Background
Echocardiography-derived linear dimensions offer straightforward indices of right ventricular (RV) structure but have not been systematically compared with RV volumes on cardiac magnetic resonance (CMR).
Methods
Echocardiography and CMR were interpreted among patients with coronary artery disease imaged via prospective (90%) and retrospective (10%) registries. For echocardiography, American Society of Echocardiography–recommended RV dimensions were measured in apical four-chamber (basal RV width, mid RV width, and RV length), parasternal long-axis (proximal RV outflow tract [RVOT]), and short-axis (distal RVOT) views. For CMR, RV end-diastolic volume and RV end-systolic volume were quantified using border planimetry.
Results
Two hundred seventy-two patients underwent echocardiography and CMR within a narrow interval (0.4 ± 1.0 days); complete acquisition of all American Society of Echocardiography–recommended dimensions was feasible in 98%. All echocardiographic dimensions differed between patients with and those without RV dilation on CMR ( P < .05). Basal RV width ( r = 0.70), proximal RVOT width ( r = 0.68), and RV length ( r = 0.61) yielded the highest correlations with RV end-diastolic volume on CMR; end-systolic dimensions yielded similar correlations ( r = 0.68, r = 0.66, and r = 0.65, respectively). In multivariate regression, basal RV width (regression coefficient = 1.96 per mm; 95% CI, 1.22-2.70; P < .001), RV length (regression coefficient = 0.97; 95% CI, 0.56-1.37; P < .001), and proximal RVOT width (regression coefficient = 2.62; 95% CI, 1.79-3.44; P < .001) were independently associated with CMR RV end-diastolic volume ( r = 0.80). RV end-systolic volume was similarly associated with echocardiographic dimensions (basal RV width: 1.59 per mm [95% CI, 1.06-2.13], P < .001; RV length: 1.00 [95% CI, 0.66-1.34], P < .001; proximal RVOT width: 1.80 [95% CI, 1.22-2.39], P < .001) ( r = 0.79).
Conclusions
RV linear dimensions provide readily obtainable markers of RV chamber size. Proximal RVOT and basal width are independently associated with CMR volumes, supporting the use of multiple linear dimensions when assessing RV size on echocardiography.
Abnormal right ventricular (RV) chamber geometry is an established prognostic marker for a broad array of cardiovascular conditions, including coronary artery disease (CAD). Echocardiography-derived linear dimensions are widely used to assess left ventricular (LV) geometry, for which their use has been validated by anatomic correlation and prediction of prognosis. However, the utility of echocardiography for RV assessment is less certain. Despite known limitations posed by RV geometric complexity, American Society of Echocardiography (ASE) guidelines encompass multiple linear measurements for the assessment of RV chamber size, including measurements acquired in apical four-chamber, parasternal long-axis, and parasternal short-axis views. The relative utility of different echocardiographic linear measurements for assessment of RV size is not known.
Cardiac magnetic resonance (CMR) provides excellent endocardial definition that allows RV chamber size to be quantified without geometric assumptions. Prior studies have shown close agreement between CMR results and ex vivo phantom volumes and demonstrated CMR measurements of RV structure and function to be reproducible. Echocardiographic RV linear measurements have been compared with those obtained on CMR in prior cohorts. However, insights regarding the utility of echocardiographic linear dimensions have been limited by methodologic issues that have included the acquisition of select echocardiographic measurements (preventing comparison of individual measurements with one another), small sample size (limiting the generalizability of previously reported weak correlations), and prolonged intervals between echocardiography and CMR (an important concern in the context of the known sensitivity of the right ventricle to loading conditions).
In this study we examined RV structure and function among a broad cohort of patients with CAD undergoing echocardiography and CMR within a narrow interval. In all patients, a uniform echocardiographic protocol was performed, which included assessment of RV chamber geometry in standard orientations concordant with consensus guidelines. The aims were twofold: (1) to determine the feasibility and reproducibility of guideline-recommended RV linear measurements in a diverse CAD cohort and (2) to compare the magnitude of association between different echocardiography-based dimensions and CMR-quantified RV chamber volumes.
