LVMI is a potent indicator of prognosis both in patients with hypertension and those with chronic kidney disease, including those on hemodialysis [1
]. Midwall fractional shortening is a sensitive index of left ventricular systolic function and is also a powerful prognostic marker among hemodialysis patients [9
]. Our study demonstrates that regression of left ventricular mass can be effected by probing dry-weight. However, midwall fractional shortening was not affected. Furthermore, it appears that the reduction in interdialytic systolic blood pressure may be more in those with a higher LVMI. This indicates that, in part, LVMI is indicative of volume overload as reflected by left ventricular chamber dilatation. To support this notion, we found that probing dry-weight reduced left ventricular chamber dilatation, but did not affect left ventricular wall thickness. To the extent this notion is true, increased LVMI among dialysis patients may reflect excess volume. However, the change in echocardiographic LVMI or its components or change in midwall fractional shortening does not appear to predict the blood pressure response to probing dry-weight.
LVMI reduced rapidly – more rapidly than what would be expected in the general population. The reduction in LVMI was most likely due to reduction in left ventricular internal diameter. Due to the geometric assumptions underlying the LVMI calculations, reduction in left ventricular diameter will most likely lead to improvement in LVMI. It is very unlikely that reduction in blood pressure by itself (in the absence of volume correction) would be associated with improvement in LVMI.
It may appear internally inconsistent that a higher LVMI was associated with a greater reduction in interdialytic systolic blood pressure, yet reduction in LVMI was not associated with changes in interdialytic systolic blood pressure. The latter negative finding is likely because our study was not powered adequately to discover a relationship between change in LVMI with probing dry-weight and change in interdialytic systolic blood pressure. On the other hand, it is possible that the association between higher LVMI and greater reduction in interdialytic ambulatory systolic blood pressure may simply be a chance finding. However, given that the relationship between higher LVMI and a greater reduction in systolic blood pressure is physiologically plausible, it is more likely that the former scenario of an underpowered study is more likely.
LVMI, as assessed in this study in the postdialysis state, can be routinely evaluated using standard echocardiographic techniques. Our study found that patients who had a higher LVMI achieved a greater reduction in interdialytic ambulatory systolic blood pressure. Thus, patients on long-term dialysis with hypertension, especially those with a higher LVMI, should have their dry-weight probed as an initial intervention as a way to improve prognosis. On the other hand, midwall fractional shortening, an objective measure of left ventricular systolic function, had no relationship with blood pressure lowering upon probing dry-weight. This finding should not be taken to imply that those with very poor systolic function, who were largely excluded from our study, cannot experience an improvement upon probing dry-weight.
The recently completed and published daily dialysis study of the Frequent Hemodialysis Network demonstrated that daily dialysis was associated with an approximately 10-gram improvement in left ventricular mass and about 10-mm Hg lowering in systolic blood pressure [27
]. The results of our study show an improvement within 8 weeks of a similar magnitude in both left ventricular mass and systolic pressure. It is possible that as in our study, frequent dialysis simply has salutary effects through achieving dry-weight over a period of time. To the extent this is true, probing dry-weight may be a simpler expedient than frequent dialysis to improve outcomes related to volume excess such as heart failure and strokes.
One strength of our study was that certified technicians performed the serial echocardiograms in the dialysis unit using a prespecified study protocol in the context of a randomized trial. Our study does, however, have some limitations. Although the analysis of LVMI was prespecified, patients were not randomized based on LVMI. In the absence of randomization based on LVMI, we cannot establish a cause-and-effect relationship between LVMI and subsequent blood pressure reduction. Before performing echocardiograms, we could have waited longer after dialysis for fluid equilibration to occur. However, this would have made our study less feasible. Finally, there were few non-African-American patients in our study. Whether the results of our study are generalizable to non-African-American patients will need to be demonstrated in future studies.
In conclusion, among chronic hemodialysis patients, LVMI, a powerful indicator of mortality, can be reduced by probing dry-weight. If probing dry-weight is causally related to improvement in LVMI, this simple and effective tool has the potential to improve dismal cardiovascular outcomes. Our study provides another reason why nephrologists should remain vigilant in continuously assessing and managing dry-weight among their long-term dialysis patients.