This study examined the association between electrocardiogram (ECG) abnormalities and death resulting from cardiovascular diseases (CVD). The study findings demonstrated that the occurrence of CVD-related death was more prevalent in individuals with ECG abnormalities compared to those without these abnormalities. Among the ECG abnormalities studied (ST, T, Q, PR, QRS), significant associations were observed between Q and T wave abnormalities and death due to CVD. this relationship was adjusted for abdominal obesity, diastolic blood pressure, HDL, LDL, total cholesterol, triglycerides, and smoking status.
Among the risk factors examined in this study, age was directly associated with CVD mortality. Several studies have also identified older age, particularly over 60 years, as a major risk factor for this mortality (24-26). However, most of the conducted studies have primarily focused on elderly individuals and those at risk of Incidence cardiovascular diseases, limiting the generalizability of the findings to younger or healthier populations and different ethnic groups (27).
Systolic blood pressure also showed a direct relationship with CVD death. A cohort study reported a gradual increase in the risk of CVD with higher baseline levels of SBP and diastolic blood pressure (DBP), where each additional 20 mmHg increase in SBP and 10 mmHg increase in DBP were associated with a twofold higher risk of Incidence CVD (28). Other evidence indicates that high blood pressure is the primary cause of long-term consequences such as heart failure (29). It has been estimated that high blood pressure accounts for 49% of the attributable risk for coronary heart disease (CHD) and 26% for stroke (30). However, these estimates may potentially underestimate the true contribution of high blood pressure to CVD due to residual confounding in many cohort studies that rely on a limited number of BP measurements (31). A meta-analysis of 42 trials reported a linear association between average SBP and the risk of death from cardiovascular and coronary artery diseases (32). Another systematic review and meta-analysis found that both long-term and short-term fluctuations in systolic blood pressure are associated with mortality from all causes (27).
Regarding the findings of this study, BMI and FBS did not demonstrate a significant association with the outcome of interest. Similarly, a study conducted by Fereydoun Azizi and colleagues using the same population data reported similar findings over a 10-year follow-up period (33). While obesity has been recognized as a risk factor for CVD in other studies (34-36), conflicting opinions exist regarding the effects of obesity and overweight on mortality. An analysis conducted in the United States estimated that obesity contributes to 300,000 deaths per year (37). Another study also showed that the risk of mortality from any cause is higher in individuals with a high BMI (38). Recent studies have presented more varied associations between obesity and mortality. The risk of mortality associated with obesity has mainly been observed among younger populations, while it has been reported to have a protective effect among older individuals (39-42). Additionally, being overweight has been associated with a 20% reduction in overall mortality risk and a 40% increase in the risk of Incidence of CVD in the Iranian population (43). Regarding FBS, contrary to the results of this study, another study estimated that diabetes accounts for 11% of deaths from cardiovascular in an adult population with a 10% prevalence of diabetes (44). Since the data from the mentioned studies are predominantly from high-income countries, it may not accurately estimate the attributed burden of cardiovascular disease to diabetes in low- and middle-income countries. Another study conducted on postmenopausal women found that fasting glucose in the high range was significantly associated with cardiovascular diseases and all-cause mortality while fasting glucose in the low range did not show such an association (45). This discrepancy in results may be due to variations in the prevalence of diabetes across different studies, which are somewhat influenced by gender distribution differences.
The present study demonstrated a significant association between LDL and the study outcome. Other studies (46-48) have also confirmed these findings. The Kronmal et al. study yielded similar results to this study in all age groups (49). A meta-analysis of 53 randomized controlled trials concluded that a reduction of 1 mmol/L in LDL-C decreases the risk of cardiovascular mortality (50). However, other studies have shown contradictory results regarding the association between LDL levels and CVD mortality compared to the findings of this study.
In this study, no association was found between WHR and death from CVD, while another study accepted this association in women (51). However, Timothybourne and colleagues stated that abdominal obesity, as assessed by waist-to-hip ratio, is a better predictor than waist circumference for CVD and CHD mortality, which, in turn, is a better predictor than BMI (52). In a meta-analysis conducted in Britain, WC and WHR were found to have the strongest association with an increased risk of CVD and all-cause mortality, and among the two, WHR showed the highest level of association. In multivariable models, BMI was not associated with CVD incidence and had an inverse association with all-cause mortality (53). Several other studies have also introduced WHR as the most useful obesity measure for identifying individuals at risk of CVD (54-58). However, in all of these studies, after age matching and controlling for other group characteristics, this association was observed.