Methods
Population
The population comprised patients with CAD accrued from separate research registries at Weill Cornell Medical College, each of which was focused on multimodality imaging for the assessment of ischemic heart disease. Among these patients, 90% ( n = 246) were accrued prospectively as part of National Institutes of Health protocols using CMR and echocardiography for CAD-associated remodeling (1R01HL128278-01 and K23 HL102249-01), and 10% were accrued through a retrospective registry of patients with chronic obstructive CAD as verified by invasive angiography.
For all patients, CMR and echocardiography were performed within 7 days, without interval coronary revascularization between imaging tests. Patients with contraindications to CMR (e.g., glomerular filtration rate < 30 mL/min/1.73 m 2 , ferromagnetic implants) were excluded from participation. Comprehensive demographic data were collected, including cardiac risk factors, medications, and invasive angiography–assigned infarct-related artery. This study was conducted with approval from the Weill Cornell Medical College Institutional Review Board.
Imaging Protocol
Echocardiography and CMR were each performed using a standardized image acquisition protocol:
Echocardiography
Transthoracic echocardiography was performed using commercial equipment (Vivid 7 [GE Healthcare, Little Chalfont, United Kingdom], SC2000 [Siemens Healthcare, Malvern, PA]). Echocardiography included evaluation of the right ventricle from the parasternal long- and short-axis and RV-focused apical four-chamber views, as specified in consensus ASE guidelines.
CMR
CMR was performed using 1.5- and 3.0-T scanners (GE Medical Systems, Waukesha, WI). Cine CMR involved a steady-state free precession pulse sequence. Images were acquired in standard LV short- and long-axis planes. Short-axis images were acquired throughout the right ventricle such that images extended from the pulmonic valve through the RV apex.
RV Chamber Quantification
Echocardiography and CMR were interpreted by experienced physicians (J.K. and J.W.W., respectively) using a prespecified analytic approach for each modality.
Echocardiography
RV linear dimensions were made in orientations concordant with ASE guidelines :
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In the apical four-chamber view, RV width was measured in two locations: (1) basal RV width (maximal transverse diameter in the basal third of the right ventricle) and (2) mid RV width (maximal transverse diameter in the middle third of the right ventricle, approximately at the level of the papillary muscles). In addition, RV length was measured as the maximal distance from the tricuspid annulus to the apex.
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In the parasternal long-axis view, proximal RV outflow tract (RVOT) width was measured as the maximal distance (perpendicularly oriented) between the RV free wall and the septal-aortic junction.
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In the parasternal short-axis (pulmonary bifurcation) view, distal RVOT width was measured as the maximal distance immediately proximal to the pulmonic valve. When pulmonary bifurcation–focused view was not available, a nonfocused view of the pulmonic valve in the short axis was used for approximation of the pulmonic valve annulus.
Figure 1 provides representative examples of each RV dimension; all were measured during both end-diastole and end-systole. For the purpose of standardization, measurements in each respective orientation were acquired using the image and cardiac cycle that provided the largest linear dimension.
RV systolic function was assessed via tricuspid annular plane systolic excursion, S′ and fractional area change, which were acquired in accordance with consensus guidelines.
CMR
Volumetric quantification was performed using short-axis cine CMR images. Basal and apical image positions were defined in accordance with standard criteria, with the basal right ventricle defined by the image in which the pulmonic valve or valve annulus was visualized and the apex defined by the distal-most image in which the RV myocardium was visualized. End-diastole and end-systole were defined on the basis of the respective frames demonstrating the largest and smallest cavity sizes. Quantification of end-diastolic volume (EDV) and end-systolic volume (ESV) was performed using short-axis images inclusive of trabeculations and papillary muscle. RV ejection fraction (RVEF) was calculated based on EDV and ESV. Cine CMR analysis was performed using a previously validated automated algorithm shown to have excellent agreement with both manual planimetry–quantified cardiac chamber size and phantom-verified volumes.
Reproducibility
Intra- and interreader reproducibility was tested in a random cohort comprising 10% ( n = 26) of the study population, among whom processing times for both CMR and echocardiography were also recorded. Interreader reproducibility was tested by a designated reader (A.S.) with expertise in both CMR and echocardiography (>2,000 examinations interpreted annually). Reproducibility data sets for each modality were standardized in relation to initial images with respect to cardiac cycle for analysis. Readers were otherwise blinded to clinical history, results of other imaging modalities, and initial measurements. Reproducibility analyses were performed ≥10 days following the initial measurement.
