Assessment of hemodynamic effects of angiotensin-converting enzyme inhibitor therapy in chronic aortic regurgitation by using velocity-encoded cine magnetic resonance imaging

Cardiac magnetic resonance imaging for the investigation of cardiovascular disorders. Part 1: current applications

Cardiac magnetic resonance imaging is a robust noninvasive technique for investigating cardiovascular disorders. The evolution of cardiac magnetic resonance and its widening span of diagnostic and prognostic applications have generated excitement as well as uncertainty regarding its potential clinical use and its role vis-à-vis conventional imaging techniques. The purpose of this evidence-based review is to discuss some of these issues by highlighting the current (Part 1) and emerging (Part 2) applications of cardiac magnetic resonance. Familiarity with the versatility and usefulness of cardiac magnetic resonance will facilitate its wider clinical acceptance for improving the management of cardiovascular disorders.

Vasodilator therapy in patients with aortic insufficiency: a systematic review

BACKGROUND

The use of vasodilators to improve long-term outcomes in asymptomatic patients with chronic aortic insufficiency (AI) is controversial.

METHODS

We reviewed MEDLINE, PREMEDLINE, Current Contents, and Cochrane databases to identify relevant clinical trials on asymptomatic patients with chronic AI of at least moderate severity. We included those studies that involved long-term vasodilator therapy (including hydralazine, calcium-channel blockers, and angiotensin-converting enzyme inhibitors) and assessed either hemodynamic and structural parameters or clinical outcomes. Data on patient demographics, study protocols, and outcomes were abstracted.

RESULTS

Ten studies with 544 asymptomatic patients with chronic AI were identified. Treatment duration with vasodilators ranged from 12 weeks to 7 years. Of these, 8 studies compared vasodilators with placebo or no therapy, with 5 demonstrating improvements in at least 1 hemodynamic or structural parameter with vasodilators and 3 showing little or no apparent benefit. The remaining 2 studies directly compared outcomes between 2 different vasodilators. Both of these studies demonstrated greater improvements in hemodynamic and structural parameters with angiotensin-converting enzyme inhibitors compared with hydralazine and nifedipine. Clinical outcomes were primarily reported in only 2 of the 10 studies. Although one study suggested that the use of vasodilators slowed the rate of progression to surgery for aortic valve replacement, another showed no difference.

CONCLUSIONS

Vasodilators inconsistently improve hemodynamic and structural parameters in asymptomatic patients with chronic AI. In addition, the impact of vasodilators on clinical outcomes is largely uncertain and requires further study.

Angiotensin-converting enzyme inhibitor captopril prevents volume overload cardiomyopathy in experimental chronic aortic valve regurgitation

The efficacy of angiotensin-converting enzyme inhibitors (ACEIs) in the treatment of chronic aortic regurgitation (AR) is not well established and remains controversial. The mechanisms by which ACEIs may protect against left-ventricular (LV) volume overload are not well understood, and clinical trials performed until now have yielded conflicting results. This study was therefore performed to assess the effectiveness of two different doses of the ACEI captopril in a rat model of chronic AR. We compared the effects of a 6-month low-dose (LD) (25 mg/kg) or higher dose (HD) (75 mg/kg) treatment with captopril on LV function and hypertrophy in Wistar rats with severe AR. Untreated animals developed LV eccentric hypertrophy and systolic dysfunction. LD treatment did not prevent hypertrophy and provided modest protection against systolic dysfunction. HD treatment preserved LV systolic function and dimensions and tended to slow hypertrophy. The cardiac index remained high and similar among all AR groups, treated or not. Tissue renin-angiotensin system (RAS) analysis revealed that ACE activity was increased in the LVs of AR animals and that only HD treatment significantly decreased angiotensin II receptor mRNA levels. Fibronectin expression was increased in the LV or AR animals, but HD treatment almost completely reversed this increase. The ACE inhibitor captopril was effective at high doses in this model of severe AR. These effects might be related to the modulation of tissue RAS and the control of fibrosis.

