Posterior deviation of left ventricular outflow tract septal components without ventricular septal defect.

OBJECTIVE: To describe 11 patients with narrowing of the left ventricular outflow tract caused by angular posterior deviation of both the outlet septum and the upper part of trabecular septum, which was diagnosed by cross sectional echocardiography in all and confirmed by angiocardiography in seven. RESULTS: Four patients had a subaortic systolic pressure gradient ranging from 23 to 70 mm Hg by Doppler echocardiography; cardiac catheterisation showed a significant (60 and 104 mm Hg) systolic pressure gradient in two. In four cases aortic regurgitation and two tricuspid pouches were shown by Doppler echocardiography, angiocardiography, or both. Four cases had a ridge at the angulation point on echocardiographic examination. Three patients were operated on for systolic pressure gradients of the left ventricular outflow tract and one for severe aortic regurgitation. There was proliferation of collagen-rich fibrous tissue in the subendocardial region on histopathological examination of the myectomy material. A ventricular septal defect had been diagnosed previously by contrast echocardiography in one patient; thus ventricular septal defects may close spontaneously over a period of time including fetal life. A subaortic ridge was detected in one patient at follow up. CONCLUSIONS: Deviation of the outlet and trabecular septa should be considered as a cause of ventricular outflow tract obstruction even when no ventricular septal defect is present.

Initial experience with dual-sensor rate-responsive pacemakers in children.

The efficacy of a new single-chamber, rate-responsive pacemaker that utilizes information from two sensors, activity and stimulus to T wave, was evaluated in 15 children during a mean follow-up period of 10.3 +/- 3.3 months (range 5-16 months). There were 10 males and five females, with a mean age of 5.9 +/- 3.8 years (range 9 months-16 years). The indication for pacing was high grade atrioventricular block in 10 (eight postoperative, two congenital), and sinus node dysfunction in five patients. In endocardial implants the mean T wave amplitude was 2.48 +/- 0.7 mV, and mean T wave sensing 91 +/- 6.3%, whereas in epicardial implants T wave amplitude and sensing were inadequate. Each patient underwent 24-h Holter monitoring and 10 performed a graded treadmill test in three sensor-blending modes (Stimulus-T = Activity, Stimulus-T > Activity, Stimulus-T < Activity), using the chronotropic assessment exercise protocol. Sensor cross-checking was analysed by continuous tapping over the pacemaker. Holter monitoring demonstrated that pacing rate variations were closely related to daily activity. At the initial phases of exercise testing, the mean percentage of increase in pacing rate was significantly lower in Stimulus-T > Activity mode, when compared to Stimulus-T = Activity (P < 0.01); however, the initial disparity among the three modes disappeared halfway through the exercise and similar heart rate changes were observed thereafter. Continuous tapping over the pacemaker in Stimulus-T = Activity mode caused an initial increase in pacing rate, and inappropriate responses were quickly corrected by sensor cross-checking. Rate modulation with a single-chamber, dual-sensor pacemaker is adequate and safe in children, and may offer significant advantages over single-sensor devices in endocardial implants.