Perioperative echocardiographic strain analysis: what anesthesiologists should know

PURPOSE

Echocardiographic strain analysis by speckle tracking allows assessment of myocardial deformation during the cardiac cycle. Its clinical applications have significantly expanded over the last two decades as a sensitive marker of myocardial dysfunction with important diagnostic and prognostic values. Strain analysis has the potential to become a routine part of the perioperative echocardiographic examination for most anesthesiologist-echocardiographers but its exact role in the perioperative setting is still being defined.

CLINICAL FEATURES

This clinical report reviews the principles underlying strain analysis and describes its main clinical uses pertinent to the field of anesthesiology and perioperative medicine. Strain for assessment of left and right ventricular function as well as atrial strain is described. We also discuss the potential role of strain to aid in perioperative risk stratification, surgical patient selection in cardiac surgery, and guidance of anesthetic monitor choice and clinical decision-making in the perioperative period.

CONCLUSION

Echocardiographic strain analysis is a powerful tool that allows seeing what conventional 2D imaging sometimes fails to reveal. It often provides pathophysiologic insight into various cardiac diseases at an early stage. Strain analysis is readily feasible and reproducible thanks to the use of highly automated software platforms. This technique shows promising potential to become a valuable tool in the arsenal of the anesthesiologist-echocardiographer and aid in perioperative risk-stratification and clinical decision-making.

Perioperative hyperoxia- impact on myocardial biomarkers, strain and outcome in high-risk patients undergoing non-cardiac surgery: Protocol for a prospective randomized controlled trial

BACKGROUND

Supplemental oxygen is used during every general anesthesia. However, for the maintenance phase of a general anesthesia, in most cases the longest part of anesthesia, only scarce evidence of dosing supplemental oxygen exists. Oxygen is a well-known coronary vasoconstrictor and thus may contribute to cardiovascular complications especially in vulnerable high-risk patients with coronary artery disease undergoing major non-cardiac surgery. Myocardial biomarkers are early indicators of myocardial injury. Oxygen supply demand mismatches due to coronary artery disease aggravated by hyperoxia might be displayed by changes from the biomarker's baseline-values. This study is designed to detect changes in myocardial biomarkers levels associated with perioperative hyperoxia.

METHODS

This prospective randomized controlled interventional trial investigates the impact of maintaining perioperative high oxygen supplementation in high-risk patients undergoing non-cardiac vascular surgery on cardiac biomarkers, myocardial strain and outcome in 110 patients. Patients are allocated to be supplemented with either 0.3 (normal) or 0.8 (high) fraction of inspired oxygen (FiO2) perioperatively. Included is a short crossover phase during which transesophageal echocardiography is used to evaluate myocardial function at FiO2 0.3 and 0.8 by strain analysis in each patient. Patients will be followed up for complications at 30 days and 1 year.

CONCLUSION

The trial is designed to evaluate perioperative changes from baseline myocardial biomarkers associated with perioperative FiO2. Furthermore, exploration and correlation of changes in biomarkers, acute early changes in myocardial function and clinical outcomes induced by different FiO2 may be possible.

Prognostic value of visual and quantitative CMR regional myocardial function in patients with suspected myocarditis

