Exercise-induced Atrioventricular Block

Third-Degree Heart Block in COVID-19 Pneumonia Complicated by Methicillin-Resistant Staphylococcus Aureus (MRSA) Bacteremia. A Case Report and Review of Literature

Coronavirus disease 2019 (COVID-19) burden has been identified to cause multiorgan damage. Respiratory compromise is still one of the most common presentations, but cardiac injuries like myocardial injury, ischemia, and conduction abnormalities are also becoming prevalent. We present a case of an 87-year-old male with a history of dementia, type 2 diabetes mellitus, hypertension, chronic kidney disease, and a left kidney transplant hospitalized for respiratory distress and generalized tonic-clonic seizures. He was bradycardic to 27 beats per minute, hypotensive with mean arterial pressure <60 mm Hg. An electrocardiogram (EKG) depicted a high-grade atrioventricular block (AV-block). The transvenous pacemaker was placed via femoral access and tested positive for COVID-19. Work-up was done to rule out possible causes of bradycardia, like hypothyroidism, ischemia, AV nodal blocking agents, and drug-induced bradycardia was negative. His hospital stay got complicated by methicillin-resistant staphylococcus aureus (MRSA) pneumonia leading to empyema and bacteremia. Unfortunately, being critically ill, the family opted for comfort measures, and he passed away. Our clinical vignette signifies cardiovascular complications in COVID-19 patients are associated with poor outcomes if not addressed. The conduction abnormalities in patients with intact cardiac structure and function are becoming more common in the setting of COVID infection. Assessment with serial EKGs and cardiac monitoring might be essential as patients can develop AV blocks at any point of the disease.

Increased reliance on coronary perfusion for cardiorespiratory performance in seawater-acclimated rainbow trout

Salmonid ventricles are composed of spongy and compact myocardium, the latter being perfused via a coronary circulation. Rainbow trout (Oncorhynchus mykiss) acclimated to sea water have higher proportions of compact myocardium and display stroke volume-mediated elevations in resting cardiac output relative to freshwater-acclimated trout, probably to meet the higher metabolic needs of osmoregulatory functions. Here, we tested the hypothesis that cardiorespiratory performance of rainbow trout in sea water is more dependent on coronary perfusion by assessing the effects of coronary ligation on cardiorespiratory function in resting and exhaustively exercised trout acclimated to fresh water or sea water. While ligation only had minor effects on resting cardiorespiratory function across salinities, cardiac function after chasing to exhaustion was impaired, presumably as a consequence of atrioventricular block. Ligation reduced maximum O2 consumption rate by 33% and 17% in fish acclimated to sea water and fresh water, respectively, which caused corresponding 41% and 17% reductions in aerobic scope. This was partly explained by different effects on cardiac performance, as maximum stroke volume was only significantly impaired by ligation in sea water, resulting in 38% lower maximum cardiac output in seawater compared with 28% in fresh water. The more pronounced effect on respiratory performance in sea water was presumably also explained by lower blood O2 carrying capacity, with ligated seawater-acclimated trout having 16% and 17% lower haemoglobin concentration and haematocrit, respectively, relative to ligated freshwater trout. In conclusion, we show that the coronary circulation allows seawater-acclimated trout to maintain aerobic scope at a level comparable to that in fresh water.