Hypertension and Myocardial Infarction: A Study and Review
- 1. Department of Medicine, Index Medical College, Hospital and Research Centre, India
Abstract
Aim: Regional pattern and significance of risk determinants paving the way to incidence and fate of myocardial infarction (MI) in hypertensive subjects is attempted elaboration through comparison with contemporary cases of MI in normotensive patients in an 18 month long study at medical college hospital setting in central India.
Method: MI cases in 35 to 75 year age range without major unrelated systemic diseases were studied in hypertensive and normotensive categories. Demographic, clinical and laboratory information, as well as complications and outcome, were examined.
Results: MI in hypertension associated earlier age, more with positive family history of ischaemic heart disease, overweight, poor physical activity, deficient fresh fruit intake and the smoking habit. Uncontrolled diabetes significantly associated MI in hypertension as also deficient plasma antioxidant capacity. Hypertensive MI also had marginally increased rates of dyslipidaemia, and renal function declines. Incidence of various cardiac complications were insignificantly higher hospital stay was prolonged in hypertensive MI.
Conclusion: Pattern of risk factors and clinical course of MI in studied categories emphasized preventive dietary and physical activity measures for weight reduction, deterrence of smoking and good control of co-existing diabetes as most pertinent to bring down incidence and possibly severity of MI in hypertension, in central Indian context. Particular reference to antihypertensive cum cardioprotective drug classes angiotensin converting enzyme (ACE) inhibitors and angiotensin (AT)-II receptor blockers, beta blockers and calcium channel blockers is made in the context.
Keywords
Hypertension, Myocardial infarction, Ischaemic heart disease, HbA1c (Glycosylated hemoglobin
Citation
Pandit A (2017) Hypertension and Myocardial Infarction: A Study and Review. J Cardiol Clin Res 5(6): 1118.
INTRODUCTION
Hypertension (HTN) is a major cause of mortality and morbidity and is expected to affect 1.56 billion people by 2025 [1].Currently 31.4% of Indian population is estimated to suffer HTN [2]. Elevated blood pressure is the key risk factor for cardiovascular disease [3,4]. Myocardial infarction (MI) is major cause of mortality and morbidity, often resulting as complication of HTN. Almost 40% of patients with ischaemic heart disease (IHD) who die suddenly have history of HTN [5]. Over 90% of MI victims bear many risk factors for coronary atherosclerosis besides HTN, viz. smoking habit, obesity, dyslipidaemia etc [6]. HTN is independent risk factor over other risk factors that may coexist [7]. Heart failure, stroke and other modes of cardiovascular mortality are higher among hypertensive patients [8,9]. Immediate and long term mortality after infarction is increased in hypertensives partly due to increased instances of myocardial and septal rupture [10].
Hypertension and IHD
HTN causes myocardial perfusion and ventricular function abnormalities, independent of the consequences associating ischaemic heart disease. HTN induces ventricular hypertrophy and together with that further compromises myocardial perfusion. The mechanisms include decrease in capillary density [11], failure of capacity to vasodilatation with increased muscle mass [12], an increased resistance for coronary collaterals [13] and more severe sub-endocardial involvement and larger ischaemic zones [13]. There is linear increase in risk of MI with increase of blood pressure status. HTN particularly raises the risk of MI in people under 65 years [14].
Commonest basis for MI is atherosclerotic disease of coronaries with thrombosis, spasm or plaque rupture, the precipitating entity being atheroma. HTN increases the prevalence of occlusive disease of coronaries [15]. Several studies have reported that hypertensive patients had higher instances of heart failure, stroke and cardiovascular death [9,16]. Hypertensive patients suffer multivessel coronary disease and complex coronary lesions contributing to worse outcome of MI. Aggravated atherosclerosis, left ventricular hypertrophy, insulin resistance, endothelial damage and ventricular arrhythmias all worsen prognosis [17]. Hypertensive MI patients suffer higher instances of postinfarct angina pectoris, recurrent silent myocardial ischaemia and infarction, atrial and ventricular fibrillation, cardiogenic shock and pulmonary oedema than normotensive MI cases [9,18,19].
