Presence of mechanical dyssynchrony in duchenne muscular dystrophy

Background

There are physiological reasons for the effects of positioning on hemodynamic variables and cardiac dimensions related to altered intra-abdominal and intra-thoracic pressures. This problem is especially evident in pregnant women due to the additional aorto-caval compression by the enlarged uterus. The purpose of this study was to investigate the effect of postural changes on cardiac dimensions and function during mid and late pregnancy using cardiovascular magnetic resonance (CMR).

Methods

Healthy non-pregnant women, pregnant women at 20^th week of gestation and at 32^nd week of gestation without history of cardiac disease were recruited to the study and underwent CMR in supine and left lateral positions. Cardiac hemodynamic parameters and dimensions were measured and compared between both positions.

Results

Five non-pregnant women, 6 healthy pregnant women at mid pregnancy and 8 healthy pregnant women at late pregnancy were enrolled in the study. In the group of non-pregnant women left ventricular (LV) cardiac output (CO) significantly decreased by 9% (p = 0.043) and right ventricular (RV) end-diastolic volume (EDV) significantly increased by 5% (p = 0.043) from the supine to the left lateral position. During mid pregnancy LV ejection fraction (EF), stroke volume (SV), left atrium lateral diameter and left atrial supero-inferior diameter increased significantly from the supine position to the left lateral position: 8%, 27%, 5% and 11%, respectively (p < 0.05). RV EDV, SV and right atrium supero-inferior diameter significantly increased from the supine to the left lateral position: 25%, 31% and 13% (p < 0.05), respectively. During late pregnancy a significant increment of LV EF, EDV, SV and CO was observed in the left lateral position: 11%, 21%, 35% and 24% (p < 0.05), respectively. Left atrial diameters were significantly larger in the left lateral position compared to the supine position (p < 0.05). RV CO was significantly increased in the left lateral position compared to the supine position (p < 0.05).

Conclusions

During pregnancy positional changes affect significantly cardiac hemodynamic parameters and dimensions. Pregnant women who need serial studies by CMR should be imaged in a consistent position. From as early as 20 weeks the left lateral position should be preferred on the supine position because it positively affects venous return, SV and CO.     

Moderate intensity supine exercise causes decreased cardiac volumes and increased outer volume variations: a cardiovascular magnetic resonance study

Background

The effects on left and right ventricular (LV, RV) volumes during physical exercise remains controversial. Furthermore, no previous study has investigated the effects of exercise on longitudinal contribution to stroke volume (SV) and the outer volume variation of the heart. The aim of this study was to determine if LV, RV and total heart volumes (THV) as well as cardiac pumping mechanisms change during physical exercise compared to rest using cardiovascular magnetic resonance (CMR).

Methods

26 healthy volunteers (6 women) underwent CMR at rest and exercise. Exercise was performed using a custom built ergometer for one-legged exercise in the supine position during breath hold imaging. Cardiac volumes and atrio-ventricular plane displacement were determined. Heart rate (HR) was obtained from ECG.

Results

HR increased during exercise from 60±2 to 94±2 bpm, (p<0.001). LVEDV remained unchanged (p=0.81) and LVESV decreased with −9±18% (p<0.05) causing LVSV to increase with 8±3% (p<0.05). RVEDV and RVESV decreased by −7±10% and −24±14% respectively, (p<0.001) and RVSV increased 5±17% during exercise although not statistically significant (p=0.18). Longitudinal contribution to RVSV decreased during exercise by −6±15% (p<0.05) but was unchanged for LVSV (p=0.74). THV decreased during exercise by −4±1%, (p<0.01) and total heart volume variation (THVV) increased during exercise from 5.9±0.5% to 9.7±0.6% (p<0.001).

Conclusions

Cardiac volumes and function are significantly altered during supine physical exercise. THV becomes significantly smaller due to decreases in RVEDV whilst LVEDV remains unchanged. THVV and consequently radial pumping increases during exercise which may improve diastolic suction during the rapid filling phase.     

Cardiovascular magnetic resonance parameters associated with early transplant-free survival in children with small left hearts following conversion from a univentricular to biventricular circulation

Background

We sought to identify cardiovascular magnetic resonance (CMR) parameters associated with successful univentricular to biventricular conversion in patients with small left hearts.

Methods

Patients with small left heart structures and a univentricular circulation who underwent CMR prior to biventricular conversion were retrospectively identified and divided into 2 anatomic groups: 1) borderline hypoplastic left heart structures (BHLHS), and 2) right-dominant atrioventricular canal (RDAVC). The primary outcome variable was transplant-free survival with a biventricular circulation.

