An autopsy case of COVID-19 with a sudden death: Clinico-pathological comparison.

Autopsy was performed on a COVID-19 patient, who suddenly died despite the extensive anti-viral and anti-inflammatory therapies. Although moderate subpleural fibrosis was seen, pathology of DAD, a well-known cause for pulmonary failure, was minimum. Instead, severe hemorrhage was observed. Therapeutic effects were indicated; however, why severe hemorrhage occurred was unclear.

Ouabain increases sarcoplasmic reticulum calcium release in cardiac myocytes.

The inotropic and toxic effects of cardiac glycosides are thought to be related to their ability to inhibit the Na,K-ATPase. We examined the effects of ouabain and its analogs on sarcoplasmic reticulum (SR) Ca(2+) release in intact cat ventricular myocytes under Na(+)-free conditions and in myocytes in which the sarcolemma was permeabilized using saponin so that cytoplasmic ionic composition was fixed by the bath solutions. We also compared ouabain actions in cat myocytes to those in rat myocytes because the latter is considered to be a glycoside-insensitive species. In intact cat myocytes (Na(+)-free conditions), spontaneous Ca(2+) sparks were prolonged and frequency, amplitude and width were reduced by exposure to ouabain (3 microM). Nearly identical results were obtained with its analogs dihydroouabain or ouabagenin (10 microM). The frequency of spontaneous Ca(2+) waves was also reduced by ouabain. In contrast, ouabain (100 microM) had negligible effects on sparks and waves in rat myocytes in Na(+)-free conditions, consistent with the decreased sensitivity to cardiac glycosides observed in this species. In cat myocytes permeabilized with saponin (0.01%), ouabain (>or=50 nM) decreased spark frequency and increased background SR Ca(2+) leak only when the SR was well loaded (free [Ca(2+)] = 275 nM) and not when SR load was low (free [Ca(2+)] = 50 nM). Similar effects were observed in rat myocytes only when ouabain concentration was 1 microM. These results suggest that the cellular actions of cardiac glycosides may include a direct effect on SR Ca(2+) release, possibly through activation of SR Ca(2+) release channels (ryanodine receptors). In addition, these results are consistent with the idea that direct activation of SR Ca(2+) release is dependent on the extent of SR Ca(2+) load, with elevated load increasing sensitivity of the channel release mechanism to activation by glycoside.

Effect of cardiac glycosides on action potential characteristics and contractility in cat ventricular myocytes: role of calcium overload.

There is increasing evidence that cardiac glycosides act through mechanisms distinct from inhibition of the sodium pump but which may contribute to their cardiac actions. To more fully define differences between agents indicative of multiple sites of action, we studied changes in contractility and action potential (AP) configuration in cat ventricular myocytes produced by six cardiac glycosides (ouabain, ouabagenin, dihydroouabain, actodigin, digoxin, and resibufogenin). AP shortening was observed only with ouabain and actodigin. There was extensive inotropic variability between agents, with some giving full inotropic effects before automaticity occurred whereas others produced minimal inotropy before toxicity. AP shortening was not a result of alterations in calcium current or the inward rectifier potassium current, but correlated with an increase in steady-state outward current (Iss), which was sensitive to KB-R7943, a Na+-Ca2+ exchange (NCX) inhibitor. Interestingly, Iss was observed following exposure to ouabain and dihydroouabain, suggesting that an additional mechanism is operative with dihydroouabain that prevents AP shortening. Further investigation into differences in inotropy between ouabagenin, dihydroouabain and ouabain revealed almost identical responses under AP voltage clamp. Thus all agents appear to act on the sodium pump and thereby secondarily increase the outward reverse mode NCX current, but the extent of AP duration shortening and positive inotropy elicited by each agent is limited by development of their toxic actions. The quantitative differences between cardiac glycosides suggest that mechanisms independent of sodium pump inhibition may result from an altered threshold for calcium overload possibly involving direct or indirect effects on calcium release from the sarcoplasmic reticulum.

Positive inotropic effects of ouabain in isolated cat ventricular myocytes in sodium-free conditions.

The inotropic and toxic effects of cardiac steroids are thought to result from Na(+)-K(+)-ATPase inhibition, with elevated intracellular Na(+)(Na)causing increased intracellular Ca(2+)(Ca) via Na-Ca exchange. We studied the effects of ouabain on cat ventricular myocytes in Na(+)-free conditions where the exchanger is inhibited. Cell shortening and Ca transients (with fluo 4-AM fluorescence) were measured under voltage clamp during exposure to Na(+)-free solutions [LiCl or N-methyl-D-glucamine (NMDG) replacement]. Ouabain enhanced contractility by 121 +/- 55% at 1 micromol/l (n = 11) and 476 +/- 159% at 3 micromol/l (n = 8) (means +/- SE). Ca transient amplitude was also increased. The inotropic effects of ouabain were retained even after pretreatment with saxitoxin (5 micromol/l) or changing the holding potential to -40 mV (to inactivate Na(+) current). Similar results were obtained with both Li(+) and NMDG replacement and in the absence of external K(+), indicating that ouabain produced positive inotropy in the absence of functional Na-Ca exchange and Na(+)-K(+)-ATPase activity. In contrast, ouabain had no inotropic response in rat ventricular myocytes (10-100 micromol/l). Finally, ouabain reversibly increased Ca(2+) overload toxicity by accelerating the rate of spontaneous aftercontractions (n = 13). These results suggest that the cellular effects of ouabain on the heart may include actions independent of Na(+)-K(+)-ATPase inhibition, Na-Ca exchange, and changes in Na.