Coronary artery disease continues to contribute significantly to the strain on healthcare resources world over. The major risk factors contributing to the development of CAD remains same throughout the world; however, there are differences in the contribution of the individual risk factor for the development of CAD in developing and developed world .
The mean age of patients in our study was 55.8 ± 9 years with 72.12% of patients between the ages of 40 to 60 years. The mean age of the patients in our study was lower, and the majority of patients were younger than that in other studies [10, 11]. This data was consistent with previous studies done in India which show that CAD presents a decade early in Indian patients [12,13,14,15,16]. A strong male preponderance was noted with male: female ratio of 5.6:1 which was consistent with the other studies conducted earlier at this centre and the rest of the country [17,18,19]. Majority of patients were having BMI in the normal range. More female patients were overweight or having grade 1 obesity than the male counterparts likely owning to the relatively sedentary lifestyle in females [17, 20]. Dyslipidemia was the most common risk factor associated with this study group of patients. Dyslipidemia prevalence is significantly higher than that reported in other studies in which no segregation of diabetic and non-diabetic patients presenting as ACS was done [19, 21].
Smoking was the second most prevalent risk factor associated in this study. 81.25% of cases had an active smoking history. It was more common in males than in females. Smoking prevalence is significantly higher in this study than other studies from across the country and abroad because the general population prevalence of smoking in our state is twice the national average as reported by the Global Adult Tobacco Survey-2 (GATS-2) 2016–2017 [15, 22, 23]. Hypertension was the third most common risk factor identified, and the prevalence of hypertension in males was nearly twice that of females. This male preponderance may be due to non-segregated nature of other studies.
ST-elevation myocardial infarction (STEMI) was the most common presentation of acute coronary syndrome (ACS). This data reinforces the fact that ACS is the most common presentation of coronary diseases in developing countries than developed countries because of lack of awareness and infrastructure for picking up patients early like stable chronic angina [24, 25].
The percentage of patients presenting in the therapeutic window for thrombolysis in our study was lower than the national average of 80%  mainly because our state is a hilly state with underdeveloped road connectivity, majority of the population resides far from urban centres, and delay in recognition of the medical condition, though the efforts are ongoing to develop infrastructure for implementing the pharmoco-invasive strategy involving early recognition of the myocardial infarction, encouraging thrombolysis at peripheral centres wherever indicated and urgent referral to PCI-capable centre. Only 11.9% of patients received primary PCI as the therapeutic intervention which was consistent with the national data from other studies from the developing world . This is in sharp contrast to the scenario in developed countries like the USA where 70–80% of the patients with acute coronary syndrome receive primary PCI due to the presence of a large number of PCI-capable centres throughout the country and majority of the population residing within 30–60 min away from these centres . The reason for low primary PCI procedure in developing countries like ours are multifactorial but the main reasons being lack of adequate number of PCI-capable centres within the quick reach of the majority of the population resulting in loss of precious time for intervention, lack of health insurance cover, low socioeconomic status, and lack of awareness .
Older non-fibrin-specific drug streptokinase was the most commonly used thrombolytic agent, and the use of never fibrin-specific drugs like tenecteplase and reteplase was low. The same reasons as for low primary PCI intervention contributed to lower penetrance of use of newer fibrin-specific thrombolytic drugs in this study. The incidence of thrombolytic drug-related complication was low within our study population, only 3 cases of minor anaphylaxis with streptokinase and only 2 cases of minor bleeding (1 with streptokinase and 1 with tenecteplase) which were managed conservatively. The probable reasons for lower drug-related complications in this study were younger age of the patients and less associated co-morbidities.
Fasting blood sugar levels were high in the majority of patients. Only 19.23% of the patients had normal (< 100 mg/dl) fasting blood sugar levels. Overall, 80.77% of patients in our study were either diabetic or were having impaired fasting blood sugars. This data is significantly higher than the data reported in other Indian and foreign studies [21, 29]. Similarly, the HbA1c levels confirmed the diagnosis of diabetes mellitus in over 40% of cases, and another 39.42% of patients were having HbA1c in the range of pre-diabetes. In total, more than 80% of cases were either diabetic or pre-diabetic, and only less than 20% of cases had HbA1c levels in the normal range. There are fewer studies in literature in this regard so far. The published literature from other countries like Japan put the incidence of diabetes in this group of patients at around 40 to 45% . The data in our study shows double the prevalence of diabetes in these patients. Our data is consistent with the results obtained by Nanayakkara et al.  who showed 47% diabetic and 53% prediabetes in their study of similar patients. The higher incidence of diabetes in this study may be due to failure to detect diabetes early in the developing nations due to lack of community-based diabetes detection programme, ignoring the symptoms and lack of routine medical care or malignant nature of this disease along with other risk factors in Indian subcontinent population. In contrast to some studies, the fasting blood sugar levels and HbA1c levels correlated well with each other in the diagnosis of diabetes status in our study [21, 31].
Single vessel involvement was most common. Half of the patients had single-vessel disease and another 1/3 of patients was having double vessel involvement and only about 12% of cases had triple-vessel disease. This data was similar to earlier studies [22, 23]. The predominant reason for single-vessel involvement could be due to the presence of a large number of young patients with fewer comorbidities in this study cohort.
In this study, we used the Gensini score to estimate the disease burden of coronary vessels. Gensini score estimates the severity of atherosclerosis in coronary vessels very well and calculates the disease burden depending upon the severity of vessel stenosis, its location, and the area at risk with the lesion [6, 8]. Patients with Gensini scores of 20 or more are defined as having severe CAD, which was approximately equal to one stenosed lesion of 70% or more in the proximal left anterior descending artery . The mean Gensini score in our study was 22.51 ± 10.37. Sixty percent of patients were having severe CAD with Gensini score of ≥ 20.
Bivariate two-tailed correlation analysis showed a significant positive correlation between HbA1c and Gensini score with Pearson correlation value of 0.586 and p value < 0.001. Similar results were obtained by correlation analysis between HbA1c and number of coronary vessels involved with Pearson correlation value of 0.566 and p value < 0.001. This data strongly supports the data from other emerging studies [10, 30, 33] strengthening the fact that besides diagnosing diabetes mellitus, HbA1c is strongly related with coronary artery disease and can be used as a marker of coronary artery disease and higher HbA1c levels predicting higher coronary artery disease burden.
The major limitation of the study is that this is a single-centre study with a relatively small number of patients; a multicenter study with larger study cohort may be required to give a better estimate of study parameters.