What’s new in Potassium: sudden cardiac death

As the Nephrology Fellow Network recently covered the etiology of cardiovascular disease in dialyzors is unique from the general public. Use of statins, the foundation of preventative cardiology, has repeatedly failed to prevent cardiovascular vascular disease (CVD) among dialyzors. One reason for this, is the propensity for these patients to die of sudden cardiac death (a lethal heart rhythm requiring a shock of electricity or luck to reverse) rather than acute myocardial infarction (heart attacks). In this study (PDF), from Italy, the investigators found that nearly half of the cardiovascular deaths were due to sudden cardiac death (SCD). The authors retrospectively looked at their data to find risk factors for SCD.

They prospectively looked at 476 patients in 5 Italian hemodialysis units. The cohort was tracked for 3 years and had 167 deaths (35%), 32 due to SCD and 35 due to other CVD. On multivariate analysis they found the following risk factors for SCD:
As important as what was significant, is what was not significant. Left ventricular hypertrophy, heart failure and valvular heart disease, all important risk factors for SCD among non-dialysis patients were not associated with SCD in their cohort.

The most interesting analysis was when they parsed out the day of the week the patients died of SCD. Instead of looking at the absolute day they related the day to the patients dialysis schedule. I have modifed their chart to reflect this, with twin X-axis: one for MWF and another for TTS patients.
The red line indicates how high the bars would be if there was no relationship to the dialysis schedule. The highest risk periods were the 24 hours before dialysis at the beginning of the week and the 24 hours after the dialysis at the beginning of the week. Not dialyzing for the two days over the week-end put patients at risk for SCD both before and after subsequent dialysis.

This sounds like an electrolyte associated complication rather than a uremic toxin because of the risk after dialysis, indicating the change in the toxin, not just the high level, is a risk-factor. This is supported by studies (1, 2) of potassium modeling in which the potassium in the dialysate is lowered sequentially during dialysis. By modeling the potassium, the speed of potassium removal is decreased. This has been shown to decrease pre-mature ventricular contractions (a benign momentary disturbance in the heart rhythm that is being used as a proxy for more serious arhythmias, like SCD. Medicine has gotten in trouble with this proxy in the past so it may not be appropriate.).

Summary: modestly high potassiums are associated increased SCD and the two day dialysis holiday on traditional three day a week dialysis is likewise associated with SCD. Hello daily dialysis!

The lecture on Potassium that this entry was drawn from:

2 Replies to “What’s new in Potassium: sudden cardiac death”

  1. Very interesting graph (showing SCD rate by day of the week in dialysis patients)–I hadn’t seen this before. I agree, it would seem to make the case for more frequent dialysis (either daily dialysis or 4x/week).

    What’s also surprising to me is the spike in SCD rate immediately AFTER the Monday dialysis treatment. The issue of fluctuating potassium levels in dialysis patients is an interesting one and the management of potassium baths on dialysis appears to be driven more by institutional tradition than actual data.

  2. I think Nathan is right that this data supports more frequent dialysis. However, it is tough to organize 4 time a week treatments for more than a few dialyzors without operating the clinic 7 days a week. That being the case why not simply offer every other day dialysis?

    This petition asks that CMS reimburse 183 treatments a year without medical justification. Right now the policy of routinely reimbursing 156 treatments mandates that people go two days without dialysis.

    The only way two days off makes economic sense to the payer (Medicare) is if you include the X factor that it is cheaper for people to die of SCD then continue on dialysis. Aside from that grim and immoral calculus, I am unable to think of a clinical OR economic justification for the mandatory two days off policy.

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