Background/Purpose:

Early cardiovascular disease is an important cause of mortality in SLE. Previous studies have shown that lupus nephritis (LN) was associated with an increased risk of cardiovascular events in SLE patients. The primary aim of the present study was to assess the role of nephritis in mortality of SLE patients hospitalized with acute myocardial infarction (AMI) in a nationally representative sample.

Methods:

We used data from the National Inpatient Sample (NIS) for the period 2005-2015 with adult AMI as a primary diagnosis and SLE, nephritis, chronic kidney disease (CKD) and end-stage renal disease (ESRD) as secondary diagnoses using ICD-9 codes. There is no specific ICD-9 code for LN and its classes. The proportion who met ACR classification criteria cannot be determined with the NIS database.

We compared the characteristics of AMI hospitalizations in SLE patients with and without nephritis and used logistic regression to calculate the odds ratios for inpatient mortality from AMI in SLE patients with nephritis. We compared this to AMI in SLE patients with all kidney disease (AKD) (defined as having ESRD or CKD or nephritis) and without kidney disease. AKD in SLE population is most likely due to LN ¹.

Results:

We identified a total of 4810 AMIs from 2005-2015 in patients with SLE. Among these, 245 had a discharge diagnosis of nephritis and 837 had AKD.

AMI hospitalizations with SLE and nephritis were younger (50.3 vs. 61.3 years; p<0.01) with a higher proportion of males (24.9% vs. 19%; p<0.05) and a higher proportion of African-Americans (36.7% vs. 22.3%; p<0.01) compared to patients with SLE without nephritis. The findings for SLE and AKD were similar: younger and with a higher proportion of males and African-Americans. The findings are summarized in the table.

The unadjusted inpatient mortality from AMI in SLE and nephritis was not statistically different from that in SLE patients without nephritis, even after adjusting for age, gender, race, comorbidities and invasive cardiac procedures (aOR=1.28; 95% CI=0.5-2.7; p=0.52). The adjusted odds-ratio for inpatient mortality from AMI in SLE and AKD, however, was 1.84 (95% CI=1.27-2.67; p<0.01).

Conclusion:

Patients with SLE and nephritis presented with AMI at a younger age compared to patients with SLE and no nephritis. The former group of SLE patients did not have a statistically different inpatient mortality due to AMI. However, AMI hospitalizations with SLE and AKD were associated with an increased probability of inpatient mortality compared to the ones with SLE and no kidney disease. Given that the most kidney diseases in SLE patients appear to be related to LN ¹, this study suggests that LN is an independent risk factor for inpatient mortality due to AMI.

Reference:

1. Plantinga LC, Drenkard C, Pastan SO, et al. Attribution of cause of end-stage renal disease among patients with systemic lupus erythematosus: the Georgia Lupus Registry. Lupus Sci Med. 2016; 3(1): e000132.