Study group
We retrospectively analyzed the data collected in the Non-invasive Haemodynamic Assessment in Hypertension (FINE-PATH) study (ClinicalTrials.gov Identifier NCT01996085), which was conducted in the Department of Cardiology and Internal Medicine within the Military Institute of Medicine during the period 2011–2014 [9]. In brief, this trial had a prospective, randomized, controlled design (144 patients enrolled) to assess a novel approach to the treatment of AH; the study involved patients with at least a three-month history of AH defined according to the European Society of Cardiology guidelines [1]. The exclusion criteria included secondary AH, chronic kidney disease, systolic heart failure, cardiomyopathy, significant arrhythmias, significant valvular heart disease, chronic obstructive pulmonary disease, previously diagnosed diabetes mellitus, polyneuropathy, and peripheral vascular disease. The following drug classes were used: beta-blockers, angiotensin- converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, and diuretics, either alone or in combination. The study protocol was approved by the Institutional Review Board at the Military Institute of Medicine (no. 21/WIM/2011), and each patient provided written consent.
In this secondary analysis from among the whole group who attended a controlled visit after 12 months of treatment (n=121), 108 patients with acceptable ultrasound image quality were selected. In the final analysis, 101 patients with normal LV diastolic function evaluated based on current guidelines [10] were included. Collected data included demographic characteristics, the results of a complete clinical examination, 24-h ambulatory blood pressure (ABP) monitoring (ABPM), antihypertensive treatment, and transthoracic echocardiography.
Ambulatory blood pressure monitoring
Ambulatory blood pressure monitoring (Spacelabs 90207, Spacelabs, Medical Inc, Redmond, USA) was performed within 2 weeks before echocardiography. The time from 6 a.m. to 10 p.m. was considered daily activity period (daytime) with automatic blood pressure measurement in 10-minute intervals. During night rest (night-time: 10 p.m. – 6 a.m.) the measurement was performed every 30 minutes. As a good blood pressure control (well-treated hypertension) was considered a mean 24-hour systolic BP<130 mmHg and diastolic BP<80 mmHg, a daytime systolic BP<135 mmHg and diastolic BP<85 mmHg, and a night-time systolic BP<120 mmHg and diastolic BP<70 mmHg
Standard transthoracic echocardiography
Transthoracic echocardiography was performed using a high-quality echocardiograph (Vivid 7 or E95, General Electric, United States). The examinations were analyzed off-line by an experienced echocardiographer accredited by the Section of Echocardiography of the Polish Cardiac Society, echocardiography laboratory. All LV and LA measurements were made according to the current guidelines of the European Society of Cardiology [11]. To estimate the size and function of the LA, the following standard parameters were measured: LA end-diastolic diameter, LA area, LA volume (LAV), and LA indexed volume (LAVI). LAV and LAVI were measured using a biplane algorithm from the apical four-chamber (A4C) and two-chamber (A2C) views. LA enlargement was defined as LAVI >34ml/m2. To assess LV function, LVEF was calculated using the biplane Simpson formula. LV mass (LVM) was calculated using the linear method according to the recommendations for cardiac chamber quantification by echocardiography in adults [11]. Using the parasternal longitudinal axis view), the thicknesses of the interventricular septal, the inferolateral walls, and the LV end-diastolic and end-systolic diameters were obtained. To diagnose LV hypertrophy, LVM was indexed to the body surface area (BSA) and calculated using the DuBois formula (indexed LVM–LVMI). Left ventricular hypertrophy (LVH) was diagnosed as recommended (cutoff values for women are LVMI >95 g/m2 and for men, LVMI >115 g/m2).
Diagnosis of LV diastolic dysfunction was based on the current guidelines [10], where the parameters for its identification and their cutoffs are as follows: LAVI >34 ml/m2, septal annular e’ velocity < 7 cm/s, lateral annular e’ velocity <10 cm/s, average E/e’ ratio >14, and peak tricuspid regurgitation velocity >2.8 m/s. Waves E and A of the mitral inflow velocity by pulsed wave Doppler from the apical four-chamber view, the E/A ratio, and the velocity waves (e’ and a’) of the mitral annulus septal and lateral regions were recorded using tissue Doppler imaging. An average value of septal and lateral mitral annulus velocities was used to estimate E/e’ ratio.