Results

In the BHLHS group (n = 22), 16 patients (73%) survived with a biventricular circulation over a median follow-up of 40 months (4–84). Survival was associated with a larger CMR left ventricular (LV) end-diastolic volume (EDV) (p = 0.001), higher LV-to-right ventricle (RV) stroke volume ratio (p < 0.001), and higher mitral-to-tricuspid inflow ratio (p = 0.04). For predicting biventricular survival, the addition of CMR threshold values to echocardiographic LV EDV improved sensitivity from 75% to 93% while maintaining specificity at 100%. In the RDAVC group (n = 10), 9 patients (90%) survived with a biventricular circulation over a median follow-up of 29 months (3–51). The minimum CMR values were a LV EDV of 22 ml/m² and a LV-to-RV stroke volume ratio of 0.19.

Conclusions

In BHLHS patients, a larger LV EDV, LV-to-RV stroke volume ratio, and mitral-to-tricuspid inflow ratio were associated with successful biventricular conversion. The addition of CMR parameters to echocardiographic measurements improved the sensitivity for predicting successful conversion. In RDAVC patients, the high success rate precluded discriminant analysis, but a range of CMR parameters permitting biventricular conversion were identified.     

Effects of Lying Position on P-Wave Dispersion in Patients with Heart Failure

Objective

It was the aim of this study to investigate the effects of the right lateral decubitus, left lateral decubitus and supine lying position on P-wave dispersion (PWD) in patients with heart failure (HF).

Subjects and Methods

Seventeen patients with HF whose ejection fraction was <35% were included in the study. Right lateral decubitus, left lateral decubitus and supine electrocardiogram (ECG) recordings were obtained. The recordings for each of the three positions were taken after the patients had maintained each position for 30 min to ensure a stabilized hemodynamic position. For the baseline recording, in supine position, there was no 30-min waiting period before the ECG.

Results

After the right lateral decubitus position, there was a statistically significant reduction in the longest P-wave duration (100.0 ± 14.5 and 84.7 ± 16.2 ms; p = 0.001) and a significant decrease in PWD (41.7 ± 8.0 and 24.1 ± 7.1 ms; p < 0.0001). After the left lateral decubitus position, there was no significant change between the baseline PWD values (41.7 ± 8.0 and 40.2 ± 9.7 ms; p = 0.606). After the supine position, there was no significant change between the baseline PWD values (41.7 ± 8.0 and 39.7 ± 9.4 ms; p = 0.427).

Conclusion

Our study revealed that patients'' PWDs and maximum P-wave durations were lower in the right lateral decubitus lying position than in other positions. The clinical implication of this study needs to be further explored.Key Words: Heart failure, P-wave dispersion, Lying position, Atrial fibrillation     

Cardiovascular magnetic resonance in pregnancy: Insights from the cardiac hemodynamic imaging and remodeling in pregnancy (CHIRP) study

Background

Cardiovascular disease in pregnancy is the leading cause of maternal mortality in North America. Although transthoracic echocardiography (TTE) is the most widely used imaging modality for the assessment of cardiovascular function during pregnancy, little is known on the role of cardiovascular magnetic resonance (CMR). The objective of the Cardiac Hemodynamic Imaging and Remodeling in Pregnancy (CHIRP) study was to compare TTE and CMR in the non-invasive assessment of maternal cardiac remodeling during the peripartum period.

Methods

Between 2010–2012, healthy pregnant women aged 18 to 35 years were prospectively enrolled. All women underwent TTE and CMR during the third trimester and at least 3 months postpartum (surrogate for non-pregnant state).

Results

The study population included a total of 34 women (mean age 29?±?3 years). During the third trimester, TTE and CMR demonstrated an increase in left ventricular end-diastolic volume from 95?±?11 mL to 115?±?14 mL and 98?±?6 mL to 125?±?5 mL, respectively (p?<?0.05). By TTE and CMR, there was also an increase in left ventricular (LV) mass during pregnancy from 111?±?10 g to 163?±?11 g and 121?±?5 g to 179?±?5 g, respectively (p?<?0.05). Although there was good correlation between both imaging modalities for LV mass, stroke volume, and cardiac output, the values were consistently underestimated by TTE.

Conclusion

This CMR study provides reference values for cardiac indices during normal pregnancy and the postpartum state.     

