Motaz Alshaher

Delayed Preconditioning-Mimetic Actions of Nitroglycerin in Patients Undergoing Exercise Tolerance Tests

Background—Nitroglycerin (NTG) induces delayed preconditioning (PC)-mimetic effects in animal models and in humans during coronary angioplasty. We tested the hypothesis that NTG mitigates ischemia and enhances functional capacity during an exercise tolerance test (ETT) in patients with coronary artery disease. Methods and Results—Twenty-eight patients with stable angina and ischemia documented by a stress test were randomized in a double-masked, crossover design to receive a titrated intravenous infusion of NTG or normal saline over 4 hours. At 24 to 28 hours after study medication infusion, each patient underwent 2 ETTs separated by a 1-week washout period. Compared with control patients, pretreatment with NTG was associated with a dose-dependent increase in exercise duration averaging 40 seconds (412±19 versus 372±24 seconds, P=0.014) and an improvement in ECG manifestations of ischemia, as shown by a decrease in maximal ST-segment depression (1.84±0.14 versus 1.63±0.13 mm, P=0.011), sum of ST-segment depressions in 12 leads (7.64±1.01 versus 6.61±0.83 mm, P=0.027), and time to resolution of ST-segment depression (229±30 versus 207±28 s, P=0.018). These benefits occurred despite an increase in myocardial workload after NTG, as indicated by a higher peak rate-pressure product (24 492±1054 versus 22 536±1019 mm Hg/min, P=0.015). Conclusions—NTG produces a late PC-mimetic effect that mitigates the ECG manifestations of ischemia during exercise and improves exercise capacity. To our knowledge, this is the first study to demonstrate that NTG can alleviate exercise-induced ischemia 24 hours after its administration, long after the hemodynamic effects have subsided. The finding that nitrate-induced late PC ameliorates a common manifestation of coronary artery disease has potentially significant implications for the management of this disorder and for the design of clinical trials.

Intrapulmonary shunt is a potentially unrecognized cause of ischemic stroke and transient ischemic attack.

BACKGROUND Ischemic stroke is a major cause of mortality and disability. Transient ischemic attack (TIA) is a harbinger of stroke. The etiology of stroke in as many as 40% of patients remains undetermined after extensive evaluation. It was hypothesized that intrapulmonary shunt is a potential facilitator of cerebrovascular accident (CVA) or TIA. METHODS Patients undergoing clinically indicated transesophageal echocardiography were prospectively enrolled. Comprehensive multiplane transesophageal echocardiographic imaging was performed and saline contrast done to assess for intrapulmonary shunt and patent foramen ovale. RESULTS Three hundred twenty-one patients with either nonhemorrhagic CVA (n = 262) or TIA (n = 59) made up the stroke group. Three hundred twenty-one age-matched and gender-matched patients made up the control group. Intrapulmonary shunt occurred more frequently in the stroke group (72 of 321) compared with the control group (32 of 321) (22% vs 10%, P < .0001). Intrapulmonary shunt was an independent predictor of CVA and/or TIA (odds ratio, 2.6; P < .0001). In subjects with cryptogenic CVA or TIA (n = 71), intrapulmonary shunt occurred more frequently (25 of 71) than in the control group (5 of 71) (35% vs 7%, P < .0001). Intrapulmonary shunt was an independent multivariate predictor of CVA or TIA in patients with cryptogenic CVA or TIA (odds ratio, 6.3; P < .005). CONCLUSIONS These results suggest that intrapulmonary shunt is a potentially unrecognized facilitator of CVA and TIA, especially in patients with cryptogenic CVA and TIA. Future studies assessing the prognostic significance of intrapulmonary shunt on cerebral vascular event recurrence rates in patients after initial CVA or TIA would be of great interest.

Cardiac manifestations of exhaustive exercise in nonathletic adults: does cardiac fatigue occur?