Speckle-tracking echocardiography (STE)
Regional and global longitudinal 2D LA and LV strain was analyzed by STE using GE EchoPAC BT 12 software. LV GLS was assessed using automated imaging software. Detection of the tracked area was performed semi-automatically with two points selected at the level of the mitral annulus and the third point at the apex with the possibility of manual adjustments. The LV GLS values were averaged for all 17 LV segments: seven in the apical four-chamber view, six in the apical two-chamber view, and six in the apical three-chamber view.
Analysis of LA strain was performed off-line, obtained from a non-foreshortened apical, both A4C- and A2C-view images, using conventional 2D gray-scale echocardiography. High frame rates (60–80 frames per second) were used for analysis as recommended in the Expert Consensus Statement [12]. The analysis was performed by an experienced echocardiographer using acoustic-tracking software (EchoPAC, General Electric, USA), allowing off-line semi-automated analysis of speckle-based strain. The LA endocardial border was manually traced in both the A4C and A2C views. An epicardial border was automatically generated by the software, creating a region of interest. The LA was contoured, extrapolating across the pulmonary veins and LA appendage orifice. Then, after eventual manual adjustment of the ROI shape, the software divided the region of interest into six segments and generated a longitudinal strain curve. To assess all LA strain values, the QRS wave onset was set as a reference point as recommended in the consensus document [13]. The obtained LA longitudinal strain (LAS) parameters were as follows [13]: positive peak strain during the reservoir phase (LASr), corresponding to the atrial reservoir function (positive value); next strain value during early diastole, corresponding to the atrial conduit function and identified as the LA-strain-during-conduit phase (LAScd—negative value), and the LA strain during late diastole, corresponding to active atrial contraction and identified as the LA-strain-during-contraction phase (LASct—negative value). LASr, LAScd, and LASct were calculated by averaging the values observed in all the LA segments (global LASr, LAScd, and LASct). When some segments were excluded due to the inability to achieve adequate tracking, LAS was calculated by averaging the values measured in the remaining segments. All measurements were obtained during sinus rhythm. As reference LA strain values, we adopted those given in a large meta-analysis carried out by Pathan et al., which included 2,542 healthy subjects [14]. Detailed measurements of LASr, LAScd, and LASct are presented in Figure 1.
To assess the intraobserver variability of LASr A4C, LASr A2C, LASct A4C, and LASct A2C, 20 patients were randomly selected. Intraobserver variability coefficients were calculated using images independently recorded at two different times by the same observer. The intraclass correlation coefficient together with the mean difference (95% CI) of two measurements in Bland-Altman analysis, divided by the mean of those two measurements and given as percentages, were calculated for intraobserver variability. The repeatability of the LAS measurements was high. The intraclass correlation coefficients for the intraobserver variability of LASs was 0.99 for LASr A4C, 0.98 for LASr A2C, 0.99 for LASct A4C, and 0.98 for LASct A2C. The mean difference divided by the mean of two measurements for intraobserver variability was 0.4 % (−1.1%–2,0%) for LASr A4C, 0.6% (−1.6%–28%) for LASr A2C, 0.2% (−3.7%–6.6%) for LASct A4C, and 0.5% (−3.1%–4.1%) for LASct A2C.
Statistical analysis
Statistical analyses were conducted with Statistica 12.0 (StatSoft Inc., Tulsa, OK, USA). The distribution and normality of data were assessed visually and with the Shapiro-Wilk test. Continuous variables were presented as the mean ± standard deviation (SD), whereas categorical variables were presented as absolute and relative values (percentages). A comparison analysis was conducted for two subgroups: patients with high GLS (>the absolute value of −20%; “High GLS”; n=30) and lower GLS (≤ the absolute value of −20%; “Lower GLS”; n=71). The cut-off value was in accordance with the current recommendations [11]. The student’s t-test was used for normally distributed data, whereas the Mann–Whitney U-test was used for data with non-normal distribution. A p-value of <0.05 was considered statistically significant.