Evaluation of left ventricular ejection fraction using through-time radial GRAPPA

Background

The determination of left ventricular ejection fraction using cardiovascular magnetic resonance (CMR) requires a steady cardiac rhythm for electrocardiogram (ECG) gating and multiple breathholds to minimize respiratory motion artifacts, which often leads to scan times of several minutes. The need for gating and breathholding can be eliminated by employing real-time CMR methods such as through-time radial GRAPPA. The aim of this study is to compare left ventricular cardiac functional parameters obtained using current gold-standard breathhold ECG-gated functional scans with non-gated free-breathing real-time imaging using radial GRAPPA, and to determine whether scan time or the occurrence of artifacts are reduced when using this real-time approach.

Methods

63 patients were scanned on a 1.5T CMR scanner using both the standard cardiac functional examination with gating and breathholding and the real-time method. Total scan durations were noted. Through-time radial GRAPPA was employed to reconstruct images from the highly accelerated real-time data. The blood volume in the left ventricle was assessed to determine the end systolic volume (ESV), end diastolic volume (EDV), and ejection fraction (EF) for both methods, and images were rated for the presence of artifacts and quality of specific image features by two cardiac readers. Linear regression analysis, Bland-Altman plots and two-sided t-tests were performed to compare the quantitative parameters. A two-sample t-test was performed to compare the scan durations, and a two-sample test of proportion was used to analyze the presence of artifacts. For the reviewers´ ratings the Wilcoxon test for the equality of the scores’ distributions was employed.

Results

The differences in EF, EDV, and ESV between the gold-standard and real-time methods were not statistically significant (p-values of 0.77, 0.82, and 0.97, respectively). Additionally, the scan time was significantly shorter for the real-time data collection (p<0.001) and fewer artifacts were reported in the real-time images (p<0.01). In the qualitative image analysis, reviewers marginally preferred the standard images although some features including cardiac motion were equivalently rated.

Conclusion

Real-time functional CMR with through-time radial GRAPPA performed without ECG-gating under free-breathing can be considered as an alternative to gold-standard breathhold cine imaging for the evaluation of ejection fraction in patients.     

Cardiovascular magnetic resonance for the assessment of patients undergoing transcatheter aortic valve implantation: a pilot study

Background

Before trans-catheter aortic valve implantation (TAVI), assessment of cardiac function and accurate measurement of the aortic root are key to determine the correct size and type of the prosthesis. The aim of this study was to compare cardiovascular magnetic resonance (CMR) and trans-thoracic echocardiography (TTE) for the assessment of aortic valve measurements and left ventricular function in high-risk elderly patients submitted to TAVI.

Methods

Consecutive patients with severe aortic stenosis and contraindications for surgical aortic valve replacement were screened from April 2009 to January 2011 and imaged with TTE and CMR.

Results

Patients who underwent both TTE and CMR (n = 49) had a mean age of 80.8 ± 4.8 years and a mean logistic EuroSCORE of 14.9 ± 9.3%. There was a good correlation between TTE and CMR in terms of annulus size (R² = 0.48, p < 0.001), left ventricular outflow tract (LVOT) diameter (R² = 0.62, p < 0.001) and left ventricular ejection fraction (LVEF) (R² = 0.47, p < 0.001) and a moderate correlation in terms of aortic valve area (AVA) (R² = 0.24, p < 0.001). CMR generally tended to report larger values than TTE for all measurements. The Bland-Altman test indicated that the 95% limits of agreement between TTE and CMR ranged from -5.6 mm to + 1.0 mm for annulus size, from -0.45 mm to + 0.25 mm for LVOT, from -0.45 mm² to + 0.25 mm² for AVA and from -29.2% to 13.2% for LVEF.

Conclusions

In elderly patients candidates to TAVI, CMR represents a viable complement to transthoracic echocardiography.     

Percutaneous closure of atrial septal defects leads to normalisation of atrial and ventricular volumes

Background

Percutaneous closure of atrial septal defects (ASDs) should potentially reduce right heart volumes by removing left-to-right shunting. Due to ventricular interdependence, this may be associated with impaired left ventricular filling and potentially function. Furthermore, atrial changes post-ASD closure have been poorly understood and may be important for understanding risk of atrial arrhythmia post-ASD closure. Cardiovascular magnetic resonance (CMR) is an accurate and reproducible imaging modality for the assessment of cardiac function and volumes. We assessed cardiac volumes pre- and post-percutaneous ASD closure using CMR.

Methods

Consecutive patients (n = 23) underwent CMR pre- and 6 months post-ASD closure. Steady state free precession cine CMR was performed using contiguous slices in both short and long axis views through the ASD. Data was collected for assessment of left and right atrial, ventricular end diastolic volumes (EDV) and end systolic volumes (ESV). Data is presented as mean ± SD, volumes as mL, and paired t-testing performed between groups. Statistical significance was taken as p < 0.05.

