To study clinical significance and possible mechanism of negative U-wave observed in hypertensive patients, we applied handgrip test (HG) to 35 patients with hypertension and 20 age-matched normal subjects. HG was sustained for 3min at 50% of maximum voluntary contraction. ECG recording and measurement of blood pressure were made before, during, and after HG.
During HG, systolic blood pressure was 188.7±3.4mmHg (mean±SE) and diastolic blood pressure was 114.8±2.1mmHg in hypertensives, while 145.3±2.6mmHg and 93.8±1.1mmHg in normals; the difference between hypertensives and normals was statistically significant (p<0.001). Incidence of HG-induced negative U-wave was 0% in normals, while 68.6% in hypertensives. In hypertensive subjects, HG-induced negative U-wave appeared in 24 of the 28 patients (85.7%) with minimum to moderate left ventricular hypertrophy, while it was not seen in all 7 patients (0%) with marked left ventricular hypertrophy shown by ECG and/or UCG findings (QRS-T angle>130° with left high voltage: left ventricular wall thickness>12mm). Further we recorded UCG during HG in 14 subjects. In 4 patients, negative U waves appeared simultaneously with increase in left ventricular dimension during diastole. In the remaining 10 cases that included both normals and hypertensives, however, neither increase in left ventricular end diastolic dimension nor negative U waves were observed.
Thus we conclude that HG-induced negative U waves may be caused by stretch of the ventricular wall resulting from acute left ventricular volume overload.