Cardiovascular diseases (CVDs) are the number one cause of death worldwide where an estimated 17.3 million people died from CVDs in 2022, representing 30% of all global deaths as seasonal variation in morbidity and mortality due to CVDs were noted in both the northern and southern hemispheres, with higher incidence rates during the winter than in the summer. This variation was linked with multiple risk factors such as temperature, physical activity, air pollution, infections and food habits.
Another potentially important seasonal risk factors such as seasonal variation in the plasma level of fibrinogen, cholesterol, Hormones and vasoactive substance including vasopressin (AVP), norepinephrine (NE), epinephrine (E) and angiotensin II, aldosterone and catecholamine which tends to rise in the winter is suggested to play an important role in the seasonal change of CVDs.
In an interview with HT Lifestyle, Dr Ajit Menon, Consultant, Cardiac Sciences at Sir HN Reliance Foundation Hospital, pointed out, “There has been an increase in the heart attacks post Covid. We do see an increased number of patients coming in with heart attacks. They are seen initially in the early phase of Covid and the immediate post Covid phase. However, at this point of time, we’re not seeing any marked increase in those patients. We have probably gone back to what we were in the earlier phases.”
Talking about how do you medically diagnose a heart attack, he said, “There are certain symptoms of a heart attack like severe chest pain, which is normally in the center of the chest, it feels more like a weight being kept in a chest. This pain can radiate to the arms or to the angle of the jaw, or it can travel down into the upper stomach area also. Some patients may only come to complain of basically an uneasiness or a burning pain or a feeling like a suffocation. So the symptoms of a heart attack are sometimes difficult to decipher but if anyone has any uneasiness or severe discomfort, which is unusual, I think they should seek medical attention and the easiest thing to do would be to do an ECG. An ECG would tell us if there is evidence of a heart attack or any compromise in the blood supply to the heart muscle.”
Seasonal variation in sudden cardiac death (SCD) has been well documented by several epidemiological studies with maximum and minimum incidences in winter and summer while few studies observed a different seasonal peak in the onset of SCD characterized by a higher frequency in the summer months. Dr Abhijit Khadtare, Cardiologist at Ruby Hall Clinic, said, “The exact cause of this variation is unknown but it is believed that a combination of external and internal factors such as cold weather, increased platelet aggregability, decreased fibrinolytic activity, and other blood components involved in thrombogenesis may be an important risk factor in bringing on the onset of SCD in winter. This approach is strengthened by the findings of similar seasonal patterns for myocardial infarction, transient myocardial ischemia, and arrhythmias.”
He highlighted, “The winter increase in the occurrence of these related disorders suggests causation by identifiable triggers. Mechanisms that could explain the association between cardiovascular diseases and temperature remain undetermined. Activation of the sympathetic nervous system and secretion of catecholamine are increased in response to cold temperatures. This could result in an increase in blood pressure through increased heart rate and peripheral vascular resistance.In patients whose coronary circulation is already compromised this extra demand may produce myocardial ischaemia therefore, angina pectoris or MI.A statistically significant positive correlation was also found between both air pressure and humidity and the incidence of PE.”
A study conducted in Scotland found that wind speed and temperature were significantly associated with seasonal peak of DVT and the effect was delayed by approximately 9-10 days but the authors calculated that every 10-mbar decrease in pressure was associated with a 2.1% increase in the relative risk of DVT. Additionally, experimental studies suggested that alterations in temperature might also influence vascular function through an effect on endothelial nitric oxide synthase and the bioavailability of nitric oxide where in rats, acute and short-term exposure to elevated environmental or core body temperatures has been shown to increase endothelial nitric oxide synthase expression.
Conversely, repeated cold exposure of rats (4°C for 4h per day for 1 week) led to the development of hypertension and impaired endothelial vasodilator function in isolated arterial tissue. Dr Abhijit Khadtare suggetsed, “The knowledge of the role of environmental and biological factors could be used to improve prevention measures and educational strategies, especially in people with a risk of diseases. People should be informed of the increased risk of cardiovascular disease during the cold seasons, and educated about the importance of regular physical activity and dressing warmly in winter. Furthermore, people should be motivated to maintain health dietary habits including a nutrient rich in vitamin D and low fat intake. There also need to manage hospital beds and other resources effectively in winter to avoid bed crisis.”