Results

There was a significant reduction in right ventricular volumes at 6 months post-ASD closure (RVEDV: 208.7 ± 76.7 vs. 140.6 ± 60.4 mL, p < 0.0001) and RVEF was significantly increased (RVEF 35.5 ± 15.5 vs. 42.0 ± 15.2%, p = 0.025). There was a significant increase in the left ventricular volumes (LVEDV 84.8 ± 32.3 vs. 106.3 ± 38.1 mL, p = 0.003 and LVESV 37.4 ± 20.9 vs. 46.8 ± 18.5 mL, p = 0.016). However, there was no significant difference in LVEF and LV mass post-ASD closure. There was a significant reduction in right atrial volumes at 6 months post-ASD closure (pre-closure 110.5 ± 55.7 vs. post-closure 90.7 ± 69.3 mL, p = 0.019). Although there was a trend to a decrease in left atrial volumes post-ASD closure, this was not statistically significant (84.5 ± 34.8 mL to 81.8 ± 44.2 mL, p = NS).

Conclusion

ASD closure leads to normalisation of ventricular volumes and also a reduction in right atrial volume. Further follow-up is required to assess how this predicts outcomes such as risk of atrial arrhythmias after such procedures.     

Comparison of wall thickening and ejection fraction by cardiovascular magnetic resonance and echocardiography in acute myocardial infarction

Objectives

The purpose of this study was to compare cardiovascular magnetic resonance (CMR) and echocardiography (echo) in patients treated with primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) with emphasis on the analysis of left ventricular function and left ventricular wall motion characteristics.

Methods

We performed CMR and echo in 52 patients with first AMI shortly after primary angioplasty and four months thereafter. CMR included cine-MR and T1-weighted first-pass and late-gadolinium enhancement (LGE) sequences. Global ejection fraction (EF_CMR, %) and regional left ventricular function (systolic wall thickening %, [SWT]) were determined from cine-MR images. In echo the global left ventricular function (EF_echo, %) and regional wall motion abnormalities were determined. A segment in echo was scored as "infarcted" if it was visually > 50% hypokinetic.

Results

EF_echo revealed a poor significant agreement with EF_CMR at baseline (r: 0.326; p < 0.01) but higher correlation at follow-up (r: 0.479; p < 0.001). The number of infarcted segments in echocardiography correlated best with the number of segments which showed systolic wall thickening < 30% (r: 0.498; p < 0.001) at baseline and (r: 0.474; p < 0.001) at follow-up. Improvement of EF was detected in both CMR and echocardiography increasing from 44.2 ± 11.6% to 49.2 ± 11% (p < 0.001) by CMR and from 51.2 ± 8.1% to 54.5 ± 8.3% (p < 0.001) by echocardiography.

Conclusion

Wall motion and EF by CMR and echocardiography correlate poorly in the acute stage of myocardial infarction. Correlation improves after four months. Systolic wall thickening by CMR < 30% indicates an infarcted segment with influence on the left ventricular function.     

Cardiovascular magnetic resonance of cardiac function and myocardial mass in preterm infants: a preliminary study of the impact of patent ductus arteriosus

Background

Many pathologies seen in the preterm population are associated with abnormal blood supply, yet robust evaluation of preterm cardiac function is scarce and consequently normative ranges in this population are limited. The aim of this study was to quantify and validate left ventricular dimension and function in preterm infants using cardiovascular magnetic resonance (CMR). An initial investigation of the impact of the common congenital defect patent ductus arteriosus (PDA) was then carried out.

Methods

Steady State Free Procession short axis stacks were acquired. Normative ranges of left ventricular end diastolic volume (EDV), stroke volume (SV), left ventricular output (LVO), ejection fraction (EF), left ventricular (LV) mass, wall thickness and fractional thickening were determined in “healthy” (control) neonates. Left ventricular parameters were then investigated in PDA infants. Unpaired student t-tests compared the 2 groups. Multiple linear regression analysis assessed impact of shunt volume in PDA infants, p-value ≤ 0.05 being significant.

Results

29 control infants median (range) corrected gestational age at scan 34⁺⁶(31⁺¹-39⁺³) weeks were scanned. EDV, SV, LVO, LV mass normalized by weight and EF were shown to decrease with increasing corrected gestational age (cGA) in controls. In 16 PDA infants (cGA 30⁺³(27⁺³-36⁺¹) weeks) left ventricular dimension and output were significantly increased, yet there was no significant difference in ejection fraction and fractional thickening between the two groups. A significant association between shunt volume and increased left ventricular mass correcting for postnatal age and corrected gestational age existed.