The aim of the study was to examine the impact of prolonged exercise leading to physical exhaustion on left ventricular (LV) systolic and diastolic function in untrained healthy subjects, and to examine cardiovascular determinants of exercise performance. Twenty‐four nonathletic healthy adults (14 males, 10 females; mean age 42 ± 11 years) were exercised on a treadmill at 70% of maximal oxygen consumption until physical exhaustion occurred after an average of 84 ± 39 minutes. Two‐dimensional and Doppler echocardiography was performed before and 15 minutes after exercise to assess LV function and geometry, and right ventricular (RV) systolic function. After prolonged exercise, LV ejection fraction and geometry were unchanged, but LV end‐diastolic volume, end‐systolic volume, and stroke volume decreased. However, due to a higher heart rate (HR), cardiac output increased at 15 minutes post exercise. RV fractional shortening was unchanged. LV peak early to atrial filling velocity ratio decreased post exercise, with an increase in percent atrial contribution. However, less preload‐dependent variables of LV diastolic function such as deceleration time, LV inflow propagation rate, mitral annular tissue Doppler and myocardial performance index were unchanged. Preexercise stroke volume and HR were the only predictors (r = 0.86, P < 0.01) of exercise duration. However, age, resting blood pressure, indices of systolic and diastolic function, and LV geometry were not predictors. Prolonged exercise leading to physical exhaustion is not associated with systolic or diastolic dysfunction. Reduced early LV diastolic filling and the relative increase in left atrial contribution seen with prolonged exercise are likely due to preload reduction rather than true diastolic dysfunction.

Rapid flow quantification in iliac arteries with spiral phase-contrast MRI

Phase contrast MRI is a powerful tool for blood flow quantification. Conventional cartesian phase contrast sequences require lengthy acquisition on the order of several minutes. Spiral acquisition phase-contrast (PC) MRI is capable of reducing the TR and TE in order to minimize flow dependent artifacts and total imaging time. Despite this, in general, spiral phase contrast sequences suffer from off-resonance artifacts and inconsistent data artifacts. In this work, we show that short interleaved spiral readout trajectories have the capability to obtain high spatio-temporal resolution flow images in the common iliac artery distal to the aortoiliac bifurcation with little or no artifacts and with significant savings in image acquisition time over the Cartesian trajectory. To verify the accuracy, we compare our results with a Conventional cartesian trajectory.

A multimodal (MRI/ultrasound) cardiac phantom for imaging experiments

A dynamic cardiac phantom can play a significant role in the evaluation and development of ultrasound and cardiac magnetic resonance (MR) motion tracking and registration methods. A four chamber multimodal cardiac phantom has been designed and built to simulate normal and pathologic hearts with different degrees of “infarction” and “scar tissues”. In this set up, cardiac valves have been designed and modeled as well. The four-chamber structure can simulate the asymmetric ventricular, atrial and valve motions. Poly Vinyl Alcohol (PVA) is used as the principal material since it can simulate the shape, elasticity, and MR and ultrasound properties of the heart. The cardiac shape is simulated using a four-chamber mold made of polymer clay. An additional pathologic heart phantom containing stiff inclusions has been manufactured in order to simulate an infracted heart. The stiff inclusions are of different shapes and different degrees of elasticity and are able to simulate abnormal cardiac segments. The cardiac elasticity is adjusted based on freeze-thaw cycles of the PVA cryogel for normal and scarred regions. Ultrasound and MRI markers were inserted in the cardiac phantom as landmarks for validations. To the best of our knowledge, this is the first multimodal phantom that models a dynamic four-chamber human heart including the cardiac valve.

Effect of V enc on accuracy of velocity profiles in multi-slice phase-contrast MR imaging of stenotic flow

Phase-contrast MRI (PC MRI) is a powerful technique for imaging the flow velocities in-vivo. In PC MRI, the velocity encoding parameter, Venc, plays a central role in fidelity of velocities acquired with this technique. Typically Venc is chosen to be the highest velocity in the flow. However, when acquiring velocity images at a number of slice locations, it may be advantageous to change the Venc as a function of position. The goal of this study was to determine the effect of Venc on the accuracy of the estimated velocity profiles in a range of locations in a phantom model of a 90% area stenosis. To this end, velocities from PC MRI were compared with velocities from computational fluid dynamics (CFD) simulations for identical geometry and flow conditions. Our results confirm that although using smaller Vencs leads to wrapping artifact, it provides more accurate velocity profiles. However, there is a lower limit to setting the Venc, beyond which phase-unwrapping becomes uncertain.

