Introducing a free-breathing MRI method to assess peri-operative myocardial oxygenation and function: A volunteer cohort study

BACKGROUND

Induction of general anaesthesia has many potential triggers for peri-operative myocardial ischaemia including the acute disturbance of blood gases that frequently follows alterations in breathing and ventilation patterns. Free-breathing oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) imaging may provide the opportunity to continuously quantify the impact of such triggers on myocardial oxygenation.

OBJECTIVE

To investigate the impact of breathing patterns that simulate induction of general anaesthesia on myocardial oxygenation in awake healthy adults using continuous OS-CMR imaging.

DESIGN

Prospective observational study.

SETTING

Single-centre university hospital. Recruitment from August 2020 to January 2022.

PARTICIPANTS

Thirty-two healthy volunteers younger than 45 years old were recruited. Data were analysed from n = 29 (69% male individuals).

INTERVENTION

Participants performed a simulated induction breathing manoeuvre consisting of 2.5 min paced breathing with a respiration rate of 14 breaths per minute, followed by 5 deep breaths, then apnoea for up to 60s inside a magnetic resonance imaging scanner (MRI). Cardiac images were acquired with the traditional OS-CMR sequence (OSbh-cine), which requires apnoea for acquisition and with two free-breathing OS-CMR sequences: a high-resolution single-shot sequence (OSfb-ss) and a real-time cine sequence (OSfb-rtcine).

MAIN OUTCOME MEASURES

Myocardial oxygenation response at the end of the paced breathing period and at the 30 s timepoint during the subsequent apnoea, reflecting the time of successful intubation in a clinical setting.

RESULTS

The paced breathing followed by five deep breaths significantly reduced myocardial oxygenation, which was observed with all three techniques (OSbh-cine -6.0 ± 2.6%, OSfb-ss -12.0 ± 5.9%, OSfb-rtcine -5.4 ± 7.0%, all P < 0.05). The subsequent vasodilating stimulus of apnoea then significantly increased myocardial oxygenation (OSbh-cine 6.8 ± 3.1%, OSfb-ss 8.4 ± 5.6%, OSfb-rtcine 15.7 ± 10.0%, all P < 0.01). The free-breathing sequences were reproducible and were not inferior to the original sequence for any stage.

CONCLUSION

Breathing manoeuvres simulating induction of general anaesthesia cause dynamic alterations of myocardial oxygenation in young volunteers, which can be quantified continuously with free-breathing OS-CMR. Introducing these new imaging techniques into peri-operative studies may throw new light into the mechanisms of peri-operative perturbations of myocardial tissue oxygenation and ischaemia.

VISUALABSTRACT

http://links.lww.com/EJA/A922.

[Oxygenation-sensitive cardiac magnetic resonance imaging]

BACKGROUND

Oxygenation-sensitive cardiac magnetic resonance imaging (OS-CMR) is an evolving cardiac imaging technique offering new perspectives to understand, predict, and diagnose cardiac pathologies.

OBJECTIVES

To provide an overview of the basic principles of OS-CMR, the current diagnostic applications and how it may aid in future diagnostic challenges.

MATERIALS AND METHODS

Description, analysis, and interpretation of the current literature on basic research and applicational studies in both humans and animals assessing OS-CMR.

RESULTS

OS-CMR is based on the paramagnetic properties of deoxygenated hemoglobin, which is visualized by a T2*-sensitive sequence. The measured signal correlates with the oxygenation of the myocardium and can analyze vascular function during pharmacological vasodilation or vasoactive breathing exercises (hyperventilation, apnea). The herewith triggered changes in myocardial oxygenation and oxygenation reserve can be used to identify relevant stenoses in coronary artery disease. Other areas of application involve myocardial hypertrophy, microvascular dysfunction, and pulmonary hypertension.

CONCLUSION

A broad number of applications for the clinical use of OS-CMR exist so far, especially in combination with breathing exercises. OS-CMR can be conducted medication- and needle-free. Limitations involve the current lack of clinically approved, automated evaluation tools and the unavailability of vendor- and site-independent normal values.