Statistical Methods
Comparisons between groups were made using Student’s t test (expressed as mean ± SD) for continuous variables. Categorical variables were compared using χ 2 test or, for fewer than five expected outcomes per cell, the Fisher exact test. Bivariate correlation coefficients, as well as univariate and multivariate regression analyses, were used to evaluate associations between continuous variables. Multivariate modeling was performed via linear regression, for which CMR volumes and echocardiographic linear dimensions were both tested as continuous variables. Interobserver and intraobserver agreement between methods was assessed using the method of Bland and Altman, yielding the mean difference as well as limits of agreement between measurements (mean ± 1.96 SDs). Interrater reliability among the two raters was estimated using the intraclass correlation coefficient, coefficient of variation (calculated as the SD of the absolute difference between two acquisitions divided by the mean of the repeated acquisitions [expressed as a percentage]), as well as relative difference (calculated as the absolute difference between two acquisitions divided by the mean of the repeated acquisitions [expressed as a percentage]). Statistical calculations were performed using SPSS version 22.0 (SPSS, Inc, Chicago, IL). Two-sided P values <.05 were considered indicative of statistical significance.
Results
Population Characteristics
The population comprised 272 patients with CAD who underwent echocardiography and CMR within a mean interval of 0.4 ± 1.0 days; 94% underwent imaging via both modalities within 1 day. RV dysfunction or dilation on CMR (defined as RVEF < 50% or EDV > 100.9 mL/m 2 in men and EDV > 94.5 mL/m 2 in women, concordant with established normative cutoffs) was present in 21% of patients ( n = 57): 18% of the population ( n = 50) had RV systolic dysfunction and 10% ( n = 26) had RV dilation (7% [ n = 19] had both).
Table 1 details clinical and imaging characteristics of the population, as well as comparisons between patients with and those without RV dilation or dysfunction. As shown, patients with RV structural or functional abnormalities were older and more likely to have had prior myocardial infarction and prior coronary revascularization ( P < .05 for all). Regarding imaging parameters, patients with RV dilation or dysfunction had larger LV volumes and decreased LV systolic function ( P < .001 for all), consistent with the concept that post–myocardial infarction RV and LV structural and functional abnormalities are closely related.
| Overall ( n = 272) | No RV dilation or dysfunction ( n = 215) | RV dilation or dysfunction ( n = 57) | P | |
|---|---|---|---|---|
| Clinical | ||||
| Age (y) | 59 ± 13 | 57 ± 12 | 63 ± 15 | .003 |
| Male gender | 84% (228) | 84% (180) | 84% (48) | .93 |
| BSA (m 2 ) | 2.0 ± 0.2 | 1.97 ± 0.24 | 1.97 ± 0.21 | .81 |
