Diastolic function in neonates after the arterial switch operation: effects of positive pressure ventilation and inspiratory time

Objective: To determine the effects positive pressure ventilation have on left ventricular diastolic function in neonates after the arterial switch operation. Design: Prospective case series. Setting: Pediatric cardiac and multi-disciplinary intensive care units in two university-affiliate children's hospitals. Patients and participants: The patient population consisted of 12 neonates weighing 2.5-4.2 kg with D-transposition of the great arteries (DTGA) who underwent arterial switch operation. Interventions: All patients were mechanically ventilated in a volume-targeted mode with a square wave flow pattern. The positive end-expiratory pressure was held constant. A long inspiratory time was set by extending it over three cardiac cycles. Measurements and results: Pulsed Doppler measurements of left ventricular diastolic function were performed during the following cardiac cycles: (1) the last diastolic period of expiration (E-L), (2) first, second and third diastolic periods of inspiration (I-1, I-2, I-3) and (3) the first diastolic period of expiration (E-F). Doppler measurements of peak E wave, peak A wave, E area/A area, E area fraction, A area fraction, 0.33 area fraction and the deceleration time were made. Doppler tracings were digitized and the data obtained from three sequential study periods were averaged. Data were statistically analyzed using the repeated measures analysis of variance procedure. During (I-1), there was a 21 % increase in the peak E wave (0.53 +/- 0.06 vs 0.64 +/- 0.08 m/s, p < 0.01) and 28 % increase in peak A wave (0.47 +/- 0.07 vs 0.60 +/- 0.08 m/s, p < 0.01) compared to (E-L). There was a 24 % increase in total area under the E and A waves when I-1 was compared to E-L (0.059 +/- 0.008 vs 0.073 +/- 0.009, p < 0.01) and there was no change in mitral valve deceleration time. Compared to the initial diastolic period during inspiration (I-1), the third diastolic period during inspiration (I-3) had a 38 % decrease in peak E (0.64 +/- 0.08 vs 0.40 +/- 0.05 m/s, p < 0.01) and 33 % decrease in peak A (0.60 +/- 0.09 vs 0.40 +/- 0.05 m/s, p < 0.01). In addition, there was a 16 % reduction in total area under the E and A waves (0.073 +/- 0.009 vs 0.061 +/- 0.008, p < 0.01). There were no changes in the other diastolic indexes that reflect changes in ventricular compliance or relaxation. Conclusions: In neonates with transposition of the great arteries (TGA) after the arterial switch operation, positive pressure ventilation augments left ventricular filling during the early phase of inspiration. Prolonging the inspiratory time over three cardiac cycles results in a reduction in left ventricular filling during the third diastolic period.