Coronary heart disease (CHD) is the leading cause of mortality worldwide. One of the main contributions of mortality and morbidity in CHD patients is acute myocardial infarction (AMI), which is the result of abrupt occlusion of an epicardial coronary artery due to a sudden rupture of atherosclerotic plaque, causing myocardial ischemia. In the initial stage of myocardial ischemia, lack of oxygen and nutrient supply results in biochemical and metabolic changes within the myocardium. Depletion of oxygen switches the aerobic cellular metabolism to anaerobic metabolism and impairs the oxidative phosphorylation pathway eventually leading to cardiomyocyte death. Several studies suggest an interlink between COVID-19 and ischemic heart disease. An increased ACE2 receptor expression in the myocardium may partly contribute to the myocardial injuries that are observed in patients affected by SARS-CoV-2. Furthermore, pre-existing cardiovascular disease, in conjunction with an aggravated inflammatory response which causes an up-regulation in pro-inflammatory cytokines. Moreover, patients with atherosclerosis are observed to be more prone to ischemic attacks when affected by COVID-19, due to hypercoagulation in the blood as well as elevated pro-inflammatory markers.
Ischemia is caused due to a reduction in blood flow in an area, as a result of a blockage in the blood vessel. Ischemic heart disease, commonly referred to as coronary heart disease (CHD), generally leads to the narrowing of coronary arteries, which primarily supply oxygenated blood to the cardiac muscles
[1][2][3]. One of the main contributions of mortality and morbidity in CHD patients is acute myocardial infarction (AMI)
[4]. Acute-ST segment elevation myocardial infarction (STEMI), which is the result of abrupt occlusion of an epicardial coronary artery due to a sudden rupture of atherosclerotic plaque, most commonly affects the left anterior descending artery (LAD) (50%), right coronary artery (30%) and left circumflex artery (20%)
[5]. Atherosclerosis is a multifactorial progressive disease of the arterial wall and is demonstrated by focal development of atherosclerotic lesion or plaque within the arterial wall. Smooth muscle cells (SMCs) and mononuclear phagocytes (MPs) as well as inflammatory cells such as macrophages, T cells, dendritic cells and mast cells accumulate in the lesions as the disease progresses
[6]. Multiple risk factors including dyslipidemia, incriminated vasoconstrictor hormones, hyperglycemia, pro-inflammatory cytokines, and smoking facilitate the progression of almost 50% of the arterial lesions. In the absence of systemic hypercholesterolemia, stimulated T lymphocytes, certain heat shock proteins and plasma lipoprotein induces inflammation that helps the atherosclerotic plaque formation
[7][8]. Chronic inflammation can rupture the plaque and may lead to ischemia and myocardial infarction
[9][10]. Delay in the restoration of the coronary blood flow leads to cardiac cell death. If acute myocardial ischemia is prolonged, cardiomyocyte death begins in the sub-endocardium, and over time, spreads towards the epicardium
[11]. In the initial stage of myocardial ischemia, lack of oxygen and nutrient supply results in biochemical and metabolic changes within the myocardium. Depletion of oxygen switches the aerobic cellular metabolism to anaerobic metabolism and impairs the oxidative phosphorylation pathway leading to mitochondrial membrane potential loss and subsequently decreases in production and inhibits the contractile function of the cardiomyocytes. This process is exacerbated by the hydrolysis of the available Adenosine triphosphate (ATP) due to the reverse function of F1F0 ATPase to maintain the mitochondrial membrane potential. Anaerobic glycolysis results in the accumulation of lactic acid, which increases the intracellular acidity by reducing the pH (to <7.0) and leads to ionic imbalances
[12]. Acidic environment damages the mitochondria and ATP production eventually ceases
[13]. Accumulation of intracellular protons activates the Na
+-H
+ ion exchanger and it drives the protons out of the cell in exchange for Na
+. The intracellular Na
+ overload in conjunction with cell membrane depolarization reverses the Na
+-Ca
2+ exchanger function and expels Na
+ out of the cell for Ca
2+ into the cell
[14]. Eventually, cellular membrane ion pumps such as Na
+/K
+ ATPase, sarcoplasmic reticulum ATPase Ca
2+ (SERCA) and active Ca
2+ excretion fail due to the drop in ATP level and ion gradients across the cell membranes collapse leading to the cell to death
[15].
A clinical syndrome, named angina pectoris, is the chest pain or discomfort that persists as a result of failure to acquire the required amount of oxygen to the cardiac muscles. National Health and Nutrition Examination (NHANES) states that as of the time frame between 2003 to 2006, it has been estimated that 17.6 million Americans of age 20 and above have had CHD. The annual incidence of myocardial infarction was 935,000, and the overall prevalence of angina pectoris was found to be 4.6%. In 2006, CHD was responsible for every one in six deaths and is the leading cause of death in both of the sexes.
It has been observed that there is a significant correlation between myocardial injury and fatal outcomes of COVID-19
[16]. In a study conducted with 187 patients that tested positive for COVID-19, 52% had a myocardial injury, which was observed by detecting higher levels of troponin T (TnT). This marker was seen to be elevated in cases of mortality from COVID-19. Furthermore, it has been noted that light should be shone onto the protection of the cardiovascular system while treating patients with COVID-19, as when severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects the host cell, acute myocardial injury is seen to take place, along with chronic damage to the cardiovascular system
[17]. The National Health Commission of China (NHC) had mortality data showing that 35% of the patients that tested positive for COVID-19 had hypertension and 17% had a history of CHD. Hence it is suggested that cardiovascular diseases can provoke pneumonia and further worsen other symptoms in patients that are infected with SARS-CoV-2.
Severe respiratory conditions such as respiratory failure and infectious diseases may induce a mismatch between oxygen demand and supply. Acute respiratory failure causes hypoxemia (reduced oxygen supply) and activates the sympathetic nervous system which increases the heart rate, cardiac output and myocardial contractility—leading to increased oxygen demand. This imbalance can lead to myocardial injury or MI, termed as type 2 MI
[18][19][20]. According to recent reports, about 7% of the COVID-19 patients have an acute cardiac injury and may present as type 2 MI or myocarditis
[21]. Atheroma was found in only a small percentage of STEMI patients after coronary angiogram
[22][23][24]. COVID-19 patients can present with cardiac conditions such as STEMI, non-STEMI (NSTEMI), heart failure, cardiac arrhythmia, thromboembolism and cardiac arrests. Hence, it is crucial to differentiate between the type 2 MI patients from the other urgent management requiring conditions.
This paper is aimed to understand the correlation between COVID-19 and ischemic heart diseases or CHD, and possibly propose a mechanism of action behind their interrelationship.