| CAD risk factors | ||||
| Hypertension | 52% (140) | 47% (100) | 73% (40) | .001 |
| Hypercholesterolemia | 53% (142) | 51% (109) | 60% (33) | .22 |
| Diabetes mellitus | 23% (50) | 22% (42) | 31% (8) | .30 |
| Tobacco use | 36% (97) | 35% (75) | 40% (22) | .48 |
| Family history | 30% (81) | 30% (65) | 30% (16) | .93 |
| Prior myocardial infarction | 15% (41) | 10% (22) | 35% (19) | <.001 |
| Prior coronary revascularization | ||||
| Percutaneous intervention | 17% (47) | 14% (30) | 31% (17) | .003 |
| Coronary artery bypass grafting | 6.3% (17) | 2.8% (6) | 20% (11) | <.001 |
| Cardiovascular medications | ||||
| β-blocker | 93% (250) | 94% (202) | 89% (48) | .23 |
| ACE inhibitor/angiotensin receptor blocker | 61% (163) | 60% (128) | 65% (35) | .48 |
| Loop diuretic | 15% (41) | 7.4% (16) | 46% (25) | <.001 |
| HMG-CoA reductase inhibitor | 91% (246) | 95% (204) | 78% (42) | <.001 |
| Aspirin | 95% (256) | 98% (211) | 83% (45) | <.001 |
| Thienopyridine | 82% (221) | 89% (191) | 56% (30) | <.001 |
| Cardiac morphology and function | ||||
| CMR | ||||
| Right ventricle | ||||
| RVEF (%) | 57 ± 11 | 61 ± 6 | 42 ± 9 | <.001 |
| EDV (mL) | 143 ± 41 (52-321) | 132.0 ± 31.2 (52-203) | 182.9 ± 47.1 (89-321) | <.001 |
| Indexed (mL/m 2 ) | 72 ± 19 (34-161) | 67.0 ± 12.8 (34-101) | 93.2 ± 23.4 (36-161) | <.001 |
| ESV (mL) | 64 ± 32 (16-242) | 51.9 ± 16.9 (16-99) | 107.8 ± 37.9 (52-242) | <.001 |
| Indexed (mL/m 2 ) | 32 ± 16 (11-121) | 26.3 ± 7.5 (11-43) | 55.2 ± 19.5 (21-121) | <.001 |
| Left ventricle | ||||
| Ejection fraction (%) | 51 ± 14 | 54 ± 12 | 38 ± 15 | <.001 |
| EDV (mL) | 164 ± 53 | 152.8 ± 40.7 | 203.8 ± 70.5 | <.001 |
| Indexed (mL/m 2 ) | 83 ± 25 | 77.7 ± 18.0 | 103.7 ± 35.9 | <.001 |
| ESV (mL) | 86 ± 51 | 72.9 ± 35.3 | 134.0 ± 69.3 | <.001 |
| Indexed (mL/m 2 ) | 44 ± 26 | 37.1 ± 17.3 | 68.6 ± 36.6 | <.001 |
RV Linear Dimensions
Complete acquisition of all linear dimensions included in ASE guidelines (five measurements in both end-systole and end-diastole) were obtainable in 98% of patients (266 of 272) (distal RVOT width was not obtainable in six patients because of a lack of requisite images). Table 2 details inter- and intraobserver reproducibility for both CMR- and echocardiography-derived RV variables. As shown, the greatest reproducibility for end-diastolic dimensions was yielded by basal RV width, RV length, and proximal RVOT width (relative differences, 4.97%, 6.65%, and 6.49%, respectively), which were slightly less reproducible than by CMR (4.34%). End-systolic dimensions were less reproducible, paralleling volumetric data by CMR. Image analysis time was shorter for linear measurements via echocardiography (49 ± 15 sec) than for volumetric segmentation via CMR (90 ± 24 sec) ( P < .001).
