Cardiac magnetic resonance assessment of mechanical dyssynchrony

The role of imaging in characterizing the cardiac natural history of Duchenne muscular dystrophy

Duchene muscular dystrophy (DMD) is a rare but devastating disease resulting in progressive loss of ambulation, respiratory failure, DMD-associated cardiomyopathy (DMD-CM), and premature death. The use of corticosteroids and supportive respiratory care has improved outcomes, such that DMD-CM is now the leading cause of death. Historically, most programs have focused on skeletal myopathy with less attention to the cardiac phenotype. This omission is rather astonishing since patients with DMD possess an absolute genetic risk of developing cardiomyopathy. Unfortunately, heart failure signs and symptoms are vague due to skeletal muscle myopathy leading to limited ambulation. Traditional assessment of cardiac symptoms by the New York Heart Association American College of Cardiology/American Heart Association Staging (ACC/AHA) classification is of limited utility, even in advanced stages. Echocardiographic assessment can detect cardiac dysfunction late in the disease course, but this has proven to be a poor surrogate marker of early cardiovascular disease and an inadequate predictor of DMD-CM. Indeed, one explanation for the paucity of cardiac therapeutic trials for DMD-CM has been the lack of a suitable end-point. Improved outcomes require a better proactive treatment strategy; however, the barrier to treatment is the lack of a sensitive and specific tool to assess the efficacy of treatment. The use of cardiac imaging has evolved from echocardiography to cardiac magnetic resonance imaging to assess cardiac performance. The purpose of this article is to review the role of cardiac imaging in characterizing the cardiac natural history of DMD-CM, highlighting the prognostic implications and an outlook on how this field might evolve in the future.

Role of Cardiac Magnetic Resonance Imaging in Heart Failure

This review describes the current role and potential future applications of cardiac magnetic resonance (CMR) for the management of heart failure (HF). CMR allows noninvasive morphologic and functional assessment, tissue characterization, blood flow, and perfusion evaluation. CMR overcomes echocardiography limitations (geometric assumptions, interobserver variability and poor acoustic window) and provides incremental information in relation to cause, prognosis, and treatment monitoring of patients with HF.

Left ventricular subclinical myocardial dysfunction in uncomplicated type 2 diabetes mellitus is associated with impaired myocardial perfusion: a contrast-enhanced cardiovascular magnetic resonance study

BACKGROUND

Early detection of subclinical myocardial dysfunction in patients with diabetes mellitus (DM) is essential for recommending therapeutic interventions that can prevent or reverse heart failure, thereby improving the prognosis in such patients. This study aims to quantitatively evaluate left ventricular (LV) myocardial deformation and perfusion using cardiovascular magnetic resonance (CMR) imaging in patients with type 2 diabetes mellitus (T2DM), and to investigate the association between LV subclinical myocardial dysfunction and coronary microvascular perfusion.

METHODS

We recruited 71 T2DM patients and 30 healthy individuals as controls who underwent CMR examination. The T2DM patients were subdivided into two groups, namely the newly diagnosed DM group (n = 31, patients with diabetes for ≤ 5 years) and longer-term DM group (n = 40, patients with diabetes > 5 years). LV deformation parameters, including global peak strain (PS), peak systolic strain rate, and peak diastolic strain rate (PSDR), and myocardial perfusion parameters such as upslope, time to maximum signal intensity (TTM), and max signal intensity (Max SI, were measured and compared among the three groups. Pearson's correlation was used to evaluate the correlation between LV deformation and perfusion parameters.

RESULTS

Pooled data from T2DM patients showed a decrease in global longitudinal, circumferential, and radial PDSR compared to healthy individuals, apart from lower upslope. In addition, increased TTM and reduced Max SI were found in the longer-term diabetics compared to the normal subjects (p < 0.017 for all). Multivariable linear regression analysis showed that T2DM was independently associated with statistically significant CMR parameters, except for TTM (β = 0.137, p = 0.195). Further, longitudinal PDSR was significantly associated with upslope (r = - 0.346, p = 0.003) and TTM (r = 0.515, p < 0.001).

CONCLUSIONS

Our results imply that a contrast-enhanced 3.0T CMR can detect subclinical myocardial dysfunction and impaired myocardial microvascular perfusion in the early stages of T2DM, and that the myocardial dysfunction is associated with impaired coronary microvascular perfusion.