Combined Analysis of Myocardial Deformation and Oxygenation Detects Inducible Ischemia Unmasked by Breathing Maneuvers in Chronic Coronary Syndrome

Introduction

In patients with chronic coronary syndromes, hyperventilation followed by apnea has been shown to unmask myocardium susceptible to inducible deoxygenation. The aim of this study was to assess whether such a provoked response is co-localized with myocardial dysfunction.

Methods

A group of twenty-six CAD patients with a defined stenosis (quantitative coronary angiography > 50%) underwent a cardiovascular magnetic resonance (CMR) exam prior to revascularization. Healthy volunteers older than 50 years served as controls (n = 12). Participants hyperventilated for 60s followed by brief apnea. Oxygenation-sensitive images were analyzed for changes in myocardial oxygenation and strain.

Results

In healthy subjects, hyperventilation resulted in global myocardial deoxygenation (-10.2 ± 8.2%, p < 0.001) and augmented peak circumferential systolic strain (-3.3 ± 1.6%, p < 0.001). At the end of apnea, myocardial signal intensity had increased (+9.1 ± 5.3%, p < 0.001) and strain had normalized to baseline. CAD patients had a similar global oxygenation response to hyperventilation (−5.8 ± 9.6%, p = 0.085) but showed no change in peak strain from their resting state (-1.3 ± 1.6%), which was significantly attenuated in comparison the strain response observed in controls (p = 0.008). With apnea, the CAD patients showed an attenuated global oxygenation response to apnea compared to controls (+2.7 ± 6.2%, p < 0.001). This was accompanied by a significant depression of peak strain (3.0 ± 1.7%, p < 0.001), which also differed from the control response (p = 0.025). Regional analysis demonstrated that post-stenotic myocardium was most susceptible to de-oxygenation and systolic strain abnormalities during respiratory maneuvers. CMR measures at rest were unable to discriminate post-stenotic territory (p > 0.05), yet this was significant for both myocardial oxygenation [area under the curve (AUC): 0.88, p > 0.001] and peak strain (AUC: 0.73, p = 0.023) measured with apnea. A combined analysis of myocardial oxygenation and peak strain resulted in an incrementally higher AUC of 0.91, p < 0.001 than strain alone.

Conclusion

In myocardium of patients with chronic coronary syndromes and primarily intermediate coronary stenoses, cine oxygenation-sensitive CMR can identify an impaired vascular and functional response to a vasoactive breathing maneuver stimulus indicative of inducible ischemia.

The Potential of Oxygenation-Sensitive CMR in Heart Failure

PURPOSE OF REVIEW

Cardiac magnetic resonance imaging (CMR) use in the context of heart failure (HF) has increased over the last decade as it is able to provide detailed, quantitative information on function, morphology, and myocardial tissue composition. Furthermore, oxygenation-sensitive CMR (OS-CMR) has emerged as a CMR imaging method capable of monitoring changes of myocardial oxygenation without the use of exogenous contrast agents.

RECENT FINDINGS

The contributions of OS-CMR to the investigation of patients with HF includes not only a fully quantitative assessment of cardiac morphology, function, and tissue characteristics, but also high-resolution information on both endothelium-dependent and endothelium-independent vascular function as assessed through changes of myocardial oxygenation. In patients with heart failure, OS-CMR can provide deep phenotyping on the status and important associated pathophysiology as a one-stop, needle-free diagnostic imaging test.

The blood oxygen level dependent (BOLD) effect of in-vitro myoglobin and hemoglobin

The presence of deoxygenated hemoglobin (Hb) results in a drop in T2 and T2* in magnetic resonance imaging (MRI), known as the blood oxygenation level-dependent (BOLD-)effect. The purpose of this study was to investigate if deoxygenated myoglobin (Mb) exerts a BOLD-like effect. Equine Met-Mb powder was dissolved and converted to oxygenated Mb. T1, T2, T2*-maps and BOLD-bSSFP images at 3Tesla were used to scan 22 Mb samples and 12 Hb samples at room air, deoxygenation, reoxygenation and after chemical reduction. In Mb, T2 and T2* mapping showed a significant decrease after deoxygenation (- 25% and - 12%, p < 0.01), increase after subsequent reoxygenation (+ 17% and 0% vs. room air, p < 0.01), and finally a decrease in T2 after chemical reduction (- 28%, p < 0.01). An opposite trend was observed with T1 for each stage, while chemical reduction reduced BOLD-bSSFP signal (- 3%, p < 0.01). Similar deflections were seen at oxygenation changes in Hb. The T1 changes suggests that the oxygen content has been changed in the specimen. The shortening of transverse relaxation times in T2 and T2*-mapping after deoxygenation in Mb specimens are highly indicative of a BOLD-like effect.

