Calf muscle perfusion at peak exercise in peripheral arterial disease: measurement by first-pass contrast-enhanced magnetic resonance imaging

PURPOSE

To develop a contrast-enhanced magnetic resonance (MR) technique to measure skeletal muscle perfusion in peripheral arterial disease (PAD).

MATERIALS AND METHODS

A total of 11 patients (age = 61 +/- 11 years) with mild to moderate symptomatic PAD (ankle-brachial index [ABI] = 0.75 +/- 0.08) and 22 normals were studied using an MR-compatible ergometer. PAD and normal(max) (Nl(max); N = 11) exercised to exhaustion. Nl(low) (N = 11) exercised to the same workload achieved by PAD. At peak exercise, 0.1 mm/kg of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was infused at 3-4 cm(3)/second followed by a saline flush at the same rate. A dual-contrast gradient echo (GRE) sequence enabled simultaneous acquisition of muscle perfusion and arterial input function (AIF). The perfusion index (PI) was defined as the slope of the time-intensity curve (TIC) in muscle divided by the arterial TIC slope.

RESULTS

Median workload was 120 Joules in PAD, 210 Joules in Nl(low), and 698 Joules in Nl(max) (P < 0.001 vs. Nl(low) and PAD). Median PI was 0.29 in PAD (25th and 75th percentiles [%] = 0.20, 0.40), 0.48 in Nl(low) (25th, 75th % = 0.36, 0.62; P < 0.02 vs. PAD), and 0.69 in Nl(max) (25th, 75th % = 0.5, 0.77; P < 0.001 vs. PAD). Area under the ROC-curve for PI differentiating patients from Nl(max) was 0.95 (95% confidence interval [CI] = 0.77-0.99).

CONCLUSION

Peak-exercise measurement of lower limb perfusion with dual-contrast, first-pass MR distinguishes PAD from normals. This method may be useful in the study of novel therapies for PAD.

Delayed calf muscle phosphocreatine recovery after exercise identifies peripheral arterial disease

OBJECTIVES

In this study we intend to characterize phosphocreatine (PCr) recovery kinetics with phosphorus-31 ((31)P) magnetic resonance spectroscopy in symptomatic peripheral arterial disease (PAD) patients compared with control subjects and determine the diagnostic value and reproducibility of this parameter.

BACKGROUND

Due to the inconsistent relationship between flow and function in PAD, novel techniques focused on the end-organ are needed to assess disease severity and measure therapeutic response.

METHODS

Fourteen normal subjects (5 men, age 45 +/- 14 years) and 20 patients with mild-to-moderate symptomatic PAD (12 men, age 67 +/- 10 years, mean ankle brachial index 0.62 +/- 0.13) were studied. Subjects exercised one leg to exhaustion while supine in a 1.5-T magnetic resonance scanner using a custom-built plantar flexion device. Surface coil-localized, free induction decay acquisition localized to the mid-calf was used. Each 31P spectrum consisted of 25 signal averages at a repetition time of 550 ms. The PCr recovery time constant was calculated by monoexponential fit of PCr versus time, beginning at exercise completion.

RESULTS

Median exercise time was 195.0 s in normal subjects and 162.5 s in PAD patients (p = 0.06). Despite shorter exercise times in patients, the median recovery time constant of PCr was 34.7 s in normal subjects and 91.0 s in PAD patients. Area under the receiver-operating characteristic curve was 0.925 +/- 0.045. Test-retest reliability was excellent.

CONCLUSIONS

The PCr recovery time constant is prolonged in patients with symptomatic PAD compared with normal subjects. The method is reproducible and may be useful in the identification of disease. Further study of this parameter's ability to track response to therapy as well as its prognostic capability is warranted.

