Oxygenation-sensitive Cardiovascular Magnetic Resonance Research Articles

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

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. 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. Prospective observational study. Single-centre university hospital. Recruitment from August 2020 to January 2022. Thirty-two healthy volunteers younger than 45 years old were recruited. Data were analysed from n = 29 (69% male individuals). 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 (OS bh-cine ), which requires apnoea for acquisition and with two free-breathing OS-CMR sequences: a high-resolution single-shot sequence (OS fb-ss ) and a real-time cine sequence (OS fb-rtcine ). 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. The paced breathing followed by five deep breaths significantly reduced myocardial oxygenation, which was observed with all three techniques (OS bh-cine -6.0 ± 2.6%, OS fb-ss -12.0 ± 5.9%, OS fb-rtcine -5.4 ± 7.0%, all P < 0.05). The subsequent vasodilating stimulus of apnoea then significantly increased myocardial oxygenation (OS bh-cine 6.8 ± 3.1%, OS fb-ss 8.4 ± 5.6%, OS fb-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. 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. http://links.lww.com/EJA/A922.

Automated Data Transformation and Feature Extraction for Oxygenation-Sensitive Cardiovascular Magnetic Resonance Images.

Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) is a novel, powerful tool for assessing coronary function in vivo. The data extraction and analysis however are labor-intensive. The objective of this study was to provide an automated approach for the extraction, visualization, and biomarker selection of OS-CMR images. We created a Python-based tool to automate extraction and export of raw patient data, featuring 3336 attributes per participant, into a template compatible with common data analytics frameworks, including the functionality to select predictive features for the given disease state. Each analysis was completed in about 2min. The features selected by both ANOVA and MIC significantly outperformed (p < 0.001) the null set and complete set of features in two datasets, with mean AUROC scores of 0.89eatures f 0.94lete set of features in two datasets, with mean AUROC scores that our tool is suitable for automated data extraction and analysis of OS-CMR images.

Kiosk 1R-TB-04 - Coronary Vascular and Structural Function in Females with History of Pre-eclampsia—an Oxygenation-sensitive Cardiovascular Magnetic Resonance Imaging Study

Kiosk 1R-TB-04 - Coronary Vascular and Structural Function in Females with History of Pre-eclampsia—an Oxygenation-sensitive Cardiovascular Magnetic Resonance Imaging Study

Kiosk 9R-TA-05 - Machine Learning for Automated Detection of Normal and Abnormal Strain in Oxygenation-sensitive Cardiovascular Magnetic Resonance (OS-CMR) of Patients with Chronic Ischemic Cardiomyopathy

Kiosk 9R-TA-05 - Machine Learning for Automated Detection of Normal and Abnormal Strain in Oxygenation-sensitive Cardiovascular Magnetic Resonance (OS-CMR) of Patients with Chronic Ischemic Cardiomyopathy

Coronary vascular function in females with history of hypertensive disorders of pregnancy an oxygenation-sensitive cardiovascular magnetic resonance imaging study

Abstract Background Hypertensive disorders of pregnancy (HDP), including gestational hypertension and preeclampsia, have been associated with increased risk for cardiovascular disease decades after HDP pregnancy. HDP is thought to unmask pre-existing cardiovascular risk in the mother; and in addition HDP triggers a cascade of inflammatory and oxidative stress which leads to vascular endothelial dysfunction and abnormalities in cardiac structure and function evident early post-partum that may persist sub-clinically. Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) is an emerging approach that can identify dynamic changes of myocardial oxygenation as a marker for coronary vascular function. The objective of this study was to assess coronary vascular function in females with history of HDP using OS-CMR. Methods We analyzed data from two short axis OS-CMR slices in 20 females with history of HDP, including gestational hypertension, preeclampsia and HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets) and 20 healthy controls with history of normal pregnancy acquired on a 1.5T MRI scanner. Images were analyzed using a prototype tissue oxygenation module. The images were normalized for signal intensity to both ventricular blood pools. We used both traditional statistics and feature selection machine learning algorithms to select for predictive biomarkers in the dataset. Finally, we used a random forest classifier model for disease classification. We report area under the receiver operating curve (AUROC) as a metric for diagnostic accuracy. Results Global breathing-induced myocardial oxygenation reserve (B-MORE) of the mid left ventricular slice was significantly reduced in HDP females (-1.6 ± 14.8) when compared to healthy controls (11.3 ± 17.2, p=0.03), when normalized to ventricular blood pools (Figure 1A). Our feature selection algorithm selected the signal intensity during end-systole normalized to the series as the most predictive biomarker. Our model, which integrated data from &amp;gt;3,300 discrete data points per participant, correctly differentiated healthy controls from women with HDP history with a 90% ± 3% AUROC accuracy, indicating high sensitivity and specificity (Figure 1B). Conclusion Compared to healthy controls, females with history of HDP have abnormal coronary vascular function, as shown by reduced myocardial oxygenation on OS-CMR. Combining advanced machine learning approaches can further enhance the potential application of OS-CMR to risk stratify females with adverse pregnancy outcomes susceptible to future cardiovascular disease.

