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:

Not nephrology, Passover

I put together a Haggadah and Coloring book for last night’s seder. Enjoy.

By the way, neat nephrology related passover tid bit in Numbers 11:31-33. You can read about it on page 4 of the handout on this page.

The Topf Haggadah 2009 The Topf Haggadah 2009 jtopf6981

Passover Coloring Book 2009

What’s new with hyperkalemia: EKG changes

Today I did a lecture for the fellows on hyperkalemia. It is interesting that nearly none of the content I use to teach the residents and students is used in a lecture for the fellows. Same subject complete rewrite.

I plan on doing four posts on hyperkalemia from this lecture:

  1. EKG changes
  2. Dialysis patients and hyperkalema
  3. Digoxen toxicity and hyperkalemia
  4. Renal adaptation to ACEi and aldo antagonists in CKD

The lecture started off with the case I blogged about last week with the scary EKG and the potassium of 9.9.

I focused on a well done study (Full Text) by Drs Montague, Ouellette and Buller from Yale. They looked at 90 patients with a potassium grreater than 6 and an EKG done within an hour of the potassium. They excluded hemolyzed specimens and patients with cardiac pacing or other conditions which would mask EKG changes.

They graded all the EKGs according to a prospective criteria and recorded the cardiologists assessment.
The average patient was 73 years old (20-93) and half had acute kidney injury (55%) and half had chronic kidney disease (47%). They did not comment on the degree of overlap between those groups. Half the patients had diabetes (55%). Only 31% were on ACEi and 30% on loop diuretics.

The reading cardiologist documented peaked T waves in only 3 of 90 patients with hyperkalemia. The investigators were able to find peaked T waves in only 29. QRS widening was found in only 6 patients. Of the 52 patients who could have been classified as having “Strict Criteria” (you needed a second EKG after resolution of the hyperkalemia and not everyone in the cohort had a second EKG) only 16 actually met strict criteria.
The authors found EKG criteria to be insensitive predictors of hyperkalemia:

  • Sensitivity of strict criteria: 18%
  • Sensitivity of any EKG change 52%

Interestingly, they found that acidosis decreased the likelihood of finding peaked T-waves.

When they looked at arrhythmias as an outcome, EKG changes continued to be a poor clinical guide. They were not sensitive: only one of the patients who subsequently developed an arrhythmia or cardiac arrest had previously met the strict criteria for EKG changes and only 7 had any T-wave findings at all. This is important because it emphasizes the fact that you can not be reassured by a normal EKG in a patient with hyperkalemia.

The study was unable to look at specificity because all of the patients had hyperkalemia. An earlier study by Wrenn, Slovis and Slovis was able to look at sensitivity and specificity because they did have patients without hyperkalemia in their cohort. They retrospectively reviewed the EKGs of 220 patients with either renal failure (n=133) or hyperkalemia (n=87):

  • Sensitivity: 39%
  • Specificity: 85%

When they restricted the cohort to patients with a potassium over 6.5 the sensitivity rose to 58%.

Take home message: a normal EKG should not rule out hyperkalemia and should not decerase your concearn for impending arrhythmia.

Here is the lecture this post is based on: