.

Schematic representation of study design and delivery. (A) Crossover, randomized, controlled trial design. Patients were randomized to HD or HDF for 2 weeks, after which they attended a cardiac MRI scan that was performed before, during, and after a dialysis session. Thereafter, participants switched to the other treatment for another 2 weeks, after which cardiac MRI assessment was again performed. (B) Details of cardiac MR scan sessions are shown, with the timing of the acquisition of each of the multiple MRI measures of cardiac structure and function that were collected in each 50-minute MR scan session. PCA, phase contrast angiography.