Lucy Hudsmith

Normal Human Left and Right Ventricular and Left Atrial Dimensions Using Steady State Free Precession Magnetic Resonance Imaging

PURPOSE The aim of this project was to establish a database of left and right ventricular and left atrial dimensions in healthy volunteers using steady-state free precession cardiac magnetic resonance imaging, the clinical technique of choice, across a wide age range. METHODS 108 healthy volunteers (63 male, 45 female) underwent cardiac magnetic resonance imaging using steady-state free precession sequences. Manual analysis was performed by 2 experienced observers. RESULTS Left and right ventricular volumes and left ventricular mass were larger in males than females: LV end-diastolic volume 160 +/- 29 mL vs. 135 +/- 26 mL, LV end-systolic volume 50 +/- 16 mL vs. 42 +/- 12 mL; RV end-diastolic volume 190 +/- 33 mL vs. 148 +/- 35 mL, RV end-systolic volume 78 +/- 20 mL vs. 56 +/- 18 mL (p < .05 for all). Normalization of values to body surface area removed the statistical differences for LV volumes, but not for LV mass or RV volumes. With increased age, males showed a significant decrease in volume and mass indices for both ventricles, while female values remained unchanged. Compared to females, males had significantly larger maximal left atrial volumes (103 +/- 30 mL vs. 89 +/- 21 mL, p = .01) and left atrial stroke volumes (58 +/- 23 mL vs. 48 +/- 15 mL, p = .01). There was no difference in left atrial ejection fraction between the sexes. CONCLUSION We have produced a large database of age-related normal ranges for left and right ventricular function and left atrial function in males and females. This will allow accurate interpretation of clinical and research datasets.

Evidence for Microvascular Dysfunction in Hypertrophic Cardiomyopathy: New Insights From Multiparametric Magnetic Resonance Imaging

Background— Microvascular dysfunction in hypertrophic cardiomyopathy (HCM) may create an ischemic substrate conducive to sudden death, but it remains unknown whether the extent of hypertrophy is associated with proportionally poorer perfusion reserve. Comparisons between magnitude of hypertrophy, impairment of perfusion reserve, and extent of fibrosis may offer new insights for future clinical risk stratification in HCM but require multiparametric imaging with high spatial and temporal resolution. Methods and Results— Degree of hypertrophy, myocardial blood flow at rest and during hyperemia (hMBF), and myocardial fibrosis were assessed with magnetic resonance imaging in 35 HCM patients (9 [26%] male/26 female) and 14 healthy controls (4 [29%] male/10 female), aged 18 to 78 years (mean±SD, 42±14 years) with the use of the American Heart Association left ventricular 16-segment model. Resting MBF was similar in HCM patients and controls. hMBF was lower in HCM patients (1.84±0.89 mL/min per gram) than in healthy controls (3.42±1.76 mL/min per gram, with a difference of −0.95±0.30 [SE] mL/min per gram; P<0.001) after adjustment for multiple variables, including end-diastolic segmental wall thickness (P<0.001). In HCM patients, hMBF decreased with increasing end-diastolic wall thickness (P<0.005) and preferentially in the endocardial layer. The frequency of endocardial hMBF falling below epicardial hMBF rose with wall thickness (P=0.045), as did the incidence of fibrosis (P<0.001). Conclusions— In HCM the vasodilator response is reduced, particularly in the endocardium, and in proportion to the magnitude of hypertrophy. Microvascular dysfunction and subsequent ischemia may be important components of the risk attributable to HCM.