IHD risk due to HTN however is seen to vary among populations and is low in black Africans who generally display lower serum cholesterol profiles [20]. In contrast to western world HTN in Asians has unique traits in terms of response to antihypertensive medication, complications and outcome [21]. Due to high prevalence of HTN and diabetes, risk of stroke and coronary disease is high in Asia [22]. Significant regional variation in prevalence of coronary heart disease is documented in Asia [23,24]. Need for studies to asses nuances and features of hypertensive patients in Asia are emphasized [25], in order to optimally translate western recommendations of prevention and management. HTN related risk factors (including obesity and diabetes) and unhealthy lifestyle particularly, deserve keen evaluation [26]. The present observational study attempted appraisal of clinical profile and course of MI among normotensive and hypertensive cases in our specific region to generate evidence base for suitable clinical practices for prevention and management
PATIENTS AND METHODS
The study is based on consecutively admitted MI patients in medical wards of Index Medical College, Indore (Central India), between January 2015 to June 2016 period. Patients above 35 years to 75 years age of either sex were included. Patients that had antecedent or subsequently diagnosed systemic diseases unrelated to occurrence of MI were excluded. Although records were not kept the excluded sample constituted around 10% of all screened. The exclusion was a preliminary measure to minimize complicated inferences on group differences. Of the 132 cases finally included, 37 were normotensive and the rest 95 were hypertensive, revealed either through history and/or detected upon examination (Blood pressure >140/90 mm Hg), at admission. MI diagnosis was based on patient meeting at least two of the following three criteria viz. typical chest pain/ discomfort lasting 30 minutes at least; an electrocardiographic prominent Q wave and/or ST segment elevation of >2mm in two contiguous precordial leads and abnormal rise of creatine kinase MB, indicative of myocardial necrosis.
The study protocol was approved by the college research ethical committee. For use of all information relating patient’s condition and care, patient/attendants consent was obtained prior to inclusion, in proposed observational study. Intent and nature of study was made known and assurance of maintaining secrecy of identity was given.
Various risk factors of coronary disease, viz. age, sex, family history, physical activity profile, fresh fruit consumption, smoking habit, obesity (BMI>25kg/m2 ), diabetes (HbA1c level >6.5g/ dl), dyslipidaemia (triglyceride (TG)/high density lipoprotein cholesterol (HDL-C) ratio >3.5), glomerular filtration rate ( cut off 60ml/min/1.73m2 ), plasma malonaldehyde level and plasma total antioxidant capacity were examined as earlier [27,28] and compared between the normotensive and hypertensive MI victims.
Family history of premature atherosclerosis was based on history of MI in parent or sibling male fewer than 55 and female less than 65 year age [29]. History of HTN, diabetes or cerebrovascular disorder constituted positive history irrespective of age. Body mass index (BMI) was calculated as ratio of body weight to height squared and >25kg/m2 was taken as indicative of obesity in our patients [30]. Glomerular filtration rate was estimated from serum creatinine levels [31]. Physical activity status was assessed by enquiring usual activity and minimum 30 minute daily brisk exercise for at least 5 days in a week was deemed as active while less than that as inactive status. Fresh fruit intake was enquired as kind and quantity of fresh fruits consumed over the week and the month. An average minimum alternate day consumption of apple size fruit irrespective of economic status was taken as positive consumption and less as negative. Standard procedures were used for estimation of HbA1c, creatinine, lipid profile as previously described [28]. Oxidative stress markers and antioxidant capacity may vary as per time since occurance of event. These parameters were also estimated on the first day of admission. Plasma malonaldehyde level was determined as thiobarbituric acid reactive substances [32], as indicator of oxidative stress. Total plasma antioxidant capacity was determined by FRAP (ferric oxide reducing ability of plasma) method [33].Infarct localization and hospital outcome in respect to complications, length of hospital stay and mortality were also studied.
Relative frequency distributions of subjects in two compared groups in respect to every parameter were analyzed. Parameters employed cut off as yes/no, general median value or given normal value. Chi square test and when necessary (for small cell numbers), Fishers exact test statistic were used.