Characterisation of cardiomyopathy by cardiac and aortic magnetic resonance in patients new to hemodialysis

Objectives

Cardiomyopathy is a key factor in accelerated cardiovascular mortality in haemodialysis (HD) patients. We aimed to phenotype cardiac and vascular dysfunction by tagged cardiovascular magnetic resonance (CMR) imaging in patients recently commencing HD.

Methods

Fifty-four HD patients and 29 age and sex-matched controls without kidney disease were studied. Left ventricular (LV) mass, volumes, ejection fraction (EF), concentric remodelling, peak-systolic circumferential strain (PSS), peak diastolic strain rate (PDSR), LV dyssynchrony, aortic distensibility and aortic pulse wave velocity were determined.

Results

Global systolic function was reduced (EF 51 ± 10%, HD versus 59 ± 5%, controls, p < 0.001; PSS 15.9 ± 3.7% versus 19.5 ± 3.3%, p < 0.001). Diastolic function was decreased (PDSR 1.07 ± 0.33s^-1 versus 1.31 ± 0.38s^-1, p = 0.003). LV mass index was increased (63[54,79]g/m² versus 46[42,53]g/m², p < 0.001). Anteroseptal reductions in PSS were apparent. These abnormalities remained prevalent in the subset of HD patients with preserved EF >50% (n = 35) and the subset of HD patients without diabetes (n = 40). LV dyssynchrony was inversely correlated to diastolic function, EF and aortic distensibility. Diastolic function was inversely correlated to LV dyssynchrony, concentric remodelling, age and aortic pulse wave velocity.

Conclusion

Patients new to HD have multiple cardiac and aortic abnormalities as characterised by tagged CMR. Cardio-protective interventions are required from initiation of therapy.

Key Points

• First characterisation of cardiomyopathy by tagged CMR in haemodialysis patients.

• Diastolic function was correlated to LV dyssynchrony, concentric remodelling and aortic PWV.

• Reductions in strain localised to the septal and anterior wall.

• Bioimpedance measures were unrelated to LV strain, suggesting volume-independent pathogenetic mechanisms.

• Multiple abnormalities persisted in the HD patient subset with preserved EF or without diabetes.

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-015-4096-2) contains supplementary material, which is available to authorized users.

Left-ventricular mechanical activation and aortic-arch orientation recovered from magneto-hydrodynamic voltages observed in 12-lead ECGs obtained inside MRIs: a feasibility study

To explore use of the Magnetohydrodynamic Voltage (VMHD), observed in intra-MRI 12-lead electrocardiograms (ECG), to indicate the timing of the onset of left-ventricular mechanical activation (LVMA) and the orientation of the aortic-arch (AAO). Blood flow through the aortic arch during systole, in the presence of the MRI magnetic field (B 0), generates VMHD. Since the magnitude and direction of VMHD are determined by the timing and directionality of blood flow relative to B 0, we hypothesized that clinically useful measures, LVMA and AAO, could be extracted from temporal and vectorial VMHD characteristics. VMHD signals were extracted from 12-lead ECG traces by comparing traces obtained inside and outside the MRI scanner. VMHD was converted into the Vectorcardiogram frame of reference. LVMA was quantified in 1 subject at 1.5T and 3 subjects at 3T, and the result compared to CINE MRI. AAO was inferred for 4 subjects at 3T and compared to anatomical imaging of the aortic arch orientation in the transverse plane. A < 10% error was observed in LVMA measurements, while a < 3° error was observed in aortic arch orientation measurements. The temporal and vectorial nature of VMHD is useful in estimating these clinically relevant parameters.

Comparison of cardiac MRI tissue tracking and myocardial tagging for assessment of regional ventricular strain

This study sought to compare regional measures of ventricular strain by tissue tracking (TT) to those derived from myocardial tagging (MT) within cardiac MR (CMR), in normal subjects and patients with hypertrophic cardiomyopathy. CMR images from 13 normal subjects and 11 subjects with hypertrophic cardiomyopathy were retrospectively analyzed. For each subject, equivalent mid-papillary level short-axis cine steady-state free precession and MT slices from the same examination were evaluated. The time to peak circumferential strain and magnitude of the peak strain were calculated for 6 matched left ventricular segments. Data from 24 slices (n = 144 segments) were compared. The mean difference between techniques in magnitude of peak strain and time to peak strain was 1 ± 9% and 1 ± 58 ms, respectively. The mean difference in the standard deviation of time to peak strain within a slice was 0 ± 19 ms (mean cardiac cycle duration 1,013 ± 204 ms). Bland-Altman analysis showed closer agreement in time to peak strain than peak strain magnitude. Measurements of segmental time to peak strain by TT and MT were in close agreement; agreement for the magnitude of peak segmental strain was more modest. The TT approach does not add to CMR examination time and may be a useful tool for the assessment of ventricular synchrony.

