Stefan Widmaier

31P NMR Spectroscopy Detects Metabolic Abnormalities in Asymptomatic Patients With Hypertrophic Cardiomyopathy

BACKGROUND Hypertrophic cardiomyopathy (HCM) often causes sudden, unexpected death in adolescents and young adults. Alterations in myocardial metabolism are considered to be causes for contractile dysfunction. We examined the question of whether metabolic abnormalities antedate the manifestation of symptoms in patients with HCM. METHODS AND RESULTS Proton-decoupled 31P NMR spectroscopy of the anterior left ventricular wall of the heart of 14 young, asymptomatic patients with HCM was performed with a 1.5-T whole-body imager. Spectra of the phosphate metabolites were compared with those of normal control subjects. The patients exhibited a significantly reduced (P<0.02) ratio of phosphocreatine (PCr) to ATP of 1.98+/-0.37 (mean+/-SD), compared with 2.46+/-0.53 obtained in 11 normal control subjects. In addition, the group of patients with severe hypertrophy of the interventricular septum (n=8) showed a significantly increased (P<0.05) Pi-to-PCr ratio, with a Pi x 100/PCr of 20.0+/-8.3 versus 9.7+/-7.2 in control subjects. Both abnormalities are similar to those found in ischemic myocardium. This view is also supported by a significantly increased (P<0.01) phosphomonoester (PME)-to-PCr ratio, with a PME x 100/PCr of 20.7+/-11.2 compared with 8.4+/-6.7 in control subjects, indicating altered glucose metabolism. CONCLUSIONS 31P NMR spectroscopy detects alterations of myocardial metabolism in asymptomatic patients with HCM. These alterations may contribute to the understanding of the pathophysiology and natural history of the disease.

Proton-decoupled myocardial 31P NMR spectroscopy reveals decreased PCr/Pi in patients with severe hypertrophic cardiomyopathy.

Disturbed myocardial energy metabolism may occur in patients with primary hypertrophic cardiomyopathy (HCM). A noninvasive way to gain insight into cardiac energy metabolism is provided by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. 31P NMR spectroscopy with proton decoupling was performed in 13 patients aged 13-36 years with HCM on a 1.5 T Magnetom with a double resonant surface coil. A 2D chemical shift imaging (CSI) sequence in combination with slice selective excitation was used to acquire spectra of the anteroseptal region of the left ventricle (volume element: 38 mL). The chemical shifts of the phosphorus metabolites, intracellular pHi, and coupling constants J(alphabeta) and J(gammabeta) were calculated. Peak areas of 2,3-diphosphoglycerate (DPG), Pi, and adenosine triphosphate (ATP) were determined and corrected for blood contamination, saturation, and differences in nuclear Overhauser enhancements (NOE). The maximum thickness of the interventricular septum (IVSmax) was determined from tomographic long-axis images and expressed as number of standard deviations above the mean of the normal population (Z score). The patients were then divided into 2 groups: 6 patients with moderate HCM (HCMm, Z score < or = 5) and 7 patients with severe HCM (HCMs, Z score > 5). No differences between both groups and a control group of healthy volunteers (n = 16) were found with respect to phosphocreatine (PCr)/gamma-ATP ratio, pHi, or the coupling constants. Only the PCr/Pi ratio differed significantly from the control group (HCM(all), alpha < 0.05, HCMs, alpha < 0.02, 2-sided U test). The decrease of the PCr/Pi ratio in patients with HCM is probably caused by ischemically decreased oxygen supply in the severely hypertrophied myocardium.

31P/1H WALTZ-4 broadband decoupling at 1.5 T: different versions of the composite pulse and consequences when using a surface coil.

Two derivatives of the wideband alternating-phase low-power technique for zero-residual splitting (WALTZ)-4 decoupling sequence for broadband decoupling named WALTZ-4a and WALTZ-4b were compared for their proton decoupling performance in 31P nuclear magnetic resonance (NMR) spectroscopy using a Siemens Magnetom SP 1.5 T whole-body imager. Version WALTZ-4a originally implemented by the manufacturer doubles and triples the transmitter amplitude of the 90 degrees pulse to achieve the 180 degrees and 270 degrees flip angle required for one composite pulse R in the WALTZ sequence. WALTZ-4b follows the sequence reported from Shaka et al. and leaves the transmitter amplitude constant but increases the durations of the 180 degrees and 270 degrees pulses. The decoupling performance of WALTZ-4b is superior because it requires less transmitter power and, therefore, it is advantageous in all in vivo studies where a low specific absorption rate is desired. When WALTZ-4 is used in combination with a surface coil for transmission the theoretically required flip angles cannot be achieved in the entire sensitive volume of the coil. The decoupling performance was therefore investigated at lower and higher flip angles. Again, WALTZ-4b is advantageous and provides, in certain ranges that are off-resonant from the decoupling frequency, a good decoupling quality even for flip angles that are only 60% of the theoretically required.