OBSERVATION AND RESULTS
Table 1,
Table 1: Distribution of patients in two studied groups around defined parameters.
| Parameters | Normotensive MI (n=37) %age | Hypertensive MI (n=95) %age | p |
| Age | |||
| >62 years | 22 59.5 | 39 41 | <0.057 |
| ≤62 years | 15 40.5 | 56 59 | -- |
| Gender | |||
| Male | 31 83.8 | 67 70.5 | <0.12 |
| Female | 6 16.2 | 28 29.5 | -- |
| BMI | |||
| >25 | 15 40.5 | 56 59 | <0.057 |
| <25 | 22 59.5 | 39 41 | -- |
| Family history of CVD | |||
| Present | 21 56.8 | 35 36.8 | <0.038 |
| Absent | 16 43.2 | 60 63.2 | -- |
| Past H/o CAD | |||
| Present | 1 2.7 | 7 7.4 | -- |
| Absent | 36 97.3 | 88 92.6 | -- |
| Physical Activity | |||
| Inactive | 14 37.8 | 58 61 | <0.016 |
| Active | 23 62.2 | 37 39 | -- |
| Fresh Fruit Consumption | |||
| Yes | 10 27 | 41 43.2 | <0.087 |
| No | 27 73 | 54 56.8 | -- |
| Smoking Habit | |||
| Yes | 21 56.8 | 36 37.9 | <0.049 |
| No | 16 43.2 | 59 62.1 | -- |
presents the comparison of presenting clinical and laboratory profile in two groups.
Higher proportion of hypertensive MI patients was younger under the median 62 years compared to the normotensive group but the gender composition was not different. Obesity defined by BMI above 25 was more prevalent among hypertensive MI group. Significantly higher prevalence of family history of coronary disease was present in hypertension group. History of past episodes of MI did not significantly differ although, more frequent in hypertension group. Significantly high proportion of the hypertensive victims reported physical inactivity in contrast to normotensives. Fresh fruit consumption was low and more so in hypertensive patients. Hypertensive MI group had significantly higher proportion of smokers.
As shown in table (2),
Table 2: Distribution of patients in two studied groups around defined biochemical parameters.
| Parameters | Normotensive MI (n=37) %age | Hypertensive MI (n=95) %age | p |
| Diabetes | |||
| Present | 15 40.5 | 54 56.8 | <0.09 |
| Absent | 22 59.5 | 41 43.2 | -- |
| HbA1c (g/dl) | |||
| >7.5 | 4 10.5 | 25 26.3 | <0.053 |
| <7.5 | 33 89.2 | 70 73.7 | -- |
| TG/HDL-C Ratio | |||
| >3.5 | 15 40.5 | 49 51.6 | -- |
| <3.5 | 22 59.5 | 46 48.4 | -- |
| eGFR ml/min/1.73m2 | |||
| >60 | 14 37.8 | 51 53.7 | -- |
| <60 | 23 62.2 | 44 46.3 | -- |
| Plasma MDA µM/L (Median=3.84) | |||
| >3.84 | 15 40.5 | 50 52.6 | -- |
| <3.84 | 22 59.5 | 45 47.4 | -- |
| Plasma FRAP µM/L (Median=514) | |||
| >514 | 24 64.9 | 42 44.2 | <0.05 |
| <514 | 13 35.1 | 53 55.8 | -- |
prevalence of diabetes and dyslipidaemia was higher among hypertensive MI patients, although the difference was not statistically significant. Significantly high proportion of diabetic hypertyensives also exhibited HbA1c levels above 7.5g/dl indicating poor glycaemic control. Large proportions of MI cases in either group had reduced GFR under 60ml/min/1.73m2 . Median plasma malonaldehyde level of 3.84 µM/L seen in the MI patients is high, near double the normal 2 µM/L level. Plasma antioxidant activity indicated by median FRAP value of 514 µM/L is nearly halved 1000 µM/L normal level. Significantly higher proportion of hypertensive MI cases display lower than median FRAP profile.
ECG based localization of infarct, the events in post MI clinical course and outcome of two groups were summarily examined. Hypertensive group had more of anterior infarcts while normotensives had more inferior infarct. Significantly high proportion of AMI cases of hypertensive group had prolonged hospital stay beyond median 8 days. However these values do not have adequate power and hence credence.Table
DISCUSSION
Classical cardiovascular risk factors as age, sex, smoking, unhealthy diet and physical inactivity, obesity, diabetes, dyslipidaemia and hypertension are widely studied for elucidation of population specific evidence base to support rational approaches to prevention and management. In the present context, the same were studied by dichotomy primarily based on blood pressure parameter in MI cases.