Conclusion

CMR assessment of left ventricular function has been validated in neonates, providing more robust normative ranges of left ventricular dimension and function in this population. Initial investigation of PDA infants would suggest that function is relatively maintained.     

The effects of posture on abnormalities of forearm venous tone in women with pregnancy-induced hypertension

1. Forearm venous tone was measured in the left lateral supine position and in response to passive leg elevation in a group of women with pregnancy-induced hypertension and compared with a group of normotensive pregnant women and a group of non-pregnant women. 2. The women with pregnancy-induced hypertension were venoconstricted in the supine position compared with the normal pregnant women (P less than 0.002). There was no difference in forearm venous tone between the women with pregnancy-induced hypertension and the non-pregnant women. 3. In response to passive leg elevation the women with pregnancy-induced hypertension venodilated (P less than 0.002) whereas there was no change in forearm venous tone in the normotensive pregnant women and the non-pregnant women. There was no change in blood pressure in any of the women after 35 min of leg elevation. 4. These results demonstrate that the abnormal venous vasoconstriction that occurs in women with pregnancy-induced hypertension in the supine position is corrected by passive leg elevation, a manoeuvre which leads to an increase in central blood volume.     

Left ventricular reverse remodeling after transcatheter aortic valve implantation: a cardiovascular magnetic resonance study

Background

In patients with severe aortic stenosis, left ventricular hypertrophy is associated with increased myocardial stiffness and dysfunction linked to cardiac morbidity and mortality. We aimed at systematically investigating the degree of left ventricular mass regression and changes in left ventricular function six months after transcatheter aortic valve implantation (TAVI) by cardiovascular magnetic resonance (CMR).

Methods

Left ventricular mass indexed to body surface area (LVMi), end diastolic volume indexed to body surface area (LVEDVi), left ventricular ejection fraction (LVEF) and stroke volume (SV) were investigated by CMR before and six months after TAVI in patients with severe aortic stenosis and contraindications for surgical aortic valve replacement.

Results

Twenty-sevent patients had paired CMR at baseline and at 6-month follow-up (N=27), with a mean age of 80.7±5.2 years. LVMi decreased from 84.5±25.2 g/m² at baseline to 69.4±18.4 g/m² at six months follow-up (P<0.001). LVEDVi (87.2±30.1 ml /m²vs 86.4±22.3 ml/m²; P=0.84), LVEF (61.5±14.5% vs 65.1±7.2%, P=0.08) and SV (89.2±22 ml vs 94.7±26.5 ml; P=0.25) did not change significantly.

Conclusions

Based on CMR, significant left ventricular reverse remodeling occurs six months after TAVI.     

Structural and functional cardiac changes in myotonic dystrophy type 1: a cardiovascular magnetic resonance study

Background

Myotonic dystrophy type 1 (MD1) is a neuromuscular disorder with potential involvement of the heart and increased risk of sudden death. Considering the importance of cardiomyopathy as a predictor of prognosis, we aimed to systematically evaluate and describe structural and functional cardiac alterations in patients with MD1.

Methods

Eighty MD1 patients underwent physical examination, electrocardiography (ECG), echocardiography and cardiovascular magnetic resonance (CMR). Blood samples were taken for determination of NT-proBNP plasma levels and CTG repeat length.

Results

Functional and structural abnormalities were detected in 35 patients (44%). Left ventricular systolic dysfunction was found in 20 cases, left ventricular dilatation in 7 patients, and left ventricular hypertrophy in 6 patients. Myocardial fibrosis was seen in 10 patients (12.5%). In general, patients had low left ventricular mass indexes. Right ventricular involvement was uncommon and only seen together with left ventricular abnormalities. Functional or structural cardiac involvement was associated with age (p = 0.04), male gender (p < 0.001) and abnormal ECG (p < 0.001). Disease duration, CTG repeat length, severity of neuromuscular symptoms and NT-proBNP level did not predict the presence of myocardial abnormalities.

Conclusions

CMR can be useful to detect early structural and functional myocardial abnormalities in patients with MD1. Myocardial involvement is strongly associated with conduction abnormalities, but a normal ECG does not exclude myocardial alterations. These findings lend support to the hypothesis that MD1 patients have a complex cardiac phenotype, including both myocardial and conduction system alteration.     

