Jayanth R. Arnold

Relationship Between Regional Myocardial Oxygenation and Perfusion in Patients With Coronary Artery Disease Insights From Cardiovascular Magnetic Resonance and Positron Emission Tomography

Background—It is recognized that the interplay between myocardial ischemia, perfusion, and oxygenation in the setting of coronary artery disease (CAD) is complex and that myocardial oxygenation and perfusion may become dissociated. Blood oxygen level–dependent (BOLD) cardiovascular magnetic resonance (CMR) has the potential to noninvasively measure myocardial oxygenation, whereas positron emission tomography (PET) with oxygen-15 labeled water is the gold standard technique for myocardial blood flow quantification. Thus, we sought to apply BOLD CMR at 3 T and oxygen-15–labeled water PET in patients with CAD and normal volunteers to better understand the relationship between regional myocardial oxygenation and blood flow during vasodilator stress. Methods and Results—Twenty-two patients (age, 62±8 years; 16 men) with CAD (at least 1 stenosis ≥50% on quantitative coronary angiography) and 10 normal volunteers (age, 58±6 years; 6 men) underwent 3-T BOLD CMR and PET. For BOLD CMR, 4 to 6 midventricular short-axis images were acquired at rest and during adenosine stress (140 &mgr;g/kg/min). Using PET with oxygen-15–labeled water, myocardial blood flow was measured at baseline and during adenosine in the same slices. BOLD images were divided into 6 segments, and mean signal intensities calculated. Taking ≥50% stenosis on quantitative coronary angiography as the gold standard, cutoff values for stress myocardial blood flow (<2.45 mL/min/g; AUC, 0.83) and BOLD signal intensity change (<3.74%; AUC, 0.78) were determined to define ischemic segments. BOLD CMR and PET agreed on the presence or absence of ischemia in 18 of the 22 patients (82%) and in all normal subjects. On a per-segment analysis, 40% of myocardial segments with stress myocardial blood flow below the cutoff of 2.45 mL/min/g did not show deoxygenation, whereas 88% of segments with normal perfusion also had normal oxygenation measurements. Conclusions—Regional myocardial perfusion and oxygenation may be dissociated, indicating that in patients with CAD, reduced perfusion does not always lead to deoxygenation.

The role of Intravascular Ultrasound in the management of spontaneous coronary artery dissection

Primary or spontaneous coronary artery dissection (SCAD) is an unusual but increasingly recognized cause of acute myocardial ischemia and sudden cardiac death. Typically, SCAD presents in younger patients without conventional risk factors for coronary artery disease. It occurs more commonly in women than in men, and frequently during pregnancy or the postpartum period. Its pathophysiology is poorly understood, and there is considerable controversy regarding the optimal management of patients with SCAD-related myocardial ischemia. Therapeutic approaches include conservative medical therapy, coronary artery bypass graft surgery and percutaneous coronary intervention (PCI). We present four cases of SCAD to illustrate specific aspects of the presentation and management of this condition, with particular reference to the importance of intravascular ultrasound (IVUS) to aid diagnosis and guide subsequent PCI.

Myocardial Oxygenation in Coronary Artery Disease: Insights From Blood Oxygen Level–Dependent Magnetic Resonance Imaging at 3 Tesla

OBJECTIVES The purpose of this study was to assess the diagnostic accuracy of blood oxygen-level dependent (BOLD) MRI in suspected coronary artery disease (CAD). BACKGROUND By exploiting the paramagnetic properties of deoxyhemoglobin, BOLD magnetic resonance imaging can detect myocardial ischemia. We applied BOLD imaging and first-pass perfusion techniques to: 1) examine the pathophysiological relationship between coronary stenosis, perfusion, ventricular scar, and myocardial oxygenation; and 2) evaluate the diagnostic performance of BOLD imaging in the clinical setting. METHODS BOLD and first-pass perfusion images were acquired at rest and stress (4 to 5 min intravenous adenosine, 140 μg/kg/min) and assessed quantitatively (using a BOLD signal intensity index [stress/resting signal intensity], and absolute quantification of perfusion by model-independent deconvolution). A BOLD signal intensity index threshold to identify ischemic myocardium was first determined in a derivation arm (25 CAD patients and 20 healthy volunteers). To determine diagnostic performance, this was then applied in a separate group comprising 60 patients with suspected CAD referred for diagnostic angiography. RESULTS Prospective evaluation of BOLD imaging yielded an accuracy of 84%, a sensitivity of 92%, and a specificity of 72% for detecting myocardial ischemia and 86%, 92%, and 72%, respectively, for identifying significant coronary stenosis. Segment-based analysis revealed evidence of dissociation between oxygenation and perfusion (r = -0.26), with a weaker correlation of quantitative coronary angiography with myocardial oxygenation (r = -0.20) than with perfusion (r = -0.40; p = 0.005 for difference). Hypertension increased the odds of an abnormal BOLD response, but diabetes mellitus, hypercholesterolemia, and the presence of ventricular scar were not associated with significant deoxygenation. CONCLUSIONS BOLD imaging provides valuable insights into the pathophysiology of CAD; myocardial hypoperfusion is not necessarily commensurate with deoxygenation. In the clinical setting, BOLD imaging achieves favorable accuracy for identifying the anatomic and functional significance of CAD.