Reproducibility and reliability of atherosclerotic plaque volume measurements in peripheral arterial disease with cardiovascular magnetic resonance

A high resolution, noninvasive approach to quantify atherosclerotic plaque in the peripheral vasculature could have significant clinical and research utility. Seventeen patients with peripheral arterial disease (PAD) were studied in a 1.5T CMR scanner. Atherosclerotic plaque volume in the superficial femoral artery was measured and interobserver, intraobserver, and test-retest variability determined. Nineteen vessels were studied with mean acquisition time of 13.1 minutes per vessel. Mean plaque volume was 7.27 +/- 3.73 cm3. Intra-observer intraclass correlation was R = 0.997, inter-observer was R = 0.987, and test-retest reproducibility was R = 0.996. Thus, high resolution measurement of plaque volume in PAD is reliable and reproducible.

The 1994 Northridge earthquake disaster response: the local emergency medical services agency experience

INTRODUCTION

This paper describes the 1994 Northridge earthquake experience of the local emergency medical services (EMS) agency. Discussed are means that should improve future local agency disaster responses.

METHODS

Data reported are descriptive and were collected from multiple independent sources, and can be reviewed publicly and confirmed. Validated data collected during the disaster by the Local EMS Agency also are reported.

RESULTS

The experience of the Los Angeles County EMS Agency was similar to that of earthquake disasters previously reported. Communication systems, water, food, shelter, sanitation means, power sources, and medical supplies were resources needed early in the disaster. Urban Search and Rescue Teams and Disaster Medical Assistance Teams were important elements in the response to the Northridge earthquake. The acute phase of the disaster ended within 48 to 72 hours and public health then became the predominant health-care issue. Locating community food and water supplies near shelters, providing transportation to medical care, and public-health visits to shelter locations helped prevent the development of long-term park encampments. An incident command system for the field, hospitals, and government responders was necessary for an organized response to the disaster.

CONCLUSION

Disaster preparedness, multiple forms of reliable communication, rapid mobilization of resources, and knowledge of available state and federal resources are necessary for a disaster response by a local EMS agency.

Magnetic resonance for the assessment of myocardial viability

PURPOSE OF REVIEW

Cardiac magnetic resonance imaging has an expanding role as a preferred modality for the detection and characterization of myocardial viability.

RECENT FINDINGS

Improving the accuracy of cardiac magnetic resonance for detecting viable myocardium has been one focus of investigators. In segments with intermediate transmurality of late gadolinium enhancement, dobutamine response improves the predictive power of cardiac magnetic resonance. A subtractive imaging technique with both short and long inversion times can enhance discrimination of subendocardial infarction and blood pool, but with increased noise and misregistration artifacts. Similar pharmacokinetics between cardiac magnetic resonance contrast agents and computed tomography contrast allows delayed enhancement imaging with computed tomography. Contrast between normal segments and scar remains vastly superior with cardiac magnetic resonance and no radiation is administered. Quantitation of blood flow demonstrated that resting myocardial blood flow is reduced in hibernating myocardium.

SUMMARY

Because of its safety, accuracy, ease of interpretation, and increasing availability, cardiac magnetic resonance-based assessment of myocardial viability has quickly transitioned from bench to bedside. Routine clinical implementation has prompted improved diagnostic capabilities and easier image interpretation. As a research tool, cardiac magnetic resonance continues to provide valuable insights into the fundamental nature of viability.

The prevalence of extracardiac findings by multidetector computed tomography before atrial fibrillation ablation

BACKGROUND AND OBJECTIVES

The study was designed to determine the prevalence of extracardiac findings discovered during multidetector computed tomography (CT) (MDCT) examinations before atrial fibrillation ablation. Multidetector CT has become a valuable tool in detailing left atrial anatomy before catheter ablation. The incidence of extracardiac findings has been reported for electron beam CT calcium scoring and coronary MDCT, but no data exist for the prevalence of extracardiac findings discovered before atrial fibrillation ablation with MDCT.