Increased oxygenation is associated with myocardial inflammation and adverse regional remodeling after acute ST-segment elevation myocardial infarction

OBJECTIVES

To explore the relationships between oxygenation signal intensity (SI) with myocardial inflammation and regional left ventricular (LV) remodeling in reperfused acute ST-segment elevation myocardial infarction (STEMI) using oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR).

METHODS

Thirty-three STEMI patients and 22 age- and sex-matched healthy volunteers underwent CMR. The protocol included cine function, OS imaging, precontrast T1 mapping, T2 mapping, and late gadolinium enhancement (LGE) imaging. A total of 880 LV segments were included for analysis based on the American Heart Association 16-segment model. For validation, 15 pigs (10 myocardial infarction (MI) model animals and 5 controls) received CMR and were sacrificed for immunohistochemical analysis.

RESULTS

In the patient study, the acute oxygenation SI showed a stepwise rise among remote, salvaged, and infarcted segments compared with healthy myocardium. At convalescence, all oxygenation SI values besides those in infarcted segments with microvascular obstruction decreased to similar levels. Acute oxygenation SI was associated with early myocardial injury (T1: r = 0.38; T2: r = 0.41; all p < 0.05). Segments with higher acute oxygenation SI values exhibited thinner diastolic walls and decreased wall thickening during follow-up. Multivariable regression modeling indicated that acute oxygenation SI (β = 2.66; p < 0.05) independently predicted convalescent segment adverse remodeling (LV wall thinning). In the animal study, alterations in oxygenation SI were correlated with histological inflammatory infiltrates (r = 0.59; p < 0.001).

CONCLUSIONS

Myocardial oxygenation by OS-CMR could be used as a quantitative imaging biomarker to assess myocardial inflammation and predict convalescent segment adverse remodeling after STEMI.

KEY POINTS

• Oxygenation signal intensity (SI) may be an imaging biomarker of inflammatory infiltration that could be used to assess the response to anti-inflammatory therapies in the future. • Oxygenation SI early after myocardial infarction (MI) was associated with left ventricular segment injury at acute phase and could predict regional functional recovery and adverse remodeling late after acute MI. • Oxygenation SI demonstrated a stepwise increase among remote, salvaged, and infarcted segments. Infarcted zones with microvascular obstruction demonstrated a higher oxygenation SI than those without. However, the former showed less pronounced changes over time.

Cardiovascular risk is associated with a transmural gradient of myocardial oxygenation during adenosine infusion

AIMS

In patients with coronary artery disease (CAD), a transmural gradient of myocardial perfusion has been repeatedly observed, with the subendocardial layer showing more pronounced perfusion deficits. Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) allows for monitoring transmural changes of myocardial oxygenation in vivo. We hypothesized that OS-CMR could help identify a transmural oxygenation gradient as a disease marker in patients at risk for CAD.

METHODS AND RESULTS

We assessed 34 patients with known CAD and 28 subjects with coronary risk factors but no evidence of significant CAD. Results were compared with 11 healthy volunteers. OS-CMR was performed at 1.5 T, applying a T2*-weighted cine steady state free precession sequence at baseline and during infusion of adenosine. A reader blinded to patient data quantified the relative change of myocardial oxygenation in OS-CMR, defined by the change of signal intensity (ΔSI%) between baseline and during adenosine infusion in the entire myocardium, the subepicardial layer, and the subendocardial layer. SI changes were homogenous throughout the myocardium in healthy subjects, whereas both, patients with risk factors only and patients with CAD, had a significantly smaller ΔSI% in the subendocardial layer than in the subendocardial layer. Both patient groups had an overall decreased ΔSI% across all layers when compared with healthy subjects (P < 0.05).