Non-invasive assessment of cardiac function and pulmonary vascular resistance in an canine model of acute thromboembolic pulmonary hypertension using 4D flow cardiovascular magnetic resonance

Background

The purpose of this study was to quantify right (RV) and left (LV) ventricular function, pulmonary artery flow (Q_P), tricuspid valve regurgitation velocity (TRV), and aorta flow (Q_S) from a single 4D flow cardiovascular magnetic resonance (CMR) (time-resolved three-directionally motion encoded CMR) sequence in a canine model of acute thromboembolic pulmonary hypertension (PH).

Methods

Acute PH was induced in six female beagles by microbead injection into the right atrium. Pulmonary arterial (PAP) and pulmonary capillary wedge (PCWP) pressures and cardiac output (CO) were measured by right heart catheterization (RHC) at baseline and following induction of acute PH. Pulmonary vascular resistance (PVR_RHC) was calculated from RHC values of PAP, PCWP and CO (PVR_RHC = (PAP-PCWP)/CO). Cardiac magnetic resonance (CMR) was performed on a 3 T scanner at baseline and following induction of acute PH. RV and LV end-diastolic (EDV) and end-systolic (ESV) volumes were determined from both CINE balanced steady-state free precession (bSSFP) and 4D flow CMR magnitude images. Q_P, TRV, and Q_S were determined from manually placed cutplanes in the 4D flow CMR flow-sensitive images in the main (MPA), right (RPA), and left (LPA) pulmonary arteries, the tricuspid valve (TRV), and aorta respectively. MPA, RPA, and LPA flow was also measured using two-dimensional flow-sensitive (2D flow) CMR.

Results

Biases between 4D flow CMR and bSSFP were 0.8 mL and 1.6 mL for RV EDV and RV ESV, respectively, and 0.8 mL and 4 mL for LV EDV and LV ESV, respectively. Flow in the MPA, RPA, and LPA did not change after induction of acute PAH (p = 0.42-0.81). MPA, RPA, and LPA flow determined with 4D flow CMR was significantly lower than with 2D flow (p < 0.05). The correlation between Q_P/TRV and PVR_RHC was 0.95. The average Q_P/Q_S was 0.96 ± 0.11.

Conclusions

Using both magnitude and flow-sensitive data from a single 4D flow CMR acquisition permits simultaneous quantification of cardiac function and cardiopulmonary hemodynamic parameters important in the assessment of PH.     

Effects of deep sedation or general anesthesia on cardiac function in mice undergoing cardiovascular magnetic resonance

Background

Genetically engineered mouse models of human cardiovascular disease provide an opportunity to understand critical pathophysiological mechanisms. Cardiovascular magnetic resonance (CMR) provides precise reproducible assessment of cardiac structure and function, but, in contrast to echocardiography, requires that the animal be immobilized during image acquisition. General anesthetic regimens yield satisfactory images, but have the potential to significantly perturb cardiac function. The purpose of this study was to assess the effects of general anesthesia and a new deep sedation regimen, respectively, on cardiac function in mice as determined by CMR, and to compare them to results obtained in mildly sedated conscious mice by echocardiography.

Results

In 6 mildly sedated normal conscious mice assessed by echo, heart rate was 615 ± 25 min^-1 (mean ± SE) and left ventricular ejection fraction (LVEF) was 0.94 ± 0.01. In the CMR studies of normal mice, heart rate was slightly lower during deep sedation with morphine/midazolam (583 ± 30 min^-1), but the difference was not statistically significant. General anesthesia with 1% inhaled isoflurane significantly depressed heart rate (468 ± 7 min^-1, p < 0.05 vs. conscious sedation). In 6 additional mice with ischemic LV failure, trends in heart rate were similar, but not statistically significant. In normal mice, deep sedation depressed LVEF (0.79 ± 0.04, p < 0.05 compared to light sedation), but to a significantly lesser extent than general anesthesia (0.60 ± 0.04, p < 0.05 vs. deep sedation).In mice with ischemic LV failure, ejection fraction measurements were comparable when performed during light sedation, deep sedation, and general anesthesia, respectively. Contrast-to-noise ratios were similar during deep sedation and during general anesthesia, indicating comparable image quality. Left ventricular mass measurements made by CMR during deep sedation were nearly identical to those made during general anesthesia (r² = 0.99, mean absolute difference < 4%), indicating equivalent quantitative accuracy obtained with the two methods. The imaging procedures were well-tolerated in all mice.