According to updated Lake-Louise Criteria, impaired regional myocardial function serves as a supportive criterion in diagnosing myocarditis. This study aimed to assess visual regional wall motional abnormalities (RWMA) and novel quantitative regional longitudinal peak strain (RLS) for risk stratification in the clinical setting of myocarditis. In patients undergoing CMR and meeting clinical criteria for suspected myocarditis global longitudinal strain (GLS), late gadolinium enhancement (LGE), RWMA and RLS were assessed in the anterior, septal, inferior, and lateral regions and correlated to the occurrence of major adverse cardiac events (MACE), including heart failure hospitalization, sustained ventricular tachycardia, recurrent myocarditis, and all-cause death. In 690 consecutive patients (age: 48.0 ± 16.0 years; 37.7% female) with suspected myocarditis impaired RLS was correlated with RWMA and LV-GLS but not with the presence of LGE. At median follow up of 3.8 years, MACE occurred in 116 (16.8%) patients. Both, RWMA and RLS in anterior-, septal-, inferior-, and lateral- locations were univariately associated with outcomes (all p < 0.001), but not after adjusting for clinical characteristics and LV-GLS. In the subgroup of patients with normal LV function, RWMA were not predictive of outcomes, whereas septal RLS had incremental and independent prognostic value over clinical characteristics (HRadjusted = 1.132, 95% CI 1.020-1.256; p = 0.020). RWMA and RLS can be used to assess regional impairment of myocardial function in myocarditis but are of limited prognostic value in the overall population. However, in the subgroup of patients with normal LV function, septal RLS represents a distinctive marker of regional LV dysfunction, offering potential for risk-stratification.

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.

Analysis of bi-atrial function using CMR feature tracking and long-axis shortening approaches in patients with diastolic dysfunction and atrial fibrillation

OBJECTIVES

Atrial function can be assessed using advancing cardiovascular magnetic resonance (CMR) post-processing methods: atrial feature tracking (FT) strain analysis or a long-axis shortening (LAS) technique. This study aimed to first compare the two FT and LAS techniques in healthy individuals and cardiovascular patients and then investigated how left (LA) and right atrial (RA) measurements are related to the severity of diastolic dysfunction or atrial fibrillation.

METHODS

Sixty healthy controls and 90 cardiovascular disease patients with coronary artery disease, heart failure, or atrial fibrillation, underwent CMR. LA and RA were analyzed for standard volumetry as well as for myocardial deformation using FT and LAS for the different functional phases (reservoir, conduit, booster). Additionally, ventricular shortening and valve excursion measurements were assessed with the LAS module.

RESULTS

The measurements for each of the LA and RA phases were correlated (p < 0.05) between the two approaches, with the highest correlation coefficients occurring in the reservoir phase (LA: r = 0.83, p < 0.01, RA: r = 0.66, p < 0.01). Both methods demonstrated reduced LA (FT: 26 ± 13% vs 48 ± 12%, LAS: 25 ± 11% vs 42 ± 8%, p < 0.01) and RA reservoir function (FT: 28 ± 15% vs 42 ± 15%, LAS: 27 ± 12% vs 42 ± 10%, p < 0.01) in patients compared to controls. Atrial LAS and FT decreased with diastolic dysfunction and atrial fibrillation. This mirrored ventricular dysfunction measurements.

CONCLUSION

Similar results were generated for bi-atrial function measurements between two CMR post-processing approaches of FT and LAS. Moreover, these methods allowed for the assessment of incremental deterioration of LA and RA function with increasing left ventricular diastolic dysfunction and atrial fibrillation. A CMR-based analysis of bi-atrial strain or shortening discriminates patients with early-stage diastolic dysfunction prior to the presence of compromised atrial and ventricular ejection fractions that occur with late-stage diastolic dysfunction and atrial fibrillation.

KEY POINTS

• Assessing right and left atrial function with CMR feature tracking or long-axis shortening techniques yields similar measurements and could potentially be used interchangeably based on the software capabilities of individual sites. • Atrial deformation and/or long-axis shortening allow for early detection of subtle atrial myopathy in diastolic dysfunction, even when atrial enlargement is not yet apparent. • Using a CMR-based analysis to understand the individual atrial-ventricular interaction in addition to tissue characteristics allows for a comprehensive interrogation of all four heart chambers. In patients, this could add clinically meaningful information and potentially allow for optimal therapies to be chosen to better target the dysfunction.