CONCLUSION

Even in the absence of overt CAD, cardiovascular risk factors are associated with a transmural gradient of the myocardial oxygenation response to adenosine as assessed by OS-CMR. An inducible transmural oxygenation gradient may serve as a non-invasive marker for cardiovascular risk.

Role of Cardiovascular Magnetic Resonance in Ischemic Cardiomyopathy

Ischemic heart disease is the most common cause of cardiovascular morbidity and mortality. Cardiac magnetic resonance (CMR) improves on other noninvasive modalities in detection, assessment, and prognostication of ischemic heart disease. The incorporation of CMR in clinical trials allows for smaller patient samples without the sacrifice of power needed to demonstrate clinical efficacy. CMR can accurately quantify infarct acuity, size, and complications; guide therapy; and prognosticate recovery. Timing of revascularization remains the holy grail of ischemic heart disease, and viability assessment using CMR may be the missing link needed to help reduce morbidity and mortality associated with the disease.

Diagnostic Accuracy of Cardiac Magnetic Resonance Versus Fractional Flow Reserve: A Systematic Review and Meta-Analysis

Background

Fractional flow reserve (FFR) is considered the gold standard for diagnosis of coronary artery disease (CAD). Stress Cardiac magnetic resonance (SCMR) has been recently gaining traction as a non-invasive alternative to FFR.

Methods

Studies comparing the diagnostic accuracy of SCMR versus FFR were identified and analyzed using Review Manager (RevMan) 5.3 and Stata software.

Results

A total of 28 studies, comprising 2,387 patients, were included. The pooled sensitivity and specificity for SCMR were 86% and 86% at the patient level, and 82% and 88% at the vessel level, respectively. When the patient-level data were stratified based on the FFR thresholds, higher sensitivity and specificity (both 90%) were noted with the higher cutoff (0.75) and lower cutoff (0.8), respectively. At the vessel level, sensitivity and specificity at the lower FFR threshold were significantly higher at 88% and 89%, compared to the corresponding values for higher cutoff at 0.75. Similarly, meta-regression analysis of SCMR at higher (3T) resolution showed a higher sensitivity of 87% at the patient level and higher specificity of 90% at the vessel level. The highest sensitivity and specificity of SCMR (92% and 94%, respectively) were noted in studies with CAD prevalence greater than 60%.

Conclusions

SCMR has high diagnostic accuracy for CAD comparable to FFR at a spatial resolution of 3T and an FFR cut-off of 0.80. An increase in CAD prevalence further improved the specificity of SCMR.

Quantitative flow ratio-guided surgical intervention in symptomatic myocardial bridging

BACKGROUND

Patients with myocardial bridging (MB) are associated with adverse cardiovascular events, but a decision to perform surgical intervention, especially for patients with systolic intermediate stenosis, is a difficult clinical issue. Fractional flow reserve (FFR) represents a novel method for the functional evaluation of coronary stenosis, but the relationship between FFR and MB remains controversial because of the cyclic dynamic stenosis of MB. Quantitative flow ratio (QFR) is a novel index allowing fast assessment of FFR from a diagnostic coronary angiography. This study aimed to investigate the relationship between QFR and MB patients and to further develop a prediction model of QFR-guided surgical intervention for these patients.

METHODS

Forty-five symptomatic lone MB patients who had undergone coronary angiography were consecutively enrolled in this study. MB was located in the middle of left anterior descending artery with intermediate stenosis during systole. The patients were retrospectively divided into a medical therapy group or a surgical therapy group. Systolic geometry based QFR (SG-QFR) and diastolic geometry based QFR (DG-QFR) were calculated based on three-dimensional quantitative coronary angiography and patient-specific flow velocity. Subsequently, time-averaged QFR (TA-QFR) is defined as the average of SG-QFR and DG-QFR.

