Breath-hold divers (BHD) enduring apnea for more than 4 min are characterized by resistance to release of reactive oxygen species, reduced sensitivity to hypoxia, and low mitochondrial oxygen consumption in their skeletal muscles similar to northern elephant seals. The muscles and myocardium of harbor seals also exhibit metabolic adaptations including increased cardiac lactate-dehydrogenase-activity, exceeding their hypoxic limit. We hypothesized that the myocardium of BHD possesses similar adaptive mechanisms. During maximum apnea 15O-H2O-PET/CT (n = 6) revealed no myocardial perfusion deficits but increased myocardial blood flow (MBF). Cardiac MRI determined blood oxygen level dependence oxygenation (n = 8) after 4 min of apnea was unaltered compared to rest, whereas cine-MRI demonstrated increased left ventricular wall thickness (LVWT). Arterial blood gases were collected after warm-up and maximum apnea in a pool. At the end of the maximum pool apnea (5 min), arterial saturation decreased to 52%, and lactate decreased 20%. Our findings contrast with previous MR studies of BHD, that reported elevated cardiac troponins and decreased myocardial perfusion after 4 min of apnea. In conclusion, we demonstrated for the first time with 15O-H2O-PET/CT and MRI in elite BHD during maximum apnea, that MBF and LVWT increases while lactate decreases, indicating anaerobic/fat-based cardiac-metabolism similar to diving mammals.

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Background Primary cardiac tumours in children are rare, with an estimated prevalence of 0.014% in foetuses, whereas in the paediatric population, a 100-fold difference in autopsy prevalence has been reported (0.0017% to 0.28%). In neonates, rhabdomyoma is the most common primary cardiac tumour, followed by teratoma and fibroma, all of which are benign. Cardiac rhabdomyomas are associated to tuberous sclerosis in >50% of cases. The prevalence of cardiac tumours in neonates has not previously been assessed in a large population-based cohort. Purpose To determine the prevalence of congenital cardiac tumours by systematic echocardiography in a large, population-based, cohort of neonates. Methods Systematic transthoracic echocardiography (TTE), including standard sub-xiphoid, apical, left parasternal, and suprasternal views, was performed in neonates included in a population study. Cardiac tumours were defined as solid, echogenic masses, and description included location, size, and numbers (one/multiple). Information regarding subsequent diagnosis of tuberous sclerosis was collected from review of medical charts. Results A total of 25,537 neonates (age 12±9 days, 51.6% male) were enrolled in the study and underwent TTE. Cardiac tumours were detected in 7 neonates (4 males), corresponding to a prevalence of 0.3 [0.1; 0.6] per 1,000 live-births. Characteristics including sex, gestational age at birth, birth length and weight, APGAR 5-score, age and weight at TTE, and maternal age and pre-pregnancy BMI, did not significantly differ between the neonates with (n=7) and without (n=25,530) cardiac tumours (all p>0.05). In 6 out of 7 neonates, the cardiac tumours were located in the ventricles (86%), with multiple tumours seen in five (83%) (Fig. 1A+B), and with size ranging from 2.0x1.9mm to 10.0x5.1mm. In the seventh neonate, two cardiac tumours were detected in close proximity to the aortic and pulmonary valves in the ascending aortic and main pulmonary artery wall (Fig. 1C), with sizes 5.1x4.7mm and 3.7x3.2mm, respectively. All seven neonates had otherwise structurally normal hearts and no flow obstruction. Three neonates with multiple cardiac tumours in the ventricles were subsequently diagnosed with tuberous sclerosis. Conclusions Systematic TTE in a population-based cohort revealed a prevalence of congenital cardiac tumours of 0.3 per 1,000 live-births. The majority of the tumours were located in the ventricles and most often multiple cardiac tumours were encountered. Detection of congenital cardiac tumours in the ventricles was associated with tuberous sclerosis in half the cases. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Danish Heart Association, Danish Children's Heart Foundation