Global longitudinal strain imaging and its utility in assessing risk in early stages of hypertension

Arterial hypertension is a major risk factor of cardiovascular diseases and is associated with increased mortality.1 It is the greatest risk factor for acquired left ventricular hypertrophy and its own associated morbidity and mortality.2 Left ventricular hypertrophy in hypertensive patients is caused by both increased myocytic diameter and collagen content. A rise in collagen type I and type III content has been proposed to increase myocardial stiffness and impair cardiac function in hypertensive heart disease.3 In addition, microcirculatory dysfunction and myocardial ischemia in the absence of epicardial vascular disease have been associated with left ventricular hypertrophy, increased left ventricular stiffness, and end‐systolic wall stress. All these factors are associated with impaired shortening of longitudinally oriented myocardial fibers in hypertensive patients.

One method of assessing the function of subendocardial longitudinal‐oriented myocardial fibers is strain imaging. Strain is a measure of deformation resulting from applied force such as muscle contraction and is calculated by the percent change in the length of muscle fibers compared with their original length. In 2D strain, echocardiography acoustic speckle tracking is used to measure strain in longitudinal, radial, and circumferential directions. The most common clinical application of strain imaging is the global longitudinal strain (GLS) of the left ventricle, using three standard views and is displayed in multiple ways, including segmental/regional strain curves, curved anatomical color M‐mode and peak systolic strain map or bull's eye. The latter is commonly used for pattern recognition in clinical applications. The normal value is −20 with absolute number being equal or great than 20 in normal patients.4 However, the technique has many variabilities, and thus, measurements may vary from one vendor or software to another. It has also many technical limitations, the most important one being the image quality. There are also interindividual variabilities in usage and data interpretation, and therefore, technique should be used only by skilled individuals. The method has many applications such as assessing diastolic function, atrial fibrillation risk, and cardiac resynchronization therapy adjustments. Further, it is one of the most sensitive methods to detect early myocardial injury after chemotherapy. Importantly, GLS is prognostic of adverse cardiovascular outcomes in various disease states as well as in the general population.5

Global longitudinal strain has been suggested as a method that reliably can distinguish between athlete heart with generally normal GLS, hypertensive heart with mildly reduced GLS, and hypertrophic cardiomyopathy with severely decreased GLS. In the study by Santos A et al6 reported in the current issue of the journal the investigators have compared baseline GLS between 91 patients with prehypertension (pre‐HTN) from PREVER‐prevention trial and 105 subjects with stage I hypertension (HTN) from PREVER‐treatment trial. They also assessed GLS after 18 months of treatment, but the results are not reported here.

PREVER trial participants were from 21 Brazilian academic medical centers between 30 and 70 years of age. pre‐HTN was defined according to JNC 7 criteria as systolic blood pressure between 120 and 139 mm Hg or diastolic blood pressure between 80 and 89 mm Hg. Stage I HTN was also defined according to JNC 7criteria as systolic blood pressure between 140 and 159 or diastolic blood pressure between 90 and 99 mm Hg. Both populations were selected from patients not on any blood pressure‐lowering medication. They both underwent 3 months of the lifestyle intervention, followed by randomization to a chlorthalidone/amiloride combination pill or placebo and followed for 18 months. A postanalysis of baseline myocardial deformation (GLS) was performed at a single site, using specific B‐mode speckle tracking. Two basal and one apical landmarks were established at the automatically detected endocardial edge at end systole. The peak GLS for each 2D apical view (two‐ and four‐chamber) was automatically obtained from the mean of 6 traced segments. They also assessed other measures of myocardial function, including LV ejection fraction, using a modified Simpson method. The results showed that LV posterior wall thickness, LV mass/height ratios, and LA diameters were higher and lateral mitral annular relaxation velocities were lower in stage I HTN compared with pre‐HTN group. The GLS was also lower in stage I HTN compared with pre‐HTN group by about 1%. While 1% difference in GLS appears as trivial, other studies have shown that small reduction in GLS is associated with a significantly greater risk including hospitalization and cardiac death.7

The study by Santos A et al6 is a small, nevertheless, a thought‐provoking study that deals with a significant medical issue as it proposes a potential novel risk factor for patients with very early hypertension. The novelty of the study is in that it compares pre‐HTN group with those with early HTN on no BP‐lowering medication. Reproducibility of the echocardiographic and Doppler measurements were previously evaluated using 20 random studies and reported as intraclass correlation coefficient, between 0.99 and 0.67.8 Nevertheless, given the complexities of GLS measurement use of two interdependent interpreters would have been preferred. Larger studies are needed to replicate these findings. Further, outcome studies in those with abnormal GLS may allow global use of this technique in assessing risk of cardiovascular morbidity and mortality in the early stages of hypertension.

CONFLICT OF INTEREST

The author has no conflict of interest to disclose.