Relation of left ventricular dyssynchrony measured by cardiac magnetic resonance tissue tracking in repaired tetralogy of fallot to ventricular tachycardia and death

The impact of left ventricular (LV) dyssynchrony on clinical outcomes in patients with tetralogy of Fallot (TOF) is unknown. The aim of this study was to test the hypothesis that LV dyssynchrony assessed by cardiac magnetic resonance (CMR)-derived tissue tracking in patients with repaired TOF is associated with ventricular tachycardia (VT) and death. Included patients had repaired TOF and CMR data from 2000 and 2008. Patients (n = 13) had histories of death or sustained VT. Control subjects (n = 26), with no death or VT, were matched by age at CMR and type of last surgical procedure. Demographic, clinical, and electrocardiographic data were recorded. CMR short-axis cine data were analyzed by tracking the motion of the endocardial border using commercial software. LV dyssynchrony was quantified as the maximum difference in time to peak radial displacement, circumferential strain, and radial strain among the 6 ventricular segments and the standard deviation of the times to peak value. There were no differences between groups in clinical, electrocardiographic, or demographic characteristics. Among CMR parameters, right ventricular volumes were higher and ejection fractions lower in the patient group. Indexes of LV dyssynchrony were higher in the patient group (e.g., maximum time difference of circumferential strain 94 vs 46 ms, p <0.001; standard deviation of circumferential strain 37.8 vs 20.3 ms, p <0.01). In a multivariate model including LV synchrony variables, the best outcome discriminator was maximum time difference to peak circumferential strain (p <0.01). In conclusion, tissue tracking applied to CMR images identifies indexes of LV synchrony associated with death and VT in patients with repaired TOF.

Assessment of the coronary venous system in heart failure patients by blood pool agent enhanced whole-heart MRI

OBJECTIVE

To investigate the feasibility of MRI for non-invasive assessment of the coronary sinus (CS) and the number and course of its major tributaries in heart failure patients.

METHODS

Fourteen non-ischaemic heart failure patients scheduled for cardiac resynchronisation therapy (CRT) underwent additional whole-heart coronary venography. MRI was performed 1 day before device implantation. The visibility, location and dimensions of the CS and its major tributaries were assessed and the number of potential implantation sites identified. The MRI results were validated by X-ray venography conventionally acquired during the device implantation procedure.

RESULTS

The right atrium (RA), CS and mid-cardiac vein (MCV) could be visualised in all patients. 36% of the identified candidate branches were located posterolaterally, 48% laterally and 16% anterolaterally. The average diameter of the CS was quantified as 9.8 mm, the posterior interventricular vein (PIV) 4.6 mm, posterolateral segments 3.3 mm, lateral 2.9 mm and anterolateral 2.9 mm. Concordance with X-ray in terms of number and location of candidate branches was given in most cases.

CONCLUSION

Contrast-enhanced MRI venography appears feasible for non-invasive pre-interventional assessment of the course of the CS and its major tributaries.

The role of cardiovascular magnetic resonance imaging in cardiac resynchronisation therapy