Conclusion

In mice with normal cardiac function, CMR during deep sedation causes significantly less depression of heart rate and ejection fraction than imaging during general anesthesia with isoflurane. In mice with heart failure, the sedation/anesthesia regimen had no clear impact on cardiac function. Deep sedation and general anesthesia produced CMR with comparable image quality and quantitative accuracy.     

The influence of left lateral position on cardiac output changes after head up tilt measured by impedance cardiography

Background.The value of the impedance cardiography (IC) method formeasuring cardiac output (CO) with the subject in the left lateral positionhas not yet been established. We compared the CO after a 30° head-up tiltwith the subjects in the supine and left lateral position. Methods.Thirty healthy young volunteers were placed in the supine horizontalposition. CO, stroke volume (SV) and heart rate (HR) were measured for fiveminutes using impedance cardiography (NCOMM3, BoMed Medical Manufacturing,Location). Then a 30° head-up tilt was done and the measurements werecontinued for an additional five minutes. After that the subjects were placedin the left lateral horizontal position and the measuring procedure wasrepeated. Results.After the tilt, SV and cardiac index (CI) decreasedand HR increased statistically significantly in the supine and in the leftlateral position. SV and CI also decreased statistically significantly but HRdid not change after the shift from the supine to the left lateral position.Although CI was smaller in the left lateral position, the time course of CIchange after the tilt was identical in the supine and in the left lateralposition. Conclusion.When using the IC method of SV measurement, theabsolute value of the CI changes when moving from the supine to lateralpositions. It is not clear whether this change is physiologic or an artifactof the measurement technique. However, changes in CI in response to a 30degree head up tilt are the same in either position. We conclude that changesin CI can be measured with the IC method in the lateral position.     

Non-invasive stroke volume assessment in patients with pulmonary arterial hypertension: left-sided data mandatory

Background

Cardiovascular Magnetic Resonance (CMR) is an emerging modality in the diagnosis and follow-up of patients with Pulmonary Arterial Hypertension (PAH). Derivation of stroke volume (SV) from the pulmonary flow curves is considered as a standard in this respect. Our aim was to investigate the accuracy of pulmonary artery (PA) flow for measuring SV.

Methods

Thirty-four PAH patients underwent both CMR and right-sided heart catheterisation. CMR-derived SV was measured by PA flow, left (LV) and right ventricular (RV) volumes, and, in a subset of nine patients also by aortic flow. These SV values were compared to the SV obtained by invasive Fick method.

Results

For SV by PA flow versus Fick, r = 0.71, mean difference was -4.2 ml with limits of agreement 26.8 and -18.3 ml. For SV by LV volumes versus Fick, r = 0.95, mean difference was -0.8 ml with limits of agreement of 8.7 and -10.4 ml. For SV by RV volumes versus Fick, r = 0.73, mean difference -0.75 ml with limits of agreement 21.8 and -23.3 ml. In the subset of nine patients, SV by aorta flow versus Fick yielded r = 0.95, while in this subset SV by pulmonary flow versus Fick yielded r = 0.76. For all regression analyses, p < 0.0001.

Conclusion

In conclusion, SV from PA flow has limited accuracy in PAH patients. LV volumes and aorta flow are to be preferred for the measurement of SV.     

Accelerated cardiovascular magnetic resonance of the mouse heart using self-gated parallel imaging strategies does not compromise accuracy of structural and functional measures

Background

Self-gated dynamic cardiovascular magnetic resonance (CMR) enables non-invasive visualization of the heart and accurate assessment of cardiac function in mouse models of human disease. However, self-gated CMR requires the acquisition of large datasets to ensure accurate and artifact-free reconstruction of cardiac cines and is therefore hampered by long acquisition times putting high demands on the physiological stability of the animal. For this reason, we evaluated the feasibility of accelerating the data collection using the parallel imaging technique SENSE with respect to both anatomical definition and cardiac function quantification.

Results

Findings obtained from accelerated data sets were compared to fully sampled reference data. Our results revealed only minor differences in image quality of short- and long-axis cardiac cines: small anatomical structures (papillary muscles and the aortic valve) and left-ventricular (LV) remodeling after myocardial infarction (MI) were accurately detected even for 3-fold accelerated data acquisition using a four-element phased array coil. Quantitative analysis of LV cardiac function (end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and LV mass) in healthy and infarcted animals revealed no substantial deviations from reference (fully sampled) data for all investigated acceleration factors with deviations ranging from 2% to 6% in healthy animals and from 2% to 8% in infarcted mice for the highest acceleration factor of 3.0. CNR calculations performed between LV myocardial wall and LV cavity revealed a maximum CNR decrease of 50% for the 3-fold accelerated data acquisition when compared to the fully-sampled acquisition.

