Vivek Rai, MD
The elastic component of arteries decreases with age and the consequent loss of elasticity results in hemodynamic changes, which are thought to be involved in pathogenesis of vascular diseases. Brachial-ankle pulse wave velocity (baPWV) is a recently developed automated tool for measurement of arterial elasticity used as an alternative to carotid-femoral pulse wave velocity (current gold standard). Carotid-femoral pulse wave velocity (cfPWV) and baPWV have been validated to produce reliable results and a high cfPWV is related to worse functional outcomes after stroke. The authors investigated whether baPWV can also be used as prognostic marker of recovery after stroke.
Kim et al analyzed data from1091 consecutive patients with first-ever acute cerebral infarction who underwent baPWV measurements. Poor functional outcomes were defined as modified Rankin Scale score of >2 at 3 months after stroke onset. The authors report that 181 (16.59%) patients had a poor functional outcome and the patients in the highest tertile of baPWV (>22.25 m/sec) were at an increased risk for poor functional outcome (adjusted OR, 1.88) compared to those in the lowest tertile (<17.55 m/sec). No significant interaction between baPWV and stroke subtype was noted.
The authors have shown that baPWV can be used as a simple, non-invasive marker for identification of patients at risk for poor recovery after stroke, regardless of stroke subtype according to TOAST criteria. In previous studies, increased baPWV and cfPWV were found to be independent predictors of new vascular events and cardiovascular mortality. It remains to be shown whether there is any causal effect to this association. Therapeutic interventions aimed at reducing progression of arterial stiffness may reduce stroke incidence and may even help in recovery after stroke. Further studies are necessary to prove these hypothesized benefits. Till then, in my view, the clinical application of this novel tool remains limited.
Why are we using secondary markers to prognosticate recovery from stroke? Wouldn't it make much more sense to use objective criteria like scans that measure the dead area in 3 dimensions? And the penumbra in 3 dimensions? Then you could have a direct correlation between observed deficits and either the damaged or dead area.
There are numerous studies of CT- and MRI-based volume-mismatch (which I think you're referring to) which provide useful information and continue to grow in sophistication but we do not as yet have a clear "good or bad" outcome threshold that can inform prognosis in all patients, especially since most of those studies focus primarily on the most ill patients, so their findings cannot necessarily be extrapolated to mild strokes.
It is important to know that there may never be such a scan that can answer this definitively because symptoms and level of disability vary widely between patients, even those with strokes of similar size and location.
It is also important to know that associational biomarkers like this, while not exquisitely elegant in letting us know what is happening to the injured area of brain and how it might recover, can provide very valuable information that we need to effectively counsel and make recommendations.
Your point is well taken, and we all wish it was as simple as you suggest, but for now it isn't. Here's to hoping this opinion is out-dated soon!