Association between myocardial oxygenation and fibrosis in Duchenne Muscular Dystrophy: analysis by oxygenation-sensitive and T1 mapping cardiovascular magnetic resonance (P7-9.002)

<h3>Objective:</h3> To explore whether myocardial hypoxia exists in DMD patients and whether an association exists between regional myocardial oxygenation and fibrosis, using oxygenation-sensitive cardiovascular magnetic resonance and native T1 mapping. <h3>Background:</h3> Myocardial hypoxia is common in many cardiomyopathies and has been proven to be closely related to the occurrence and development of myocardial fibrosis. However, limited studies are available on the relationship between myocardial oxygenation and fibrosis in DMD patients using oxygenation-sensitive magnetic resonance, and whether myocardium hypoxia exists in DMD patients and its underlying relationship with fibrosis in DMD remains unclear. <h3>Design/Methods:</h3> In this prospective study, 91 DMD patients and 30 volunteers underwent CMR. The correlation between oxygenation SI and native T1 value was assessed by Pearson or Spearman correlation coefficients and the association between oxygenation SI and LGE was analyzed by logistic regression. The survival curves were generated by the Kaplan–Meier analysis and compared by the log-rank test. <h3>Results:</h3> In LGE-patients, the oxygenation SI of all segments except the septal segments was significantly decreased than those of the controls. Inferolateral SI and anterolateral SI were weakly correlated with native T1 values. As for LGE+ patients, a further and significant reduction in oxygenation SI was observed relative to the controls. SI was moderately correlated with native T1 values in both negative and positive segments. Multivariable regression modeling indicated inferolateral SI independently associated with LGE. At an average follow-up of 18.63 months, 31 patients experienced progress of LGE. Patients with reduced inferolateral SI were more likely to have an exacerbation of fibrosis. <h3>Conclusions:</h3> Analysis of OS-CMR and native T1 mapping revealed that myocardial hypoxia is common and related to the onset of myocardial fibrosis in DMD patients. And myocardial oxygenation by OS-CMR might be used as the quantitative imaging biomarker for the assessment of myocardial damage and prediction of fibrosis progression in DMD patients. <b>Disclosure:</b> Ms. Zhou has nothing to disclose.

The reproducibility of breathing maneuvers as a vasoactive stimulus in the heart: an oxygenation-sensitive resonance imaging study

BackgroundEndothelial dysfunction and impaired oxygenation of the heart is a hallmark of several diseases, including coronary artery disease, hypertension, diabetes, and sleep apnea. Recent studies indicate that oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) imaging combined with breathing maneuvers may allow for assessing coronary vascular responsiveness as a marker for coronary vascular function in various clinical settings. However, despite the use of OS-CMR in evaluating tissue oxygenation, the reproducibility of these standardized, combined breathing maneuvers as a vasoactive stimulus has yet to be systematically assessed or validated. In this study, we aimed to assess the reproducibility of vasoactive breathing maneuvers to assess vascular function in a population of healthy volunteers. MethodsEighteen healthy volunteers were recruited for the study. Inclusion criteria were an age over 18 years and absence of any evidence or knowledge of cardiovascular, neurological, or pulmonary disease. MRI was performed on a clinical 3 T MRI system (MAGNETOM Skyra, Siemens Healthineers, Erlangen, Germany). The OS-CMR acquisition was performed as previously described (1 min hyperventilation followed by a maximal, voluntary breath-hold). Standard statistical tests were performed as appropriate. ResultsData from 18 healthy subjects was analyzed. The healthy volunteers had a mean age of 42 ± 15 years and a mean BMI of 25.4 ± 2.8 kg/m2, with an average heart rate of 72 ± 11 beats per minute, and ten of whom (56%) were female. There were no significant differences between global myocardial oxygenation (%Δ SI) after hyperventilation (HV1: − 7.82 ± 5.2; HV2: − 7.89 ± 6.4, p = 0.9) or breath-hold (BH1: 5.34 ± 3.1; BH2: 6.0 ± 3.3, p = 0.5) between the repeated breathing maneuvers. The Bland–Altman analysis showed good agreement (bias: 0.074, SD of bias: 2.93). ConclusionWe conclude that in healthy individuals, the myocardial oxygenation response to a standardized breathing maneuver with hyperventilation and a voluntary breath-hold is consistent and highly reproducible. These results corroborate previous evidence for breathing-enhanced OS-CMR as a robust test for coronary vascular function.

Abstract 13267: Angina Burden and Coronary Vascular Function in Women With Ischemia and No Obstructive Coronary Arteries—Role of Oxygenation-Sensitive Cardiovascular Magnetic Resonance Imaging

Introduction: Patients with ischemia and no obstructive coronary arteries (INOCA) often have coronary microvascular dysfunction (CMD). An association between higher angina burden (lower Seattle Angina Questionnaire [SAQ] scores) and increased severity of CMD has previously been reported. Oxygenation-Sensitive Cardiovascular Magnetic Resonance (OS-CMR) is a novel approach that can potentially evaluate CMD. To date, the relationship between angina burden and OS-CMR biomarkers has not been elucidated. Methods: We investigated the association between angina burden, quantified by the mean and 5 individual components of the SAQ, with measures of myocardial oxygenation, using OS-CMR. More severe CMD is reflected by a decreased % signal intensity (SI) change after hyperventilation (Breathing-enhanced Myocardial REserve, B-MORE), calculated by [(Hyperventilation - Breath Hold)/Breath Hold] x 100%. Univariable linear regression analysis was used to investigate the associations. Results: In 44 women with INOCA (mean age 55.1±0.9 years), B-MORE was 5.0±1.4% (Table). Several components of the SAQ were associated with OS-CMR measures of CMD [physical limitation (R 2 =0.281, Beta=0.530, p=0.042), angina frequency (R 2 =0.216, Beta=0.465, p=0.039), disease perception (R 2 =0.254, Beta=0.504, p=0.024), and the mean overall SAQ (R 2 =0.285, Beta=0.534, p=0.015)] (Panel Figure). Conclusion: In women with INOCA, angina burden is associated with coronary vascular function, as assessed by OS-CMR. Therefore, this novel approach may provide objective information to detect the presence of CMD.

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

IntroductionIn 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.MethodsA 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.ResultsIn 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.ConclusionIn 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.

Insights Into Myocardial Oxygenation and Cardiovascular Magnetic Resonance Tissue Biomarkers in Heart Failure With Preserved Ejection Fraction.