Patients with syndrome X have normal transmural myocardial perfusion and oxygenation: a 3-T cardiovascular magnetic resonance imaging study.

Background— The pathophysiology of chest pain in patients with cardiac syndrome X remains controversial. Advances in perfusion imaging with cardiovascular magnetic resonance (CMR) now enable absolute quantification of regional myocardial blood flow (MBF). Furthermore, blood oxygen level-dependent (BOLD) or oxygenation-sensitive CMR provides the unprecedented capability to assess regional myocardial oxygenation. We hypothesized that the combined assessment of regional perfusion and oxygenation with CMR could clarify whether patients with syndrome X show evidence of myocardial ischemia (reduced perfusion and oxygenation) during vasodilator stress compared with normal volunteers. Methods and Results— Eighteen patients with syndrome X (chest pain, abnormal exercise treadmill test, normal coronary angiogram without other causes of microvascular dysfunction) and 14 controls underwent CMR scanning at 3 T. Myocardial function, scar, perfusion (2–3 short-axis slices), and oxygenation were assessed. Absolute MBF was measured during adenosine stress (140 &mgr;g/kg per minute) and at rest by model-independent deconvolution. For oxygenation, using a T2-prepared BOLD sequence, signal intensity was measured at adenosine stress and rest in the slice matched to the midventricular slice of the perfusion scan. There were no significant differences in MBF at stress (2.35 versus 2.37 mL/min per gram; P=0.91), BOLD signal change (17.3% versus 17.09%; P=0.91), and coronary flow reserve measurements (2.63 versus 2.53; P=0.60) in patients with syndrome X and controls, respectively. Oxygenation and perfusion measurements per coronary territory were also similar between the 2 groups. More patients with syndrome X (17/18 [94%]) developed chest pain during adenosine stress than controls (6/14 [43%]; P=0.004). Conclusions— Patients with syndrome X show greater sensitivity to chest pain compared with controls but no evidence of deoxygenation or hypoperfusion during vasodilatory stress.Background— The pathophysiology of chest pain in patients with cardiac syndrome X remains controversial. Advances in perfusion imaging with cardiovascular magnetic resonance (CMR) now enable absolute quantification of regional myocardial blood flow (MBF). Furthermore, blood oxygen level-dependent (BOLD) or oxygenation-sensitive CMR provides the unprecedented capability to assess regional myocardial oxygenation. We hypothesized that the combined assessment of regional perfusion and oxygenation with CMR could clarify whether patients with syndrome X show evidence of myocardial ischemia (reduced perfusion and oxygenation) during vasodilator stress compared with normal volunteers. Methods and Results— Eighteen patients with syndrome X (chest pain, abnormal exercise treadmill test, normal coronary angiogram without other causes of microvascular dysfunction) and 14 controls underwent CMR scanning at 3 T. Myocardial function, scar, perfusion (2–3 short-axis slices), and oxygenation were assessed. Absolute MBF was measured during adenosine stress (140 μg/kg per minute) and at rest by model-independent deconvolution. For oxygenation, using a T2-prepared BOLD sequence, signal intensity was measured at adenosine stress and rest in the slice matched to the midventricular slice of the perfusion scan. There were no significant differences in MBF at stress (2.35 versus 2.37 mL/min per gram; P =0.91), BOLD signal change (17.3% versus 17.09%; P =0.91), and coronary flow reserve measurements (2.63 versus 2.53; P =0.60) in patients with syndrome X and controls, respectively. Oxygenation and perfusion measurements per coronary territory were also similar between the 2 groups. More patients with syndrome X (17/18 [94%]) developed chest pain during adenosine stress than controls (6/14 [43%]; P =0.004). Conclusions— Patients with syndrome X show greater sensitivity to chest pain compared with controls but no evidence of deoxygenation or hypoperfusion during vasodilatory stress.

