Assessment of Left Ventricular Systolic Function by Cardiovascular Magnetic Resonance Compressed Sensing Real-Time Cine Imaging Combined With Area-Length Method in Normal Sinus Rhythm and Atrial Fibrillation

Abstract

Background: The most-commonly used multi-slice Simpson's method employed with routine two-dimensional segmented cine images makes it difficult to evaluate left ventricular (LV) volume and function due to endocardial border blurring and beat-to-beat variation during atrial fibrillation (AF) status.

Objectives: To assess the feasibility of compressed sensing real-time (CSRT) cine imaging combined with an area-length method for quantification of LV systolic function in normal sinus rhythm (NSR) and AF.

Methods: The CSRT cine sequence and routine segmented balanced Steady-State-Free-Precession cine sequence were performed in 71 patients with NSR (n = 36) or AF (n = 35). Image quality and edge sharpness for both sequences were assessed. The LV functional measurements in patients with NSR included end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), cardiac output (CO), cardiac index (CI), and LV mass (LVM); all were assessed using segmented cine with Simpson's rule in short axis (SegSA_Simpson, as a reference standard) and area-length (AL) method in the two chamber (Seg2CH_AL) or four chamber (Seg4CH_AL) and CSRT cine with AL method in the two chamber (CSRT2CH_AL) or four chamber (CSRT4CH_AL). Finally, the mean, maximum, and minimum values of each LV functional parameter [EDV/ESV/SV/EF/CO/CI/LVM/heart rate (HR)] from 4~5 consecutive heartbeats were measured using CSRT2CH_AL in patients with AF.

Results: In patients with NSR, measurements of EDV (p > 0.05), ESV (p > 0.05), SV (p > 0.05), EF (p > 0.05), and LVM (p > 0.05) assessed with CSRT2CH_AL did not differ significantly from those obtained with SegSA_Simpson. In patients with AF, CSRT image quality score (p < 0.001) and edge sharpness (p < 0.001) both were significantly higher than those obtained from segmented cine. The CSRT2CH_AL provided significantly different results among mean, maximum, and minimum values of each LV parameter from 4~5 consecutive heartbeats (all p < 0.001) with strong inter- and intra-observer agreement in AF.

Conclusions: The CSRT cine sequence combined with two chamber area-length analysis accurately assessed LV systolic function in NSR. This approach is expected to permit the assessment of multiple parameters in consecutive heartbeats with good inter- and intra-observer reproducibility for beat-to-beat analysis of LV function in AF.

Keywords: area-length; atrial fibrillation; cardiovascular magnetic resonance; compressed sensing real-time; normal sinus rhythm.

Figure 1

Example of edge sharpness assessment for a 37-year-old female patient with heart failure and atrial fibrillation, as performed in our study. The image of the 4CH view at end-diastole was acquired with segmented (A) or CSRT (C) bSSFP cine sequence. A line (white star) was drawn perpendicularly to the mid-cavity interventricular septum border with the left ventricular blood pool on each image. In the intensity profile (blue curve) of each line from the segmented cine (B) or CSRT cine (D), the edge sharpness (ε, expressed in mm⁻¹) was calculated as the inverse of the distance [(D), expressed in mm] between the positions (red stars) corresponding to 20% and 80% of the difference between the maximum and minimum signal intensities along the line. 4CH, four-chamber; CSRT, compressed sensing real-time; bSSFP, balanced Steady-State-Free-Precession.

