Left ventricular outflow obstruction

Surgical pathology of subaortic septal myectomy not associated with hypertrophic cardiomyopathy: a study of 98 cases (1996-2000)

BACKGROUND

No series have described the surgical pathology of subaortic septal myectomy in patients with conditions other than hypertrophic cardiomyopathy (HCM).

METHODS

Medical records and microscopic slides were reviewed from 98 non-HCM patients undergoing septal myectomy at Mayo Clinic Rochester from 1996 to 2000. Concurrently, 204 other patients had myectomy for HCM.

RESULTS

The study group (65 women, 33 men) ranged in age from 1.5 to 92 years (mean, 61). Seventy underwent surgery for aortic stenosis (Group 1), 25 for congenital subaortic stenosis (Group 2) and 3 for other conditions (Group 3). Group 1 patients were older than Group 2 patients (72 vs. 26 years; P<.0001). Microscopic evaluation showed myocyte hypertrophy (97%), vacuolization (35%), left bundle branch tissue (26%) (33% in Group 1 vs. 8% in Group 2; P=.02) and disarray (19%); interstitial fibrosis (92%), inflammation (10%) and amyloidosis (7%, all prealbumin type, all Group 1, >80 years old); arterial thickening (18%) and dysplasia (12%), and dilated venules (6%); and endocardial fibrosis (74%) (64% in Group 1 vs. 100% in Group 2; P=.0001) and chronic inflammation (17%).

CONCLUSIONS

Of 302 patients undergoing subaortic septal myectomy, 32% had conditions other than HCM. Myocyte disarray was present in 19% of patients without HCM (and was absent in 21% of HCM patients in a companion study). Thus, disarray alone cannot be used reliably to include or exclude a diagnosis of HCM in small surgical specimens. Because amyloid was found unexpectedly in seven elderly patients, we recommend routine amyloid staining on surgical myectomy tissue from patients >/=65 years old.

Comparison of respiratory function and fluid balance in very low birthweight infants given artificial or natural surfactant or no surfactant treatment

Exogenous surfactant administration improves respiratory function. The speed of improvement appears greater if a natural rather than an artificial surfactant is used, our aim was to determine if that effect was explained by differences in fluid balance, evidenced by the timing of the diuresis onset (i.e. output greater than input). Thirty infants (median gestational age 29 weeks), 10 given an artificial surfactant (Exosurf), 10 a natural surfactant (Survanta) and 10 no surfactant (controls) were studied. During the first three days, compliance and functional residual capacity were measured daily, arginine vasopressin (AVP) levels estimated on days 1, 3 and 5 and, in 8-hourly intervals, the median arterial/alveolar ratio was calculated for each individual and urine output and fluid input recorded. Throughout the three-day period, the median arterial/alveolar ratio was always significantly higher in the control compared to the two surfactant groups (p < 0.05). On day 3 the Exosurf-treated babies had lower compliance and functional residual capacity (p < 0.05) than the other two groups. Neither the timing of diuresis onset, timing of the maximum diuresis nor the AVP levels, however, differed significantly between the groups. Only surfactant treatment and type of surfactant, but not the timing of the onset nor of the maximum diuresis, related significantly to changes in lung function. These results do not support the hypothesis that differences in fluid balance explain differences in the lung function improvement rate following natural and artificial surfactant.

Changes in lung volume, compliance and oxygenation in the first 48 hours of life in infants given surfactant

Changes in lung volume (functional residual capacity) compliance and oxygenation in the first 48 h of life in infants given surfactant replacement therapy were studied. Fourteen infants, median gestational age 30 weeks (range 26-35), who were given two doses of an artificial surfactant (Exosurf) at approximately 2 h of age and 12 h later, were examined. Compared to baseline, functional residual capacity, compliance of the respiratory system and oxygenation, significantly improved at 24 and 48 hours, but specific compliance (compliance/functional residual capacity) decreased. The greater changes, however, were experienced between baseline and 24 h. These data suggest that the elevation of FRC over the first 48 hours of life may be due to increased distension as well as recruitment of alveoli.