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Ann Thorac Surg 1995;60:268-271
© 1995 The Society of Thoracic Surgeons

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Original Articles: General Thoracic

MRI Complements Standard Assessment of Right Ventricular Function After Lung Transplantation

Departments of Cardiac and Thoracic Surgery, Radiology and Radiological Sciences, Divisions of Pulmonary and Critical Care Medicine, Pediatric Cardiology, and the Vanderbilt Transplant Center, Vanderbilt University Medical Center, Nashville, Tennessee

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Background. Changes in right ventricular mass and ejection fraction after single-lung transplantation for pulmonary hypertension are poorly understood.

Methods. To complement functional data provided by echocardiography, radionuclide ventriculography, and right heart catheterization, magnetic resonance imaging was used to assess right ventricular function in 5 single- lung transplant recipients with preoperative pulmonary hypertension and right ventricular dysfunction (right ventricular ejection fraction, 0.21 ± 0.09). The right and left ventricular mass, ejection fraction, and mass ratio (left ventricular mass/right ventricular mass) were calculated from the magnetic resonance images.

Results. The mean pulmonary artery pressure fell from 72 ± 18 to 21 ± 8 mm Hg after transplantation. At 3 months after transplantation both the left ventricular and right ventricular ejection fractions approached normal values, as shown by both radionuclide ventriculography and magnetic resonance imaging, but the right ventricular mass remained abnormally high with slightly low mass ratios. By 1 year both the left ventricular and right ventricular masses had regressed to normal with near-normal mass ratios.

Conclusions. Right ventricular performance returns to nearly normal early after transplantation, but the right ventricular mass regresses over a more prolonged time. Cine magnetic resonance imaging provides a noninvasive means of assessing changes in right ventricular function and mass after lung transplantation.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
See also page 271.

We report our experience with cine magnetic resonance imaging (MRI), which was used to complement traditional imaging techniques in the documentation of changes in right ventricular function and mass after single-lung transplantation in 5 patients with severe pulmonary hypertension. These patients displayed pronounced right ventricular dysfunction preoperatively; their response to the right ventricular afterload reduction brought about by transplantation was prompt. The effects of the dramatic decrease in pulmonary artery pressure and pulmonary vascular resistance on right ventricular mass and function were quantitated using cine MRI.

Gradient-echo cine MRI, or cine MRI, provides high-resolution images of any plane within the heart at a temporal resolution of 25 to 50 ms. Previous studies have shown that cine MRI is capable of providing quantitative information on the function of the left ventricle [1, 2]. The right ventricle, which is of greatest interest in patients with severe dysfunction secondary to pulmonary hypertension, has been difficult to evaluate using any of the traditional imaging methods because of its geometric structure and location within the chest cavity. Various methods, including right heart catheterization, echocardiography, and radionuclide scanning, have been used in attempts to characterize right ventricular function. The tomographic capability of MRI overcomes many of the limitations of these more conventional methods in imaging the right ventricle [3--6].

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
At our institution 5 patients were evaluated (3 women and 2 men) who had undergone single-lung transplantation for severe pulmonary hypertension (Table 1). The mean age of the patients was 33 ± 20 years (range, 11 to 57 years). The cause was primary pulmonary hypertension in 2, severe pulmonary arterial medial hypertrophy with associated emphysema in 1, progressive pulmonary hypertension occurring late after successful repair of a ventricular septal defect in 1, and pulmonary venoocclusive disease in 1.

In all patients single-lung transplantation was performed using partial cardiopulmonary bypass. Femoral artery and right atrial cannulation was used in 2; aorta and right atrial cannulation in 2; and femoral artery and femoral vein cannulation in 1. Bronchial anastomoses were performed using interrupted absorbable sutures, and four of the five anastomoses were wrapped with an omental pedicle. The total ischemic time was 165 ± 32 minutes. Patients were extubated at 6 ± 3 days (range, 1 to 23 days) postoperatively.

Cine MRI was performed in the short-axis view in contiguous 7-mm slices from the atrioventricular valve plane to the apex. All imaging was performed on a Siemens SP4000 1.5T scanner (Siemens Medical Systems, Iselin, NJ). The temporal resolution was 50 ms. All acquisitions were electrocardiography-triggered. Image analysis consisted of manual definition of the endocardial and epicardial borders of both the right and left ventricles at end-diastole and of definition of the endocardial borders at end-systole. The end-diastolic image was considered the first image in each cine loop (acquired just after the R-wave trigger), and the end-systolic image was determined visually as the image in the cine loop with the smallest blood volume. The image analysis was performed using an independent three-dimensional image-processing workstation (MaxiView; Dimensional Medicine, Minnetonka, MN). The volumes contained within the epicardial and endocardial borders were calculated by integrating over all slices. Myocardial mass was calculated as the difference between the volumes contained within the epicardial and endocardial borders in each ventricle at end-diastole multiplied by an assumed density of 1.05 g/cm³. Stroke volume was calculated as the difference between endocardial volumes at end-diastole and end-systole. Ejection fraction was calculated as the stroke volume divided by the end-diastolic volume. This analytic method was validated previously in our laboratory in dogs by correlating MRI findings with anatomic abnormalities [5].

