BACKGROUND AND PURPOSE:Nonimaging transcranial Doppler sonography (TCD) and imaging TCD (TCDI) are used for determination of the risk of stroke in children with sickle cell disease (SCD). The purpose was to compare angle-corrected, uncorrected TCDI, and TCD blood flow velocities in children with SCD.

The inability to achieve 85% of the maximum predicted heart rate (MPHR) on dobutamine stress echocardiography (DSE) is defined as chronotropic incompetence and is a predictor of major cardiac events after orthotopic liver transplantation (OLT). The majority of patients with end-stage liver disease (ESLD) receive beta-blockers for the prevention of variceal bleeding. In these patients, it is impossible to determine whether chronotropic incompetence is secondary to cirrhosisrelated autonomic dysfunction or is merely a beta-blocker effect. We evaluated the usefulness of the maximum achieved heart rate (MAHR) and the heart rate reserve (HRR) in the detection of chronotropic incompetence in ESLD patients on beta-blocker therapy before DSE. We also evaluated the usefulness of a new index, the modified heart rate reserve (MHRR), in diagnosing chronotropic incompetence and predicting major cardiovascular adverse events after OLT. The study population consisted of 284 ESLD patients. The mean values of MAHR (expressed as a percentage of 85% of MPHR) and HRR were significantly lower for patients on beta-blockers versus patients off beta-blockers [97.1% versus 101.6% (t ¼ 5.01, P < 0.001) and 71.7% versus 77.3% (t ¼ 4.03, P < 0.001), respectively], whereas the values of MHRR were similar in patients on beta-blockers and patients off beta-blockers [102.3% versus 102.1% (t ¼ 0.04, P ¼ 0.97)]. A regression analysis showed a significant association of MAHR (P < 0.001) and HRR (P < 0.001) with beta-blockers, whereas MHRR was not associated with beta-blocker treatment (P ¼ 0.92). MAHR and HRR were found to have no value for diagnosing chronotropic incompetence in ESLD patients. MHRR was not affected by beta-blocker therapy. Patients who developed heart failure (HF) and myocardial infarction (MI) after OLT had significantly lower MHRR values according to pretransplant DSE. MHRR was significantly associated with the subsequent development of HF (P ¼ 0.01) and MI (P ¼ 0.01) after OLT. MHRR may be useful for the determination of the target heart rate for stress testing, the diagnosis of chronotropic incompetence, and the prediction of adverse cardiac events after OLT.

SUMMARY -This study evaluated the relationship of cerebrovascular reactivity in young healthy