Optimal interpretation of the supine exercise electrocardiogram in patients with right bundle branch block.

A detailed analysis of the exercise ECG was performed in 82 patients with right bundle branch block who underwent supine exercise equilibrium radionuclide angiography. The sensitivity and specificity of each individual electrocardiographic lead for the detection of a positive radionuclide angiogram was determined. Leads V5 and V6 had a sensitivity of 58 percent and a specificity of 89 percent. The limb leads and lead V4 had a lower sensitivity, but an equivalent specificity. Leads V1 and V3 each had a clearly lower specificity that ranged from 56 to 67 percent. Receiver operating characteristic curve analysis demonstrated that the optimal interpretation of the exercise ECG included the limb leads and V4 to V6, but not V1 to V3. The results of coronary angiography in the subset of 16 patients who underwent this procedure confirmed these findings.

Right aortic sinus of Valsalva-to-right ventricle fistula complicating bacterial endocarditis of membranous ventricular septal defect: evaluation by two-dimensional, color flow, and Doppler echocardiography.

Rupture of the aortic sinus of Valsalva into the right ventricle is a rare complication of bacterial endocarditis. The majority of previous cases have been reported in patients with aortic valve endocarditis. This report describes this complication in association with infective endocarditis of a congenital membranous ventricular septal defect. Color flow imaging showed a mosaic-colored continuous flow signal from the right aortic sinus to the right ventricle. Continuous wave Doppler interrogation showed high-velocity systolic and diastolic flow signals due to continuous left-to-right shunt from the aorta to the right ventricle. The left-to-right shunt through a restrictive membranous ventricle septal defect was visualized as a mosaic-colored high-velocity systolic flow signal. These echocardiographic-Doppler findings permitted surgical correction of these defects without cardiac catheterization.

Maturation of respiratory responses to graded hypoxia in rabbits.

The respiratory effects of graded hypoxia were determined in 8 rabbits on postnatal days 1, 6 and 21. Ventilation was measured in the unanesthetized state by plethysmography. Graded hypoxia was produced by reducing the fraction of inspired O2 to 0.15 (mild hypoxia) for 15 min and then lowering it further to 0.10 (moderate hypoxia) for another 15 min. Mild hypoxia initially stimulated breathing to the same extent in all 3 groups; however, with moderate hypoxia, the percent increase in ventilation was greater for older rabbits. The rise in ventilation was due to an increase in tidal volume and frequency in 1- and 21-day-old rabbits, and it was almost entirely the result of changes in frequency in 6-day-old rabbits. After 2-3 min of hypoxia (mild or moderate), a decline in ventilation was observed in all 3 groups. This reduction of respiration was greater in younger animals and with moderate hypoxia. Decreases in frequency and tidal volume contributed significantly to this fall in ventilation for 1- and 2-day-old rabbits. However, the fall in ventilation for 6-day-old pups occurred almost entirely by changes in tidal volume. It is concluded that the magnitude of phase 1 (increased ventilation) and phase 2 (decreased ventilation) responses to hypoxia depend upon the level of hypoxia and the age of the rabbit.