SummaryIn order to determine if an increase in heart rate is associated with an increase of left ventricular contractile function during the neonatal period we recorded phasic and mean aortic blood pressure. left atrial mean or left ventricular end diastolic Dressure. phasic left ventricular blood pressure, aortic blood flow velocity and the instantaneous first derivatives of left ventricular blood pressure (dP/dt) and aortic blood flow velocity (dV/dt) during pacing-induced tachycardia in conscious newborn and adult sheep. There was a significant positive linear correlation between heart rate and both indices of contractility (dP/dt and dV/dt) in both age groups. Left ventricular end diastolic pressure was unchanged except for a decrease at the most rapid heart rate in the newborns. There was no change in aortic mean blood pressure during the study. Our data demonstrate that an increase of heart rate is associated with an increase of left ventricular contractile function in conscious neonatal and adult sheep. Investigations of the effects of potential inotropic agents on left ventricular contractile performance in newborns and adults must evaluate the independent effect of any simultaneously occurring increase in heart rate.The positive inotropic effect of an increase of contraction frequency was originally demonstrated in vitro by Bowditch (5). Multiple recent investigations in vitro have demonstrated that atrial pacing-induced tachycardia is associated with a small but significant increase in left ventricular contractile function in conscious adult humans and dogs (9, 17-19, 28, 33). Although there is some information available concerning the effect of a heart rate increase on left ventricular contractility in the unanesthetized lamb fetus (1, 23) and in neonatal cat and lamb heart muscle in vitro (1,8), to our knowledge there is no such information available in conscious neonates of any species. Therefore, we studied the effect of a pacing-induced heart rate increase on left ventricular contractile function in conscious newborn lambs. As species variability has been reported in adults (25) we also performed a pacing study in conscious adult sheep.
MATERIALS AND METHODSSurgical technique. We operated on 1 1 Western newborn lambs 1-25 (9 + 2, mean + S.E.) days after birth and on 8 nulliparous female adult sheep. The lambs weighed 6.5 f 0.6 g. We anesthetized the animals with 1-2% fluothane (Halothane), intubated the trachea, and ventilated the lungs with an animal ventilator (Methomatic, Pittman-Moore). We performed a thoracotomy in the left fourth intercostal space and inserted polyvinyl catheters (inside diameter, 0.10 cm; outside diameter, 0.15 cm) into the ascending aorta via the left internal thoracic artery and into the left atrium through a purse-string suture in the atrial appendage. The catheters were closed after they were filled with heparin. We sutured a pair of stainless steel pacing wires (#A5633 hookup wire, Cooner Wire Co., Chatsworth, CA) to the left atrial epicardium. Through a separate incis...
An umbilical catheter fragment embolus in a neonate was difficult to approach due to fixation of both ends, in the left atrial appendage and the ductus venosus, respectively. A tip-deflecting guide wire was used in unique fashion to free the catheter fragment and allow its percutaneous removal via the femoral vein approach.
The clinical spectrum of neonatal endocarditis, including bacterial and nonbactenal types, is examined in five case reports that were drawn from nursery experiences over a recent 2-year period. In contrast to previous reports of 100% mortality from neonatal endocarditis, one patient survived. Changing heart murmur and hematuria were most frequently associated with bacterial and nonbacterial endocarditis in four of the five cases. Pulmonary hypertension, thrombocytopenia, and coagulopathy were also associated with nonbacterial endocarditis. Echocardiograms were performed on four of the patients; only one was suggestive of endocarditis. Staphylococcus aureus was isolated from both cases of bacterial endocarditis, including the single survivor. Thus, it is suggested that the initial antibiotic coverage of any neonate with the clinical syndrome of sepsis, hematuria, and a heart murmur include antistaphylococcal coverage for the possibility of bacterial endocarditis.
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