COVID-19 And The Heart
The case for the young to protect the elderly
As most of us already know, COVID-19 is caused by a novel respiratory coronavirus or SARS-CoV-2. It is droplet-borne and in the absence of an actual viral vaccine, social distancing is the best protection from the transmission, particularly to the elderly
Pathology of SARS-CoV-2
SARS-CoV-2 typically elicits a respiratory infection leading to acute respiratory distress syndrome (ARDS, x-ray below) in severe cases.
It causes rapid, widespread inflammation of the lung leading to respiratory failure.
Inadequate oxygenation due to the inflammation of lung tissue manifests in shortness of breath (a compensatory mechanism to suck more oxygen from the air) and organ damage (from hypoxia, or lack of oxygen and blood supply to tissues).
The effect of SARS-CoV-2 on lungs is well established owing to quick, cheap chest x-rays that are widely available globally.
The typical progression of events leading from the lung inflammation is hypoxic shock, multi-organ damage and in severe cases, patients then succumb to death.
COVID-19, unfortunately, affects all ages with cases of mortality in the younger population. It does, however, have a pattern of a more severe impact in those that are elderly and/or have co-morbidities.
Key points related to age and SARS-CoV-2:
- The summary of 72,314 cases from the Chinese Centre for Disease Control and Prevention reports a higher incidence of new cases in the younger population but higher mortality in the elderly. 97% of patients were in the age bracket of 20–79 years, however, the mortality was highest, 14.8% in patients aged >80 years.
- Similar findings were reported from Italy with case fatality rates of 12% and 20% among those aged 70 to 79 years and 80 years or older respectively.
- In the United States, a study of 2449 patients reported that although the incidence of COVID-19 was higher in aged anyone aged >45 years (67%), approximately 80% of deaths occurred in those aged > 65 years.
The World Health Organization considers cardiovascular disease as the number 1 cause of death globally. With this wide-spread burden of cardiovascular disease, several COVID-19 studies have aimed to ascertain if cardiac co-morbidities could have a role in a more severe impact of COVID-19 on certain populations.
Overall, underlying cardiovascular disease and hypertension have been reported to have significantly high-case fatality rates (10.5% compared to 0.9% without comorbidities) in patients with COVID-19.
Pathophysiology of cardiac disease
The heart is supplied by its local, blood supply or coronary artery circulation. Co-morbidities impede oxygen supply to this coronary system and result in a reduced capability of the heart to withstand a further insult, as in the case of SARS-CoV-2.
- High cholesterol levels — fatty deposition in arteries reducing available diameter for flow
- High blood pressure — Haemodynamic or flow stress on the vessel wall creating resistance.
- Previous heart attacks — weakened pump action of the heart and in some circumstances, the formation of scar tissue.
- Diabetes — accelerates tissue damage due to excess circulating glucose.
Consequences of SARS-CoV-2 on the heart
People have heart attacks due to one of the two reasons:
- Type 1 — pre-existing plaque disruption causing acute obstruction of blood flow to the heart
- Type 2 — secondary process (such as a viral infection) leading to a global deficit in oxygen supply to the heart and other organs.
In SARS-CoV-2, type 2 attacks are more commonly related to the primary respiratory derangement. However, the elderly, with pre-existing cardiac problems are at a higher risk of both type 1 and type 2 heart attacks.
Heart attacks have a cause and effect cycle with manifestations such as irregular rhythms and weakened tissue, both seen in higher proportions in any severe infection.
People with pre-existing co-morbidities or cardiac risk factors are more likely to have heart attacks. Any factor reducing oxygen or blood flow to the heart can disrupt the normal electrical conduction in the heart leading to irregular rhythms, or arrhythmias.
Electrolyte abnormalities are also known to cause arrhythmias. What is important about irregular heart rhythms, regardless of the cause is their ability to cause significant cardiac dysfunction.
Symptoms include palpitations, dizziness in addition to the typical symptoms of chest pain or shortness of breath.
- Palpitations were reported as an initial symptom in 7.3% of 137 COVID-19 patients studied in the Hubei province.
- In another study originating from Wuhan involving 138 patients, 17% of the overall cohort of COVID-19 patients had an arrhythmia. More importantly, 44% of patients who eventually got admitted in intensive care due to COVID-19 had an arrhythmia in the same study.
Cardiac Muscle Injury
Troponin is an enzyme found in muscle tissue. When muscle breaks down, troponin leaks into blood and levels can, therefore, be examined from a blood sample.
Cardiac troponin is a highly sensitive, more specific marker for damage to heart tissue, or the myocardium.
Typically, myocardial injury can only be proven by undertaking a biopsy from the heart muscle and examining it under a microscope. No studies show autopsy results to shed light on a gross examination of the heart in COVID-19 patients.
However, troponin levels are considered standard diagnostic measures of cardiac injury.
Although the causes of myocardial injury in patients with COVID-19 has not been fully elucidated, there appears to be a cardiac involvement.
- In the first study reported from Wuhan of 41 cases, published in The Lancet, cardiac injury was seen in 12% of patients in the form of raised troponin levels.
- The largest study conducted at Wuhan University examined 416 patients, median age 64 years with proven COVID-19. Of these patients, 19.7% or 82 patients had evidence of cardiac injury in the form of a raised troponin level. These patients were significantly older (74 vs. 60 years), had higher co-morbidities and presented more severe end-organ damage particularly in the lungs and kidneys. They were also significantly more likely to require a ventilator than those with evidence of cardiac injury. The mortality in patients with cardiac injury was 51.2%, much higher than 4.8% in the non-cardiac injury group.
- A similar mortality rate was seen in smaller studies undertaken in the Seattle Region.
COVID-19 has resulted in over 100,000 deaths globally. The effect of age and cardiac co-morbidities, although not proven, seems to have some effect on mortality.
Younger populations are affected more often possibly due to increased social involvement. It can be postulated that they act as asymptomatic vectors.
The responsibility of social distancing is, therefore, higher in the younger population to protect the more vulnerable, elderly members, of our society.
I am a doctor practising in Australia with a masters in surgery. I am currently training to be a general surgeon with a special interest in public health, cancer surgery and trauma. I write about health, meditation and mindfulness and self-improvement.
Original article published on Medium
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