INTRODUCTION
Acute myocardial infarction (AMI) is one of the most common diseases among the developing countries.[ 1 ] It occurs when there is a sudden block in blood flow in one or more of the coronary arteries and this cuts off the blood supply to a part of the heart muscle, causing necrosis. Myocardial infarction usually begins in the endocardium and spread towards the epicardium.[ 2 , 3 ]
The incidence of myocardial infarction in the world varies greatly. In the United States and the United Kingdom, nearly 650,000 and 180,000 patients get an AMI every year, respectively.[ 4 ] Worldwide, more than 3 million people have ST-elevation myocardial infarction (STEMI) and 4 million have non-STEMI.[ 5 ] Indians are four times more prone to AMI as compared to the people of other countries due to a combination of the genetic and lifestyle factors that promote metabolic dysfunction.[ 6 ] The incidence of myocardial infarction in India is 64.37/1000 people.[ 7 ] The mortality rate of myocardial infarction is approximately 30%, and 1 of every 25 patients who survive the initial hospitalisation dies in the 1st year after AMI.[ 6 ] In India, 31.7% of deaths occur due to myocardial infarction.[ 3 ]
The concurrence of metabolic risk factors for endothelial dysfunction and atherosclerotic cardiovascular disease (CVD), which include abdominal obesity, hyperglycaemia, dyslipidaemia and hypertension, suggests the existence of metabolic syndrome (MetS). The MetS is defined by a constellation of interconnected physiological, biochemical, clinical and metabolic factors that directly increases the risk of CVD.[ 8 ] It is associated with a 2-fold increase in cardiovascular outcomes and an 1.5-fold increase in all-cause mortality.[ 9 ] In 2001, the National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III had defined MetS.[ 10 ]
Worldwide, the prevalence of MetS ranges from <10% to as much as 84%, depending on the region, urban or rural environment, composition (sex, age, race and ethnicity) of the population studied and the definition of the syndrome used.[ 11 ] In general, the International Diabetes Federation estimates that one-quarter of the world’s adult population have the MetS.[ 12 ] Higher socioeconomic status, sedentary lifestyle and high body mass index (BMI) were significantly associated with MetS. The observed prevalence of the MetS in the National Health and Nutrition Examination Survey (NHANES) was 5% among the subjects of normal weight, 22% among the overweight and 60% among the obese.[ 13 ] It further increases with age (10% in individuals aged 20–29, 20% in individuals aged 40–49 and 45% in individuals aged 60–69 years).[ 11 ] The prevalence of MetS (based on NCEP-ATP III criteria, 2001) varied from 8% to 43% in men and from 7% to 56% in women around the world.[ 14 ]
In the third NHANES population, MetS was a significant univariate correlate of prevalent coronary heart disease, but was not independently correlated with coronary heart disease in multivariate analyses adjusted for blood pressure (BP), high-density lipoprotein (HDL) cholesterol (HDLc) level and diabetes mellitus.[ 15 ] These findings may reflect the substantially worse baseline characteristics of patients with, compared with those without, MetS. There was a consistent and marked increase in the incidence of heart failure and cardiogenic shock in patients with MetS. The strong association between MetS and the occurrence of severe heart failure remained highly significant, even after adjustment for confounding factors.[ 16 ] Studies have shown that, among the 5 criteria for MetS, only hyperglycaemia was an independent determinant for the prediction of cardiogenic shock, even when adjusted for age, female sex, previous MI, anterior wall MI, creatinine clearance and the other components of MetS. Hyperglycaemia, as part of the MetS criteria, was a strong and independent predictor of severe heart failure.[ 16 ]
The prevalence of this syndrome in patients with acute coronary syndrome has been studied very less in India. In particular, the impact of MetS on hospital outcomes after presentation for an AMI is unknown. Therefore, the present study was planned to evaluate the prevalence of MetS in patients admitted with AMI and its impact on the hospital outcomes.
MATERIAL AND METHODS
The study was a single-centre, observational, cross-sectional study conducted on patients in the cardiology and medicine intensive care units of a tertiary care hospital. The study was conducted for a period of 2 years (January 2017 to December 2018). A total of 210 patients were enrolled in the study. The study was initiated after obtaining approval from the institutional ethics committee (No IEC/PG/153/Oct/2017, dated 30 October 2017). Patients with pre-existing renal disease and hepatic diseases were excluded from the study.