| Intraobserver reproducibility | Interobserver reproducibility | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Intraclass correlation coefficient | Limits of agreement | Coefficient of variation (%) | Relative difference (%) | Mean ± SD | Intraclass correlation coefficient | Limits of agreement | Coefficient of variation (%) | Relative difference (%) | |
| Echocardiography | ||||||||||
| Diastole | ||||||||||
| Basal RV width (mm) | −0.4 ± 2.3 | 0.89 | −4.9 to 4.1 | 3.60 | 4.97 | −0.5 ± 2.4 | 0.87 | −5.1 to 4.2 | 4.21 | 4.37 |
| Mid RV width (mm) | 1.4 ± 3.3 | 0.81 | −5.1 to 8.0 | 7.72 | 9.81 | 2.6 ± 4.1 | 0.63 | −5.5 to 10.6 | 10.83 | 14.93 |
| RV length (mm) | −0.8 ± 6.8 | 0.69 | −14.2 to 12.6 | 5.34 | 6.65 | −0.8 ± 5.1 | 0.78 | −10.9 to 9.2 | 4.36 | 4.74 |
| Proximal RVOT width (mm) | 0.7 ± 3.0 | 0.82 | −5.3 to 6.6 | 6.69 | 6.49 | −0.1 ± 2.6 | 0.89 | −5.1 to 4.9 | 5.59 | 5.79 |
| Distal RVOT width (mm) | 1.0 ± 3.1 | 0.74 | −5.0 to 7.0 | 8.78 | 9.61 | −2.2 ± 4.1 | 0.69 | −10.3 to 5.9 | 13.44 | 11.89 |
| Systole | ||||||||||
| Basal RV width (mm) | 0.8 ± 3.8 | 0.67 | −6.7 to 8.3 | 8.53 | 12.06 | −0.5 ± 3.4 | 0.75 | −7.2 to 6.1 | 8.50 | 10.44 |
| Mid RV width (mm) | 1.2 ± 3.9 | 0.61 | −6.5 to 8.8 | 13.56 | 17.52 | 0.6 ± 3.3 | 0.68 | −5.9 to 7.1 | 14.29 | 12.51 |
| RV length (mm) | −0.9 ± 7.2 | 0.60 | −15.0 to 13.1 | 6.81 | 7.78 | −0.5 ± 3.7 | 0.85 | −7.9 to 6.8 | 2.71 | 4.69 |
| Proximal RVOT width (mm) | 0.3 ± 3.3 | 0.81 | −6.2 to 6.8 | 8.98 | 10.66 | −0.1 ± 4.4 | 0.67 | −8.5 to 8.6 | 16.03 | 9.10 |
| Distal RVOT width (mm) | 1.8 ± 3.0 | 0.79 | −4.0 to 7.7 | 13.90 | 15.98 | −1.3 ± 3.3 | 0.75 | −7.8 to 5.3 | 16.20 | 14.88 |
| CMR | ||||||||||
| EDV (mL) | −1.1 ± 5.9 | 0.99 | −12.8 to 10.5 | 2.32 | 4.34 | −4.0 ± 7.9 | 0.98 | −19.6 to 11.5 | 4.10 | 5.48 |
| ESV (mL) | −3.5 ± 4.6 | 0.98 | −12.5 to 5.5 | 7.64 | 7.64 | −1.8 ± 5.7 | 0.97 | −13.0 to 9.4 | 7.80 | 8.32 |
Table 3 compares echocardiographic linear dimensions stratified by the combined partition of RV dilation or dysfunction on CMR, as well as each of the two individual parameters. As shown, all RV linear dimensions were larger among patients with CMR-evidenced RV dilation ( P < .05 for all). Regarding RV systolic dysfunction, fractional shortening as measured in each linear plane was lower among patients with reduced RVEFs (<50%) defined by CMR ( P < .05 for all).
| No RV dilation or dysfunction ( n = 215) | RV dilation or dysfunction ( n = 57) | P | No RV dysfunction ( n = 222) | RV dysfunction ( n = 50) | P | No RV dilation ( n = 246) | RV dilation ( n = 26) | P | |
|---|---|---|---|---|---|---|---|---|---|
| Right ventricle | |||||||||
| End-diastolic dimensions | |||||||||
| Basal RV width (mm) | 35.7 ± 5.2 | 43.7 ± 7.3 | <.001 | 35.9 ± 5.4 | 43.9 ± 7.3 | <.001 | 36.3 ± 5.7 | 47.1 ± 6.2 | <.001 |
| Mid RV width (mm) | 26.3 ± 5.8 | 31.9 ± 7.0 | <.001 | 26.4 ± 6.0 | 32.0 ± 6.8 | <.001 | 26.7 ± 5.9 | 35.0 ± 6.7 | <.001 |
| RV length (mm) | 78.5 ± 8.2 | 89.5 ± 9.0 | <.001 | 78.9 ± 8.4 | 89.5 ± 9.3 | <.001 | 79.7 ± 8.8 | 91.5 ± 9.6 | .001 |
