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

Abstract

Background: Prolonged QT intervals and/or increased QT dispersion (QT_d) are associated with various pathological conditions and predict death in healthy 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 parameters 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 database. Black and white subjects were matched for age, sex, BP and LVMI. Male and female subjects were matched for age, race, BP and the presence or absence of echocardiographic LVH. Maximum QT intervals (QT_m), rate-corrected 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 QT parameters were sought between groups using Student’s t-tests.

Results: No ethnic or gender differences in QT parameters achieved statistical significance. However there was a tendency for QT_m and QT_c to be prolonged 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 prolonged in females compared with males (479 ± 52 vs 461 ± 45 ms; P= 0.13).

Conclusion: In small groups of matched hypertensives, no ethnic or gender differences in QT parameters achieved statistical significance. However, similar to findings in normotensives, QT_c tended to be longer in hypertensive females than males. In hypertensives, we failed to confirm the finding that QT_c is shorter in blacks than whites, as seen in US normotensives. Whether this represents a difference between hypertensives and normotensives, or between US and UK blacks requires further investigation. Whether the prognostic significance of QT parameters in hypertensives differs between different gender and ethnic groups needs to be established from prospective studies.