Chemical Exchange Saturation Transfer Magnetic Resonance Imaging Identifies Abnormal Calf Muscle-Specific Energetics in Peripheral Artery Disease.

BACKGROUND: Peripheral artery disease (PAD) results in exercise-induced ischemia in leg muscles. 31Phosphorus (P) magnetic resonance spectroscopy demonstrates prolonged phosphocreatine recovery time constant after exercise in PAD but has low signal to noise, low spatial resolution, and requires multinuclear hardware. Chemical exchange saturation transfer (CEST) is a quantitative magnetic resonance imaging method for imaging substrate (CEST asymmetry [CESTasym]) concentration by muscle group. We hypothesized that kinetics measured by CEST could distinguish between patients with PAD and controls. METHODS: Patients with PAD and age-matched normal subjects were imaged at 3T with a transmit-receive coil around the calf. Four CEST mages were acquired over 24-second intervals. The subjects then performed plantar flexion exercise on a magnetic resonance imaging-compatible ergometer until calf exhaustion. Twenty-five CEST images were obtained at end exercise. Regions of interest were drawn around individual muscle groups, and (CESTasym) decay times were fitted by exponential curve to CEST values. In 10 patients and 11 controls, 31P spectra were obtained 20 minutes later after repeat exercise. Five patients and 5 controls returned at a mean of 1±1 days later for repeat CEST studies. RESULTS: Thirty-five patients with PAD (31 male, age 66±8 years) and 29 controls (11 male, age 63±8 years) were imaged with CEST. The CESTasym decay times for the whole calf (341±332 versus 153±72 seconds; P<0.03) as well as for the gastrocnemius and posterior tibialis were longer in patients with PAD. Agreement between CESTasym decay and phosphocreatine recovery time constant was good. CONCLUSIONS: CEST is a magnetic resonance imaging method that can distinguish energetics in patients with PAD from age-matched normal subjects on a per muscle group basis. CEST agrees reasonably well with the gold standard 31P magnetic resonance spectroscopy. Moreover, CEST has higher spatial resolution, creates an image, and does not require multinuclear hardware and thus may be more suitable for clinical studies in PAD.

Functional and Economic Impact of INOCA and Influence of Coronary Microvascular Dysfunction.

OBJECTIVES: This study sought to better characterize the quality of life and economic impact in patients with symptoms of ischemia and no obstructive coronary disease (INOCA) and to identify the influence of coronary microvascular dysfunction (CMD). BACKGROUND: Patients with INOCA have a high symptom burden and an increased incidence of major adverse cardiac events. CMD is a frequent cause of INOCA. The morbidity associated with INOCA and CMD has not been well-characterized. METHODS: Sixty-six patients with INOCA underwent stress cardiac magnetic resonance with calculation of myocardial perfusion reserve (MPR); MPR 2.0 to 2.4 was considered borderline-reduced (possible CMD) and MPR <2.0 was defined as reduced (definite CMD). Subjects completed quality of life questionnaires to assess the morbidity and economic impact of INOCA. Questionnaire results were compared between INOCA patients with and without CMD. In addition, logistic regression was used to determine the predictors of CMD within the INOCA population. RESULTS: The prevalence of definite CMD was 24%. Definite or borderline CMD was present in 59% (MPR ≤2.4). Patients with INOCA reported greater physical limitation, angina frequency, and reduced quality of life compared to referent stable coronary artery disease and acute myocardial infarction populations. In addition, Patients with INOCA reported frequent time missed from work and work limitations, suggesting a substantial economic impact. No difference was observed in reported symptoms between INOCA patients with and without CMD. Glomerular filtration rate and body-mass index were significant predictors of CMD in multivariable regression analysis. CONCLUSIONS: INOCA is associated with high morbidity similar to other high-risk cardiac populations, and work limitations reported by Patients with INOCA suggest a substantial economic impact. CMD is a common cause of INOCA but is not associated with increased morbidity. These results suggest that there is significant symptom burden in the INOCA population regardless of etiology.

Recent Advances in Imaging of Hypertensive Heart Disease.

PURPOSE OF REVIEW: To review recent advances in the imaging of hypertensive heart disease (HHD) with an emphasis on developments in the imaging of diffuse myocardial fibrosis using cardiac magnetic resonance (CMR). RECENT FINDINGS: HHD results from long-standing hypertension and is characterized by the development of left ventricular hypertrophy and diffuse interstitial fibrosis. Diffuse fibrosis traditionally required endomyocardial biopsy to diagnose, but recent developments using T1 mapping in CMR allow for noninvasive assessment. Studies using T1 mapping have shown an increase in extracellular volume fraction (ECV) in patients with HHD compared to normal controls, suggesting ECV can be used as a noninvasive marker for fibrosis in HHD. In addition to T1 mapping, other recent advances in HHD imaging include improvements in three-dimensional echocardiography, allowing for accurate real-time volumetric measurements, and the use of speckle tracking echocardiography to detect subclinical systolic dysfunction. Measurement of ECV using T1 mapping in CMR can be used as a noninvasive marker of diffuse myocardial fibrosis in HHD. While further studies are needed to validate this approach with larger patient cohorts, ECV can potentially be used to both monitor disease progression and assess therapeutic interventions in HHD.

Treatment of Non-ST Elevation Myocardial Infarction: A Process Analysis of Patient and Program Factors in a Teaching Hospital.

As part of a quality improvement project, we performed a process analysis to evaluate how patients presenting with type 1 non-ST elevation myocardial infarction (STEMI) are diagnosed and managed early after the diagnosis has been made. We performed a retrospective chart review and collected detailed information regarding the timing of the first 12-lead electrocardiogram, troponin order entry and first positive troponin result, administration of anticoagulation and antiplatelet medications, and referral for coronary angiography to identify areas of treatment variability and delay. A total of 242 patients with type 1 non-STEMI were included. The majority of patients received aspirin early after presentation to the emergency department; however, there was significant variability in the time from presentation to administration of other medications, including anticoagulation and P2Y12 therapy, even after an elevated troponin level was documented in the chart. Lack of a standardized non-STEMI admission order set, inconsistency regarding whether the emergency department physician or the cardiology admitting team order these medications after the diagnosis is made, and per current protocol, the initial call regarding the patient made to the cardiology fellow, not the admitting house staff, were identified as possible contributors to the delay. Patients who presented during "nighttime" hours had higher rates of atypical symptoms (P = 0.036) and longer delays to coronary angiography (46.5 versus 24 hours, P < 0.001) even in those deemed intermediate to high risk. A process analysis revealed considerable variation in non-STEMI treatment in our teaching hospital and identified specific areas for quality improvement measures.