The pathophysiology of heart failure with preserved ejection fraction is not well understood, but evidence strongly suggests involvement of microvascular dysfunction. We studied the myocardial oxygenation reserve as a direct marker of coronary vascular function and its relation to myocardial deformation and tissue characteristics by cardiovascular magnetic resonance (CMR). In a dual-center case-control study, patients with heart failure and preserved ejection fraction (>50%) and healthy controls older than 50 years underwent quantitative CMR for ventricular volumes and functional assessment with feature tracking, as well as tissue characterization (T1, T2, extracellular volume). Coronary vascular function was measured by oxygenation-sensitive (OS)-CMR of the myocardial oxygenation response to a vasoactive breathing maneuver. Twenty-nine patients completed the CMR exam. Compared with cutoffs derived from 12 control subjects, circumferential peak strain was attenuated in 97% of patients. Native T1 was elevated in 93%, extracellular volume was elevated in 83%. Sixty-six percent of patients revealed either regional or global myocardial edema, defined by an increased myocardial T2. An attenuated global myocardial oxygenation reserve (<4.4%) was observed in 96% of the patients (1.7±3.9% versus 9.1±5.3% in controls, P<0.001). This was correlated with septal wall thickness (r=-0.54, P=0.003), edema (myocardial T2; β=-0.26% oxygenation-sensitive/ms [95% CI, -0.49 to -0.03], P=0.029), and reduced diastolic strain rate (β=1.50% oxygenation-sensitive/s-1 [95% CI, 0.06-2.90], P=0.042). In patients with clinical heart failure with preserved ejection fraction, vascular dysfunction as measured by an attenuated myocardial oxygenation reserve is associated with myocardial edema, a thicker septum, and diastolic dysfunction. A quantitative comprehensive CMR exam including oxygenation-sensitive-CMR allows for comprehensive imaging-based phenotyping of heart failure with preserved ejection fraction.

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

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). 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. 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). 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. • 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.

Impact of rapid versus gradual changes in arterial partial pressure of carbon dioxide on blood flow and myocardial oxygenation in an experimental anaesthetized model

Introduction Hyper- and hypocapnia have known vaso-modulatory effects in the coronary circulation. Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) detects changes in tissue oxygenation and can provide a comprehensive assessment of the impact of systemic blood gas changes on the myocardium. The purpose of this study was to compare the physiological responses to rapid blood gas changes induced by hyperventilation followed by apnea in comparison to steady-state levels of hypocapnia and hypercapnia in an experimental animal model. Methods Eighteen anaesthetized female swine were used in this study. A blood flow probe was attached to the left descending coronary artery (LAD) after a left-sided thoracotomy. In ten animals a hemodynamically significant LAD stenosis was induced, while eight animals served as controls. In a 3 Tesla MRI, paCO2 was modulated from a pre-set baseline (paO2=100mmHg/paCO2=40mmHg) to 30mmHg and subsequently 50mmHg by minor changes in ventilation rate. Rapid changes in paCO2 were achieved by 60s of hyperventilating (30/min) from baseline followed by an apnea of up to 90 seconds. OS-CMR images, coronary blood flow (CBF) of the LAD and arterial blood gases were recorded at each state. Results Targeting stable hypocapnia of 30mmHg from baseline did not alter CBF or myocardial oxygenation. Subsequent stable hypercapnia (paCO2=50mmHg) increased CBF significantly in control (5±5%, p=0.007) and stenosed (4±6%, p=0.036) animals, and myocardial oxygenation rose in both post-stenotic territories (4.2±6.2%, p=0.036) and in control subjects (6.2±6.2%, p=0.011). Rapid hyperventilation induced a similar degree of hypocapnia (control: paCO2=25±7mmHg, stenosed: 27±3mmHg) and showed a significant decrease of CBF by -34±23% (p=0.012) in healthy animals, and a significant decrease of -10±6% (p=0.010) in stenosed animals. This had no effect on tissue oxygenation. Apnea resulted in a similar paCO2 (control: paCO2=52±9mmHg, stenosed: 47±7mmHg) compared to steady-state blood gas levels, which increased CBF significantly in controls 346±327% (p=0.008) and stenosed 82±110 (p=0.039) animals markedly. By the end of apnea, a rise in tissue oxygenation of 2.9±2.2% was observed in controls (p=0.008), -2.7±5.1 (0.125) was observed in the stenosed group (Figure). Significant difference in myocardial oxygenation responses observed between control and stenosed subject was exclusively observed with apnea (p=0.011). Discussion Rapid hyperventilation followed by apnea results in more pronounced changes in myocardial blood flow than similar steady state deflections in paCO2. Only apnea after hyperventilation induced deoxygenation in the stenotic myocardium, which is in agreement with the concept of hypercapnia induced intercoronary steal, while steady state deviation did not compromise myocardial oxygenation. Similar breathing maneuvers may be seen in the induction phase of anaesthesia, which could potentially be a harbinger of perioperative ischemic myocardial events.

