Endothelial dysfunction is the main cause for coronary artery disease in patients with traditional cardiovascular risk factors (diabetes, smoking, hypertension, and older age)
[29]. As the thrombotic complications in patients with COVID-19 increase, endothelial injury is incriminated, either by a direct viral effect or by the action of inflammatory cytokines
[30][31]. A direct effect of SARS-CoV-2 on the vascular endothelial glycocalyx (VEGLX) is suspected
[32]. Glycocalyx damage usually is associated with pathological situations as inflammatory response, hyperglycemia, hypoxia, and ischemia/reperfusion injury, which may also be present in COVID-19 pneumonia
[32][33][34][35]. The theory is supported by the measurements of circulating levels of VEGLX components in COVID-19 patients, where higher concentrations were detected for VEGLX injury biomarkers such as syndecan-1, hyaluronic acid, and sTie-2
[4][36]. In the presence of an inflammatory state, the endothelium loses its antithrombotic, anticoagulant, and profibrinolytic capacity as a result of tissue factor expression, von Willebrand factor release, thromboxane production, and plasminogen activator inhibitor-1 (PAI-1) production
[37]. Moreover, the inflammatory cytokines act on the endothelial cells to generate superoxide anions, with enhanced local oxidative stress
[38]. Overproduction of endothelin-1 contributes, as well, to the endothelial imbalance, acting as a prothrombotic agent and vasoconstrictor
[39].
Troponin is the gold standard biomarker used for detection of myocardial ischemia, as reflects the presence of cardiomyocyte damage. In ACS, either STEMI or NSTEMI, the dynamic of circulating troponin levels is similar, regardless of the ECG pattern (ST-elevation, ST-depression, or inverted T wave), the main factor influencing its value is the moment of detection after symptom onset
[57]. Typically, troponin cannot be detected in the first 1–2 h of myocardial necrosis, but only approximately 2–4 h after the onset of myocardial injury. Thereby, in cases where patients seek early medical advice, the troponin levels may be normal or slightly increased, which is an indication for repeating the troponin measurements. Serum levels can persist being elevated for up to 4–7 days for troponin I, and 10–14 days for troponin T
[58]. researchers did not find studies indicating correlations between troponin levels and particular ECG aspects of myocardial ischemia or infarction. However, a certain type of ACS that should be mentioned is Wellens syndrome which, despite its great severity and high risk, manifests frequently with troponin within normal limits, which can be falsely reassuring
[59]. In COVID-19 patients, troponin levels have often been elevated as a result of cardiac injury, with or without AMI, which highlights the important role of ECG in establishing the diagnosis
[60]. However, troponin proved to be valuable in anticipating the prognosis of COVID-19 patients, as Santoso et al. presented in a meta-analysis, which concluded that troponin levels were associated with higher mortality, need for care in the intensive care unit (ICU) and a more severe form of COVID-19 infection
[61]. The hypothesis is also confirmed by a research that investigated the risk of mortality in patients with COVID-19, new T-wave inversions (TWI) and troponin levels. Jorge Romero et al. showed in their research that patients with elevated troponin and TWI had an 80% mortality risk, compared with a 35% mortality risk when isolated TWI with normal values of troponin were present
[62].
2. ST-T Abnormalities
ST-T abnormalities are well-known and described in patients with myocardial ischemia and they include ST-elevation or depression, T-wave inversion, and nonspecific ST-T-wave changes. While acute subendocardial ischemia causes ST-segment depression, acute transmural ischemia causes ST-segment elevation, due to the electrical repolarization currents responsible for the ST-segment, which are deviated towards the inner layer of the heart in the first case and towards the outer layer of the heart in the latter. Even though the ECG signs of an acute ST-elevation are more accurate than an acute non-ST-elevation, the repolarization abnormalities of a myocardial infarction can persist indefinitely
[63][64].
Patients infected with SARS-CoV-2 who associate myocardial injury may show ST-segment elevation, ST-segment depression, or T-wave inversion on ECG
[65][66]. Howbeit, the ST-segment elevation in COVID-19 patients requires differential diagnosis with pericarditis and myocarditis, while myocardial ischemia may be due to both obstructive coronary artery diseases and a mismatch between oxygen supply and demand
[67]; these findings have been observed more frequently in severe patients
[68][69]. Among the critically ill patients, an abnormal ECG with ST-T changes reaches a frequency of 48.5%, while in patients with a severe type of COVID-19, 25.7% have this abnormality according to Wang et al.