RESULTS

Receiver operating characteristic curve analysis revealed that TA-QFR (AUC = 0.91; 95% CI: 0.79-0.98) was found to be the best pre-operative index for surgical intervention to MB, when compared with DG-QFR (AUC = 0.69; 95% CI: 0.53-0.82; difference: 0.22; 95% CI: 0.04-0.41; p = 0.02) and SG-QFR (AUC = 0.87; 95% CI: 0.74-0.95; difference: 0.04; 95% CI: 0.00-0.08; p = 0.03).

CONCLUSIONS

TA-QFR improved the performance of functional evaluation in MB patients with intermediate stenosis during systole and is useful for guiding surgical intervention.

Relationship between myocardial oxygenation and blood pressure: Experimental validation using oxygenation-sensitive cardiovascular magnetic resonance

Background

The relationship between mean arterial pressure (MAP) and coronary blood flow is well described. There is autoregulation within a MAP range of 60 to 140 mmHg providing near constant coronary blood flow. Outside these limits flow becomes pressure-dependent. So far, response of myocardial oxygenation to changes in pressure and flow has been more difficult to assess. While established techniques mostly require invasive approaches, Oxygenation-Sensitive (OS) Cardiovascular Magnetic Resonance (CMR) is a technique that can non-invasively assess changes in myocardial tissue oxygenation. The purpose of this study was to follow myocardial oxygenation over a wide range of blood pressure variation within and outside known coronary autoregulatory limits using OS-CMR, and to relate these data to coronary hemodynamics.

Methods

Ten anaesthetized swine (German Large White) underwent left-sided thoracotomy and attachment of a perivascular flow probe to the proximal left anterior descending (LAD) coronary artery for continuous measurement of blood flow (Q_LAD). Thereafter, animals were transferred into a 3T MRI scanner. Mean arterial pressure (MAP) was varied in 10–15 mmHg steps by administering alpha₁-receptor agents phenylephrine or urapidil. For each MAP level, OS-CMR images as well as arterial and coronary sinus blood gas samples were obtained simultaneously during brief periods of apnea. Relative changes (Δ) of coronary sinus oxygen saturation (ScsO₂), oxygen delivery (DO₂) and demand (MVO₂), extraction ratio (O₂ER) and excess (Ω) from respective reference levels at a MAP of 70 mmHg were determined and were compared to %change in OS-signal intensity (OS-SI) in simultaneously acquired OS-CMR images.

Results

Q_LAD response indicated autoregulation between MAP levels of 52 mmHg (lower limit) and127 mmHg (upper limit). OS-CMR revealed a global myocardial oxygenation deficit occurring below the lower autoregulation limit, with the nadir of OS-SI at -9.0%. With MAP values surpassing 70 mmHg, relative OS-SI increased to a maximum of +10.6%. Consistent with this, ΔScsO₂, ΔDO₂, ΔMVO₂, ΔO₂ER and ΔΩ responses indicated increasing mismatch of oxygenation balance outside the autoregulated zone. Changes in global OS-CMR were significantly correlated with all of these parameters (p≤0.02) except with ΔMVO₂.

Conclusion

OS-CMR offers a novel and non-invasive route to evaluate the effects of blood pressure variations, as well as of cardiovascular drugs and interventions, on global and regional myocardial oxygenation, as demonstrated in a porcine model. OS-CMR identified mismatch of O₂ supply and demand below the lower limit of coronary autoregulation. Vasopressor induced acute hypertension did not compromise myocardial oxygenation in healthy hearts despite increased cardiac workload and O₂ demand. The clinical usefulness of OS-CMR remains to be established.

Feasibility of cardiovascular magnetic resonance to detect oxygenation deficits in patients with multi-vessel coronary artery disease triggered by breathing maneuvers

BACKGROUND

Hyperventilation with a subsequent breath-hold has been successfully used as a non-pharmacological vasoactive stimulus to induce changes in myocardial oxygenation. The purpose of this pilot study was to assess if this maneuver is feasible in patients with multi-vessel coronary artery disease (CAD), and if it is effective at detecting coronary artery stenosis > 50% determined by quantitative coronary angiography (QCA).