Ventricular strain is compromised outside of the coronary autoregulatory range – assessment by cardiovascular magnetic resonance

Introduction Coronary autoregulation maintains near-constant myocardial blood flow in a range of approximately 60-140 mmHg of mean arterial pressure (MAP). Using oxygenation-sensitive (OS) cardiovascular magnetic resonance (CMR), we showed that myocardial oxygenation is compromised at MAP levels below the lower limit of this range. Above its upper limit we observed luxury perfusion and mild oxygen excess. There is a lack of data exploring the relationship between coronary autoregulation, myocardial oxygenation and ventricular function. CMR feature tracking software allows to quantify myocardial deformation and strain in OS images. Our aim was to explore our data from an animal study for associations between myocardial function, myocardial oxygenation and coronary blood flow (CBF) over a wide range of MAP levels. Methods In ten anaesthetized swine a flow probe was surgically attached to the proximal left anterior descending coronary artery before the animals were placed into a 3 Tesla MRI scanner. Starting from a baseline of 70 mmHg, MAP was varied in steps of 10-15 mmHg using phenylephrine and urapidil, respectively. At each MAP level, OS cine images and CBF readings of the anterior descending coronary artery were obtained, as well as arterial and coronary sinus blood gas samples to determine myocardial oxygen extraction ratio. Using feature tracking-software, strain data were acquired from images by tracing endo- and epicardial contours in end-diastole, from which peak global circumferential strain (GCS) was calculated for both ventricles. The relationships of peak GCS to MAP, CBF and myocardial oxygenation were established. Results We analysed 101 MAP levels, which ranged between 35 and 196 mmHg. Oxygenation as assessed by OS-CMR showed a curvi-linear relationship to MAP, with a steeper decrease below the lower limit of the autoregulatory range and an increase above its upper limit. Peak GCS of both ventricles became progressively impacted when MAP was forced from its baseline (70 mmHg) towards and beyond the lower and upper autoregulatory limit (dashed yellow lines in figure). There was no apparent association between changes of peak GCS and CBF. GCS of left ventricular myocardium decreased linearly with increasing myocardial oxygen extraction ratio (r=0.261, p=0.026), and in a non-linear fashion with decreasing myocardial tissue oxygenation. Discussion In a porcine model with non-diseased hearts, biventricular systolic function becomes compromised when MAP reaches levels either below or above coronary autoregulatory limits. Contractile dysfunction at pressures below the lower limit appears to be caused by myocardial deoxygenation. Conversely, hypertension-induced systolic dysfunction is associated with increased coronary flow and oxygen excess, which points to high afterload rather than O2 demand/supply imbalance as the most likely mechanism. We conclude that in hearts without coronary disease, global strain abnormalities elicited by hypotensive or hypertensive stress also differ in their underlying pathophysiological mechanisms.

When Less Is More: Why Extubation With Less Than Routine 100% Oxygen May Be a Reasonable Strategy.

When Less Is More: Why Extubation With Less Than Routine 100% Oxygen May Be a Reasonable Strategy.

22Effects of myoglobin oxygenation on oxygenation-sensitive cardiovascular magnetic resonance images: an in-vitro study

22Effects of myoglobin oxygenation on oxygenation-sensitive cardiovascular magnetic resonance images: an in-vitro study

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

BackgroundThe 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.MethodsTen 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 (QLAD). 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.ResultsQLAD 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.ConclusionOS-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.

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

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. 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). 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.

Oxygenation-sensitive cardiovascular magnetic resonance in hypertensive heart disease with left ventricular myocardial hypertrophy and non-left ventricular myocardial hypertrophy: Insight from altered mechanics and cardiac BOLD imaging.