| Proximal RVOT width (mm) | 31.9 ± 4.7 | 37.7 ± 5.7 | <.001 | 32.1 ± 4.9 | 37.3 ± 5.9 | <.001 | 32.5 ± 5.0 | 39.2 ± 5.5 | <.001 |
| Distal RVOT width (mm) | 24.3 ± 4.5 | 27.1 ± 4.6 | <.001 | 24.3 ± 4.6 | 27.1 ± 4.4 | <.001 | 24.5 ± 4.5 | 28.4 ± 4.9 | <.001 |
| End-systolic dimensions | |||||||||
| Basal RV width (mm) | 25.0 ± 4.9 | 33.7 ± 7.0 | <.001 | 25.2 ± 5.1 | 34.2 ± 6.7 | <.001 | 25.8 ± 5.6 | 36.2 ± 6.8 | <.001 |
| Mid RV width (mm) | 16.5 ± 4.5 | 23.0 ± 5.9 | <.001 | 16.6 ± 4.6 | 23.3 ± 6.0 | <.001 | 17.0 ± 4.8 | 25.7 ± 5.8 | <.001 |
| RV length (mm) | 66.9 ± 7.6 | 78.5 ± 8.6 | <.001 | 67.2 ± 7.7 | 78.8 ± 9.0 | <.001 | 68.1 ± 8.3 | 81.1 ± 8.8 | <.001 |
| Proximal RVOT width (mm) | 23.2 ± 4.4 | 29.9 ± 5.9 | <.001 | 23.5 ± 4.6 | 29.6 ± 6.2 | <.001 | 23.9 ± 4.9 | 31.4 ± 5.7 | <.001 |
| Distal RVOT width (mm) | 17.1 ± 3.9 | 19.7 ± 4.7 | <.001 | 17.1 ± 3.9 | 19.9 ± 4.7 | <.001 | 17.2 ± 3.9 | 21.4 ± 5.3 | .001 |
| Fractional shortening | |||||||||
| Basal RV (%) | 29.9 ± 8.9 | 23.1 ± 7.9 | <.001 | 29.9 ± 9.0 | 22.2 ± 7.0 | <.001 | 29.0 ± 9.1 | 23.6 ± 8.0 | .004 |
| Mid RV (%) | 36.9 ± 12.4 | 27.9 ± 9.5 | <.001 | 36.7 ± 12.3 | 27.4 ± 9.6 | <.001 | 35.9 ± 12.4 | 26.7 ± 8.6 | <.001 |
| RV length (%) | 14.7 ± 6.2 | 12.2 ± 5.2 | .006 | 14.6 ± 6.2 | 12.0 ± 4.9 | .005 | 14.4 ± 6.0 | 11.2 ± 5.9 | .01 |
| Proximal RVOT (%) | 27.3 ± 7.5 | 20.9 ± 7.8 | <.001 | 27.0 ± 7.6 | 21.0 ± 7.7 | <.001 | 26.5 ± 7.7 | 20.0 ± 8.0 | <.001 |
| Distal RVOT (%) | 29.7 ± 7.7 | 27.7 ± 8.5 | .09 | 29.8 ± 7.6 | 27.0 ± 8.7 | .03 | 29.7 ± 7.6 | 25.4 ± 9.4 | .009 |
| Left ventricle | |||||||||
| End-diastolic diameter (mm) | 56.4 ± 4.8 | 59.2 ± 7.6 | .01 | 56.4 ± 4.8 | 59.6 ± 7.8 | .007 | 56.7 ± 5.2 | 59.3 ± 8.2 | .13 |
| End-systolic diameter (mm) | 42.0 ± 6.1 | 48.4 ± 10.5 | <.001 | 42.0 ± 6.1 | 49.3 ± 10.4 | <.001 | 42.8 ± 6.9 | 48.5 ± 11.7 | .02 |
| Fractional shortening (%) | 25.8 ± 6.6 | 19.2 ± 9.2 | <.001 | 25.8 ± 6.7 | 18.2 ± 8.7 | <.001 | 25.0 ± 7.1 | 19.2 ± 10.3 | .009 |
RV Volumes
Table 4 reports correlations between CMR-quantified RV chamber volumes and echocardiography-quantified RV dimensions. Echocardiographic dimensions in all planes correlated significantly with CMR RV volumes ( P < .001 for all). Regarding EDV, the greatest magnitudes of correlation were observed for basal RV width ( r = 0.70), proximal RVOT width ( r = 0.68), and RV length ( r = 0.61). Similar correlations were observed for corresponding end-systolic dimensions ( r = 0.68, r = 0.66, and r = 0.65, respectively). Table 4 also demonstrates that proximal RVOT fractional shortening (measured in the parasternal long-axis view) was the linear parameter that yielded the greatest correlation with RVEF ( r = 0.38, P < .001). Echocardiography-quantified fractional area change ( r = 0.55, P < .001) as well as tricuspid annular plane systolic excursion ( r = 0.48, P < .001) yielded slightly higher correlations with CMR-quantified RVEF.