Dynamic exercise imaging with an MR-compatible stationary cycle within the general electric open magnet

Many cases of muscular ischemia do not manifest without increased metabolic demand. Hence, diagnosis of intermittent claudication often requires inducing physiologic challenge, such as by exercise. Cine phase-contrast MRI can concurrently acquire cross-sectional vascular anatomy and through-plane blood velocities, enabling blood flow rate quantification. An MR-compatible stationary cycle was designed, constructed, and tested for flow quantification in large arteries during lower-limb exercise in a General Electric Signa SP 0.5 T open magnet. The cycle demonstrated smooth cycling during image acquisition, has freewheeling capability, is adjustable for subject size and strength, and can quantify workload. A healthy 59-year-old male was imaged at the supraceliac and infrarenal levels of the abdominal aorta at rest and during exercise. An exercise workload of 47.9 W was achieved. His heart rate increased from 52 to 78 bpm, supraceliac flow increased from 1.7 to 3.7 L/min, and infrarenal flow increased from 0.4 to 3.2 L/min from rest to exercise.

Perindopril effect on uncoupling protein and energy metabolism in failing rat hearts

Uncoupling proteins, inner mitochondrial membrane proton transporters, are important for regulating myocardial energy efficiency. We investigated the effects of the ACE inhibitor perindopril on cardiac performance, myocardial energy efficiency, and uncoupling protein expression in an aortic regurgitation rat model. Twenty male Sprague-Dawley rats, in which aortic regurgitation was produced, were divided into untreated and perindopril-treated (5 mg x kg(-1) x d(-1)) rats. The treatments were initiated 3 days after operation. Ten control rats were sham-operated. Measurements of blood pressure and echocardiography were repeated before and 100 days after operation (endpoint). Left ventricular uncoupling protein-2 expression, creatine phosphate, and adenosine triphosphate were measured at endpoint. In perindopril-treated rats, systolic and diastolic blood pressure decreased after treatment (92+/-4/65+/-2 mm Hg). At endpoint, left ventricular end-diastolic dimension in untreated (10.7+/-0.2 mm) and treated rats (9.2+/-0.2 mm) was increased, and fractional shortening was reduced in untreated rats (28+/-1%) but did not change in treated rats (36+/-2%). Uncoupling protein-2 mRNA expression increased in untreated rats (3.7-fold) and was suppressed by perindopril (1.5-fold). The creatine phosphate was reduced in untreated rats (10.6+/-0.7 micro mol/g) but not in treated rats (15.9+/-2.0 micro mol/g). In the chronic stage of aortic regurgitation, perindopril improved cardiac performance and myocardial energy efficiency, in which the suppression of uncoupling protein-2 may play an important role.

Left ventricular remodeling after infarction: sequential MR imaging with oral nicorandil therapy in rat model

PURPOSE

To use magnetic resonance (MR) imaging in quantification of the short- and long-term effects of therapy with orally administered nicorandil on left ventricular (LV) geometry and function independent of infarction size.

MATERIALS AND METHODS

Forty-six rats were subjected to reperfused infarction and randomly divided into two groups. Group 1 rats (n = 21) were treated with nicorandil (3 mg/kg/day in drinking water) for 4 days before infarction and 8 weeks after infarction (hereafter, the nicorandil group). Group 2 rats (n = 25) received tap water for the same period and served as the control group. Mesoporphyrin- (as a necrosis-specific agent) enhanced MR imaging was used to define necrotic myocardium on day 2 after infarction in all 46 animals. Contrast material-enhanced MR images showed large but identical infarction size in 11 control and 11 nicorandil rats. Only these 22 rats underwent repeat MR imaging at 8 weeks after infarction. The following variables were measured: LV volumes, ejection fraction, mass, wall thickness, and infarction size. Student t test and analysis of variance for repeated measurements were used for statistical analysis.