[70]. Most studies found that ST-T abnormalities were the most common changes, occurring in up to 40% of patients from different hospitals, including Wuhan Asia General Hospital
[66][67][71][72]. T-wave inversion was the most common repolarization change in several studies, including the one of Galidevara et al., who reported that 27.7% of ECG changes were due to this abnormality
[69][73]. However, while Rosen et al. reported in his research that 21% patients had an ECG with ST-T modification, Poterucha et al. reported that 10% of the presentations had this abnormality, T-wave inversion was observed in up to 29% of this group, which is similar to other studies. This may be due to the number of patients included in the studies, the second one having a number of patients seven times higher
[74][75].
Regarding the localization of the repolarization abnormality, lateral and antero-lateral changes on the ECG were the most frequently described, being also associated with worse clinical outcomes
[76][77][78].
The ST-T modifications on the ECG can be used as an indicator for poor prognosis, including more frequent need for mechanical ventilatory support, increased need for ICU admission, and finally increased mortality
[66][68][70]. Patients with ST-T changes on the admission ECG are more likely to show progression towards a severe form, being associated with the severity of the COVID-19 infection and a worse prognosis
[68][69][79]. Therefore, the COVID-19 patients detected with myocardial ischemia on the ECG should be monitored for sudden cardiac death
[68].
Patients with ST-T abnormalities had elevated cardiac biomarkers, such as troponin, and more frequent requirement for vasoactive treatment
[74][80][81]. Although mild troponin elevation was a frequent finding in the research of Chorin et al., which is often associated with non-vascular etiologies, biomarkers of cardiac damage should alert clinicians of a poor prognosis
[81].
2.1. STEMI Pattern
The ST-segment elevation is sometimes associated with a fatal evolution or a worse prognosis in patients, especially in those with COVID-19 infection. Several studies attest the presence of an ST-segment elevation, characteristic for myocardial infarction, in patients with SARS-CoV-2 infection. Therefore, it is important, especially in patients with COVID-19, to differentiate the ischemic ST-elevation from the one in a possible myopericarditis
[53][82][83].
The ST-segment elevation myocardial infarction (STEMI) is defined as new ST-elevation at the J point in two or more contiguous leads, ≥0.25 mV in men below the age of 40 years, ≥0.2 mV in men over the age of 40 years, or ≥0.15 mV in women in leads V2–V3, and/or ≥0.1 mV in other leads
[63][84][85].
A multicenter case series research from six hospitals in New York, which included patients with ST-segment elevation and COVID-19, showed that in 44% of patients a diagnosis of myocardial infarction was established, whereas 56% had a non-coronary myocardial injury. Half of the patients underwent invasive intervention with angiography, but only two-thirds of them had obstructive disease. This finding suggests that a more prevalent COVID-19 was associated with a non-obstructive type of MI, probably determined by type 2 myocardial infarction
[53][82][83]. However, univariate analyses showed that ST-segment elevation had a strong correlation with patients’ mortality, being an independent prognostic factor. Sonzor et al. demonstrated in their research in American Journal of The Medical Science that ST-segment elevation can be associated with clinical outcomes in hospitalized patients with COVID-19
[86]. Moreover, the occurrence of ST-segment elevation during hospitalization is also an alarm sign for a poor prognosis, this manifestation being due to the side effects of therapeutic agents, the direct attack of the virus on myocardial tissue, or an indicator of myocardial ischemia
[87].
Mccullough et al. reported that only 0.7% of the presentations had localized ST-segment elevation on the ECG, their data suggesting that this was not a common finding in the New York Presbyterian Hospital in the first months of the pandemic
[71]. These data were sustained by another research which showed that localized ST-segment elevation was observed in only 0.5% of the presentations during the same months
[81].
There was no specific localization of the myocardial infarction in COVID-19 patients as several studies have shown, some concluding that inferior myocardial infarction was the most frequent, while others showing that anterior myocardial injury was the most common type
[52][78][85]. An important aspect to mention is that STEMI represented the first clinical manifestation of COVID-19 for most patients with myocardial infarction and only a few developed ST-segment elevation during hospitalization for COVID-19
[52]. Even though researchers need to be aware of the atypical clinical presentation of COVID-19 with cardiovascular manifestations, physicians should not misdiagnose STEMI even after admission, especially if the patient has chest pain
[88][89]. researchers researched almost all published cases of STEMI and researchers found an approximately equal localization of the myocardial infarction, with no statistical significance between the affected walls: inferior myocardial infarction-5 cases, inferolateral myocardial infarction-4 cases, anterior myocardial infarction-5 cases, or anterolateral myocardial infarction-3 cases. Interestingly, patients who had a subacute myocardial infarction, with ST-segment elevation and Q waves, had an anterior STEMI with late presentation
[82][88][89][90][91][92][93][94][95][96][97]. Patients with COVID-19 and STEMI who were admitted to the hospital had several cardiovascular risk factors with a past medical history of type 2 diabetes mellitus, hypertension, hyperlipidemia, or overweight body mass index (BMI)
[83][90]. This suggests that cardiovascular risk factors in patients with COVID-19 infection play an important role, as this association leads to a more prevalent occurrence of a myocardial infarction. The mean age of the total cases of STEMI associated with COVID-19 infection found in literature was 54.4 years of age, and the majority of patients were male, only four being female with acute STEMI
[82][88][89][90][91][92][93][94][95][96][97]. However, it was observed that the youngest patients with ST-segment elevation myocardial infarction and COVID-19 were female
[95][96]. Different researchers published research which included patients with STEMI, but without COVID-19 and concluded that the prognostic for those patients was better, not only because they did not have SARS-CoV-2 infection, but also because the angiography was performed faster
[90].
