Attenuated myocardial vasodilator response in patients with hypertensive hypertrophy revealed by oxygenation-dependent magnetic resonance imaging.

BACKGROUND: Oxygen (O(2)) homeostasis is central to myocardial tissue functioning, and increased O(2) demand is thought to be satisfied by a vasodilatory mechanism that results in increased blood and O(2) delivery. We applied blood oxygenation level-dependent (BOLD) MRI in conjunction with vasodilatory stress to index the ability to augment intramyocardial oxygenation in hypertensive hypertrophy, the primary cause of heart failure. METHODS AND RESULTS: Nine healthy controls and 10 hypertensive subjects with moderate-to-severe hypertrophy underwent imaging on a 1.5 T clinical scanner. The dipyridamole-induced change in the apparent transverse relaxation rate, R2*, which correlates with hemoglobin oxygenation, was -5.4+/-2.2 s(-1) (95% CI, -4.0 to -6.8 s(-1)) in controls compared with -1.7+/-1.4 s(-1) (95% CI, -0.8 to -2.6 s(-1)) in hypertensive patients (P=0.0003). CONCLUSIONS: Patients with hypertensive hypertrophy demonstrate an impaired ability to increase intramyocardial oxygenation during vasodilatory stress, as indexed by BOLD MRI. The capacity to image vascular function with BOLD MRI may advance the understanding of the development of ventricular dysfunction in hypertension.

Assessment of myocardial systolic function by tagged magnetic resonance imaging.

Tagged magnetic resonance imaging (MRI) can assess myocardial function by tracking the motion of the myocardium during the various phases of the cardiac cycle. In contrast to experimental methods, such as implantation of radiopaque markers or sonomicrometry, tagged MRI is noninvasive, carries no risk of radiation exposure, and can be used in the context of clinical routine. For the physician, using tagged MRI to its fullest potential requires an understanding of the technique and the derived parameters of myocardial systolic function. This work describes the tagged MRI technique and explains the quantification of systolic function with respect to the underlying theory of the mechanics of a continuous medium. The advantages of tagged MRI in coronary artery disease are emphasized, and currently available data on tagged MRI in coronary artery disease are reviewed.

Imaging perfusion deficits in ischemic heart disease with susceptibility-enhanced T2-weighted MRI: preliminary human studies.

AIM: This feasibility study explores relative myocardial perfusion characterization with an investigational T2/T2 contrast agent. METHODS: Dysprosium-DTPA bis (methylamide) was administered peripherally in six patients with thallium defects. Rest and stress multi-section, gated, T2-weighted images were acquired with a 1.5 T echo-planar imager. Change in transverse relaxation rate was calculated in four segments for each subject. RESULTS: Magnetic resonance (MR) identified five of five instances of ischemia or infarction, at a dose of agent (0.25 mmol/kg) that was comparable to that currently used with clinically approved gadolinium agents. Injection at twice this dose resulted in saturation of the signal change, and the one ischemic segment corresponding to the higher dose was not identified by MR. MR was negative in two segments which, on final diagnosis, were determined to manifest thallium attenuation artifact. CONCLUSION: MR perfusion imaging with high susceptibility agents has the potential to characterize myocardial perfusion deficits.

Intramural mechanics in hypertrophic cardiomyopathy: functional mapping with strain-rate MR imaging.

PURPOSE: To characterize systolic and diastolic intramural mechanics in hypertrophic cardiomyopathy (HCM) with a new metric of contractile activity. MATERIALS AND METHODS: Eleven healthy subjects and eight patients with HCM underwent velocity-encoded echo-planar magnetic resonance (MR) imaging (6-8-frame gated breath-hold movies, 3 x 3-mm resolution). A scalar strain rate (SR) parameter was compared with wall thickness and symptoms. RESULTS: The normal pattern of SR included regional uniformity, a monotonically increasing subepicardial to subendocardial gradient, and minimum transmural shear rate. In HCM, heterogeneity of SRs increased in diastole. Regional diastolic SR correlated with regional wall thickness (r = .785, P = .0001). Interobserver global SR assignment agreed in seven of eight patients. All four patients with New York Heart Association class 1 disease had a low global SR deficit score, whereas three of four patients with class 2 or 3 disease had a high SR deficit score (Spearman r = .775, P = .187). CONCLUSION: SR characterization may provide an objective measure of disease course in HCM.

Motionless movies of myocardial strain-rates using stimulated echoes.

We present methods to acquire and analyze NMR movies of myocardial strain rates in which cardiac motion is suppressed and the histories of strain rates are accurately defined for each voxel of myocardial tissue. By means of stimulated echoes, the myocardial strain-rate tensor is phase-encoded at progressive delays in the cardiac cycle while the slice-select and spatial encoding of the image acquisition are performed at a constant cardiac delay. In these data, every image shows the identical myocardial tissue, and the anatomic configuration of the heart appears motionless. The myocardial strain-rate data, however, indicate the state of motion which existed in this slice at the time of the velocity phase-encoding, and these data evolve with the progressive delay as a movie. Using echo-planar MRI, motionless movies of myocardial strain rate of four to eight cardiac delays are obtained in a breath-hold. As an application, a quantitative characterization of cardiac mechanical synchrony is accomplished by principal component analysis (PCA) of the time series of strain rates.