About 72% of all selected sample of MI were having hypertension. This reflects high incidence of hypertension in patients admitted with MI as also reported [34,35]. Many other studies found MI in hypertensives as occurring at relatively older age than in the normotensive people [36,37]. This may characterize as feature of local population with unexplored lifestyle and possibly other phenotypic determinants. Significantly more instances of positive family history of IHD in HTN group also imply significant shared genotype/phenotype of HTN and MI in studied patient population. Obesity and dyslipidaemia are also significantly more prevalent among hypertensive victims of MI. This may suggest large prevalence of metabolic syndrome among the hypertensives with MI. Overweight and obesity are independent coronary risk factors [38,39]. Poor consumption of fresh fruit would particularly detrimental in hypertensives depriving antioxidant nutrients. High prevalence of smoking among the HTN group would inflict oxidative stress increasing atherogenicity of lipids. Smoking is independent strong risk factor for MI [40,41].
Proportion of diabetics among the HTN group is marginally higher. In the group with HTN uncontrolled hyperglycaemia shown as plasma HbA1c above 7.5g/dl, was present in significantly high number there by constituting additional risk factor for IHD [42,43]. Basis for hypertension in majority of studied MI cases therefore could be metabolic syndrome. TG/HDL-C ratio >3.5 is indicative of insulin resistance, and atherogenic dyslipidaemia [44], which was similar in both. eGFR below 60ml/kg/1.73m2 indicates renal insufficiency [28] which is a coronary disease risk factor [45,46], and was also marginally more prevalent among HTN group. Oxidative stress indicated by elevated plasma malonaldehyde levels was also similar in both groups. Plasma antioxidant capacity was low in both but significantly worse in HTN group. Oxidative stress and inflammation are significant CAD risk factors [47]. Poor plasma antioxidant capacity associates greater severity of infarct [48,49].
Higher incidence of variety of cardiac complications observed in hypertensive MI cases is in agreement with other reports [8,9]. Hypertensive cases have high likelihood of more severe atherosclerosis, endothelial damage, insulin resistance, ventricular hypertrophy and ventricular arrhythmias [50]. High likelihood of multiple vascular diseases in coronary arteries is known to occur in the hypertensives [51]. This may explain the observed significantly higher mortality of AMI in hypertensive group. Hypertension is associated with increased risk of atrial fibrillation [52]. High rate of adverse outcome in AMI in hypertension including left ventricular failure and recurrent AMI are reported [53].
Hypertension accelerates atherogenesis primarily dependent on cholesterol. Coronary artery atherosclerotic disease is 2 to 3 fold more prevalent among hypertensive individuals in contrast to that in normotensive people [54]. Clustering of cardiovascular risk factors causes high rate of cardiovascular events [55], and this is frequently the case in Indian patients [56]. Risk increases with increase in number of risk factors [57]. Reduction in number of risk factors yields healthier life and longevity [58,59]. The in hospital mortality in MI cases varies between 7.7% to 19.2% across the globe, while mortality over one year post infarct touches 23% to 25.3% [60,61]. Promotion of healthy diet and increase in physical activity to maintain optimal weight ought to be very intensively persued as cardinal preventive measures.
Increased prevalence of decline in eGFR is found in hypertensive MI cases and there is frequent altered blood sugar stress response associating acute high insulin resistance [62]. Careful metabolic monitoring is therefore required in hypertensive MI cases [63]. Aggressive blood pressure reduction may be pertinent in cases with coronary disease. Control of blood pressure is often suboptimal in clinical practice and this may be the case in over 50% of cases as per Asian study [64]. Association of physicians of India ordinarily encourages blood pressure control at 140/80 mm Hg [65]. High risk cases with clustered risk factors would need tighter control while very old would be better served with systolic 150mm Hg. Optimal treatment of hypertension frequently would require combination drug therapy for prevention of cardiovascular events [66].
