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lifting, wrestling) or the eccentric hypertrophy that occurs in sports requiring isotonic exercise ( long distance running and cycling) are consistent with normal LV systolic and diastolic functions.112
2.8 METHODS OF DETECTING LEFT VENTRICULAR
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wave, colour flow) and contrast echocardiography. It uses sound waves in the frequency ratio of 1 to 10 MHz to study the heart.
M – mode echo was the earliest form of cardiac ultrasonography used clinically. The ultrasound beam is focused into a narrow beam and structures depicted graphically are particularly useful for accurate timing of cardiac events such as the opening and closure of heart valves.
It can also be used to calculate the LV mass, measure septal and posterior wall thickness and left ventricular internal diameters.
Two dimensional echo, is created when a fan shaped array consisting of multiple interrogated lines, is emitted typically over a 90 degree sector from the transducer and analyzed. There are two methods (phase array or mechanical probe) by which the fan shaped sector of ultrasound, beam can be created. In phased, a linear array of ultrasound crystals is electronically steered through an imaging arc. It visualizes the four chambers of the heart and the structures within it. In mechanical probe the piezoelectric element or elements scan through a section of the heart with the help of an electric motor. Two dimensional imaging can be used to measure LV function. It is also useful in cases where there is regional wall motion abnormality or abnormal septal motion, which are not well displayed for measurement on M – mode.
Echocardiographic studies have enhanced the understanding of the aetiology of hypertensive left ventricular hypertrophy in epidemiologic studies.
Echo provides visualization of structural and functional abnormalities, which
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appear long before the detection of overt clinical disease. Pathologic hypertrophy may be associated with an absence of symptoms for many years before the development of complications such as heart failure and sudden death.
Thus in contemporary studies, the firm diagnosis of LVH depends predominantly on echocardiography or other non – invasive technologies.
Methods for 2D targeted M-mode echocardiographic measurement of LV dimensions and calculation of LV mass are standardized.114
Echocardiographic LVH is more prevalent than LVH detected by electrocardiography (ECG) with overall rates of 17.4% versus 2.4%
respectively.115 LVH can also be defected by CT scan, MRI scan, thallium scan, but studies on these are limited.
LV Mass calculation
There are different echocardiographic formulae for calculation of LV mass.
They are derived from M – mode techniques.
1. Using the Penn convention 116
LVM (in grams) = 1.04 (IVSd + LVIDd + PWTd)3 – LVIDd) – 13.6 r = 0.96 described by Devereux and Reichek in 1977.
2. Using ASE (American Society of Echocardiography) convention which is divided into two 117, 118
a) LV mass (grams) = 1.05 (LVIDd + IVSd + PWTd)3 – LVIDd3) it was described by Troy et. al. in 1972.117
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b) LV mass (grams) = 0.8 (1.04 (IVSd + LVIDd + PWTd)3 – LVIDd3) +0.6 It is also called Devereux – modified ASE cube formula. Described by Devereux et. al. 118 in 1986. r = 90
Where,
LVIDd = Left ventricular internal diameter, in diastole.
PWTd = Posterior wall thickness in diastole
IVSd = Interventricular septal thickness in diastole.
The development of anatomically validated formula using echocardiography has permitted an accurate assessment of LV mass, which has proven to be a more sensitive tool for detection of LVH than other, techniques available.
ASE and Penn conventions differ in how LV interfaces are identified and where on the ECG the end – diastolic measurement are made.
ASE convention recommends M – mode measurements from leading edge to leading edge, end – diastole is been indicated by the Q-wave on the ECG rather than the R wave. The endocardial echoes in the interventricular septum and posterior wall of the left ventricle are measured.
Penn convention recommends that the endocardial echoes are excluded from the measurements of the interventricular septum and posterior wall of the left ventricle.
End diastole is measured at the peak of the R – wave on the ECG.
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Normal ranges of LV and right ventricular mass have also been described in healthy male and female subjects using Cine - MRI and ultra fast CT scan but studies on this are limited.119
Indexation of LV mass LV mass is indexed by
1. Body surface area (m2) – using the Dubois formula120 (0.0001) (71.84) (wt
0.425 x ht 0.725) Where:
wt - weight in kilograms ht - height in centimeters 2. Height (m)
3. Height 2 (m2) 4. Height 2.7 (m2.7)
Body surface area (BSA) indexing may however underestimate LVH due to obesity. Rosa et. al.121 studied the criteria for indexing the left ventricular mass and detection of hypertrophy in obese hypertensives using echocardiography. In the study, LV mass was indexed for body surface area (LV mass/BSA) and for height 2 (LV mass/h2). The two indexes were then compared in both populations in subgroups stratified according to body mass index. Results showed that left ventricular hypertrophy has been underestimated in the obese with the use of LV mass/BSA criteria because this index considers obesity as a physiological
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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