• Hanjay Wang, Camille E Hironaka, Danielle M Mullis, Haley J Lucian, Hye Sook Shin, Nicholas A Tran, Akshara D Thakore, Shreya Anilkumar, Matthew A Wu, Michael J Paulsen, Yuanjia Zhu, Sam W Baker, and WooY JosephYJDepartment of Cardiothoracic Surgery, Stanford University, Stanford, Calif; Stanford Cardiovascular Institute, Stanford University, Stanford, Calif; Department of Bioengineering, Stanford University, Stanford, Calif. Electronic address: joswo.
• Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif; Stanford Cardiovascular Institute, Stanford University, Stanford, Calif.
• J. Thorac. Cardiovasc. Surg. 2022 Dec 1; 164 (6): e389e405e389-e405.

ObjectivesNeonatal rodents and piglets naturally regenerate the injured heart after myocardial infarction. We hypothesized that neonatal rabbits also exhibit natural heart regeneration after myocardial infarction.MethodsNew Zealand white rabbit kits underwent sham surgery or left coronary ligation on postnatal day 1 (n = 94), postnatal day 4 (n = 11), or postnatal day 7 (n = 52). Hearts were explanted 1 day postsurgery to confirm ischemic injury, at 1 week postsurgery to assess cardiomyocyte proliferation, and at 3 weeks postsurgery to assess left ventricular ejection fraction and scar size. Data are presented as mean ± standard deviation.ResultsSize of ischemic injury as a percentage of left ventricular area was similar after myocardial infarction on postnatal day 1 versus on postnatal day 7 (42.3% ± 5.4% vs 42.3% ± 4.7%, P = .9984). Echocardiography confirmed severely reduced ejection fraction at 1 day after postnatal day 1 myocardial infarction (33.7% ± 5.3% vs 65.2% ± 5.5% for postnatal day 1 sham, P = .0001), but no difference at 3 weeks after postnatal day 1 myocardial infarction (56.0% ± 4.0% vs 58.0% ± 3.3% for postnatal day 1 sham, P = .2198). Ejection fraction failed to recover after postnatal day 4 myocardial infarction (49.2% ± 1.8% vs 58.5% ± 5.8% for postnatal day 4 sham, P = .0109) and postnatal day 7 myocardial infarction (39.0% ± 7.8% vs 60.2% ± 5.0% for postnatal day 7 sham, P < .0001). At 3 weeks after infarction, fibrotic scar represented 5.3% ± 1.9%, 14.3% ± 4.9%, and 25.4% ± 13.3% of the left ventricle area in the postnatal day 1, postnatal day 4, and postnatal day 7 groups, respectively. An increased proportion of peri-infarct cardiomyocytes expressed Ki67 (15.9% ± 1.8% vs 10.2% ± 0.8%, P = .0039) and aurora B kinase (4.0% ± 0.9% vs 1.5% ± 0.6%, P = .0088) after postnatal day 1 myocardial infarction compared with sham, but no increase was observed after postnatal day 7 myocardial infarction.ConclusionsA neonatal leporine myocardial infarction model reveals that newborn rabbits are capable of age-dependent natural heart regeneration.Copyright © 2021. Published by Elsevier Inc.

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