researchers also found studies with cases of transient ST-segment elevation on the ECG, the possible explanations being a type 2 myocardial infarction due to inflammatory activation, respiratory failure, and severe hypoxia
[81][98]. MINOCA due to type 2 acute myocardial infarction causes the appearance of deep Q waves on the subsequent electrocardiograms
[99]. Stefanini et al. showed in their research that in approximately 40% of patients with COVID-19 and STEMI, a culprit lesion was not identifiable in the angiography
[52]. Therefore, it is not necessary to perform an angiography in all patients with STEMI and COVID-19, but researchers need to place in balance the risks and benefits and to understand the pathophysiological mechanisms behind de ECG aspects
[90][94].
2.2. ST-Depression Pattern
ST-segment depression is defined as a new horizontal or down-sloping ST-depression of at least 0.05 mV in two contiguous leads
[64][84]. The non-ST-elevation myocardial infarction (NSTEMI) is seen on ECG as ST-segment depression, T-wave inversion or nonspecific ST-segment, and T-wave changes
[63]. The variety of ECG findings requires a detailed analysis and raises differential diagnosis problems, as ST-T abnormalities were the most reported ECG findings in patients with COVID-19 infection
[67][70][72].
Although various studies have not shown any cases of ST-segment elevation, they have found ST-segment depression, reported in approximately 5.3% of cases, this manifestation also being associated with a high mortality
[100][101][102]. As researchers described above, MINOCA can be challenging due to the atypical clinical presentation, especially in patients with NSTEMI
[100]. Moreover, ST-segment depression related to MINOCA was associated with high levels of cardiac biomarkers
[86]. Antwi-Amoabeng et al. showed an incidence of 8.6% of ST-segment depression, with a significant association between this ECG finding and troponin levels
[103]. Due to the more frequent cases of ST-segment depression compared with ST-segment elevation, researchers did not find in literature specific cases of NSTEMI, but only studies on large cohorts
[100][102][104].
2.3. T-Wave Inversion and Other Patterns of ST-Abnormalities
T waves are normally inverted in leads III, aVR, and V1. T-wave inversions (TWI) produced by myocardial ischemia are classically narrow, symmetric, and have variable depth. Moreover, they have mirror patterns, start in the second part of the repolarization, and may be accompanied by a positive or negative U wave
[84][103].
Heberto et al. showed that ischemic T-wave inversion was the most frequent electrocardiographic finding in COVID-19 patients and observed a relationship with mortality in these patients
[105]. Other studies demonstrated that T-wave abnormalities were present in up to 49% of the COVID-19 patients
[106][107]. Almost all studies showed that T-wave inversion appeared more frequently in the cardiac injury group and in patients over 74 years of age
[97][108]. However, Capaccione et al. reported a case of a 36-year-old patient with myocardial ischemia and inferior T-wave inversion, confirming the hypothesis of various studies showing that patients with COVID-19 infection have an increased risk of developing severe cardiovascular disease at a younger age
[109]. The number of leads with T-wave inversion pattern was significantly correlated with the elevation of cardiac injury biomarkers, such as troponin
[107]. Both of these findings were associated with increased mortality and the need for intubation. Romero et al. conducted a research on 3225 patients with COVID-19 infection, where T-wave inversion was observed in 6% of patients, with the most frequent localization (71%) in the lateral leads (DI, aVL, V5–V6)
[65]. Therefore, T-wave inversion remains the most frequent repolarization abnormality and is associated with poor outcomes and death, especially in those with elevated troponin levels
[74][109]. The issue for patients with T-wave inversions due to NSTEMI is that during the COVID-19 era, even if the patients were classified as high-risk NSTEMI, angiography was not performed, and conservative treatment during isolation was preferred due to the high risk of infection. However, this strategy may contribute to increasing mortality, as Suryawan et al. reported in their case presentation
[110][111].