Figure 2

Representative images and measures of LV function from a representative study patient. CSRT2CH_AL (A1,A2) or CSRT4CH_AL (B1,B2) utilized CSRT cine combined with the 2CH or 4CH AL method. Seg2CH_AL (C1,C2) or Seg4CH_AL (D1,D2) utilized segmented cine combined with the 2CH or 4CH AL method. SegSA_Simpson (E1,E2) utilized segmented cine combined with SA Simpson method. The AL method is based on a rotational ellipsoid with a volume calculated using the formula: $volume=0.85\times \frac{are{a}^2}{L}$ (F). The ‘area' in the formula was obtained from the 2CH or 4CH view; the ‘L' was measured as the length of the line from the LV apex to the mitral valve annulus in the same view. In Simpson's rule, the LV volume is estimated as the sum of the cross-sectional area of multiple single slices multiplied by the slice thickness plus gap. The visualization of end-diastolic volume measured by Simpson's rule was shown in (G). End-diastolic (upper row) and end-systolic (middle row) phases were defined manually, based on the smallest and largest LV cavities during the cardiac cycle. The endocardial contours (red) and epicardial contours (green) were drawn automatically with manual correction. CSRT2CH_AL, area-length method using two-chamber compressed sensing real time cine; CSRT4CH_AL, area-length method using four-chamber compressed sensing real time cine; Seg2CH_AL, area-length method using two-chamber segmented cine; CSRT4CH_AL, area-length method using four-chamber segmented cine; AL, area-length; SegSA_Simpson, Simpson method using short axis segmented cine, 2CH, two-chamber; 4CH, four-chamber; SA, short axis. LV, left ventricular.

Figure 3

Images of segmented and CS real-time bSSFP cine sequences from a patient with NSR [(A1–A6) and (B1–B6), respectively] and a patient with AF [(C1–C6) and (D1–D6)]. Specifically, in a 41-year-old female patient with NSR, each image from a segmented cine in end diastolic (A1) or end systolic (A2) 2CH, end diastolic (A3), or end systolic (A4) 4CH, or end Diastolic (A5) or end systolic (A6) middle SA appears clearer and sharper than the corresponding images from a CS real-time cine [(B1–B6), respectively] In contrast, in a 54-year-old female patient with AF, the images of a segmented cine appear blurrier and of lower diagnostic value. Specifically, each image from a CS real-time cine in end diastolic (D1) or end systolic (D2) 2CH, end diastolic (D3) or end systolic (D4) 4CH, or end diastolic (D5) or end systolic (D6) middle SA appears clearer and sharper than the corresponding images from a segmented cine [(C1–C6), respectively]. An additional movie file shows this in more detail. CS, compressed sensing; bSSFP, balanced Steady-State-Free-Precession; AF, atrial fibrillation; NSR, normal sinus rhythm; 2CH, two-chamber; 4CH, four-chamber; SA, short axis.

Figure 4

The results of multiple group comparisons and further pairwise comparisons of EDV (A), ESV (B), SV (C), EF (D) or LVM (E) derived from 5 different methods in patients with NSR. There were significant differences in EDV, ESV, EF, and LVM but no significant difference in SV among the 5 methods. Further pairwise analyses indicated no significant differences in EDV, ESV, EF, and LVM between CSRT2CH_AL and SegSA_Simpson (red bar), and between CSRT2CH_AL and Seg2CH_AL (blue bar). There were significant differences in EDV, ESV, and EF between CSRT4CH_AL and SegSA_Simpson. CSRT2CH_AL, area-length method using two-chamber compressed sensing real time cine; CSRT4CH_AL, area-length method using four-chamber compressed sensing real time cine; Seg2CH_AL, area-length method using two-chamber segmented cine; CSRT4CH_AL, area-length method using four-chamber segmented cine; SegSA_Simpson, Simpson method using short axis segmented cine; NSR, normal sinus rhythm; EDV, end-diastolic volume; ESV, end-systolic volume; SV, stroke volume; EF, ejection fraction; LVM, left ventricular mass; NS, no significant difference.

Figure 5

Bland-Altman plots and linear regression trendlines for LV functional measurements by CSRT2CH_AL and SegSA_Simpson in patients with NSR. The diagrams in the left column represent Bland-Altman plots for EDV (A), ESV (C), SV (E), EF (G), and LVM (I). The red-dashed lines indicate the difference between two methods; the black-dashed lines indicate the 95% limit agreement interval. On the diagrams in the right column, linear regression analysis indicates strong correlations in EDV (B), ESV (D), SV (F), EF (H) and LVM (J) between CSRT2CH_AL and SegSA_Simpson. CSRT2CH_AL, area-length method using two-chamber compressed sensing real-time cine; SegSA_Simpson, Simpson method using short axis segmented cine; NSR, normal sinus rhythm; EDV, end-diastolic volume; ESV, end-systolic volume; SV, stroke volume; EF, ejection fraction; LVM, left ventricular mass; LV, left ventricular.