Assessment of Speckle Tracking Strain Predictive Value for Myocardial Fibrosis in Chagas Disease
Condition: Chagas Disease
MeSH terms: Chagas Disease
Study type: Observational

Summary: 
      One of the most challenging issues of chronic Chagas disease is to provide earlier detection
      of heart involvement. Two-dimensional speckle tracking (2-D ST) echocardiography, a new
      imaging modality with useful applications in several cardiac diseases, has been validated for
      subjects with myocardial infarction against cardiac magnetic resonance (CMR). Here the
      investigators hypothesize that the longitudinal global strain (LGS) has an incremental value
      to ejection fraction for predicting myocardial fibrosis in subjects with Chagas disease.
    

Detailed description: 
      We conducted a cross-sectional study, in which adult subjects with Chagas disease were
      invited to participate. From January 2011 to December 2013, we included 58 subjects from a
      convenience sample, in the Chagas disease outpatient clinics at our institution. Inclusion
      criteria were disease established based on microbiological confirmation by two positive
      serologic tests (indirect hemagglutination and indirect immunofluorescence), and age between
      18 and 70 years. Exclusion criteria were: previous myocardial infarction or history of
      coronary artery disease; primary valve disease; dialysis treatment of terminal renal failure,
      liver disease in activity; hematologic, neoplastic or bone diseases; and MRI
      contraindications.

      The study complied with the Declaration of Helsinki and was approved by the Ethics Committee
      of the Hospital São Rafael. All subjects gave written informed consent before their inclusion
      in the study.

      We obtained a structured medical history, and all subjects underwent physical examination,
      blood analysis, 12-lead ECG, chest X-Ray, 24-h Holter monitoring, conventional Doppler
      echocardiogram plus speckle tracking strain, and cardiac magnetic resonance.

      Doppler echocardiogram Standard transthoracic echocardiographic examinations were recorded in
      all subjects using the Vivid 7 digital ultrasound system (GE Vingmed Ultrasound AS, Horten,
      Norway). Three cardiac cycles were stored in cine loop format for online analysis. LV and
      left atrial dimensions were measured according to the American Society of Echocardiography's
      recommendations [13]. The LV EF was measured using the biplane Simpson's method. S0 systolic
      velocity at the lateral mitral annulus was assessed using pulsed-wave DTI. Diastolic function
      was evaluated by the analysis of the mitral Doppler inflow, pulsed- wave DTI at the lateral
      mitral annulus, and mitral propagation velocity using color M-mode echocardiography. Mitral
      regurgitation (MR) was obtained using the proximal isovelocity surface area method. Right
      ventricular function was assessed with the S0 systolic velocity in the lateral wall. Systolic
      pulmonary arterial pressure was obtained from the tricuspid regurgitation flow. In subjects
      with adequate Doppler MR signals, dP/dt was determined noninvasively from the rate of change
      of MR velocity, according to American Society of Echocardiography guidelines.

      Strain Measurements Two-dimensional gray-scale images were acquired in the standard apical
      four-chamber, three-chamber, and two-chamber views at a frame rate of 80 frames/sec. The
      dimensions of the computation area were an angle of 80o and at a depth of 13 cm. The left
      ventricle was divided into 17 segments, and each segment was analyzed individually. GLS and
      segmental longitudinal strain were obtained as previously described [14]. Average
      longitudinal strains were calculated automatically by the software. Two-dimensional strain is
      a non-Doppler-based method for the evaluation of systolic strain using standard 2D
      acquisitions. After placing three endocardial markers in an end-diastolic frame, the software
      automatically tracks the contour on subsequent frames. Adequate tracking can be verified in
      real time and corrected by adjusting the region of interest or by manually correcting the
      contour to ensure optimal tracking. Two-dimensional longitudinal strain was assessed in
      apical views. Average longitudinal strains were calculated for the 17 segments.

      Magnetic resonance imaging Cardiac magnetic resonance exams were performed on all subjects
      using the General Electric Sigma HDx 1.5-T system (Fairfield, CT, USA). Images were acquired
      and gated to the ECG during breath-hold, four-chamber, short axis and long axis of the left
      ventricle, in the exact same location in different sequences. This allows a precise
      comparison between cardiac function and regional myocardial structure. The parameters used in
      the dynamic sequences were repetition time (RT) of 3.5 ms, echo time (ET) of 1.5 ms, flip
      angle 60°, bandwidth of receipt of ± 125 kHz, field of view (FOV) of 35 x 35 cm, 256x148
      matrix, temporal resolution (TR) 35 ms, 8.0 mm slice thickness, without a space between the
      slices. Following this acquisition, a dose of gadolinium-based contrast (0.1 mmol / kg) was
      injected. The myocardial delayed enhancement (MDE) technique was used to investigate
      myocardial fibrosis, an inversion-recovery pre-pared gradient-echo acquired 10 to 20 min
      after contrast application, with the following parameters: Repetition time (RT) 7.1 ms, echo
      time (ET) 3.1 ms, flip angle 20°, cardiac phases 1, views per segment 16 to 32, matrix 256 X
      192, slice thickness 8 mm, gap between slices 2 mm and field of view 32 to 38 cm, inversion
      time 150 to 300 ms, receiver bandwidth 31.25 kHz, number of excitations 2, acquisition every
      heart beat. The mass of fibrosis was estimated by a quantitative visual method.

      Statistical analysis Categorical data were presented as numbers (percentages), and continuous
      data were expressed as mean (SD) or median (interquartile range). Comparisons of continuous
      variables among groups were performed with analysis of variance (ANOVA) test or
      Kruskal-Wallis, depending on normality assessed by Shapiro-Wilk test. Chi-Square or Fisher
      tests were applied for proportions comparisons. Correlations between continuous variables
      were evaluated by Pearson or Spearman coefficients, depending on normality.
      Receiver-operating characteristic (ROC) curve analysis was used to evaluate if the
      longitudinal global strain would add accuracy to the ejection fraction in the predicted
      fibrosis. C-Statistic (area under the curve) was presented as a unified estimate of
      sensitivity and specificity. To determine the ability to predict myocardial fibrosis,
      multiple linear regression was performed, adjusting longitudinal global strain to left
      ventricular ejection fraction. Analyses in subgroups with normal and low ejection fraction
      were also accomplished. Cases with missing data were not included in the analysis. Analyses
      were performed using SPSS version 20.0 (IBM), and p < 0.05 (two-tailed) was considered
      statistically significant.
    

Intervention name(s): No intervention was performed.
Intervention type(s): Other
Intervention description(s): No intervention was performed.
Observational model: Other
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Adult subjects in the Chagas disease outpatient clinics at our institution from January
        2011 to December 2013 were invited to participate in this study.
      
Keywords: Chagas disease; longitudinal global strain; speckle tracking