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
All 5 patients survived, and the current mean length of follow-up is 712 days. All patients experienced a substantial immediate decrease in pulmonary artery pressure, which was sustained throughout the follow-up period. The mean pulmonary artery pressure preoperatively was 72 ± 22 mm Hg (range, 47 to 110 mm Hg) and declined to 21 ± 6 mm Hg postoperatively (range, 14 to 27 mm Hg) at a mean of 65 days (range, 25 to 98 days). Resolution of pulmonary hypertension was slower in patients with graft dysfunction but was normal at 1 year.

As expected, the pulmonary vascular resistance decreased significantly from a mean of 1607 ± 876 dynes • s/cm⁵ preoperatively (range, 509 to 2800 dynes • s/cm⁵) to 219 ± 124 dynes • s/cm⁵ postoperatively (range, 49 to 400 dynes • s/cm⁵), remaining normal at 1 year. The transpulmonary gradient declined from 66 ± 18 mm Hg preoperatively to 11 ± 4 mm Hg at 2 months and was 15 ± 6 mm Hg at 1 year.

The cardiac index, measured at rest by the thermodilution method by means of right heart catheterization, increased in 4 patients and was unchanged in the fifth patient. The mean cardiac index preoperatively was 2.3 ± 0.42 L • min^-1 • m^-2 and increased postoperatively to 3.3 ± 0.50 L • min^-1 • m^-2.

The ejection fraction of both the right and left ventricles was obtained by radionuclide ventriculography in 4 patients preoperatively and in all 5 patients postoperatively. The right ventricular ejection fraction increased dramatically from 0.21 ± 0.09 preoperatively (range, 0.05 to 0.28) to 0.47 ± 0.10 postoperatively at 1 month (range, 0.35 to 0.55). The left ventricular ejection fraction did not change substantially with transplantation (0.55 preoperatively and 0.56 postoperatively).

The tomographically derived ejection fractions determined by cine MRI are shown in Table 2. The right ventricular ejection fraction was normal at 3 months and remained normal at 1 year. In contrast, the right ventricular mass remained markedly high at 79 ± 11 g (normal, 49 ± 12 g) at 3 months and did not decline to normal values until the 1-year study. The left ventricular mass remained in the normal range throughout the postoperative evaluation period. The ratio of the left ventricular mass to the right ventricular mass was below normal at 3 months but had normalized by the time of the 1-year study.

The echocardiographically determined septal thickness decreased from 1.3 ± 0.1 cm preoperatively to 0.9 ± 0.1 cm at 3 months and 1 year. The preoperative left ventricular end-diastolic dimension (2.7 ± 0.2 cm) was well below normal (3.5 to 5.6 cm); it increased to a normal dimension at 3 months (4.4 ± 0.2 cm) and remained normal at 1 year. The increase in the left ventricular end-diastolic dimension is consistent with the restoration of normal left ventricular geometry. The left ventricle, which had an abnormal D shape with bowing of the septum into the left ventricular cavity before transplantation, returned to normal postoperatively.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
All 5 patients with pulmonary hypertension underwent successful single-lung transplantation at our institution. Significant and prompt lowering of the pulmonary artery pressure and pulmonary vascular resistance occurred with improvement in right ventricular performance, as shown by cine MRI and radionuclide ventriculography. The right ventricular mass, as measured by cine MRI, did not return to normal for months. The favorable hemodynamic results occurred acutely at the time of operation and persisted, allowing each patient's functional status to recover fully.

The right ventricular ejection fraction improved significantly, as shown by both radionuclide ventriculography and MRI, whereas the left ventricular ejection fraction remained normal. The cardiac index increased significantly in response to the reduction in the pulmonary vascular resistance to normal. Most of the increase in cardiac output is delivered to the transplanted lung because of its lower vascular resistance. In patients who undergo transplantation for pulmonary hypertension, the grafted lung typically receives 85% or more of the resultant cardiac output, as measured by radionuclide perfusion scanning.