31P NMR studies of human soleus and gastrocnemius show differences in theJγβ coupling constant of ATP and in intracellular free magnesium

Localized proton decoupled31Pin vivo NMR spectroscopy of the human calf muscle was performed using a 1.5-T whole-body imager and the slice selective two-dimensional chemical-shift-imaging (2D-CSI) technique. The31P-31P coupling constants and the chemical shifts of ATP were compared in gastrocnemius and soleus. Significant differences were found in the coupling constantJγβ: (18.1±0.7) Hz versus (17.1±0.6) Hz (means ± SD,P<10−5). Differences were also observed in the chemical shift separation δαβ between the α- and β-ATP signal: (8.498±0.023) ppm versus (8.522 ± 0.022) ppm (p<0.001) in gastrocnemius and soleus, respectively. Ahigher [MgATP]/[ATPfree] ratio and a significantly higher level of intracellular free magnesium of (0.52±0.06) mM in gastrocnemius versus (0.46 ± 0.05) mM in soleus (p<0.001) can be derived based on δαβ and KDMgATP. Heterogeneity needs to be taken into account in clinical studies on magnesium by NMR methods in calf muscle. The coupling constantJγβ provides additional information, possibly on enzymatic processes, and correlates with [Mgfree2−]. The detailed analysis of muscles with different fiber type characteristics lends support to the significance of this parameter in evaluating metabolism. The data reported can be used as prior knowledge for fits in which the coupling constants are set to a fixed value.

Detection of monoester signals in human myocardium by 31P-MRS

Localized 3~p-NMR spectroscopy can be used to gain insight into the metabolism of the human myocardium. Typically, the signals of phosphocreatine (PCr), adenosinetriphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG), and phosphodiesters (PDE) are observed. Depending on the resolution of the spectra, the signal from inorganic phosphate (Pi) can also be observed slightly separated from the 2-DPG signal (Fig. 1). In addition, we show in this study that using an appropriate technique a phosphomonoester signal (PME) can be observed mainly in patients with hypertrophic cardiomyopathy (HCM).

Change in Chemical Shift and Splitting of 31P γ-ATP Signal in Human Skeletal Muscle During Exercise and Recovery

Proton decoupled 31P in vivo NMR spectroscopy of the human finger flexor muscles was performed during exercise and recovery using a 1.5 T whole‐body imager. Predominantly the γ‐ATP signal shows a splitting caused by different signal contributions with chemical shifts that vary independently. Studies on the human gastrocnemius and biceps femoris muscle were undertaken to investigate the appearance of the splitting in these muscles as well. In all cases more than one signal contribution was found which might represent the different muscle fibre types and their recruitment pattern following exercise. An analysis of the chemical shifts of ATP results in changes of up to 0.4 ppm and 0.1 ppm for δγ‐ and δβ‐ATP, respectively. Based solely on the chemical shifts of the ATP 31P signals the tissue pH value following exercise was determined. The result was in good agreement with the value derived from δPi.

Potential pitfall in the determination of free [Mg2+] by 31P NMR when using the β/α-ATP peak height ratio method

Recently, Clarke et al., (Clarke K, Kashiwaya Y, King MT, Gates D, Keon CA, Cross HR, Radda GK, Veech RL. The β/α peak height ratio of ATP. A measure of free [Mgfree2+] using31 P NMR, J. Biol. Chem. 1996;271:21142–21150.) reported a new method to noninvasively determine the concentration of intracellular free magnesium ([Mgfree2+]) based on the measurement of the peak height ratiohβ/α of the β- and α-ATP signals in31P NMR spectra.hβ/α varies with Mgfree2+], however, the study presented here shows thathβ/α also strongly depends on the homogeneity of the static magnetic field. For this reason, we performed at a magnetic field strength of 1.5 T31P NMR measurements of solutions that mimic intracellular medium. The magnetic field homogeneity was varied by changing the currents in the shim coils, and the effect onhβ/α is demonstrated with and without proton decoupling. In both cases,hβ/α strongly depends on the magnetic field homogeneity and can therefore lead to a pitfall in the determination of [Mgfree2+].