Clinical Investigations Appearance of Electrocardiographic Initial U-Wave Inversion Dependent on Pressure-induced Early Diastolic Impairment in Patients with Hypertension
Address for correspondence: Kunihisa Miwa, MD Department of Internal Medicine Nanto Family and Community Medical Center 577 Matsubara, Nanto, Toyama 939–1518 Japan
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Kunihisa Miwa, MD Department of Internal Medicine, Nanto Family and Community Medical Center, Toyama, Japan
Background: ECG U-wave inversion can be classified as initial and terminal U inversion according to the phasic relationship to positive U-wave deflection. Initial U inversion is occasionally observed in hypertensive patients while terminal U inversion frequently appears during severe myocardial ischemia. Hypothesis: The genesis of initial U inversion may be related to pressure-induced diastolic dysfunction. Methods: To clarify the genesis of initial U-wave inversion, we studied 11 consecutive hypertensive patients with both initial U inversion and impaired left ventricular early relaxation who were evaluated using Doppler echocardiography. Results: The U inversion disappeared during acute pressure lowering by sublingual administration of nitroglycerin. The U inversion also disappeared and relaxation improved significantly after chronic blood pressure lowering. Initial U inversion reappeared during a cold pressor test. Conclusion: The appearance of initial U inversion was dependent on the pressure-induced impaired left ventricular early relaxation in hypertensive patients.
Electrocardiographic (ECG) extra deflection around the end of the obvious repolarization sequence which was named ‘‘U-wave’’ by Einthoven in 1903, is often seen in normal subjects.1 However, the genesis of U-waves is poorly understood and the various hypotheses underlying its origin have been a matter of both controversy and debate.2 The mechanism of negative U-waves or U-wave inversion is also unknown. U-wave inversion with respect to an upright T-wave is of diagnostic importance because the U-wave in normal subjects has the same polarity as the T-wave.3 Previously we have reported that U-wave inversion can be classified as initial and terminal U inversion according to the phasic relationship to positive U-wave deflection (Figure 1).4 The latter is observed in association with regional myocardial ischemia.4 – 6 The former seems to be related to elevated blood pressure rather than to myocardial ischemia.4 However, the genesis of both types of U inversion is uncertain. The hypotheses for U-wave genesis include late repolarization of the Purkinje fibers7,8 and alterations in the normal action potential shape by afterpotentials related to stretching of myocardial fibers by rapid ventricular filling.9,10 Recently several studies attributed U-waves to the late repolarization of M cells, found in the mid-myocardium.11 – 13 It has been suggested that initial U inversion are related to afterpotentials which are most likely generated by mechanoelectric feedback in association with possible impaired relaxation in hypertensive patients that might be Received: January 11, 2008 Accepted with revision: February 10, 2008
modified by afterload reduction.4,9,10 To clarify the genesis of initial U-wave inversion, the relationship between the pressor-induced appearance of initial U inversion and left ventricular (LV) diastolic dysfunction was investigated.
Materials and Methods Study Patients
Among consecutive 131 patients with uncomplicated hypertension (systolic pressure ≥140 mm Hg and/or diastolic pressure ≥90 mm Hg) and normal left ventricular (LV) systolic function, but without massive LV hypertrophy (wall thickness
