Exercise-Induced
Microvolt T-wave Alternans in the Congenital Long QT Syndrome |
Presentation
Time: Tuesday,
1:00 p.m. - 2:00 p.m. |
Kathryn A. Glatter, Michael J. Ackerman, Gioia
Turitto, Nabil El-Sherif, Nitish Badhwar, Richard Hongo, George F. Van Hare,
Matti Viitasalo, Melvin M. Scheinman, University of California, San
Francisco, San Francisco, California, University of California, Davis,
Sacramento, California. |
Presentation
Number: 1186-107 |
Poster
Board Number: 107 |
Keyword:
QT
syndrome-inherited, Risk factors, Diagnosis, computer-assisted, Spectrum
analysis |
Background: Macrovolt T-wave alternans (TWA)
with alternating changes in the T-wave have been described in congenital Long
QT Syndrome (LQTS). However, the presence of microvolt TWA has not been evaluated
systematically in LQTS pts. Methods: We enrolled 67 consecutive LQTS
pts (age = 38 + 16 yrs; 43 F, 64%) from 30 distinct families and 78
unaffected control pts (age = 35 + 11 yrs; 38 F, 49%) in a prospective
exercise study. 20 LQTS pts were taking beta-blocking agents (BB) at time of
study, and 3 had sympathectomy. No controls were taking BB or had coronary
disease. TWA was measured at rest and during bicycle exercise testing (n=67
LQTS) or with atrial pacing (n=18 LQTS pts) by the spectral method using a
CH2000 system (Cambridge Heart, Bedford, MA). If there was sustained
alternans voltage > 1.9 µV and alternans ratio > 3 with
an onset heart rate (HR) <120 beats/min (BPM) during exercise in either 1
orthogonal or 2 adjacent precordial leads for at least one minute which then
persisted above that HR, the test was considered positive ("classic
pattern TWA,’ CP TWA). Max negative HR was defined as the highest interval HR
at which sustained alternans was not present. Onset HR was defined as the HR
above which CP TWA (> 1 minutes) was consistently present. Results:
LQTS pts exercised 7.8 + 2.4 min and achieved a peak HR of 149 +
171 bpm. Control pts exercised 9.6 + 3.3 min and achieved peak HR =
141 + 21 bpm. Study pts reached a peak HR > 105 bpm for at least 1
minute with exercise or atrial pacing. Five LQTS pts (5/67, 7%) had classic
pattern TWA with onset HR of 106 + 5 bpm. One LQTS pts had CP TWA
before and after BB. No control pts (0/75, 0%) demonstrated CP TWA
(p<0.05). We defined transient pattern TWA (TP TWA) as presence of > 1
min microvolt TWA for exercise HR between 105-120 bpm which did not persist
throughout exercise above the onset HR. Nine LQTS pts and 6 control pts had
TP TWA. The max negative HR for LQTS pts was 112 + 8 bpm and for
control pts 121 + 7 bpm (p > 0.05). 14/67 LQTS (21%) vs. 6/78
normals (8%) had either CP TWA or TP TWA (p < 0.02). Conclusions:
(1) The presence of either transient or classic pattern microvolt TWA may be
a new diagnostic tool for LQTS. (2) The classic pattern of microvolt TWA with
bicycle stress testing alone is uncommon in congenital LQTS. |
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