Dysfunction of the right ventricle is an important problem in both children and adults after the transplantation of thoracic organs. The potential clinical impact of a noninvasive, reproducible means of assessing right ventricular function is substantial. Right ventricular dysfunction may develop in patients with chronic right ventricular pressure and volume overload resulting from pulmonary hypertension or from right ventricular outflow tract obstruction stemming from any cause. With improved understanding of the adaptation of the right ventricle to overload, the optimal therapy (eg, single-lung versus heart-lung transplantation versus afterload reduction) for individual patients could be determined. Few methods are currently available for the noninvasive, serial assessment of right ventricular function. Magnetic resonance imaging has the ability to quantitate right ventricular function without the many limitations inherent in other imaging methods.

The only other technique that has been shown to yield accurate estimates of both right and left ventricular mass has been ultrafast computed tomography [7]. Although MRI is currently more expensive and time-consuming than ultrafast computed tomography, it has wider applicability. Ultrafast computed tomography is not available in many centers, whereas MRI has generally become widely available. Moreover, MRI does not require the use of contrast agents and the patient is not exposed to ionizing radiation.

Because many patients with pulmonary hypertension eventually succumb to progressive right ventricular failure, transplantation of a single lung or reduction in the right ventricular afterload achieved by other means can ameliorate the cause of the right ventricular failure. This study demonstrates the regression in right ventricular function and mass abnormalities that occurs in these patients after lung transplantation. It has yet to be shown what degree of right ventricular dysfunction, if any, is not reversible when afterload is reduced. Cine MRI is a method that has the potential for accomplishing an accurate serial assessment of right ventricular mass and function.

In conclusion, right ventricular function returns to normal early in patients with pulmonary hypertension who undergo single-lung transplantation, whereas right ventricular mass regresses more slowly. As an adjunct to more traditional imaging methods, cine MRI permits the quantitation of right ventricular mass and volume without geometric assumptions and should be useful for further defining the adaptive properties of the right ventricle.

	Acknowledgments

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
This research was supported in part by the Ken and Barbara Mandrell Dudney Medical Fund, Nashville, TN (W.H.F.), the Fleming Foundation, Nashville, TN (W.H.F.), and an American Heart Association, Tennessee Affiliate Fellowship (E.S.W.).

We thank Ms Victoria L. Morgan for help with analysis of the magnetic resonance images.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Presented at the Fortieth Annual Meeting of the Southern Thoracic Surgical Association, Panama City Beach, FL, Nov 4--6, 1993.

Address reprint requests to Dr Frist, c/o Daryl P. Pearlstein, 344 Village at Vanderbilt, Nashville, TN 37212.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 

1. Ostrzega E, Maddahi J, Honma H, et al. Quantification of left ventricular myocardial mass in humans by nuclear magnetic resonance imaging. Am Heart J 1989;117:444–52.[Medline]
2. Mogelvang J, Thomsen C, Mehlsen J, Brackle G, Stubgaard M, Henriksen O. Evaluation of left ventricular volumes measured by magnetic resonance imaging. Eur Heart J 1986;7:1016–21.[Abstract/Free Full Text]
3. Mackey ES, Sandler MP, Campbell RM, et al. Right ventricular myocardial mass quantification with magnetic resonance imaging. Am J Cardiol 1990;65:529–32.[Medline]
4. Mogelvang J, Stubgaard M, Thomsen C, Henriksen O. Eval-uation of right ventricular volumes measured by magnetic resonance imaging. Eur Heart J 1988;9:529–33.[Abstract/Free Full Text]
5. Lorenz CH, Graham TP, Holburn GE, et al. Noninvasive estimation of right and left ventricular myocardial mass by gated cine magnetic resonance imaging. Magn Reson Imaging 1990;8(Suppl 1):33.[Medline]
6. Doherty NE, Fujita N, Caputo GR, Higgins CB. Measurement of right ventricular mass in normal and dilated cardiomyopathic ventricles using cine magnetic resonance imaging. Am J Cardiol 1992;69:1223–8.[Medline]
7. Hajduczok ZD, Weiss RM, Stanford W, Marcus ML. Determination of right ventricular mass in humans and dogs with ultrafast cardiac computed tomography. Circulation 1990;82:202–12.[Abstract/Free Full Text]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): William H. Frist James R. Stewart Steven P. Key Walter H. Merrill Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Frist, W. H. Articles by Merrill, W. H. Search for Related Content PubMed PubMed Citation Articles by Frist, W. H. Articles by Merrill, W. H. Related Collections Related Article