All concepts, explanations, trials, and studies have been
re-written in plain English and may contain errors. I am
not a doctor
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TWA and CHF

TWA means T-Wave Alternans. TWA is a beat-to-beat change
in the T wave of an EKG. A standard EKG can't detect
these small changes so special sensors are used, much like
regular EKG sensors stuck to your chest.
	TWA testing requires gradually raising your heart
rate to 105 to 120 BPM (beats per minute). This means
either doing it during an exercise stress test or using
a pacemaker to raise heart rate.
	TWA results are reported as the number of standard
deviations by which the peak signal of the T-wave exceeds
background noise. This number is called the "alternans
ratio." An alternans ratio of 3 or more is usually called
a positive result; an absent alternans ratio is called a
negative result; and anything in between is indeterminate.
	This is really a measure of how prone you are to
having irregular heart rhythms. TWA changes as heart rate
changes.
	TWA predicts whether tachycardia may happen. TWA
seems to predict this in patients with CAD (coronary
artery disease), nonischemic cardiomyopathy, and CHF.

There have been a series of studies on TWA testing, using
different patient groups. Early results from one TWA study
show that in CHFers, TWA predicts mortality regardless of
EF or cause of heart failure.
	Perhaps TWA can identify high-risk patients who
need therapy to prevent SCD (sudden cardiac death). In
patients who fit the MADIT trial's standards for ICD
implant, TWA testing might show who does *NOT* need an
ICD.
	Study patients were all over 18 years of age; in
sinus (normal) heart rhythm; and had an EF less than 41%.
	Patients with a past arrhythmic event, class 4
CHF, unstable CAD, or persistent a-fib were not included.
All patients did exercise testing, during which they
stayed on their meds, including beta-blockers. Patients
also had 24-hour Holter monitoring. Follow-up was done
every 4 months by telephone.
	TWA results were interpreted using these rules:

Positive:      sustained TWA greater than 1.8 muV with
               starting at a heart rate less than 111
               BPM.
Negative:      maximum negative heart rate greater than
               104 BPM.
Indeterminate: all others.

Primary endpoint was arrhythmic death or nonfatal
cardiac arrest. All-cause mortality was also tracked.
	TWA data were available on 542 patients, 71% male,
47% with ischemic cardiomyopathy; most had nonischemic
cardiomyopathy. Average EF was 25% and most were class 2
(52%) or class 3 (28%). Thirty percent had diabetes, 43%
had suffered a past heart attack, 26% had gone through
bypass surgery, and 59% had been in the hospital for CHF
at least once. Most patients were on beta-blockers (78%)
and ACE inhibitors (92%).
	TWA results were:

30% positive;
34% negative;
36% indeterminate.

Many of the indeterminate results were because of lots of
PVCs during testing. Such patients are now known to be at
high risk.
	At one-year follow-up, there were 20 deaths (all-
cause) and the 2-year survival rate was 93%. Two-year
mortality rates were 1% in patients with a negative TWA
test, 11% in patients with a positive test, and 9% in
patients with an indeterminate test. There were 10 deaths
among the indeterminate patients, and 8 in patients with
lots of PVCs during exercise testing.
	Analysis showed that patients with a positive TWA
test were almost 10 times more likely to die than those
with a negative TWA test. After adjusting for EF, TWA
still predicted mortality risk whether EF was over or
under 30%.
	EF did not predict mortality after adjusting for
TWA results.