Postnatal neonatal myocardial adaptation is associated with loss of tolerance to tachycardia: a simultaneous invasive and noninvasive assessment

Abstract

Fortin-Pellerin E, Khoo NS, Mills L, Coe JY, Serrano-Lomelin J, Cheung PY, Hornberger LK. Postnatal neonatal myocardial adaptation is associated with loss of tolerance to tachycardia: a simultaneous invasive and noninvasive assessment. Am J Physiol Heart Circ Physiol 310: H598 -H607, 2016. First published December 30, 2015; doi:10.1152/ajpheart.00595.2015-Doppler studies at rest suggest left ventricular (LV) diastolic function rapidly improves from the neonate to infant. Whether this translates to its response to hemodynamic challenges is uncertain. We sought to explore the impact of early LV maturation on its ability to tolerate atrial tachycardia. As tachycardia reduces filling time, we hypothesized that the neonatal LV would be less tolerant of atrial tachycardia. Landrace cross piglets of two age groups (1-3 days; NPs; 14 -17 days, YPs; n ϭ 7/group) were instrumented for an atrial pacing protocol (from 200 to 300 beats/min) and assessed by invasive monitoring and echocardiography. NPs maintained their LV output and blood pressure, whereas YPs did not. Although negative dP/dt in NPs at baseline was lower than that of YPs (Ϫ1,599 Ϯ 83 vs. Ϫ2,470 Ϯ 226 mmHg/s, respectively, P ϭ 0.007), with increasing tachycardia negative dP/dt converged between groups and was not different. Both groups had similar preload reduction during tachycardia; however, NPs maintained shortening fraction while YPs decreased (NPs: 35.4 Ϯ 1.4 vs. 31.8 Ϯ 2.2%, P ϭ 0.35; YPs: 31.4 Ϯ 0.8 vs. 22.9 Ϯ 0.8%, P Ͻ 0.001). Contractility measures did not differ between groups. Peak LV twist and untwisting rate also did not differ; however, NPs tended to augment LV twist through increased apical rotation and YPs through increasing basal rotation (P ϭ 0.009). The NPs appear more tolerant of atrial tachycardia than the YPs. They have at least similar diastolic performance, enhanced systolic performance, and different LV twist mechanics, which may contribute to improved tachycardia tolerance of NPs. HEMODYNAMIC MANAGEMENT OF the critically ill term newborn is complex. Understanding the functional nature of the neonatal myocardium and how it evolves through the first few weeks and months after birth is key to optimizing care. Although many authors have provided their opinions regarding clinical management strategies (1, 12, 32), more translational and clinical studies are needed to provide insight into the functional capacity of the early postnatal heart. In particular, changes in diastolic reserve during the first few weeks and months of life in relation to the known disproportionate left ventricular (LV) growth (3, 27) have been poorly explored.In human infants, most of our understanding of the evolution of diastolic function has been derived from noninvasive Doppler-based studies (16,26,31). These investigations have suggested that the neonatal LV myocardium has less robust diastolic relaxation (16) with greater dependency on atrial contraction for filling, much like that of the diseased adult heart with diastolic dysfunction (15). In the first few mo...

Transthoracic Echocardiography of the Neonatal Laboratory Piglet

“…In both views, there is possibility to determine the diameter of the aortic valve. This can be used for calculation of cardiac output as shown by Fugelseth et al, Fortin-Pellerin et al, and Solevåg et al (6, 19, 29). Tilting toward the right side of the thorax allowed the RVOT, the pulmonary valve (PV) and the main pulmonary artery (MPA) to be visualized.…”

“…Induction of apnea was not necessary to achieve adequate image quality. Other TTE planes like four-chamber view, or subcostal and apical five-chamber planes can be visualized as well, but may need more experience, as shown by Solevåg et al in piglets weighing ~2 kg (29) and shown by Fortin-Pellerin et al (19) or Fugelseth et al (26). Other studies have shown that TTE can also be done in the right lateral, supine position as well as in the left lateral, half supine position (6, 26).…”

“…This has been effectively demonstrated in pediatric patients and neonates (16, 17). In addition, TTE allows to ensure the correct position of the used Millar catheters (5, 6, 18, 19). Therefore, transthoracic echocardiography may be extremely useful to for hemodynamic assessment in studies with animals, especially in small newborn animals (6).…”

Effects of Early Myocardial Postnatal Maturation on Tolerance to Atrial Tachycardia With Altered Loading Conditions: An in vivo Swine Model

“…Experiments were completed in 2016. Partial data from two of the groups (NP, YP) has been previously published (6). With the exception of Table 1, which shows that the groups were comparable at baseline, no direct statistical comparisons were made between subjects from the 3 series of experiments (see statistical analysis section for details).…”

“…Using a piglet model of rapid atrial pacing, we previously demonstrated that tolerance to tachycardia actually decreases in the first few weeks ( 6 ), a finding associated with differences in the twist pattern of the left ventricle (LV). Whether changes in preload and afterload impact the tolerance of the neonatal and young infant heart to tachycardia is not certain.…”