Early Diagnosis of Perioperative Myocardial Infarction After Coronary Bypass Grafting: A Study Using Biomarkers and Cardiac Magnetic Resonance Imaging

BACKGROUND Myocardial injury related to coronary artery bypass grafting (CABG) is poorly characterized, and understanding the characteristic release of biomarkers associated with revascularization injury might provide novel therapeutic opportunities. This study characterized early changes in biomarkers after revascularization injury during on-pump CABG. METHODS This prospective study comprised 28 patients undergoing on-pump CABG and late gadolinium enhancement (LGE) cardiac magnetic resonance imaging (CMRI) who underwent measurements of cardiac troponin I (cTnI), creatine kinase-MB, and inflammatory markers (C-reactive protein, serum amyloid A, myeloperoxidase, interleukin 6, tumor necrosis factor-α, matrix metalloproteinase 9a, monocyte chemotactic protein-1, plasminogen activator inhibitor-1a) at baseline, at 1, 6, 12, and 24 hours, and at 1 week (inflammatory markers only) post-CABG. Biomarker results at 1 hour were studied for a relationship to new myocardial infarction as defined by CMRI-LGE, and the diagnostic utility of combining positive biomarkers was assessed. RESULTS All patients had an uneventful recovery, but 9 showed a new myocardial infarction demonstrated by new areas of hyperenhancement on CMR. Peak cTnI at 24 hours (ρ = 0.66, p < 0.001) and CK-MB (ρ = 0.66, p < 0.001) correlated with the amount of new LGE. At 1 hour, 3 biomarkers--cTnI, interleukin 6, and tumor necrosis factor-α--were significantly elevated in patients with vs those without new LGE. Receiver operating curve analysis showed cTnI was the most accurate at detecting new LGE at 1 hour: a cutoff of cTnI exceeding 5 μg/L at 1 hour had 67% sensitivity and 79% specificity for detecting new LGE. CONCLUSIONS Unexpected CABG-related myocardial injury occurs in a significant proportion of patients. A cTnI test at 1 hour after CABG could potentially differentiate patients with significant revascularization injury.

Left ventricular lipomatous metaplasia following myocardial infarction

We present 3 cases of left ventricular lipomatous metaplasia after myocardial infarction evaluated with cardiovascular magnetic resonance (CMR). Delayed enhancement CMR alone cannot differentiate lipomatous metaplasia from scar. T1-weighted images with and without fat suppression are needed to identify this condition. The aetiology, pathophysiology, and possible clinical significance of lipomatous metaplasia in infarcted myocardium are still unknown. The multi-parametric capabilities of CMR make it the ideal modality to identify non-invasively, and without exposure to radiation, individuals with lipomatous metaplasia.

Residual Ischemia After Revascularization in Multivessel Coronary Artery Disease Insights From Measurement of Absolute Myocardial Blood Flow Using Magnetic Resonance Imaging Compared With Angiographic Assessment

Background—Revascularization strategies for multivessel coronary artery disease include percutaneous coronary intervention and coronary artery bypass grafting. In this study, we compared the completeness of revascularization as assessed by coronary angiography and by quantitative serial perfusion imaging using cardiovascular magnetic resonance. Methods and Results—Patients with multivessel coronary disease were recruited into a randomized trial of treatment with either coronary artery bypass grafting or percutaneous coronary intervention. Angiographic disease burden was determined by the Bypass Angioplasty Revascularization Investigation (BARI) myocardial jeopardy index. Cardiovascular magnetic resonance first-pass perfusion imaging was performed before and 5 to 6 months after revascularization. Using model-independent deconvolution, hyperemic myocardial blood flow was evaluated, and ischemic burden was quantified. Sixty-seven patients completed follow-up (33 coronary artery bypass grafting and 34 percutaneous coronary intervention). The myocardial jeopardy index was 80.7±15.2% at baseline and 6.9±11.3% after revascularization (P<0.0001), with revascularization deemed complete in 62.7% of patients. Relative to cardiovascular magnetic resonance, angiographic assessment overestimated disease burden at baseline (80.7±15.2% versus 49.9±29.2% [P<0.0001]), but underestimated it postprocedure (6.9±11.3% versus 28.1±33.4% [P<0.0001]). Fewer patients achieved complete revascularization based on functional criteria than on angiographic assessment (38.8% versus 62.7%; P=0.015). After revascularization, hyperemic myocardial blood flow was significantly higher in segments supplied by arterial bypass grafts than those supplied by venous grafts (2.04±0.82 mL/min per gram versus 1.89±0.81 mL/min per gram, respectively; P=0.04). Conclusions—Angiographic assessment may overestimate disease burden before revascularization, and underestimate residual ischemia after revascularization. Functional data demonstrate that a significant burden of ischemia remains even after angiographically defined successful revascularization. Clinical Trial Registration—URL:http://www.controlled-trials.com. Unique identifier:ISRCTN25699844.