Cardiac electromechanical resynchronisation therapy (CRT) is an effective non-pharmacological treatment of patients suffering from drug refractory heart failure. However, approximately 20–30% of patients are non-responder. Cardiac magnetic resonance imaging (CMR) may play significant role in clarifying many questions in this patient population. Forty-five patients, suffering from severe drug refractory heart failure, underwent CMR before applying CRT. Left ventricular end-diastolic, end-systolic volumes, ejection fraction, myocardial mass, wall motion disturbances, localisation of non-viable myocardium were determined. Left ventricular dyssynchrony was determined by illustrating wall-time thickening in short-axis slices of left ventricle from basis to apex. CMR-proved underlying heart disease were postinfarction heart failure, dilated cardiomyopathy and non-compaction cardiomyopathy in 62, 27 and in 11%, respectively. Mean left ventricular ejection fraction was 24.5±10%, intraventricular dyssynchrony was 200±78 ms. In four patients, requiring surgical revascularisation after unsuccessful coronary sinus electrode implantation, optimal position for epicardial screw-in electrode was selected. According to the results of CMR, biventricular device was not implanted in 7 patients. During the follow-up of the 38 patients, 5 patients (13.16%) were non-responders, despite the approximately 22% non-responder ratio in our whole patient population treated by CRT but without performing previous CMR examination. In this patient population CMR may have a significant role in the selection of responder patient population.

MRI assessment of pacing induced ventricular dyssynchrony in an isolated human heart

This study demonstrates the capabilities of MRI in the assessment of cardiac pacing induced ventricular dyssynchrony, and the findings support the need for employing more physiological pacing. A human donor heart deemed non-viable for transplantation, was reanimated using an MR compatible, four-chamber working perfusion system. The heart was imaged using a 1.5T MR scanner while being paced from the right ventricular apex (RVA) via an epicardial placed lead. Four-chamber, short-axis, and tagged short-axis cines were acquired in order to track wall motion and intramyocardial strain during pacing. The results of this study revealed that the activation patterns of the left ventricle (LV) during RVA pacing demonstrated intraventricular dyssynchrony; as the left ventricular mechanical activation proceeded from the septum and anterior wall to the lateral wall, with the posterior wall being activated last. As such, the time difference to peak contraction between the septum and lateral wall was approximately 125 msec. Likewise, interventricular dyssynchrony was demonstrated from the four-chamber cine as the time difference between the peak LV and RV free wall motion was 180 msec. With the ongoing development of MR safe and MR compatible pacing systems, we can expect MRI to be added to the list of imaging modalities used to optimize cardiac resynchronization therapy (CRT) and/or alternate site pacing.

The role of non-invasive imaging in patient selection

Cardiac resynchronization therapy (CRT) is an established therapy for patients with advanced heart failure, depressed left ventricular (LV) function and wide QRS complex. A substantial amount of patients do not respond to CRT. Recent studies suggest that assessment of mechanical dyssynchrony may allow identification of potential CRT responders. In addition, presence of scar tissue and venous anatomy may play a role in the selection of candidates. This article summarizes the role of non-invasive cardiac imaging modalities addressing these issues in the selection of CRT candidates.

The role of cardiovascular magnetic resonance imaging in heart failure

Noninvasive imaging plays a central role in the diagnosis of heart failure, assessment of prognosis, and monitoring of therapy. Cardiovascular magnetic resonance (CMR) offers a comprehensive assessment of heart failure patients and is now the gold standard imaging technique to assess myocardial anatomy, regional and global function, and viability. Furthermore, it allows assessment of perfusion and acute tissue injury (edema and necrosis), whereas in nonischemic heart failure, fibrosis, infiltration, and iron overload can be detected. The information derived from CMR often reveals the underlying etiology of heart failure, and its high measurement accuracy makes it an ideal technique for monitoring disease progression and the effects of treatment. Evidence on the prognostic value of CMR-derived parameters in heart failure is rapidly emerging. This review summarizes the advantages of CMR for patients with heart failure and its important role in key areas.

[Update on cardiac imaging techniques: echocardiography, cardiac magnetic resonance, and multidetector computed tomography]

This article contains a review of the most important publications on cardiac imaging that have appeared during 2008. During the year, we assisted with the clinical implementation of three-dimensional real-time transesophageal echocardiography, with the use of echocardiography for selecting patients for and monitoring those who underwent percutaneous aortic valve replacement (the majority of centers performing the technique were still in the learning phase), and with the emergence in the clinic of techniques for studying myocardial deformation. Also reviewed are the most significant developments in the application of echocardiography to coronary heart disease and cardiac resynchronization therapy and in 2 other techniques whose use is constantly increasing: cardiac magnetic resonance and multidetector cardiac computed tomography. The review ends with a description of the current state of the art in contrast echocardiography, with particular emphasis on safety in the context of recommendations made by the US Food and Drug Administration at the end of 2007.