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.