Manganese-enhanced magnetic resonance imaging in dilated cardiomyopathy and hypertrophic cardiomyopathy

AIMS

The aim of this study is to quantify altered myocardial calcium handling in non-ischaemic cardiomyopathy using magnetic resonance imaging.

METHODS AND RESULTS

Patients with dilated cardiomyopathy (n = 10) or hypertrophic cardiomyopathy (n = 17) underwent both gadolinium and manganese contrast-enhanced magnetic resonance imaging and were compared with healthy volunteers (n = 20). Differential manganese uptake (Ki) was assessed using a two-compartment Patlak model. Compared with healthy volunteers, reduction in T1 with manganese-enhanced magnetic resonance imaging was lower in patients with dilated cardiomyopathy [mean reduction 257 ± 45 (21%) vs. 288 ± 34 (26%) ms, P < 0.001], with higher T1 at 40 min (948 ± 57 vs. 834 ± 28 ms, P < 0.0001). In patients with hypertrophic cardiomyopathy, reductions in T1 were less than healthy volunteers [mean reduction 251 ± 86 (18%) and 277 ± 34 (23%) vs. 288 ± 34 (26%) ms, with and without fibrosis respectively, P < 0.001]. Myocardial manganese uptake was modelled, rate of uptake was reduced in both dilated and hypertrophic cardiomyopathy in comparison with healthy volunteers (mean Ki 19 ± 4, 19 ± 3, and 23 ± 4 mL/100 g/min, respectively; P = 0.0068). In patients with dilated cardiomyopathy, manganese uptake rate correlated with left ventricular ejection fraction (r2 = 0.61, P = 0.009). Rate of myocardial manganese uptake demonstrated stepwise reductions across healthy myocardium, hypertrophic cardiomyopathy without fibrosis and hypertrophic cardiomyopathy with fibrosis providing absolute discrimination between the healthy myocardium and fibrosed myocardium (mean Ki 23 ± 4, 19 ± 3, and 13 ± 4 mL/100 g/min, respectively; P < 0.0001).

CONCLUSION

The rate of manganese uptake in both dilated and hypertrophic cardiomyopathy provides a measure of altered myocardial calcium handling. This holds major promise for the detection and monitoring of dysfunctional myocardium, with the potential for early intervention and prognostication.

Manganese-Enhanced T1 Mapping in the Myocardium of Normal and Infarcted Hearts

Background

Manganese-enhanced MRI (MEMRI) has the potential to identify viable myocardium and quantify calcium influx and handling. Two distinct manganese contrast media have been developed for clinical application, mangafodipir and EVP1001-1, employing different strategies to mitigate against adverse effects resulting from calcium-channel agonism. Mangafodipir delivers manganese ions as a chelate, and EVP1001-1 coadministers calcium gluconate. Using myocardial T1 mapping, we aimed to explore chelated and nonchelated manganese contrast agents, their mechanism of myocardial uptake, and their application to infarcted hearts.

Methods

T1 mapping was performed in healthy adult male Sprague-Dawley rats using a 7T MRI scanner before and after nonchelated (EVP1001-1 or MnCl2 (22 μmol/kg)) or chelated (mangafodipir (22-44 μmol/kg)) manganese-based contrast media in the presence of calcium channel blockade (diltiazem (100-200 μmol/kg/min)) or sodium chloride (0.9%). A second cohort of rats underwent surgery to induce anterior myocardial infarction by permanent coronary artery ligation or sham surgery. Infarcted rats were imaged with standard gadolinium delayed enhancement MRI (DEMRI) with inversion recovery techniques (DEMRI inversion recovery) as well as DEMRI T1 mapping. A subsequent MEMRI scan was performed 48 h later using either nonchelated or chelated manganese and T1 mapping. Finally, animals were culled at 12 weeks, and infarct size was quantified histologically with Masson's trichrome (MTC).

Results

Both manganese agents induced concentration-dependent shortening of myocardial T1 values. This was greatest with nonchelated manganese, and could be inhibited by 30-43% with calcium-channel blockade. Manganese imaging successfully delineated the area of myocardial infarction. Indeed, irrespective of the manganese agent, there was good agreement between infarct size on MEMRI T1 mapping and histology (bias 1.4%, 95% CI -14.8 to 17.1 P>0.05). In contrast, DEMRI inversion recovery overestimated infarct size (bias 11.4%, 95% CI -9.1 to 31.8 P=0.002), as did DEMRI T1 mapping (bias 8.2%, 95% CI -10.7 to 27.2 P=0.008). Increased manganese uptake was also observed in the remote myocardium, with remote myocardial ∆T1 inversely correlating with left ventricular ejection fraction after myocardial infarction (r=-0.61, P=0.022).

Conclusions

MEMRI causes concentration and calcium channel-dependent myocardial T1 shortening. MEMRI with T1 mapping provides an accurate assessment of infarct size and can also identify changes in calcium handling in the remote myocardium. This technique has potential applications for the assessment of myocardial viability, remodelling, and regeneration.