Height and weight were measured with the participant wearing light clothing and no shoes; BMI was calculated as weight (Kg)/height (m2 ). Subjects were assessed for the five components of the MetS. A physician diagnosis of high BP was queried. BP was measured using a standard mercury sphygmomanometer in the right upper limb in the supine position. The mean value of two measurements taken at least 1 Min apart was used in the analysis. Fifth-phase Korotkoff sound was used for diastolic BP. Fasting blood samples were drawn for glucose and lipid profile in the first 24 h after acute coronary insult. Fasting plasma glucose was measured with glucose oxidase method. In patients who have had AMI, lipoprotein levels measured within the first 24 h provide an approximation of their usual levels; otherwise, the levels may not be stable for up to 6 weeks. Total cholesterol and triglycerides were measured by enzymatic methods (EM 360 autoanalyser). The HDLc was measured by precipitation with magnesium and phosphotungstic acid. LDL cholesterol was calculated from the Friedewald equation (provided the triglycerides were <400 mg/dL). Waist circumference was measured using a non-stretchable flexible tape in horizontal position just above the iliac crest at the end of normal respiration, in the fasting state. NCEP ATP III definition criteria were used for the diagnosis of MetS.[ 10 ]
Statistical analysis
The data were recorded in a pro forma, entered into Microsoft Excel 2015 and analysed using GraphPad Prism (GraphPad Software, San Diego, CA, USA). Descriptive statistics for quantitative variables was represented as mean ± standard deviation. Qualitative variables were represented as frequency and percentages. Unpaired t -test or Mann–Whitney U -test was used to compare continuous variables. For each type of complication and site of involvement, relative risk (RR) of death was calculated between patients with and without MetS. A P < 0.05 was considered statistically significant.
RESULTS
During the study period, 220 patients presenting with AMI were screened for inclusion in the study: 10 were excluded (reasons for exclusion: pre-existing renal disease [n = 4], pre-existing hepatic disease [n = 3] and both hepatic and renal diseases [n = 3]) and 210 patients were included. Their mean age was 56.5 ± 5.2 years; there were 141 (67.1%) males (male: female = 2.04:1). Majority of the participants were in the age group of 46–60 years (73.3%), followed by those in 61–75 years (25.2%).
Chest pain was the most common complaint (86.7%), followed by breathlessness (36.7%), palpitations (26.7%), sweating (25.7%), cough (20.5%) and vomiting (15.2%). Of the 210 patients studied, 3 of the 5 features of MetS were evident in 101 (48.1%). The comparison of features of patients with and without MetS is shown in Table 1 . No significant difference was seen in the mean age (P = 0.70) and male–female distribution (P = 0.55) in patients with and without MetS. A significant difference was seen in the BMI, waist circumference, triglyceride, fasting blood sugar level, HDL and systolic–diastolic BP in patients with and without MetS.
Table 1: Comparison of features in patients with and without metabolic syndrome
The prevalence of individual components of MetS among the MetS group as compared to the non-MetS group is shown in Table 2 . There was a significant difference in the numbers of patients with increased waist circumference, low HDL, increased BP and increased fasting blood sugar level. No significant difference was seen in the percentage of participants with hypertriglyceridaemia. There was a significant difference in the numbers of patients with increased waist circumference, low HDL, increased BP and increased fasting blood sugar level. No significant difference was seen in the percentage of participants with hypertriglyceridaemia.
Table 2: The prevalence of individual components of MetS among patients with and without MetS
Three, four and all five components of MetS were evident in 101 (48.1%), 9 (4.3%) and 16 (7.6%) patients, respectively. Anterior was the most common site involved. However, there was no significant difference in the distribution of the site of AMI in patients with and without MetS (Table 3 ) (P = 0.22). A significantly higher proportion of patients with MetS had died compared to those without MetS (16/101 vs. 4/109; P = 0.003). The mean duration of hospital stay was longer in patients with MetS compared to those without MetS (7.11 ± 1.79 vs. 5.85 ± 1.72; P < 0.0001). The comparison of complications among patients with MetS compared to those without MetS is shown in Table 4 . A significantly higher proportion of patients with MetS manifested heart failure compared to those without MetS (P = 0.009) (Table 4 ). The association of mortality with occurrence of complications and site of involvement in survivors and non-survivors with and without MetS is shown in Table 5 . Bundle block had two times the risk of death in the presence of MetS, whereas heart failure had nearly 1.5 times more risk for those with MetS than those without MetS. The other two complications, however, do not show a significant RR. Among different sites of involvement leading to death, ‘inferior’ had a significant risk of more than three times for MetS patients than those without MetS. This is followed by ‘posterior’ and ‘lateral’.