METHODS

Twenty-six patients with coronary artery stenosis (QCA > 50% diameter stenosis) underwent a contrast-free cardiovascular magnetic resonance (CMR) exam in the time interval between their primary coronary angiography and a subsequent percutaneous coronary intervention (PCI, n = 24) or coronary artery bypass (CABG, n = 2) revascularization procedure. The CMR exam involved standard function imaging, myocardial strain analysis, T2 mapping, native T1 mapping and oxygenation-sensitive CMR (OS-CMR) imaging. During OS-CMR, participants performed a paced hyperventilation for 60s followed by a breath-hold to induce a vasoactive stimulus. Ten healthy subjects underwent the CMR protocol as the control group.

RESULTS

All CAD patients completed the breathing maneuvers with an average breath-hold duration of 48 ± 23 s following hyperventilation and without any complications or adverse effects. In comparison to healthy subjects, CAD patients had a significantly attenuated global myocardial oxygenation response to both hyperventilation (- 9.6 ± 6.8% vs. -3.1 ± 6.5%, p = 0.012) and apnea (11.3 ± 6.1% vs. 2.1 ± 4.4%, p < 0.001). The breath-hold maneuver unmasked regional oxygenation differences in territories subtended by a stenotic coronary artery in comparison to remote territory within the same patient (0.5 ± 3.8 vs. 3.8 ± 5.3%, p = 0.011).

CONCLUSION

Breathing maneuvers in conjunction with OS-CMR are clinically feasible in CAD patients. Furthermore, OS-CMR demonstrates myocardial oxygenation abnormalities in regional myocardium related to CAD without the use of pharmacologic vasodilators or contrast agents. A larger trial appears warranted for a better understanding of its diagnostic utility.

TRIAL REGISTRATION

Clinical Trials Identifier: NCT02233634 , registered 8 September 2014.

The impact of hematocrit on oxygenation-sensitive cardiovascular magnetic resonance

BACKGROUND

Oxygenation-sensitive (OS) Cardiovascular Magnetic Resonance (CMR) is a promising utility in the diagnosis of heart disease. Contrast in OS-CMR images is generated through deoxyhemoglobin in the tissue, which is negatively correlated with the signal intensity (SI). Thus, changing hematocrit levels may be a confounder in the interpretation of OS-CMR results. We hypothesized that hemodilution confounds the observed signal intensity in OS-CMR images.

METHODS

Venous and arterial blood from five pigs was diluted with lactated Ringer solution in 10 % increments to 50 %. The changes in signal intensity (SI) were compared to changes in blood gases and hemoglobin concentration. We performed an OS-CMR scan in 21 healthy volunteers using vasoactive breathing stimuli at baseline, which was then repeated after rapid infusion of 1 L of lactated Ringer's solution within 5-8 min. Changes of SI were measured and compared between the hydration states.

RESULTS

The % change in SI from baseline for arterial (r = -0.67, p < 0.0001) and venous blood (r = -0.55, p = 0.002) were negatively correlated with the changes in hemoglobin (Hb). SI changes in venous blood were also associated with SO2 (r = 0.68, p < 0.0001) and deoxyHb concentration (-0.65, p < 0.0001). In healthy volunteers, rapid infusion resulted in a significant drop in the hemoglobin concentration (142.5 ± 15.2 g/L vs. 128.8 ± 15.2 g/L; p < 0.0001). Baseline myocardial SI increased by 3.0 ± 5.7 % (p = 0.026) following rapid infusion, and in males there was a strong association between the change in hemoglobin concentration and % changes in SI (r = 0.82, p = 0.002). After hyperhydration, the SI response after hyperventilation was attenuated (HV, p = 0.037), as was the maximum SI increase during apnea (p = 0.012). The extent of SI attenuation was correlated with the reduction in hemoglobin concentration at the end of apnea (r = 0.55, p = 0.012) for all subjects and at maximal SI (r = 0.63, p = 0.037) and the end of breath-hold (r = 0.68, p = 0.016) for males only.

CONCLUSION

In dynamic studies using oxygenation-sensitive CMR, the hematocrit level affects baseline signal intensity and the observed signal intensity response. Thus, the hydration status of the patient may be a confounder for OS-CMR image analysis.