A biventricular multimodal (MRI/ultrasound) cardiac phantom

A cardiac phantom can be of crucial importance in the development and validation of ultrasound and cardiac magnetic resonance (MR) imaging and image analysis methods. A biventricular multimodal cardiac phantom has been manufactured in-house that can simulate normal and pathologic hearts with different degrees of infarction. The two-chamber structure can simulate the asymmetric left ventricular motion. Poly Vinyl Alcohol (PVA) is utilized as the basic material since it can simulate the shape, elasticity, and MR and ultrasound properties of the heart. The cardiac shape is simulated using a two-chamber acrylic mold. An additional pathologic heart phantom has been built to simulate aneurysm and infarction. Segmental dyskinesis is modeled based on three inclusions of different shapes and different degrees of elasticity. The cardiac elasticity is adjusted based on freeze-thaw cycles of the PVA cryogel for normal and scarred regions.

An Optical Flow Approach to Assessment of Ventricular Shape Change Based on Echocardiography

The quantitative analysis of cardiac motion from echocardiographic images helps clinicians in the diagnosis and therapy of patients suffering from heart disease. Quantitative analysis is usually based on TDI (Tissue Doppler Imaging) or speckle tracking. These methods are based on two techniques which to a large degree are independent—the Doppler phenomenon and image sequence processing, respectively. Herein, to increase the accuracy of the speckle tracking technique and to cope with the angle dependency of TDI, a combined approach dubbed TDIOF (Tissue Doppler Imaging Optical Flow) is proposed. TDIOF is formulated based on the combination of B-mode and Doppler energy terms minimized using algebraic equations and is validated on simulated images, a physical heart phantom, and in-vivo data. It was observed that the additional Doppler term is able to increase the accuracy of speckle tracking, compared to two popular motion estimation and speckle tracking techniques (Horn-Schunck and block matching methods). This observation was more pronounced when noise was present. . The magnitude and angular error for TDIOF applied to simulated images when comparing estimated motion with ground-truth motion were 15 % and 9.2 degrees/frame, respectively. The magnitude and angular error for images acquired from physical phantoms were 22 % and 15.2 degrees/frame, respectively. As an additional validation, echocardiography-derived strains were compared to tagged MRI-derived myocardial strains in the same subjects. The correlation coefficient (r) between the TDIOF-derived radial strains and tagged MRI-derived radial strains value were 0.83 (\(\mathrm{P}<0.001\) ). The correlation coefficient (r) for the TDIOF-derived circumferential strains compared to the tagged MRI-derived circumferential strains were 0.86 (\(\mathrm{P}<0.001\) ). The comparison of TDIOF-derived and block matching speckle tracking and Horn-Schunck optical flow strain values using student t-test demonstrated superiority of TDIOF (95 % confidence interval, \(\mathrm{P}<0.001\) ).

Cardiac deformation analysis from orthogonal CSPAMM (OCSPAMM) tagged MRI

Background Magnetic resonance imaging (MRI) is a highly advanced and sophisticated imaging modality for cardiac motion assessment and quantitative analysis. The myocardial tagging techniques have seen wide applications for cardiac deformation analysis (see [1-4] for example). Among different image post-processing techniques, frequency-based methods have played an important role in analysis of heart displacement from tagged MRI images [5,6]. In this abstract, we apply the SinMod technique to data from a new tagging pulse sequence which we have recently developed called Orthogonal CSPAMM (OCSPAMM) [7].

Orthogonal CSPAMM (OCSPAMM) MR tagging for imaging ventricular wall motion

Tagged magnetic resonance imaging (MRI) has the ability to directly and non-invasively alter tissue magnetization and produce tags on the deforming tissue [1], [2]. Since its development, the Spatial Modulation of Magnetization (SPAMM) [2] tagging pulse sequence has been widely available and is the most commonly used technique for producing sinusoidal tag patterns. However, SPAMM suffers from tag fading which occurs in the later phases of the cardiac cycle. Complementary SPAMM (CSPAMM) was introduced to solve this problem by acquiring and subtracting two SPAMM images [3]. The drawback of CSPAMM is that it results in doubling of the acquisition time. In this paper, we propose a novel pulse sequence, termed Orthogonal CSPAMM (OCSAPMM), which results in the same acquisition time as SPAMM for 2D deformation estimation while keeping the advantages of CSPAMM. Different from CSPAMM, in OCSPAMM the second tagging pulse orientation is rotated 90 degrees relative to the first one so that motion information can be obtained simultaneously in two directions. A cardiac motion phantom, which independently models cardiac wall thickening and rotation in the human heart was used to show the effectiveness of the proposed pulse sequence.