Hello

This message forwarded on behalf of David Sackett, who has signed off for
a few days.

The CAT can be found in our CATbank, at:

http://cebm.jr2.ox.ac.uk/cats/atrial_fibrillation_stroke_warfarin_rx.html

Replies to me will be forwarded to Prof Sackett.

cheers

Douglas Badenoch

---------- Forwarded message ----------
Date: Thu, 22 Oct 1998 10:08:02 +0100 (GMT Daylight Time)
From: Dave Sackett <[log in to unmask]>
To: Douglas Badenoch <[log in to unmask]>
Subject: Rejected [non-member submission] Re: 86 yr old with AF (fwd)


although there's a more recent review (that is simply a dichotomy of low
and high risks), the sources we use on my service [see the CAT at the
above URL] is a combo of:
a.	the placebo group in the SPAF (Stroke Prevention in Atrial
Fibrillation) Trial1; so that they would get an estimate of the risks
without treatment.
  b.	the average efficacy from warfarin (Relative Risk Reduction of
about 80% from both the SPAF2 and BATAF3 [Boston Area Anticoagulation
Trial for Atrial Fibrillation] trials).
  c.	the pooled estimate of the efficacy of aspirin from the SPAF
(RRR=42%) and Scandinavian4 (RRR=16%) trials (Relative Risk Reduction of
about 35%).

they are taken from:
1. SPAF Investigators: Predictors of thromboembolism in atrial
fibrillation:
I. Clinical features in patients at risk. Ann Intern Med 1992:116:1-5.
	SPAF Investigators: Predictors of thromboembolism in atrial
fibrillation: II. Echocardiographic features in patients at risk. Ann
Intern Med 1992:116:6-12.
2.	SPAF Investigators: Preliminary report of the SPAF study. NEJM
1990;322:863-8.
	SPAF Investigators: Stroke prevention in atrial fibrillation:
final results. Circulation 1991;84:527-39.
3.	The BATAF Investigators: The effect of low-dose warfarin on the
risk of stroke in patients with non-rheumatic atrial fibrillation. NEJM
1990;323:1505-11.
4.	Petersen P, Boysen G: Prevention of stroke in atrial fibrillation.
NEJM 1990;323:482.

for control event rates for stroke (almost all the emboli we detect are
strokes) we determine their annual risk (CER) based on:

     Clinical Features:
	  i.	hypertension? (BP >160 and/or >90 or chronic Rx)
	 ii.	heart failure within 100 days? (orthopnea, dyspnea on
exertion or edema responding to diuretics; S3 gallop + rales; CXR
cardiomegaly or redistribution; or elevated LV or wedge at
catheterization)
	iii.	prior arterial thromboembolism? (ischemic stroke of any
cause, TIA, or systemic embolism)

     Echocardiographic Features:
	  i.	Global left ventricular dysfunction
	 ii.	Left atrial size >2.5 cm/m2 by M-mode

and based on these we can estimate the CER for stroke in the next year to
lie between 1% and 19%; coupling this with our best guess at the ARR from
warfarin (RRR of 67% doesn't seem to change in any humanly important way
over different risk groups) at each of these levels, we get NNTs to
prevent 1 more stroke at one year of 286 to 16. 


then we try to extimate the risk of serious haemorrhage (bad enough to
require admission and transfusion).  this varies widely from 1% (NNH 100)
in careful trials to 5% (NNH 20) in frail elderly

then the recent work of sharon straus (not for publication, please!) takes
over:
1. we describe the typical stroke and the typical bleed to our patient and
ask them to tell us how severe the bleed is compared to the stroke.  the
median figure on our in-pt medical service is about 0.2. (we usually do
this twice (one day apart), so that they can ruminate on it, discuss it
with family members, etc) 

2. we then incorporate (at the bedside, so that they can see what we're up
to) their own beliefs about severity into the likelihood of helping vs.
harming them (LHH).  this can be expressed as: 
 
	 ARR for stroke vs. ARI for bleed x their personal severity 

3. if the LHH is >1, we ask them if this benefit is worth the hassel of
taking warf, having INRs done, etc (if it's not, we suggest aspirin, but
our best guess at its RRR is 35%, so the LHH falls)

4. then we discuss all this, plus our recommendation, with their GP on the
phone, since she knows tehm better than we ever will and is the one who
will have to juggle the warf and follow the INRs! 

to our pleasant surprise, both oxford and toronto patients can do this as
long as they're of clear mind.

sorry for the long explanation (folks confused by the jargon can visit
the glossary on our website), but hope it's helpful.

cheers
dls

ps: i'm off to oz and canada, so i'm signing off the ebh discussion list
until mid november.  folks who find errors in the stuff above, or have
additional questions about it, should communicate with sharon straus at:

[log in to unmask]


............................................................................
Prof David L. Sackett
Director, NHS R&D Centre for Evidence-Based Medicine
Consultant in Medicine                    Editor, Evidence-Based Medicine
Nuffield Department of Medicine,          University of Oxford
Level 5, John Radcliffe Hospital,         Oxford OX3 9DU, England
Phone: +44-(0)1865-221320                 Fax:  +44-(0)1865 222901
Email: [log in to unmask]          WWW:  http://cebm.jr2.ox.ac.uk
............................................................................


On Wed, 21 Oct 1998, Huw Thomas wrote:

> I need to do a risk assessment - 86 year old with Af and valvular heart
> disease - 
> 
> warfarin ?? Pro's and cons Can anyone point me at some good resources?
> Last minute tutorial stuff again!!!
> 
> Huw thomas
> 
> GP Somerset UK
> -- 
> Huw Thomas
>