Table 3: Site of acute myocardial infarction in patients with and without MetS
Table 4: Complications among patients with metabolic syndrome compared to those without MetS
Table 5: Association of mortality with complications in patients with and without MetS
DISCUSSION
The mean age of the participants enrolled in our study was 56.5 ± 5.2 years. Majority of the participants were in the age group of 46–60 years (73.3%), followed by those in 61–75 years (25.2%). This can be compared to the results reported in another study,[ 17 ] where the average of patients was 58 ± 9.8 years. Another study[ 18 ] reported the mean age to be 62.4 ± 11.9 years. The mean age of participants enrolled in a study[ 19 ] was 56 years with majority of the participants in the age group of 51–60 years. Another study[ 20 ] from India reported 45% of patients in the age group of 60 years and above. Increasing age is a potent risk factor for the development of atherosclerotic CVD, and it is also a powerful predictor of adverse outcomes following an incident cardiovascular event. Gender-wise distribution of study participants showed that majority of the participants enrolled in our study were male (67.1%). The male-to-female ratio in our study was 2.04:1. Male preponderance was also reported in another study,[ 17 ] where 80% of the participants were male. The incidence in males was 92.5% in a study.[ 20 ] Similar results were reported in a study,[ 19 ] where 72% of study participants were male. Another study[ 21 ] also reported male preponderance, with 65.47% of participants being male. Studies in literature have highlighted that for the people aged above 40 years, the lifetime risk of developing CVD is 49% in men and 32% in women. For those reaching age 70 years, the lifetime risk is 35% in men and 24% in women.[ 22 ] Chest pain was the most common complaint among 86.7% in our study. The other common complaints were breathlessness, cough, vomiting, palpitation and sweating. A study[ 19 ] reported that the most common presenting symptom was chest pain (94%), followed by sweating (78%) and breathlessness. In a study,[ 23 ] which compared signs and symptoms of acute coronary syndrome in male and female patients, symptoms such as fatigue, light-headedness, dizziness, nausea, dyspepsia and fear were more common in females. A study[ 24 ] had reported the most common presenting symptoms as chest pain and sweating, regardless of age. In a study,[ 25 ] dyspnoea was the most common sign of AMI in patients over 85 years and nausea and vomiting increased the odds of AMI two-fold. Dyspnoea, weakness, fatigue, coughing and nausea can be due to neuropathy and dysfunction of autonomic nerve fibres.[ 26 ] Although chest pain is the most important symptom of AMI, it may be invariably absent in some patients. Another study[ 27 ] also found that some patients may present with symptoms other than chest discomfort; such ‘angina equivalent’ symptoms include dyspnoea (most common), nausea and vomiting, diaphoresis and unexplained fatigue. The prevalence of MetS in our study was 48.09%, where 48.09% of participants presented with at least 3 out of 5 clinical features of MetS. The average age of participants with MetS was 56.7 ± 5.4 years, with 69.3% of male patients. A study[ 17 ] reported 40% prevalence of v on applying the criteria. Among these, 29 patients were male and 11 were female accounting for 36% of the males and 55% of the females, respectively. Results similar to our study were reported in another study,[ 28 ] where the prevalence of MetS was reported to be 45.5%. The mean age at presentation was 56.2 ± 11.6 in those with MetS and 54.8 ± 10.9 in those without MetS. Male predominance was also reported in this study,[ 28 ] where 116 (71.2%) male patients were in the MetS group and 152 (77.9%) male patients were in the non-MetS group. A higher prevalence of MetS was reported in another study,[ 29 ] where 59% prevalence of MetS was reported. The mean age of participants with MetS was 56.8 years as compared to 57.6 years in those without MetS. A lower prevalence was reported in a study,[ 21 ] where 26.19% of AMI cases had the MetS; this was mainly in females and the older age groups. The average age of the patients with MetS was 60.7 ± 11.7 years and those without MetS was 61.4 ± 10.1 years. A study[ 16 ] reported 46% incidence of MetS with male preponderance. In this study,[ 16 ] the mean age of participants with MetS was 70 years. A significant difference was seen in the average BMI (P = 0.0001), waist circumference (P = 0.0001), serum triglycerides (P = 0.0001), serum HDL (P = 0.0001), FBS (P = 0.0001), systolic BP (P = 0.0001) and diastolic BP (P = 0.0003) in participants with MetS as compared to those without MetS. A study[ 30 ] reported a significant difference in the BMI, FBS and HDL, but no significant difference in the total cholesterol and LDL. In our study, there was a significant difference in the numbers of patients with increased waist circumference, low HDL, raised BP and raised