Wednesday, July 30, 2014

Topic Discussion: Stones: HEART of the MATTER

Last year, a prospective study was published in JAMA suggesting that having a history of kidney stones as an independent risk factor for cardiac disease (CHD). 
            In short, this was a prospective study of 45748 men and 196357 women in the United States without a history of CHD at baseline who were participants in the three study cohort registries. Coronary heart disease was defined as fatal or nonfatal myocardial infarction (MI) or coronary revascularization. The outcome was identified by biennial questionnaires and confirmed through review of medical records.
            Of a total of over 240,000 participants, over 19,000 reported a history of kidney stones. After up to 24 years of follow-up in men and 18 years in women, 16838 incident cases of CHD occurred. After adjusting for all confounders, amongst the 2 cohorts of women, a history of kidney stones was associated with a modest but statistically significantly increased risk of CHD; there was no significant association in a separate cohort of men.
The knowledge of history of kidney stones was obtained via an independently validated survey.
When looking at the covariates, most risk variants of both formation of kidney stones and CHD were evaluated and controlled for.

Why this risk?

1.    CHD and stone formers share the same risk factors- obesity, metabolic syndrome, DMII, HTN, high lipids but when controlled for all this, the risk of getting CHD was independently associated with history of stones
2.    Perhaps common dietary factors- sugary drinks, low calcium diet, high protein diet, but dietary adjustments were also made in the study.
3.    One adjustment that was not made was renal disease. Stone formers can perhaps have CKD and CKD becomes then a CHD risk factor.  This was not analyzed per authors in the manuscript.
What is the mechanism?
1.    Perhaps there is a unknown metabolic state that is both a risk factor for stones and CHD
2.    The stone might increase some other factor that we don’t know that leads to CHD
3.    There might be some other confounding factor we haven’t found.

Why Women: - No clear explanation can be found, perhaps an unknown factor that is not clear yet.
Major limitations: Self reported questionnaire, stone analysis not clear, most patients were white and not many blacks, Asians or Hispanics.

Very fascinating study but leaves us with more questions than answers.  At this point, would not make any major statements based on this observational study re risk of cardiac disease and stones.

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