SPARCtool Notes

SPARCtool Notes

Who created SPARCtool?

Peter Loewen, B.Sc.(Pharm), ACPR, Pharm.D., FCSHP. Assistant Professor, Faculty of Pharmaceutical Sciences, University of British Columbia; Pharmacotherapeutic Specialist, Vancouver General Hospital, Vancouver, BC, Canada

Dr. Loewen has no financial or other conflicts of interest related to SPARCtool or the stroke prevention therapy options it does or does not include.

Where do the stroke risk estimates come from?

I read a different paper about CHADS2 or CHA2DS2-VASc and it shows different numbers than SPARCtool. Why?

Every validation study will produce different numbers for thromboembolism risk in every stratum of CHADS2 or CHA2DS2-VASc score. SPARCtool uses data from what is currently the largest and longest-term evaluation of the scores (see above).

HAS-BLED bleeding risk estimation

Where do the efficacy and bleeding risks of the antithrombotic therapies come from?

How are the “population avg.” bleeding risks derived?

The bleeding risks present in the tool are based on the best available population averages from the published literature, and in the tool are fixed based on trials and meta-analyses thereof which are not influenced by the data entered into the tool.

What about paroxysmal (intermittent) atrial fibrillation?

No trials of efficacy of antithrombotic therapy in patients with paroxysmal atrial fibrillation have been conducted. Current antithrombotic therapy guidelines (eg, ACCP 2012 Antithrombotic Therapy Guidelines) suggest treating similarly to chronic atrial fibrillation. In reality, recent evidence here and here indicates stroke risk is probably somewhat proportional to the amount of time the patient is actually in atrial fibrillation, up to the maximums estimated by the CHADS2 system.

Can these ANNUAL risks of stroke be added together to estimate longer-term risks?

Since the risk of stroke in atrial fibrillation is approximately constant over time (ie, your chance of a stroke during each day, week, month, year that you have atrial fib is similar), the annual risk estimate should be approximately cumulative over successive years. The more years you project forward, however, the greater the uncertainty about the risk. This is because the confidence intervals around the annual risk estimates get larger as the risk gets higher (ie, higher CHADS2 scores). For example, in a patient with an estimated 20% per year stroke risk, it would probably not be accurate to state that they have a 100% chance of a stroke within the next 5 years. Hence, for someone with a relatively low annual stroke risk (eg, 4%), I would be comfortable estimating that their 5 year risk is around 20%. For someone with a relatively high annual stroke risk (eg, 18%), I would not be as comfortable saying they have a 90% 5-year stroke risk, although I would be very comfortable saying their risk is between 50% and 100% (using the confidence intervals around a CHADS2 score of 6, which are 10–27%, derived from the original CHADS2 publication).

Renal dysfunction

Why does SPARCtool extend the HAS-BLED bleeding risk to dabigatran, rivaroxaban, apixaban, and edoxaban?

I believe this is reasonable for two reasons: (1) Head-to-head trials so far show major bleeding risk to be similar between warfarin and new oral anticoagulants (RE-LY, ROCKET-AF, ARISTOTLE) and (2) HAS-BLED was validated in a population which included both warfarin and ximelagatran patients in the SPORTIF trials.

Has this system been evaluated in clinical practice?

An earlier version has, yes. Am J Health-Syst Pharm 2003;60:427–9.

Release Notes

version 8.1 release notes (June 2016)


version 8 release notes (June 2016)



version 7 release notes (January 2015)



version 6.21 release notes



version 6.1 release notes