BOLD (blood oxygen level dependent) MRI can detect regional condition of myocardial oxygen supply and demand by means of paramagnetic properties. Noninvasive assessment of myocardial oxygenation by BOLD MRI in hypertensive patients with hypertension (HTN) left ventricular myocardial hypertrophy (LVMH) and HTN non-LVMH and its correlation with myocardial mechanics were performed. Prospective. Twenty patients with HTN LVMH, 21 patients with HTN non-LVMH, and 23 normotensive controls were enrolled. Cine imaging, T2* and T1 mapping sequences were achieved at 3.0T. Dedicated T1 mapping, T2*, and cine imaging analysis were performed by two radiologists using cvi42. One-way analysis of variance, Kruskal-Wallis test, Bland-Altman analysis, Pearson's correlation coefficient, Spearman's rank correlation. T2* values of HTN LVMH group were significantly lower versus the controls (23.78 ± 3.09 versus 30.77 ± 2.71; P < 0.001) and HTN non-LVMH group (23.78 ± 3.09 versus 28.64 ± 4.23; P < 0.001). Left ventricular peak circumferential strain were reduced in HTN LVMH patients compared with other two groups (-11.32 [-15.64, -10.3], -16.78 [-19.35, -15.34], and -19.73 [-20.57, -18.73]; P < 0.05); and longitudinal strain of HTN LVMH patients were lower than other two groups (-11.31 ± 2.91, -15.1 ± 3.06, and -18.85 ± 1.85; P < 0.05); radial strain of HTN LVMH patients were also lower than other two groups (25.03 ± 16, 40.95 ± 17.5 and 47.9 ± 10.23; P < 0.05). Extracellular volume correlated with peak circumferential, longitudinal, and radial strain (spearman rho = 0.6, 0.64, and -0.69; P < 0.05), respectively; T2* negatively correlated with peak circumferential and longitudinal strain (spearman rho = -0.43 and -0.49; P < 0.05), respectively. Patients with lower T2* values had significant decreases in myocardial mechanics (P < 0.05). HTN LVMH patients have both impaired myocardial mechanics and decreased T2* values compared with HTN non-LVMH and normotensive groups. BOLD MRI could provide a feasible assessment modality for detecting altered T2* due to the change of de-oxygenated hemoglobin and hence to the change of signal intensity in oxygenation-sensitive images. 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1297-1306.

Breathing Maneuvers as a Vasoactive Stimulus for Detecting Inducible Myocardial Ischemia - An Experimental Cardiovascular Magnetic Resonance Study.

BackgroundBreathing maneuvers can elicit a similar vascular response as vasodilatory agents like adenosine; yet, their potential diagnostic utility in the presence of coronary artery stenosis is unknown. The objective of the study is to investigate if breathing maneuvers can non-invasively detect inducible ischemia in an experimental animal model when the myocardium is imaged with oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR).Methods and FindingsIn 11 anesthetised swine with experimentally induced significant stenosis (fractional flow reserve <0.75) of the left anterior descending coronary artery (LAD) and 9 control animals, OS-CMR at 3T was performed during two different breathing maneuvers, a long breath-hold; and a combined maneuver of 60s of hyperventilation followed by a long breath-hold. The resulting change of myocardial oxygenation was compared to the invasive measurements of coronary blood flow, blood gases, and oxygen extraction. In control animals, all breathing maneuvers could significantly alter coronary blood flow as hyperventilation decreased coronary blood flow by 34±23%. A long breath-hold alone led to an increase of 97±88%, while the increase was 346±327% (p<0.001), when the long breath-hold was performed after hyperventilation. In stenosis animals, the coronary blood flow response was attenuated after both hyperventilation and the following breath-hold. This was matched by the observed oxygenation response as breath-holds following hyperventilation consistently yielded a significant difference in the signal of the MRI images between the perfusion territory of the stenosis LAD and remote myocardium. There was no difference between the coronary territories during the other breathing maneuvers or in the control group at any point.ConclusionIn an experimental animal model, the response to a combined breathing maneuver of hyperventilation with subsequent breath-holding is blunted in myocardium subject to significant coronary artery stenosis. This maneuver may allow for detecting severe coronary artery stenosis and have a significant clinical potential as a non-pharmacological method for diagnostic testing in patients with suspected coronary artery disease.

The impact of hematocrit on oxygenation-sensitive cardiovascular magnetic resonance.

BackgroundOxygenation-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.MethodsVenous 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.ResultsThe % 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.ConclusionIn 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.