Systemic levels of endothelin correlate with systemic inflammation and not with myocardial injury or left ventricular ejection fraction in patients undergoing percutaneous coronary intervention and on-pump coronary artery bypass grafting☆

Endothelin (ET-1) is a potent vasoconstrictor. We compared patterns of ET-1 in percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) and correlated it with markers of inflammation. Patients with multivessel disease were enrolled in a prospective randomized study of PCI vs. on-pump CABG. Procedural myocardial injury was assessed biochemically (CK-MB) and with new late gadolinium enhancement (LGE) on magnetic resonance imaging (MRI) one week postprocedure. ET-1 was measured at baseline, 1 h, 6 h, 12 h, 24 h and one week postprocedure. Log ET-1 values were compared between PCI and CABG and between patients without significant myocardial injury. Measurement of ET-1 values was performed in 36 PCI and 31 CABG patients. Baseline ET-1 values were similar between PCI and CABG patients (0.91 ± 0.36 vs. 1.0 ± 49 pg/ml, P = 0.38). Peak values were reached at 1 h in PCI and at 24 h in CABG patients and patients undergoing CABG had significantly higher log ET-1 values at 6 h, 12 h and 24 h. ET-1 did not correlate with biochemical or morphological markers of myocardial injury or change of left ventricular ejection fraction (LV-EF) but good linear correlation between max logET-1 and max logCRP was found (r = 0.44, P = 0.0002). ET-1 rise is more pronounced in on-pump CABG and ET-1 production could be driven by periprocedural inflammatory reaction.

Myocardial perfusion imaging after coronary artery bypass surgery using cardiovascular magnetic resonance: a validation study.

Background— Absolute quantification of perfusion with cardiovascular magnetic resonance has not previously been applied in patients with coronary artery bypass grafting (CABG). Owing to increased contrast bolus dispersion due to the greater distance of travel through a bypass graft, this approach may result in systematic underestimation of myocardial blood flow (MBF). As resting MBF remains normal in segments supplied by noncritical coronary stenosis (<85%), measurement of perfusion in such territories may be utilized to reveal systematic error in the quantification of MBF. The objective of this study was to test whether absolute quantification of perfusion with cardiovascular magnetic resonance systematically underestimates MBF in segments subtended by bypass grafts. Methods and Results— The study population comprised 28 patients undergoing elective CABG for treatment of multivessel coronary artery disease. Eligible patients had angiographic evidence of at least 1 myocardial segment subtended by a noncritically stenosed coronary artery (<85%). Subjects were studied at 1.5 T, with evaluation of resting MBF using model-independent deconvolution. Analyses were confined to myocardial segments subtended by native coronary arteries with <85% stenosis at baseline, and MBF was compared in grafted and ungrafted segments before and after revascularization. A total of 249 segments were subtended by coronary arteries with <85% stenosis at baseline. After revascularization, there was no significant difference in MBF in ungrafted (0.82±0.19 mL/min/g) versus grafted segments (0.82±0.15 mL/min/g, P=0.57). In the latter, MBF after revascularization did not change significantly from baseline (0.86±0.20 mL/min/g, P=0.82). Conclusions— Model-independent deconvolution analysis does not systematically underestimate blood flow in graft-subtended territories, justifying the use of this methodology to evaluate myocardial perfusion in patients with CABG.

Diabetic cardiomyopathy: a controversial entity

We read with interest the study by Konduracka et al. , 1 which concludes that patients with long-term type 1 diabetes mellitus under intensive insulin treatment do not have echocardiographic, biochemical, or morphological signs of diabetic cardiomyopathy. However, as the authors admit, this is directly opposed to several previous studies which clearly show the presence of myocardial diastolic dysfunction in patients with type 1 diabetes, when compared with control subjects.2–4 Importantly, like Konduracka et al. , these studies excluded patients with coronary artery disease and hypertension. These co-morbidities may themselves result in diastolic impairment, thus precluding any firm conclusions …