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variable. Indexing by height2 allows differences between subgroups to become apparent and seems to be more appropriate for defecting LVH in obese populations.121
Numerous cut offs for LVH have been proposed and these are shown in table 3 Table 3 Echocardiographic criteria for LVH used in studies of LV mass
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After adjusting for age and blood pressure, body mass index remained a strong independent predictor of left ventricular mass, left ventricular wall thickness and left ventricular internal dimension.31
In another interesting study by Hammond et al 124, it was concluded that obesity as measured by body mass index is as important a potential determinant of left ventricular mass as is systolic blood pressure and is of greater statistical significance in an adult employed population than is diastolic blood pressure, height, gender, age or dietary sodium intake.124 The increase in left ventricular mass attributable to obesity was due to eccentric ventricular hypertrophy because end – diastolic relative wall thickness was similar in obese and non obese subjects.124
Comparative studies on prevalence of LV hypertrophy among normal weight, overweight and obese have also demonstrated an increasing trend from normal weight to obese .125,126
The relationship of other measures of obesity to left ventricular hypertrophy has also been studied. A positive correlation between LV mass and waist to hip ratio, BMI, basal metabolism and lean and fat body mass was found by Avignon et. al.127
Two dimentional echocardiography performed in 29 normotensive obese subjects and 21 hypertensive obese subjects in a Chilean population showed that the left ventricular mass did not correlate with height or body surface area but correlated positively with body mass index (BMI) triceptal skinfold thickness
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and blood pressure. Posterior wall thickness was independently associated with blood pressure while interventricular septal thickness was positively associated with waist to hip ratio 128
Significant correlations between increased left ventricular mass and visceral fat, BMI and waist circumference amongst Indonesian women was also demonstrated by Sukmoko et. al.129
As has been discussed, the evaluation of the impact of obesity on hypertrophy in certain populations has been subjected to distortion due to indexing with the body surface area leading to an underestimation of hypertrophy in the obese.121
Recent studies among them the LIFE130 study and the VITAE131 study evaluated the impact of the different selection criteria on the left ventricular mass based on different indexes (BSA, height, height2) and identified a higher proportion of obese in groups where the mass was indexed by height or height raised to a power. This fact has already been observed in a few studies that evaluated the impact of the different indexes on the prevalence of cardiac structural alterations in their populations. 121,132-133
2.10 COMPLICATIONS OF OBESITY
Obesity is associated with numerous comorbidities and these include:- 1) Cardiovascular disease
* Stroke
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* Coronary Artery Disease
* Hypertension
* Congestive Heart failure
* Left ventricular hypertrophy
* Dyslipidemia
* Arrythmia 2) Metabolic syndrome 3) Type 2 Diabetes Mellitus 4) Reproductive disorders
* Menstrual disorders
* Polycystic ovarian syndrome (POCS)
* Erectile dysfunction 5) Fatty liver and gall stones
6) Cancers – breast, uterus, colorectum 7) Bone, joint and cutaneous disease
* Osteoarthritis
* Gout
* Acanthosis Nigricans 8) Respiratory disease
* Obstructive sleep apnoea
* Obesity hypoventilation syndrome The cardiac complications of obesity are:-
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1) Left ventricular hypertrophy 2) Cardiomyopathy of obesity 3) Coronary Artery Disease 4) Heart failure
5) Arrythmias and sudden death
Left Ventricular Hypertrophy
Eccentric LVH, which is commonly present in morbidly obese patients (BMI) ≥ 40kg/m2) is often associated with left ventricular diastolic dysfunction.
Moreover as with left ventricular mass, longer duration of obesity, are associated with poorer left ventricular systolic and greater impairment of left ventricular diastolic function.134 Age or cardiac hypertrophy of the concentric
135,136 or more commonly the eccentric type137,138 predispose to left ventricular systolic dysfunction. Moreover the enlarged muscle tissue compresses its own blood supply or blood vessels, the coronary arteries and may restrict its own blood supply. All these predispose the patient to ischemic heart disease, congestive heart failure, abnormal heart rhythm and sudden death.
Cardiomyopathy of obesity (Adipositas cordis)
Obesity cardiomyopathy was recognized as early as 1818.139 The case described by Cheyne is of historic interest because it was the first reported case of Cheyne – stokes respiration. The fatty heart is initially characterized by metaplasia. Later cords of cells gradually accumulate fat between muscle fibers
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or cause myocyte degeneration resulting in cardiac conduction defects.140,141 Occasionally a type of restrictive cardiomyopathy develops.142,143
Coronary Artery Disease
Obesity is often associated with advanced atherosclerosis in adults.
Indeed post mortem examination of arteries from individuals aged 15 to 34 years old (Determinants of Atherosclerosis in youth (PDAY) study) who died from accidental injury, homicides or suicides revealed that the extent of fatty streaks and advanced lesions (fibrous plaques and plaques with calcification or ulceration) in the right coronary artery (RCA) and abdominal aorta were associated with obesity and with the size of the abdominal panniculus.144,145 Obesity in young men as crudely defined by BMI was associated with both fatty streaks and raised lesions in the RCA.
Black subjects had more extensive fatty streaks than did white subjects in all arterial segments examined and men did have more extensive raised lesions in RCA than did women.146 Importantly when BMI and abdominal panniculus thickness were simultaneously considered in men, a BMI ≥30kg/m2 was associated with raised lesions in RCA only amongst individuals with a large panniculus thickness (≥17mm) which reinforcess the concept that central distribution is more important than total fat as a risk factor for atherosclerosis.146
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The preferential deposition of fat centrally after the menopause may explain in part why the risk for CHD events increases 10 – 20 years later in women than in men.25,147-149
Overall the data from the PDAY study provide convincing evidence that obesity in adolescents and young adults accelerates the progression of atherosclerosis decades before the appearance of clinical manifestation.
Prospective studies that have reported follow – up data over 2 decades, such as the Framingham Heart Study, the Manitoba study, have documented that obesity is an independent predictor of clinical CHD. 150-152
Congestive Heart Failure
Congestive Heart failure (CHF) is the only common cardiovascular condition that is increasing in incidence and prevalence and mortality rates worldwide. Although several new therapies have been introduced for the treatment of CHF, the overall 5 year mortality rate is estimated at 50% 153. An elevated BMI predisposes to CHF by promoting hypertension, left ventricular hypertrophy, cardiomyopathy of obesity and coronary artery disease. Excess obesity is associated with increased risk of development of CHF. 153 – 154
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Arrythmias
The statement “sudden death is more common in those who are naturally fat than in the lean” is attributed to Hippociates.155 Arrhythmia in obese patients is mediated through left ventricular hypertrophy, coronary heart disease, hypertension and diabetes. Prolonged QTc interval has also been reported in association with obesity, hypertension and diabetes.156 However no specific ECG abnormalities have been reported in association with lipodystrophy.