METHODS AND RESULTS

Clinical reports from MDCT examinations before atrial fibrillation ablation and interpretations by 2 radiologists blinded to the clinical reports were reviewed for significant additional extracardiac findings and recommendations for follow-up. In 149 patients who underwent MDCT, the mean age was 55.9 +/- 11.0 years, 75% were men, and 47% had a history of smoking. Extracardiac findings were identified in 69% of patients with clinical, 90% of reader 1, and 97% of reader 2 interpretations (kappa = 0.086). Follow-up was recommended in 30% of clinical, 50% of reader 1, and 38% of reader 2 interpretations (kappa = 0.408). Pulmonary nodules were the most common additional finding and reason for suggested follow-up for all interpreters.

CONCLUSIONS

The prevalence of extracardiac abnormalities detected by MDCT is considerable. Significant variability in their identification exists between interpreters, but there is good agreement about the need for further follow-up. It is important that those who interpret these examinations are adequately trained in the identification and interpretation of both cardiac and extracardiac findings.

Interaction between bradykinin subtype 2 and angiotensin II type 2 receptors during post-MI left ventricular remodeling

Angiotensin II type 2 receptor (AT2R) overexpression (AT2TG) attenuates left ventricular remodeling in a mouse model of anterior myocardial infarction (MI). We hypothesized that the beneficial effects of cardiac AT2TG are mediated via the bradykinin subtype 2 receptor (B2R). Fourteen transgenic mice overexpressing the AT2R (AT2TG mice), 10 mice with a B2R deletion (B2KO mice), 13 AT2TG mice with B2R deletion (AT2TG/B2KO mice), and 11 wild-type (WT) mice were studied. All mice were on a C57BL/6 background. Mice were studied by cardiac magnetic resonance imaging at baseline and days 1, 7, and 28 after MI induced by 1 h of occlusion of the left anterior descending artery followed by reperfusion. Short-axis images from apex to base were used to compare ventricular volumes and ejection fraction (EF). At baseline, end-diastolic volume index (EDVI) and end-systolic volume index (ESVI) were lower and EF higher in AT2TG mice compared with the other three strains. Infarct size was similar between groups. No differences were observed in global remodeling parameters at day 28 between AT2TG and AT2TG/B2KO mice; however, EDVI and ESVI were lower and EF higher in both transgenic groups than in WT or B2KO mice. Both strains lacking B2R demonstrated increased collagen content and less hypertrophy in adjacent noninfarcted regions at day 28. Attenuation of postinfarct remodeling by overexpression of AT2R is not directly mediated via a B2R pathway. However, B2R does appear to have a role in the smaller cavity size and hyperdynamic function observed at baseline in AT2TG mice and in limiting collagen deposition during postinfarct remodeling.

The Evolving Role of Cardiovascular Magnetic Resonance Imaging in Nonischemic Cardiomyopathy

Over the last several years, the role of cardiac magnetic resonance imaging in the diagnosis and management of heart failure has been rapidly expanding. The techniques unrivaled flexibility, accuracy in defining ventricular structure and function, and capacity to characterize tissue makes it particularly well suited for the study of the nonischemic cardiomyopathies. In this article, we provide an overview of the existing literature highlighting the diagnostic utility and prognostic power of cardiac magnetic resonance imaging in the nonischemic cardiomyopathies.

Can late gadolinium enhancement by cardiovascular magnetic resonance identify coronary artery disease as the etiology of new onset congestive heart failure?

BACKGROUND

New left ventricular systolic dysfunction affects 500,000 Americans and coronary artery disease (CAD) is responsible for two-thirds of cases. Identifying CAD has both prognostic and therapeutic implications. We evaluated the ability of late gadolinium enhancement (LGE) by cardiovascular magnetic resonance imaging (CMR) to detect CAD as the etiology of recent onset congestive heart failure (CHF).

METHODS

CMR and LGE were performed in 26 patients with new onset left ventricular systolic dysfunction. All patients received an x-ray angiography for identification of CAD. Patients with an acute coronary syndrome with troponin I > 1.0 ng/ml or a history of CAD were excluded. The presence and distribution of LGE was evaluated.