fasting blood sugar levels in the group with MetS, but no significant difference was seen in the percentage of participants with raised triglycerides. Results similar to our study were reported in another study,[ 31 ] significant difference was seen in the numbers of patients with increased waist circumference, low HDL, raised BP and elevated fasting blood glucose level, but no significant difference was seen in the percentage of participants with raised triglycerides in group with and without MetS. A study[ 21 ] reported a significant difference in the numbers of patients with low HDL, raised fasting blood sugar level and raised triglycerides, but no significant difference was seen in the percentage of participants with increased waist circumference and raised BP. Another study[ 17 ] reported a significant difference in the number of patients with all the components of MetS in the MetS group. A study[ 29 ] reported a significant difference in the prevalence of patients with increased waist circumference, raised BP, raised fasting blood sugar level and raised triglycerides, but no difference in patients with low HDL in both the groups. Recently, there has been a growing interest in the components of MetS, not only in relation to the number present but also their different combinations, in the prediction of cardiovascular risk. In our study, hyperglycaemia and low HDLc levels were the most prevalent components of MetS, followed by waist circumference. This can be compared to a study,[ 30 ] where hyperglycaemia and low HDLc levels were the most prevalent components of MetS, followed by hypertension. In another study,[ 32 ] this was also the most frequent combination observed in patients with ischaemic heart disease. In the present study, majority of participants (48.1%) in the MetS group presented with three components. Four components were seen only in 4.3% of participants, whereas all the 5 components were seen in 7.6% of participants. Another study[ 28 ] also reported majority (52.1%) of patients with MetS having 3 components followed by those with 4 components (35%). A study[ 21 ] also reported that majority of patients with MetS had three components of MetS. Anterior wall MI was the most common in patients with (53.4%) and without (38.5%) MetS (P = 0.22) between the two groups. The other common sites involved were septal, lateral, posterior and inferior. Heart failure was the most common complication in both the groups; there was a significant difference seen in the incidence of heart failure in the two groups (P = 0.009), but no significant difference was seen in the incidence of bundle block, ventricular tachycardia and cardiogenic shock in patients with and without MetS. Similar to our study, a significant difference in the heart failure was seen in another study[ 28 ] and no difference in bundle block, ventricular tachycardia and cardiogenic shock. Heart failure was also the common complication in both the groups. A study[ 16 ] also reported a significant difference in the incidence of heart failure, but not in the incidence of bundle block, ventricular tachycardia and cardiogenic shock in patients with and without MetS. Mortality was higher in patients with MetS (P = 0.003) as compared to those without MetS. Majority of patients patients with and without MetS had heart failure as a predisposing condition for mortality. Anterior wall was the most common site of infarction in all non-survivors in both the groups of patients. No significant difference was seen in the distribution of site of infarction in patients with MetS and those without MetS. A similar result was reported in a study,[ 16 ] where significant differences in the case fatality rate were seen between the two groups. In contrast to the above finding, no difference in the mortality was reported in some studies.[ 21 , 29 ]
A significant difference (P < 0.0001) was seen between the two groups in the duration of hospital stay in the present study. Similar results were reported in another study,[ 33 ] where a statistically significant difference (P = 0.02) was seen in the average duration of hospital stay in patients with (10.1 ± 3.8 days) and without (9.2 ± 3.2) MetS. The study[ 33 ] recorded longer period of hospitalisation among the patients with MetS after STEMI. In contrast to our study, in another study,[ 21 ] the median duration of hospital stay was 4 days in the non-MetS group and 5 days in the MetS group (P = NS). We had observed that MetS was evident in almost half (48.1%) of the patients presenting with AMI. The presence of MetS significantly increased the risk of complications, fatality and duration of hospital stay in patients with AMI.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgements
The authors wish to thank Dr N. O. Bansal, Professor and Head, Department of Cardiology, Grant Government Medical College, Mumbai, for permitting us to include patients admitted in the Cardiology ICCU in the present study.
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