Diagnostic Performance and Clinical Utility of Myocardial Perfusion MRI for Coronary Artery Disease with Fractional Flow Reserve as the Standard Reference: A Meta-analysis

BACKGROUND

Stress myocardial perfusion imaging is a noninvasive alternative to invasive fractional flow reserve for evaluating haemodynamically significant coronary artery disease. We aimed to systematically analyse the diagnostic performance and clinical utility of myocardial perfusion MRI for coronary artery disease (CAD) using fractional flow reserve (FFR) as the standard reference.

METHODS

We searched PubMed, EMBASE, and Cochrane Library to July 2015 for studies using perfusion MR as a diagnostic test for CAD versus FFR. The meta-analysis was performed based on Cochrane guideline.

RESULTS

We identified 20 studies with 1,570 patients. Pooled analyses were performed at per-patient level (1,041 patients) and per-territory level (2,690 coronary territories). The sensitivity, specificity, area under sROC curve were 0.88 (95% CI: 0.85, 0.91), 0.88 (95% CI: 0.84, 0.90), and 0.94 (95% CI: 0.92, 0.96) at per-patient level, and 0.86 (95% CI: 0.81, 0.90), 0.88 (95% CI: 0.84, 0.92), and 0.93 (95% CI: 0.91, 0.95) at per-territory level. Post-test probability was altered by positive (likelihood ratio) LR of 7.1 (95% CI: 5.6, 9.0) and negative LR of 0.13 (95% CI: 0.10, 0.17) based on Bayes' theorem.

CONCLUSIONS

Diagnostic accuracy of myocardial perfusion MRI for CAD is high and can alter the post-test probability of CAD.

Impaired Myocardial Oxygenation Response to Stress in Patients With Chronic Kidney Disease

BACKGROUND

Coronary artery disease and left ventricular hypertrophy are prevalent in the chronic kidney disease (CKD) and renal transplant (RT) population. Advances in cardiovascular magnetic resonance (CMR) with blood oxygen level-dependent (BOLD) technique provides capability to assess myocardial oxygenation as a measure of ischemia. We hypothesized that the myocardial oxygenation response to stress would be impaired in CKD and RT patients.

METHODS AND RESULTS

Fifty-three subjects (23 subjects with CKD, 10 RT recipients, 10 hypertensive (HT) controls, and 10 normal controls without known coronary artery disease) underwent CMR scanning. All groups had cine and BOLD CMR at 3 T. The RT and HT groups also had late gadolinium CMR to assess infarction/replacement fibrosis. The CKD group underwent 2-dimensional echocardiography strain to assess fibrosis. Myocardial oxygenation was measured at rest and under stress with adenosine (140 μg/kg per minute) using BOLD signal intensity. A total of 2898 myocardial segments (1200 segments in CKD patients, 552 segments in RT, 480 segments in HT, and 666 segments in normal controls) were compared using linear mixed modeling. Diabetes mellitus (P=0.47) and hypertension (P=0.57) were similar between CKD, RT, and HT groups. The mean BOLD signal intensity change was significantly lower in the CKD and RT groups compared to HT controls and normal controls (-0.89±10.63% in CKD versus 5.66±7.87% in RT versus 15.54±9.58% in HT controls versus 16.19±11.11% in normal controls, P<0.0001). BOLD signal intensity change was associated with estimated glomerular filtration rate (β=0.16, 95% CI=0.10 to 0.22, P<0.0001). Left ventricular mass index and left ventricular septal wall diameter were similar between the CKD predialysis, RT, and HT groups. None of the CKD patients had impaired global longitudinal strain and none of the RT group had late gadolinium hyperenhancement.

CONCLUSIONS

Myocardial oxygenation response to stress is impaired in CKD patients and RT recipients without known coronary artery disease, and unlikely to be solely accounted for by the presence of diabetes mellitus, left ventricular hypertrophy, or myocardial scarring. The impaired myocardial oxygenation in CKD patients may be associated with declining renal function. Noncontrast BOLD CMR is a promising tool for detecting myocardial ischemia in the CKD population.