Operator Induced Variability in Left Ventricular Measurements with Cardiovascular Magnetic Resonance is Improved After Training

BACKGROUND Accurate and reproducible measurement of left ventricular (LV) mass and function is a significant strength of Cardiovascular Magnetic Resonance (CMR). Reproducibility and accuracy of these measurements is usually reported between experienced operators. However, an increasing number of inexperienced operators are now training in CMR and are involved in post-processing analysis. The aim of the study was to assess the interobserver variability of the manual planimetry of LV contours amongst two experienced and six inexperienced operators before and after a two months training period. METHODS Ten healthy normal volunteers (5 men, mean age 34+/-14 years) comprised the study population. LV volumes, mass, and ejection fraction were manually evaluated using Argus software (Siemens Medical Solutions, Erlangen, Germany) for each subject, once by the two experienced and twice by the six inexperienced operators. The mean values of experienced operators were considered the reference values. The agreement between operators was evaluated by means of Bland-Altman analysis. Training involved standardized data acquisition, simulated off-line analysis and mentoring. RESULTS The trainee operators demonstrated improvement in the measurement of all the parameters compared to the experienced operators. The mean ejection fraction variability improved from 7.2% before training to 3.7% after training (p=0.03). The parameter in which the trainees showed the least improvement was LV mass (from 7.7% to 6.7% after training). The basal slice selection and contour definition were the main sources of errors. CONCLUSIONS An intensive two month training period significantly improved the accuracy of LV functional measurements. Adequate training of new CMR operators is of paramount importance in our aim to maintain the accuracy and high reproducibility of CMR in LV function analysis.

Magnetic Resonance Spectroscopy in Myocardial Disease

Magnetic resonance spectroscopy (MRS) is the only noninvasive, nonradiation exposure technique for the investigation of cardiac metabolism in vivo. MRS uses magnetic resonance signals from nuclei, such as (31)phosphorus, (1)hydrogen, and (23)sodium, to provide comprehensive metabolic and biochemical information about cardiac muscle. This method is highly versatile and can provide metabolic insights into the role of cardiac metabolism, in particular, cardiac energetics, in a wide number of conditions, including hypertensive, valvular, and ischemic heart disease, heart failure, and cardiac transplantation, as well as cardiomyopathies. This method can also be used to monitor patient responses to therapeutic interventions: pharmacologic, surgical, or interventional. When combined with cardiovascular magnetic resonance imaging, MRS enables detailed pathophysiologic insights into the inter-relations among cardiac structure, function, perfusion, and metabolism. However, MRS is currently used primarily as a research tool because of low temporal and spatial resolution and low reproducibility. It is hoped that future technical developments and use of higher magnetic field strengths (such as 7-T) may enable application of cardiac MRS in clinical practice.

Determination of cardiac volumes and mass with FLASH and SSFP cine sequences at 1.5 vs. 3 Tesla: A validation study

To compare cardiac cine MR imaging using steady state free precession (SSFP) and fast low angle shot (FLASH) techniques at 1.5 and 3 T, and to establish their variabilities and reproducibilities for cardiac volume and mass determination in volunteers. To assess the feasibility of SSFP imaging in patients at 3 T and to determine comparability to volume data acquired at 1.5 T.

Assessment of left atrial volumes at 1.5 Tesla and 3 Tesla using FLASH and SSFP cine imaging.

PURPOSE To investigate left atrial volumes and function and their variability in healthy volunteers using steady state free precession (SSFP) and fast low angle shot (FLASH) sequences at both 1.5 and 3 T using both the short-axis and biplane area-length methods. MATERIALS AND METHODS Ten healthy volunteers underwent CMR at both 1.5 and 3 Tesla. The biplane area-length method utilized volumes from the horizontal and vertical long axis images. RESULTS There were no significant differences between left atrial short-axis volumes or function between 1.5 and 3 T assessed using either FLASH or SSFP sequences. The biplane area-length method underestimated maximal left atrial volume using FLASH by 12 mL at 3 T (18%) and by 10 mL (14%) at 1.5 T (p = 0.003 and p = 0.05 respectively). Variability was larger for left atrial measurements using the biplane area-length method. CONCLUSION Field strength had no effect on left atrial volume and function assessment using either FLASH or SSFP. The use of the short-axis method for the acquisition of left atrial parameters is more reproducible than the biplane area-length for serial measurements.