RESULTS

The size of the necrotic region on mesoporphyrin-enhanced MR images was 39% +/- 3 of the size of the left ventricle in the control group and 41% +/- 2 in the nicorandil group (difference not significant, unpaired Student t test). Pretreatment with nicorandil for 6 days before imaging did not reduce LV dilation or improve function compared with those in control animals with identical infarction size. Eight weeks after infarction, control animals showed deterioration in LV function, wall thinning, and gradient in regional dysfunction (analysis of variance test). Nicorandil produced significant salutary effects on LV ejection fraction (37% +/- 3 in the nicorandil group vs 24% +/- 3 in the control group), end-diastolic volume (0.53 mL +/- 0.03 vs 0.65 mL +/- 0.04), end-systolic volume (0.36 mL +/- 0.03 vs 0.49 mL +/- 0.05), LV wall thickening in remote noninfarcted myocardium (28% +/- 2 vs 19% +/- 1), and a rim of infarction (16% +/- 2 vs 8% +/- 1) (P <.05 for all parameters). The increase in LV mass was reduced in the nicorandil group (0.73 g +/- 0.03) compared with that in the control group (0.89 g +/- 0.04) (P <.05).

CONCLUSION

In animals studied longitudinally, MR imaging demonstrated the deleterious changes in LV geometry and function in the period after infarction and the salutary effects of medical therapy.

Blood pool contrast-enhanced MRI detects suppression of microvascular permeability in early postinfarction reperfusion after nicorandil therapy

Nicorandil is an adenosine triphosphate-sensitive potassium channel opener with a nitrate-like effect. It is approved for clinical use in Europe and Japan as an antianginal drug. The purpose of this investigation was to assess the acute effects of nicorandil therapy on microvascular injury using the blood pool MR contrast medium, NC100150 injection (Clariscan). Microvascular injury was produced in 24 rats using 45 min of coronary occlusion / 3 hr reperfusion. Nicorandil was infused at 15 min of occlusion and during reperfusion. Control animals received a saline solution. MR imaging was used to characterize microvascular permeability, quantify the extent of microvascular injury, LV volume, and wall thickness. Hyperenhancement at 30 min after administration of 0.05 mmol/kg Clariscan mapped the extent of ischemia-induced loss of microvascular integrity. The accumulation of Clariscan in the injured region was significantly suppressed in nicorandil compared to control rats. Nicorandil reduced the extent of microvascular injury from 44 +/- 2% to 18 +/- 2% (P < 0.01) and true infarction size from 29 +/- 2% to 12 +/- 1%. The extent of the hyperenhanced region correlated with the true size of area at risk at autopsy. On spin-echo MRI during end-diastole, nicorandil reduced LV end-diastolic volume and preserved wall thickness in remote myocardium; both parameters are markers of LV dilatation caused by acute infarction (remodeling). In conclusion, blood pool contrast-enhanced MRI has the potential to depict and quantify the extent of microvascular permeability and injury. Nicorandil suppressed microvascular permeability, reduced infarction size, and improved LV function in early postinfarction reperfusion.

Computed tomography and magnetic resonance imaging of patients with valvular heart disease

Although computed tomographic (CT) and magnetic resonance (MR) evaluation of patients with valvular heart disease is almost never performed as a first line of diagnostic intervention, their performance does provide important morphologic and physiologic information concerning the etiology and the current status of the valvular dysfunction. Evaluation of chamber and great artery size as well as ventricular wall thickness provide the basis for diagnosing and analyzing severity of valvular heart disease. Furthermore, additional findings, including calcification and evidence of interstitial pulmonary edema, increase diagnostic sensitivity and confidence in diagnosis. MR examination has the advantage over CT of providing direct demonstration of the signal void jets of dysfunctional valves, as well as a means of quantitating regional and global ventricular function and severity of valvular pressure gradients.

Vasodilatation with felodipine in chronic asymptomatic aortic regurgitation

BACKGROUND

Afterload reduction decreases volume overload on the left ventricle and may thereby delay the need for valve replacement in chronic asymptomatic aortic regurgitation. The aims of this randomized double-blind, placebo-controlled trial were to examine short- and long-term hemodynamic effects of felodipine in chronic asymptomatic aortic regurgitation.

METHODS

Sixteen patients were randomly assigned to an intravenous infusion of either felodipine 0. 3 mg or placebo followed by 3 months' treatment with felodipine 10 mg or placebo orally once daily. Magnetic resonance imaging was performed at baseline, immediately after intravenous treatment, and after 3 months of oral treatment.