3. Q Waves
Pathological Q waves are defined as the occurrence of Q waves in at least two contiguous leads as follows: any Q wave in leads V2–V3 of at least 0.02 s or QS complex in leads V2 and V3; Q wave of at least 0.03 s and at least 0.1 mV deep or QS complex in leads I, II, aVL, aVF, or V4–V6; R wave of at least 0.04 s in V1–V2 and R/S of at least one with a concordant positive
[63][84].
researchers found in literature some cases of subacute myocardial infarction in COVID-19 patients, with Q wave being observed on ECG in approximately 4% of cases. The location was in both the anterior and inferior territories, and the patients maintained the ST-segment elevation on ECG
[76][101]. Because the Q wave remains the only sign of myocardial infarction on ECG, a remote myocardial infarction is more difficult to recognize. Moroni et al. presented three cases of myocardial infarction with late presentation, due to the patients’ fear of being infected with COVID-19 in the hospital, who treated themselves at home and were hospitalized long after a good therapeutical procedure could have been performed
[91].
4. Specific Electrocardiographic Patterns
4.1. Takotsubo Pattern
Takotsubo syndrome (TTS) was first described in the 1990s, as an acute myocardial infarction, but with normal angiography and patients recovering within days or weeks. Even though it was initially considered a benign disease, subsequent studies have demonstrated a higher mortality rate than in the normal population. The most common finding on ECG is the ST-segment elevation in the precordial leads, with less common ST-segment depression or abnormal Q waves than for myocardial infarction and with transient changes
[112][113][114][115].
TTS occurs in 90% of cases in women, often being preceded by emotional stress, therefore the COVID-19 pandemic can be considered a triggering factor
[116]. The pathophysiology is associated with high plasma levels of catecholamines, the impact of adrenergic activity on cardiac myocytes causing ascending ST-segment elevation and J point depression. Moreover, high catecholamine levels might increase oxygen demand, inducing vasospasm and myocardial injury, patients with SARS-CoV-2 infection being exposed to a high endogenous secretion as a compensatory intravenous infusion, which are used as a therapeutic method
[117][118]. Another determinant mechanism involves the hypothalamic-pituitary-adrenal (HPA) axis, which is activated in COVID-19; several studies have shown that cortisol and adrenocorticotrophic hormones were dysregulated. As the levels of cortisol are significantly higher in COVID-19 patients and the HPA axis induces catecholamine secretion, a relationship between TTS and hypercortisolemia was described. An important aspect to mention is the BNP/troponin ratio used to differentiate TTS from acute myocardial infarction, as TTS is associated with higher brain natriuretic peptide (BNP) and lower troponin levels
[118].
Literature presents many cases of TTS in patients with COVID-19, the most specific ECG abnormalities being ST-segment elevation in the anterior leads
[82]. Approximately 2–4% of patients with COVID-19 had TTS, with a higher prevalence in critically ill patients, as some studies have reported. Although TTS predominates in women, about 30% of the patients with COVID-19 and TTS are males
[118]. The first typical case of TTS with apical ballooning observed on echocardiography in a patient with COVID-19 was reported by Meyer et al. Both emotional and physical stress by the pandemic were considered trigger factors
[119].
ST-segment elevation in leads I and aVL and diffuse ST-T-wave changes were found in two female patients with COVID-19, who were subsequently diagnosed with TTS because the cardiac catheterization revealed normal coronary arteries. One of them even admitted to feeling anxious by the reports and images of the COVID-19 pandemic, TTS being an indirect outcome of quarantine-induced stress
[116][118][119].
Although it was considered a benign disease, TTS patients with COVID-19 have a higher mortality rate than patients who have only TTS
[120][121]. Furthermore, Barbieri et al. showed that in a hospital from Lombardy, during the COVID-19 pandemic, more patients with TTS have been diagnosed with TTS than in the same months of the previous years. This is an additional argument for the impact of COVID-19 on stress-induced cardiomyopathy
[122].
