Replies to post #49554 on Biotech Values

[lumpy9200]

CAMH

Urche, I believe you failed to BOLD Text the most important part of that article. Here's my emphasis:


Apples and oranges?
In the analysis of 286 adult patients with an LVEF <35% referred for EP testing due to NSVT or syncope, TWA testing was performed during atrial pacing in the course of a standard EP study. The technique differs from the more traditional approach of noninvasive TWA testing during exercise stress, complicating comparisons of the current TWA study with most others.

Iwai observed that there is support in the literature for both forms of TWA testing in risk stratification, although they tend to yield different predictive values. Exercise, unlike atrial pacing performed in an EP lab, greatly alters autonomic tone and catecholamine levels, "so you can't say the ways are comparable, and that's a bit of a limitation in the study."

A bit of a limitation? Much more than that, I would say. This study, using atrial pacing, came up with results that simply do not jive with all the studies conducted using the traditional method of exercise to get heartbeat up to 109 BPM.

Best regards,
Geoff

[lumpy9200]

CAMH

Here is the accompanying editorial in JACC on the MTWA article:

"...Without adjustment for potential confounders, a negative TWA result significantly predicted arrhythmia-free survival, with a hazard ratio (HR) of 2.33 (p<0.01) compared with only 1.27 (p=0.21) for a negative EP study. The HR for TWA testing remained significant in an analysis that controlled for age, sex, QRS duration, LVEF, NYHA class, ischemic vs nonischemic etiology, and subsequent ICD implantation.

In an accompanying editorial, Dr Thomas Klingenheben (JW Goethe University, Frankfurt, Germany) points out that EP testing has different predictive values in ischemic and nonischemic cardiomyopathy [2]. So findings based on the current study's mix of etiologies—in 75% and 25% proportions, respectively—don't necessarily apply to the majority of ICD candidates, who have ischemic disease.

For that group, Klingenheben notes, there are data from the Alternans Before Cardioverter-Defibrillator (ABCD) trial, which compared noninvasive TWA with EP studies in patients with ischemic disease, NSVT, no prior ventricular tachyarrhythmias, and an LVEF <40%. ABCD was presented at the American Heart Association 2006 Scientific Sessions and reported by heartwire at the time.

"In that study, both tests were equivalent in predicting appropriate ICD shocks or arrhythmic death, and their negative predictive values were 95%, rising to 98% if both tests were combined," Klingenheben notes. Those numbers are much higher than the 79% negative predictive value observed for TWA testing in the current study's ischemic patients, who had additional risk factors, he observes. "Putting the currently available studies of microvolt TWA in LV dysfunction in perspective, it can be concluded that the predictive efficacy of the test is largely dependent on the patient population studied."