Our study demonstrates that myocardial dysfunction is present in intubated ICU patients with severe Covid-19 ARDS, as depicted by the echocardiographic findings of impaired left and right ventricular function, mild pericardial effusion and mild elevation of troponin levels. However, New Onset Atrial Fibrillation occurred in ICU, Covid-19 ARDS patients, mainly in relation to a secondary infection that led to severe sepsis/septic shock. Demographics, ARDS severity, respiratory system mechanics, mechanical ventilatory modes and electrolytes did not differ between groups, while hypoxemia degree was quite improving in NOAF patients on the day AF occurred. We suggest that sepsis triggered NOAF occurrence, in the setting of an affected, from Covid-19, myocardium; sepsis resolution was crucial to maintain SR (under amiodarone infusion).
Our understanding on the cardiovascular effects of Covid-19 is still limited [4]. In our cohort, Left Ventricular EF was rather normal, although impaired global longitudinal strain indicated occult myocardial injury in the majority (74%) of Covid-19 ARDS patients upon ICU admission; abnormal GLSLV (< 16.6%) has been reported in 42% of Covid-19 patients admitted in the ward, while data on ICU patients are scarce [26–29]. In addition, a moderate RV enlargement was observed, which is in accordance with various Covid-19 reports [30, 31]. However, multiple factors may explain this finding apart from Covid-19; RV dilation is exacerbated by mechanical ventilator settings (PEEP), especially when lung compliance is preserved [32, 33]. Interestingly, 45.6% of the patients had a mild pericardial effusion. Pericardial effusion incidence has not been thoroughly evaluated in Covid-19 [34, 35]. In addition, troponin levels were elevated on ICU admission, a finding that has been linked to myocardial involvement in Covid-19 [3–6]. The above data support the notion that a degree of myocardial injury is present in severe Covid-19 patients, admitted in the ICU [36]. However, there was no difference between the NOAF and control group, in any parameter concerning the cardiac involvement.
Among atrial arrhythmias, AF is the most frequent in Covid-19 patients; NOAF prevalence varies between 3–10% in non-ICU patients [10, 11]. In our study, NOAF incidence was 24%, which is in accordance with the higher incidence reported in ICU patients [9–11, 13, 37–39]. Colon et al, noted a NOAF incidence of 16.5% in ICU patients [14]. However, no reference is made on possible secondary conditions and the timing of arrhythmia occurrence. Increased inflammatory markers and vasopressor need were reported during AF appearance, without specifying whether AF occurrence was coincidental to a secondary infection episode [2, 9]. Other studies confirm the increased NOAF incidence in ICU Covid-19 patients, varying between 16.5–40%, yet, without specifying whether the virus or other factors, frequently present in critically-ill patients, are associated to its occurrence [9, 10, 11, 13–15, 37–39]. Similarly, existing data lack information about the exact time of NOAF appearance in the course of Covid-19 [10, 11, 13, 14, 37–39]. An early, in the course of the infection, virally driven hyperinflammation-cytokine storm has been proposed as a possible mechanism, partially explaining NOAF occurrence in patients hospitalized in the wards [2, 9]. In our study, NOAF appeared late in the course of the disease, approximately during the 18th post symptom onset day (8th ICU day), when COVID-19 symptoms usually subside [39]. Although myocarditis has also been suggested as a possible mechanism for arrythmias in Covid-19, histological findings indicate macrophage infiltration, with no clear association to myocardial injury, and, although troponin is high, myocarditis is established in only 4.5% of the severely ill, Covid-19 patients with heart failure, undergoing endomyocardial biopsies; thus, the virus does not seem to directly invade the cardiac cells in order to initiate AF [12, 40]. Our findings support that non cardiac causes, such as systemic infection, may contribute to NOAF.
New-onset AF is a common arrhythmia in non-Covid-19 ICU patients, occurring in 19–35% of patients, sepsis being the main triggering factor [16, 41, 42]. Walkey et. al, reported an increased incidence (35%) of NOAF among septic patients, further increasing with disease severity [16]. In our study, 84.2% of the patients presented sepsis and 68.4% had septic shock on NOAF episodes. Inflammation markers, vasopressor need, and lactate levels presented a gradual increase in the preceding the AF days. The positive fluid balance during the last three days, and the rise in ScVO2 values, further supported NOAF’s association to sepsis-induced vasodilation [43].
An increased incidence of secondary infections has been observed in our cohort; 42% in the control group and 89% in the NOAF group, consistent with recent reports. Buetti et al, reported an increased daily risk (HR 4.5) to acquire an ICU-BSI in Covid-19 compared to non-Covid-19 patients; BSIs usually occurred after the 7th ICU day [17]. Similarly, Rouze et al, reported that ventilator associated lower respiratory tract infections were more frequent in Covid-19 ARDS patients (50.5%) compared to influenza (30.3%) and ICU patients with non-viral infections (25.3%), similarly occurring after the 7th ICU day [18]. Corticosteroids, Tocilizumab and Anakinra, used in COVID-19 ARDS, may be partly responsible [17, 18, 44]. In our study, NOAF occurred on the 8.5 ± 2.1 ICU day, mostly coinciding with the first BSI/VAP septic episode. We suggest that sepsis, with adrenergic overstimulation, due to endogenous elevated catecholamine levels and exogenous catecholamine administration (as in septic shock), constitutes the second “hit”, to trigger AF in a diseased/affected, from SARS-CoV-2, myocardium [2, 16]. Interestingly, patients in both groups were of comparable age and did not present factors indicating apparent cardiovascular disease, known to increase AF occurrence risk [11].
Troponin levels were significantly raised on the AF day compared to admission, further supporting the association of NOAF to secondary sepsis. Troponin elevation has been repeatedly reported in bacterial sepsis, reflecting altered cardiomyocyte permeability or some degree of necrosis, frequently associated with cardiac dysfunction [45, 46]. Sepsis induced myocardial dysfunction is very frequent, attributed to increased circulating catecholamine and cytokine levels, found in severe sepsis and septic shock [47, 48]. However, decreased systemic vascular resistance may mask the altered myocardial performance. We believe that sepsis-induced vasoplegia is responsible for the apparently preserved LVEF in our patients when NOAF appeared.
Rhythm control has been found more beneficial than rate control in ICU patients [42]. Most patients in our study returned to sinus rhythm with pharmacologic cardioversion (amiodarone); AF could not be restored in patients with non-resolving sepsis or re-occurred in those with recurrent septic episodes.
Our study has limitations. It was conducted in a single center serving an urban population, thus the number of patients is limited. However, although our findings may not be generalizable across the world, they may have particular importance in South Europe and other countries with an increased incidence of nosocomial infections from PDR/XDR, as in our study [49]. In addition, we consider an advantage that the study population was rather homogenous: we prospectively enrolled consecutive, intubated patients with severe Covid-19, with no obvious preexisting cardiovascular disease in order to eliminate known factors triggering AF. Cardiac Magnetic Resonance tomography was not performed, but its utility in ICU is limited by the out-of-hour availability and the requirement for some breath-holding, while no patients underwent endomyocardial biopsy (caring inherent risks), as it is not suggested due to the low incidence of myocarditis in Covid-19 [12]. Instead, in all patients, troponin levels and a full echocardiographic examination were performed, which seem appropriate to reveal cardiac involvement in Covid-19.