4.2. Wellens Pattern
Wellens syndrome is a specific disease for critical stenosis of the proximal left anterior descending coronary artery. The ECG shows deeply inverted or biphasic T waves in leads V2–V3, often in leads V1 and V4 and occasionally in leads V5–V6. Patients with Wellens syndrome are at risk of a large anterior wall myocardial infarction, even though they are pain-free and the cardiac enzymes are normal
[59][123][124].
researchers found in literature four cases of Wellens syndrome in patients with SARS-CoV-2 infection, three of them were male and one female. The mean age was 73 years old, significatively higher than the group with ST-segment elevation. On the ECG, all patients had biphasic T waves in V2–V3, three of them with additionally negative T waves in leads V4–V6. Only one patient had typical chest pain, three patients had only dyspnea. The female patient did not have an angiography performed, in one patient an emergency angiography was performed and the other two patients had a coronary angiography after a few days of medical treatment. All patients were treated with drugs for NSTEMI, with a high-intensity statin, dual antiplatelet aspirin, P2Y12 inhibitors, and anticoagulant
[124][125]. Regarding the therapeutic approach, researchers observed a difference during the pandemic. If the first published case of Wellens syndrome did not receive an angiography because of the COVID-19 status and the risk of infection, Caiati et al., the researchers who published the latest case of Wellens syndrome during the COVID-19 pandemic, chose another therapeutic approach and the patient underwent an angiography
[125][126][127][128]. This may be due to the fact that at the beginning of the pandemic, information about COVID-19 was scarce, a conservatory treatment was preferred in order to keep as little physical contact as possible. Even though for the diagnosis of Wellens syndrome physicians need to perform an angiography, during the pandemic, the European Society of Cardiology and the American College of Cardiology recommended medical management during the acute phase
[125].
In addition to the ECG aspect, patients should be investigated for cardiovascular risk factors, as well as a structural evaluation with echocardiography, coronary angiography being the investigation that assists the ECG findings
[125]. However, because the high risk of infection during the COVID-19 pandemic required new diagnostic methods, Caiati et al. proposed a non-invasive way that can assess the obstructive atherosclerosis through transthoracic enhanced Doppler echocardiography (E-Doppler TTE). This allows the identification of the coronary blood flow velocity, even though this investigation has never been tested in a Wellens syndrome. The researchers used it for the first time the E-Doppler TTE in an acute syndrome and this can open new perspectives on the management of an acute coronary syndrome
[128].
4.3. De Winter Pattern
The De Winter ECG pattern shows an upsloping ST-segment depression at the J-point in leads V1–V6, followed by peaked symmetrical T waves, being associated with left anterior descending artery occlusion, with a positive predictive value of 95%
[129][130][131].
Almendro-Delia et al. published the only case of De Winter syndrome associated with COVID-19 infection, which occurred in a 33-year-old male patient. Due to his infectious disease, atypical chest pain suggestive for pericarditis, and the ECG aspect with ST-segment depression in V1–V6 followed by tall T waves, the first diagnosis was acute pericarditis. The laboratory result which revealed high troponin levels and the echocardiographic aspect with apical and antero-lateral hypokinesis with an apical thrombus at this region, led to the reinterpretation of the ECG as a De Winter aspect. The angiography confirmed the thrombotic occlusion of the proximal left anterior descending artery, the outcome being favorable. Therefore, in the COVID-19 era, it is necessary to make a detailed differential diagnosis, even in apparently young healthy patients. The ECG aspects can be misinterpreted as early repolarization or pericarditis, delaying proper reperfusion treatment. Thus, the De Winter pattern is the equivalent of an early STEMI, an aspect which should not be ignored
[132].
4.4. Triangular Electrocardiographic Pattern
Another unique ECG presentation of STEMI is represented by the triangular QRS-ST-T waveform, also known as the “shark fin pattern”, which is defined as a giant wave resulting from the fusion of the QRS complex, the ST-segment and the T wave
[53][133]. This uncommon ECG pattern reflects the left main coronary artery involvement, with a large area of transmural myocardial ischemia and poor in-hospital prognosis
[53].
A 32-year-old female patient with COVID-19 infection and shortness of breath, showed a “shark fin pattern” in leads I, II, III, and aVL post-cardiac arrest. Although an angiography was necessary, given her critically ill clinical status and the echocardiographic aspect with mid-wall hypokinesis suggestive for Takotsubo, the intervention was postponed. The “shark fin pattern” is a rare ECG finding, typical for left main coronary artery, but because of the patient’s past history of intravenous drug abuse and hepatitis C, over which the COVID-19 infection overlapped, this ECG aspect can be determined by several other factors, such as abnormal laboratory tests
[134].
5. Other Electrocardiographic Aspects Associated with Myocardial Ischemia in COVID-19 Patients
Even though new left bundle branch block, right bundle branch block, or poor R-wave progression were described as different changes suggestive for myocardial ischemia, in COVID-19 patients researchers did not find specific publications or studies regarding only the incidence of these aspects in infected patients
[74][77].