Cold spells translate to increased NSTEMI incidence in Singapore

In warmer parts of the world such as Singapore, a drop in temperature may raise the risk of non-ST segment elevation myocardial infarction (NSTEMI).

In a recent study with 10 years of nationally collected data, a team of local investigators reported that a decrease in ambient temperature from the median to the 10th percentile contributed to a delayed cumulative, nonlinear increase in NSTEMI risk over 10 days after exposure (relative risk [RR], 1.12, 95 percent confidence interval [CI], 1.02–1.24). [Sci Total Environ 2022;850:158010]

Furthermore, older people seemed more susceptible to the effect of cold spells (RR, 1.19, 95 percent CI, 1.06–1.33) than did younger people (RR, 1.00, 95 percent CI, 0.85–1.18; p=0.087 for difference).

The investigators also noted an independent association between warmer temperature and NSTEMI risk, although the lags for the warm effects was shorter, about 0–1 day, as opposed to the 2–10-day lags for the cool effects. These findings, they added, were consistent with those reported in other studies. [Heart 2009;95:1760-1769; Environ Res 2019;175:167-177; Sci Rep 2019;9:13790]

“A number of physiological mechanisms have been suggested for temperature-driven biological pathways of myocardial infarction. Temperature declines from approximately 27 °C to 20 °C (and even below that range) have been associated with higher blood pressure, higher platelet counts, and higher low-density lipoprotein-cholesterol concentrations, and can increase plasma viscosity, platelet aggregation, and risk of plaque rupture, leading to an increased risk of myocardial infarction,” the investigators explained. [Sci Total Environ 2012;435:74-79; Heart 2015;101:808-820]

Meanwhile, the greater susceptibility of older individuals to cold could be related to the differences in blood pressure (BP) response, they added. One study found that the magnitude of cold-induced BP elevations in older individuals were greater than that in younger ones when exposed to cooling temperatures that reached 15 °C, with central arterial stiffness being an important factor in explaining the BP response variability between these groups. [J Appl Physiol 2009;107:1076-1082]

In the study, there were 60,643 reports of NSTEMI from 2009 to 2018, corresponding to a daily mean of 16.6. More than half of the cases were in men (61.7 percent), and almost two-thirds were among people aged ≥65 years. Mean daily ambient air temperature was 27.8 °C, ranging between 26.4 °C (10th percentile) and 29.2 °C (90th percentile) and peaking in the middle of each year. There was high mean relative humidity over the study period (80 percent).

“There are several individual-level risk factors for cardiovascular disease, but none are as widely experienced as weather patterns,” said Dr Joel Aik, an environmental epidemiologist and co-senior investigator of the study, in a statement.

“Daily weather variations have the capacity to trigger cardiovascular disease events in at-risk individuals, with particular implications for Singapore’s ageing population. In the context of climate change, these findings highlight a risk factor of substantial public health concern,” he added.

Aik and colleagues believe that the findings of their study may be applicable and have policy implications for several other tropical cosmopolitan cities, which have similar thermal amplitudes and ageing populations, for which studies on the weather-NSTEMI relationship are scarce.

The investigators called for more studies to identify the biological pathways for the increased vulnerability of cold-related NSTEMI risk in the elderly within the tropics where mean temperatures in the coldest month is at least 18 °C (defined by the Köppen climate classification).