Ethnic and gender differences in electrocardiographic QT length and QT dispersion in hypertensive subjects

Background: Prolonged QT intervals and/or increased QT dispersion (QT(d)) a re associated with various pathological conditions and predict death in hea lthy individuals. Among hypertensives, QT(d) correlates with blood pressure (BP) and left ventricular mass index (LVMI) and QT intervals are prolonged in those with left ventricular hypertrophy (LVH), In normotensives, heart- rate corrected QT length (QT(c)) is longer in females than males, but QT(d) is greater in males than females. There are few data comparing QT paramete rs between different ethnic groups and none specifically in hypertensives. Among normotensives, compared with whites, QT(c) is reported to be shorter in African-Americans and longer in Chinese. We looked for ethnic and gender differences in QT parameters in hypertensive subjects. Methods: Untreated hypertensives were selected from a Hypertension Clinic d atabase, Black and white subjects were matched for age, sex, BP and LVMI, M ale and female subjects were matched for age, race, BP and the presence or absence of echocardiographic LVH. Maximum QT intervals (QT(m)), rate-correc ted maximum QT intervals (QT(c)) and QT dispersion (QT(d)) were measured or calculated from ECGs, Data are presented as mean +/- s,d. Differences in Q T parameters were sought between groups using Student's t-tests, Results: No ethnic or gender differences in QT parameters achieved statisti cal significance. However there was a tendency for QT(m) and QT(c) to be pr olonged in blacks compared with whites (443 +/- 52 vs 421 +/- 47; P = 0.08 and 480 +/- 65 vs 463 +/- 40: P = 0.24 respectively), and for QTc to be pro longed in females compared with males (479 +/- 52 vs 461 +/- 45 ms; P = 0.1 3). Conclusion: In small groups of matched hypertensives, no ethnic or gender d ifferences in QT parameters achieved statistical significance. However, sim ilar to findings in normotensives, QT(c) tended to be longer in hypertensiv e females than males. In hypertensives, we failed to confirm the finding th at QT(c) is shorter in blacks than whites, as seen in US normotensives. Whe ther this represents a difference between hypertensives and normotensives, or between US and UK blacks requires further investigation. Whether the pro gnostic significance of QT parameters in hypertensives differs between diff erent gender and ethnic groups needs to be established from prospective stu dies.