RESULTS

Significant coronary stenoses were present in 5 of 26 patients (19%). LGE in an infarct pattern was found in 2 of the 5 patients with CAD. Of the 21 patients without CAD, 2 had midwall enhancement but none had evidence of LGE in an infarct pattern.

CONCLUSIONS

When present, LGE in an infarct pattern suggests CAD as the etiology of new onset CHF. However, the absence of LGE does not exclude CAD as the underlying etiology. A small proportion of patients with a nonischemic cause of new onset CHF have LGE limited to the midwall.

The role of transesophageal echocardiography in atrial fibrillation

Transesophageal echocardiography (TEE) is very useful in the evaluation and management of selected patients with atrial fibrillation, primarily by clear visualization of left atrial appendage thrombus. Insights gained from two-dimensional and Doppler interrogation of the appendage include recognition of the association of dense spontaneous contrast and reduced mechanical appendage function with increased risk of thromboembolism. TEE-guided cardioversion has been shown to be safe and effective for a subset of patients, provided it is performed by experienced operators familiar with imaging the appendage and recognizing artifacts.

Reaction of neprilysin (neutral endopeptidase) and thermolysin with cyclic peptides

The reaction of neprilysin and thermolysin with a series of cyclic beta-turn peptides, varying in length from 6 to 14 residues, has been studied. All of the cyclic peptides bind to neprilysin with their affinity increasing from 113 microM for the 6-membered ring to 17 microM for the 14-membered ring. The 6-membered cyclic peptide was not hydrolyzed. However, kcat increased from 1.5 min-1 for the 8-membered cyclic peptide to 148 min-1 for the 14-membered cyclic peptide. With thermolysin binding of the 6- or 8-membered cyclic peptides was not detected. The Km values for the 10-, 12-, and 14-membered cyclic peptides were all in the 100 microM range. With thermolysin, kcat increased from 7 min-1 for the 10-membered cyclic peptide to 27,000 min-1 for the 14-membered cyclic peptide. Cyclic peptides were all cleaved at N-terminally directed sites. Modeling of the binding of a cyclic peptide, structurally similar to the 12-membered cyclic beta-turn peptide described above, into the active site of thermolysin shows that only half of the substrate makes contact with the enzyme and that only residues on one side of the peptide could fit into the active site. From these studies it is concluded that key factors which influence catalysis include not only peptide sequence, but the flexibility of the peptide and the orientation of the S'1 residue in a cyclic peptide.

Surgical intervention utilizing cardiopulmonary bypass for coronary unroofing of anomalous coronary artery

Coronary arteries originating from the opposite coronary cusp and crossing the path between the aorta and the pulmonary artery are associated with ischemia and sudden cardiac death. An increased prevalence of these cases may be attributed to diagnostic advances in computed tomographic angiography (CTA).

We report a retrospective review of ten patients referred for surgical intervention from March 2008 to present. Nine patients were diagnosed with right coronary arteries arising from the left coronary cusp and one patient with a left coronary artery arising from the right coronary cusp. Seven patients were male and the median age was 40 years (range, 21 to 51). Symptoms included atypical chest pain, tachy-arrythmias, diaphoresis, and dyspnea on exertion. CTA demonstrated anomalous coronary arteries arising from the opposite coronary cusp and traveling between the aorta and the pulmonary artery.

Surgical intervention was performed on all ten patients with no mortality and only one re-operation requiring bypass grafting. The sixth patient in the series had concomitant atherosclerotic disease, requiring left internal mammary artery grafting to the left anterior descending coronary artery. Cardiopulmonary bypass (CPB) was utilized with moderate hypothermia in all ten patients, with retrograde and/or coronary ostial cardioplegia administration. At routine surgical follow-up, all patients were without original presenting symptoms.

Patients with anomalous coronary arteries arising from the opposite coronary cusp are at risk of acute myocardial infarction and sudden cardiac death. Surgical unroofing is a viable option for this patient population and avoids coronary artery bypass grafting. Since March 2008, we have operated on ten patients presenting with this anomaly and have had excellent short-term results. Further long-term follow-up is necessary.