RESULTS

Intravenous felodipine caused a statistically significant reduction in the systemic vascular resistance from (mean +/- SD) 1160 +/- 400 to 970 +/- 320 dynes. s. cm(-5) (P <.05), in the regurgitant volume index from 1.5 +/- 0.8 to 1.3 +/- 0.8 L. min(-1). m(-2) (P <.05), and in the regurgitant fraction from 0.31 +/- 0.15 to 0.26 +/- 0.14 (P <.05). The forward cardiac output index increased significantly from 3.2 +/- 0.9 to 3.5 +/- 0.7 L. min(-1). m(-2) (P <.05). Three months of oral treatment with felodipine caused a corresponding but more pronounced decrease in systemic vascular resistance of 880 +/- 330 dynes. s. cm(-5) (P <.05), regurgitant volume index of 1.2 +/- 0.7 L. min(-1). m(-2) (P <.05), and regurgitant fraction 0.25 +/- 0.11 (P <.05), whereas the forward cardiac output index increased to 3.6 +/- 0.7 L. min(-1). m(-2) (P <.05). No significant changes were found in the placebo group. Left ventricular volumes and ejection fraction remained unaffected by treatment, but compared with the placebo group left ventricular myocardial mass decreased significantly from 137 +/- 24 to 132 +/- 21 g. m(-2) (P <.01).

CONCLUSION

In chronic asymptomatic aortic regurgitation, felodipine causes beneficial hemodynamic effects that may postpone the need for valve replacement.

Magnetic resonance imaging of valvular heart disease

The optimum management of patients with valvular heart diseases requires accurate and reproducible assessment of the valvular lesion and its hemodynamic consequences. Magnetic resonance imaging (MRI) techniques, such as volume measurements, signal-void phenomena, and velocity mapping, can be used in an integrated approach to gain qualitative and quantitative information on valvular heart disease as well as ventricular dimensions and functions. Thus, MRI may be advantageous to the established diagnostic tools in assessing the severity of valvular heart disease as well as monitoring the lesion and predicting the optimal timing for valvular surgery. This paper reviews the validation of these MRI techniques in assessing valvular heart disease and discusses some typical pitfalls of the techniques, including suggestions for solutions.J. Magn. Reson. Imaging 1999;10:627-638.

Integrated MR imaging approach to valvular heart disease

With development of cine and velocity encoded magnetic resonance imaging, it is now feasible to detect and quantify aortic and mitral stenosis and regurgitation accurately. In addition, magnetic resonance imaging has the capabilities to assess simultaneously left and right ventricular mass, volumes, and function precisely. The high accuracy and reproducibility of magnetic resonance imaging in quantification of regurgitation and ventricular function has the potential to provide improved monitoring of therapy and optimal timing of surgery in patients with valvular dysfunction. In comparison to echocardiography and angiography, some current limitations of magnetic resonance imaging to an integrated approach of valvular heart disease exist, which may be removed with future refinement of magnetic resonance imaging technology for cardiovascular imaging.

Magnetic resonance imaging in valvular heart disease

Magnetic resonance techniques can be employed to depict valvular abnormalities but are especially helpful in quantifying regurgitant or stenotic lesions which cannot be quantitatively assessed by other noninvasive techniques. Gradient echo techniques and phase velocity mapping are the most important magnetic resonance pulse sequences employed for these purposes. Valvular regurgitation can be quantitated by measuring the area of signal void on conventional gradient-echo images, by calculating stroke volume differences from k-space segmented gradient echo images, by measuring the proximal convergence zone from velocity encoded images or by comparing stroke volumes of the ventricles from velocity measurements. In contrast to this variety of possibilities in regurgitant lesions, stenotic lesions can only be quantitated by using velocity mapping techniques. Magnetic resonance spectroscopy can be used to assess myocardial metabolism in chronic valvular lesions. However, this tool needs further development and more clinical data before its use can be recommended to assess the necessity and optimal timing of surgical intervention.