Conclusions

We have demonstrated the feasibility of accelerated self-gated retrospective CMR in mice using the parallel imaging technique SENSE. The proposed method led to considerably reduced acquisition times, while preserving high spatial resolution at sufficiently high CNR. The accuracy of measurements of both structural and functional parameters of the mouse heart was not compromised by the application of the proposed accelerated data acquisition method.     

Late gadolinium enhancement cardiovascular magnetic resonance predicts clinical worsening in patients with pulmonary hypertension

Background

Late gadolinium enhancement (LGE) occurs at the right ventricular (RV) insertion point (RVIP) in patients with pulmonary hypertension (PH) and has been shown to correlate with cardiovascular magnetic resonance (CMR) derived RV indices. However, the prognostic role of RVIP-LGE and other CMR-derived parameters of RV function are not well established. Our aim was to evaluate the predictive value of contrast-enhanced CMR in patients with PH.

Methods

RV size, ejection fraction (RVEF), and the presence of RVIP-LGE were determined in 58 patients with PH referred for CMR. All patients underwent right heart catheterization, exercise testing, and N-terminal pro-brain natriuretic peptide (NT-proBNP) evaluation; results of which were included in the final analysis if performed within 4 months of the CMR study. Patients were followed for the primary endpoint of time to clinical worsening (death, decompensated right ventricular heart failure, initiation of prostacyclin, or lung transplantation).

Results

Overall, 40/58 (69%) of patients had RVIP-LGE. Patients with RVIP- LGE had larger right ventricular volume index, lower RVEF, and higher mean pulmonary artery pressure (mPAP), all p < 0.05. During the follow-up period of 10.2 ± 6.3 months, 19 patients reached the primary endpoint. In a univariate analysis, RVIP-LGE was a predictor for adverse outcomes (p = 0.026). In a multivariate analysis, CMR-derived RVEF was an independent predictor of clinical worsening (p = 0.036) along with well-established prognostic parameters such as exercise capacity (p = 0.010) and mPAP (p = 0.001).

Conclusions

The presence of RVIP-LGE in patients with PH is a marker for more advanced disease and poor prognosis. In addition, this study reveals for the first time that CMR-derived RVEF is an independent non-invasive imaging predictor of adverse outcomes in this patient population.     

Assessment of left atrial volumes in sinus rhythm and atrial fibrillation using the biplane area-length method and cardiovascular magnetic resonance imaging with TrueFISP.

OBJECTIVES: To determine whether the biplane area-length method can be used for the evaluation of left atrial volumes and ejection fraction with cardiovascular magnetic resonance imaging (CMR) by TrueFISP in normal subjects and patients with atrial fibrillation. BACKGROUND: Atrial fibrillation is the most common arrhythmia in elderly patients. Left atrial size and volumes play an important role in predicting short and long-term success after cardioversion. METHODS: Fifteen healthy subjects (mean age 65.6+/-6.4 years) and 18 patients (mean age 67.2+/-8.8 years) with atrial fibrillation were examined by CMR (Magnetom, Siemens, Erlangen, Germany). Images were acquired by TrueFISP using the horizontal and vertical long-axis plane to measure left atrial end-diastolic and end-systolic areas and longitudinal dimensions. Volumes were determined with commercially available software. Left atrial end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were determined by the biplane area-length method and compared to findings obtained by the standard short-axis method. Images were acquired and analyzed a second time in the patients with atrial fibrillation. RESULTS: There was no difference in age between men and women (p=0.147) and healthy subjects and patients (p=0.128) included in the study. EDV and ESV were significantly higher and SV and EF significantly lower in patients with atrial fibrillation than in healthy subjects (p < or = 0.009), regardless of the method used. The values obtained for EDV and ESV by the biplane area-length method were significantly higher in both healthy subjects (p<0.001) and patients with atrial fibrillation (p<0.001) than those obtained by the standard short-axis approach, whereas SV (p> or = 0.057) and EF (p> or = 0.118) did not differ significantly. In the second investigation in patients with atrial fibrillation, ESV, SV, and EF did not differ significantly between the two methods (p> or =0.481). Assessment of interobserver variability revealed good agreement in the findings of the two observers, both in normal sinus rhythm and atrial fibrillation (overall variability 0.8+/-6.5%). CONCLUSIONS: The biplane area-length method can be used in CMR images obtained by TrueFISP to assess left atrial volumes and ejection fraction in normal subjects and patients with varying cardiac cycle length, as in atrial fibrillation.