Ventricular hypertrophy and cavity dilatation in relation to body mass index in women with uncomplicated obesity

Objective The traditionally accepted mechanism for ventricular adaptation to obesity suggests that cavity dilatation in response to increased blood volume and elevated filling pressure results in ventricular hypertrophy as a compensatory mechanism. Our hypothesis was that, instead, initiation of ventricular hypertrophy in obesity may be explained by changes in hormonal milieu and not by cavity dilatation. Research design and methods 88 female subjects without identifiable cardiovascular risk factors, covering a wide range of body mass indices (BMI), from normal (21.2±1.6 kg/m2) to severely obese (45.0±4.6 kg/m2), underwent cardiovascular MRI to determine left ventricular (LV) and right ventricular (RV) mass and volumes. Results BMI correlated positively with LV and RV mass and end-diastolic volumes (EDV). However overweight is associated with a significant LV and RV hypertrophy (LV: 78±11 g vs 103±16 g, p<0.01; RV: 26±7 g vs 40±11 g, p<0.01) was observed in the absence of differences in LV and RV volumes (LV: EDV 119±15 vs 121±21 ml, p>0.99, RV: 131±17 vs 130±24 ml; p>0.99). Furthermore, significant increases of serum leptin occurred at this pre-obese stage (15.6±19 vs 36.5±22 ng/ml; p=0.013). Conclusion In a cohort of healthy female subjects with a wide range of BMIs, ventricular hypertrophy occurs without associated cavity dilatation in overweight individuals, while in manifest obesity, both cavity dilatation and ventricular hypertrophy occur. Elevated leptin levels may have a role in this effect on ventricular mass.

Echocardiographically guided catheter closure of arterial ducts in small preterm infants on the neonatal intensive care unit

Objective: To describe closure of haemodynamically significant arterial ducts in preterm infants using an echocardiographically guided cardiac catheter technique in selected infants in the neonatal nursery and in preference to cardiac surgery. Background: Persistently patent arterial ducts are common in preterm infants and are associated with significant morbidity and mortality. Cardiac catheter techniques continue to improve and occlusion of arterial ducts in preterm infants is becoming technically feasible. Closure of arterial ducts by cardiac catheter techniques would enable selected infants to avoid surgery and a lateral thoracotomy, as well as potentially obviating the need for transfer of sick preterm infants between units for duct closure. Methods and Results: This brief report describes placement of coils or Amplatzer duct devices to occlude arterial ducts in small premature infants exclusively under echocardiographic guidance in the Neonatal Intensive Care Unit. Conclusions: Closing arterial ducts in the neonatal nursery by an echocardiographically guided cardiac catheter technique with minimal morbidity is becoming achievable and is a significant advance in neonatal care.

Sex-Specific Characteristics of Cardiac Function, Geometry, and Mass in Young Adult Elite Athletes

To study young adult elite athletes with age‐ and sex‐matched sedentary controls to assess sex‐specific differences for left ventricular (LV) and right ventricular (RV) volumes and mass as well as for LV contraction and relaxation.

A comparison of cardiac (31)P MRS at 1.5 and 3 T.

31P MRS was evaluated on normal volunteers at 1.5 and 3 T, and the signal‐to‐noise ratio (SNR) of the two field strengths was calculated. The in vivo spin‐lattice, T1, relaxation times for PCr and γ‐ATP, which are essential for correcting for the effects of radiofrequency saturation on the PCr/ATP ratio, were determined at 3 T. The T1 values for six volunteers were 3.8 ± 0.7 s for PCr (mean ± SD) and 2.4 ± 1.1 s for γ‐ATP, which are similar to reported values at 1.5 T, allowing us to use protocols developed at 1.5 T at the new clinical field strength of 3 T. Direct comparison between 1.5 T and 3 T in the same 10 subjects, using coils of identical geometry and identical pulse sequences gave a mean SNR for PCr at 3 T which was 206 ± 94% of that at 1.5 T. The linewidth for PCr increased from 13 ± 6 Hz at 1.5 T to 22 ± 12 Hz at 3 T. The coefficient of variation in the measurement of PCr/ATP, based on the Cramer–Rao lower bounds, was reduced from 32 ± 25% at 1.5 T to 18 ± 13% at 3 T. Thus, 31P MRS at 3 T is greatly improved by the increase in SNR compared with acquisitions at 1.5 T because of the higher field strength. Copyright