In this study, the odds ratio of death from CVD was higher in men than in women, and the study by Woodward and colleagues also reached a similar conclusion (25). Another study stated that the rate of CVD mortality is higher in men during younger ages but higher in women, particularly around the age of 60 (26).
Multiple studies have found that being unmarried (never married, divorced, or widowed) is associated with an increased likelihood of Incidence of CVD and death from CHD (59-62). Another study showed that CVD mortality is higher in married men than in unmarried men, but in women, the reverse relationship holds (63). This study did not show a significant association between marital status and death from CVD.
The association between electrocardiogram (ECG) abnormalities and death from cardiovascular diseases (CVD) has been examined in previous studies. This study findings demonstrated that abnormal ECG findings initially increased the risk of CVD mortality by 3.3 times and, after adjusting for known risk factors, increased the risk of CVD-related mortality by 1.93 times. Similar results were reported by the Health ABC study, which showed a significant association between major and minor ECG abnormalities and an increased risk of cardiovascular disease (CAD) (64).
In a prospective population-based study conducted by Adam Goldman and colleagues, involving 2,601 individuals without known CVD, the cumulative occurrence of CVD and overall mortality was monitored over 23 years. They also found that ECG abnormalities were associated with a more than 46% increased risk of developing CVD, and non-specific T-wave changes and left ventricular axis deviation were significantly associated with mortality (65).
A study in Lithuania reported that individuals with ECG abnormalities, MI, and ischemic changes had a 2.5-fold and 4.4-fold increased risk of death from CVD in men and a 1.51-fold and 2.56-fold increased risk in women compared to those without ECG abnormalities. Utilizing ECG abnormalities alongside established risk factors improved the early identification of individuals at risk of CVD (66).
In a systematic review conducted by Daniel E. Jonas and colleagues, which examined the screening of cardiovascular risk using resting and exercise ECG, 16 studies (N=77,140) were reviewed. In two clinical trials (n=1,151) involving adults aged 50 to 75 with diabetes, no significant relationship was found between screening with exercise ECG and cardiovascular outcomes. No clinical trial evaluating screening with resting ECG was found in their searches. Evidence from 5 cohort studies (n=9,582) screening with exercise ECG and 9 cohort studies (n=66,407) screening with resting ECG demonstrated that adding ECG abnormalities to known risk factors improved the prediction of cardiovascular diseases (67).
In a prospective study by Jingya Niu and colleagues, involving 2,470 participants with ECG abnormalities, 464 CVD events were observed during the follow-up period (68, 69).
Several studies have also found a significant association between ECG abnormalities and known risk factors for cardiovascular diseases, including a cross-sectional study conducted on 31,399 Korean participants that used the Novacode system to examine ECG abnormalities (70), another cross-sectional study on an Iranian population with 3,723 participants that used the Minnesota coding system to classify ischemic ECG manifestations (71), and a multi-ethnic cross-sectional study in the United States involving 6,765 participants (Caucasian, Chinese, African-American, and Hispanic) that used the Minnesota coding system to classify ECG abnormalities (72). Recent studies have also shown that ECG analysis using artificial intelligence-based ECG learning approaches may predict mortality, cardiac arrhythmias, cardiac function, heart failure, and valvular heart diseases (73-79).
In the study by Xiaojian Zhang et al., patients with T-wave abnormalities, ST segment abnormalities, and ST-T abnormalities had lower overall and cardiovascular survival rates compared to patients without any ECG abnormalities (80). Other studies have demonstrated the association of ischemic ECG findings or ST-T abnormalities with an increased risk of Incidence of CVD, cardiovascular mortality, and all-cause mortality (81, 82). However, in this study, a significant relationship between ST abnormalities and death from cardiovascular diseases was not observed, which is consistent with the findings of the study by Caravallo et al., suggesting that these differences in results may be due to the use of different models in the studies or differences in the selected sample populations (83).
The main strengths of this study include a large sample size, a long-term cohort study design, the involvement of a minimal number of cardiovascular specialists in interpreting all ECGs, and efforts to minimize observer variability through adjustment using numerous intervention variables. However, the study also has limitations, such as the possibility that despite the use of many intervention variables in the adjustment method, some unmeasured confounders may still interfere with the association between ECG abnormalities and the risk of death from CVD.