Focal and diffuse myocardial fibrosis both contribute to regional hypoperfusion assessed by post-processing quantitative-perfusion MRI techniques

Introduction

Indications for stress-cardiovascular magnetic resonance imaging (CMR) to assess myocardial ischemia and viability are growing. First pass perfusion and late gadolinium enhancement (LGE) have limited value in balanced ischemia and diffuse fibrosis. Quantitative perfusion (QP) to assess absolute pixelwise myocardial blood flow (MBF) and extracellular volume (ECV) as a measure of diffuse fibrosis can overcome these limitations. We investigated the use of post-processing techniques for quantifying both pixelwise MBF and diffuse fibrosis in patients with clinically indicated CMR stress exams. We then assessed if focal and diffuse myocardial fibrosis and other features quantified during the CMR exam explain individual MBF findings.

Methods

This prospective observational study enrolled 125 patients undergoing a clinically indicated stress-CMR scan. In addition to the clinical report, MBF during regadenoson-stress was quantified using a post-processing QP method and T1 maps were used to calculate ECV. Factors that were associated with poor MBF were investigated.

Results

Of the 109 patients included (66 ± 11 years, 32% female), global and regional perfusion was quantified by QP analysis in both the presence and absence of visual first pass perfusion deficits. Similarly, ECV analysis identified diffuse fibrosis in myocardium beyond segments with LGE. Multivariable analysis showed both LGE (β = -0.191, p = 0.001) and ECV (β = -0.011, p < 0.001) were independent predictors of reduced MBF. In patients without clinically defined first pass perfusion deficits, the microvascular risk-factors of age and wall thickness further contributed to poor MBF (p < 0.001).

Discussion

Quantitative analysis of MBF and diffuse fibrosis detected regional tissue abnormalities not identified by traditional visual assessment. Multi-parametric quantitative analysis may refine the work-up of the etiology of myocardial ischemia in patients referred for clinical CMR stress testing in the future and provide a deeper insight into ischemic heart disease.

Predictive value of cardiac magnetic resonance right ventricular longitudinal strain in patients with suspected myocarditis

BACKGROUND

Recent evidence underlined the importance of right (RV) involvement in suspected myocarditis. We aim to analyze the possible incremental prognostic value from RV global longitudinal strain (GLS) by CMR.

METHODS

Patients referred for CMR, meeting clinical criteria for suspected myocarditis and no other cardiomyopathy were enrolled in a dual-center register cohort study. Ejection fraction (EF), GLS and tissue characteristics were assessed in both ventricles to assess their association to first major adverse cardiovascular events (MACE) including hospitalization for heart failure (HF), ventricular tachycardia (VT), recurrent myocarditis and death.

RESULTS

Among 659 patients (62.8% male; 48.1 ± 16.1 years), RV GLS was impaired (> - 15.4%) in 144 (21.9%) individuals, of whom 76 (58%), 108 (77.1%), 27 (18.8%) and 40 (32.8%) had impaired right ventricular ejection fraction (RVEF), impaired left ventricular ejection fraction (LVEF), RV late gadolinium enhancement (LGE) or RV edema, respectively. After a median observation time of 3.7 years, 45 (6.8%) patients were hospitalized for HF, 42 (6.4%) patients died, 33 (5%) developed VT and 16 (2.4%) had recurrent myocarditis. Impaired RV GLS was associated with MACE (HR = 1.07, 95% CI 1.04-1.10; p < 0.001), HF hospitalization (HR = 1.17, 95% CI 1.12-1.23; p < 0.001), and death (HR = 1.07, 95% CI 1.02-1.12; p = 0.004), but not with VT and recurrent myocarditis in univariate analysis. RV GLS lost its association with outcomes, when adjusted for RVEF, LVEF, LV GLS and LV LGE extent.

CONCLUSION

RV strain is associated with MACE, HF hospitalization and death but has neither independent nor incremental prognostic value after adjustment for RV and LV function and tissue characteristics. Therefore, assessing RV GLS in the setting of myocarditis has only limited value.

Hyperoxia-induced deterioration of diastolic function in anaesthetised patients with coronary artery disease - Randomised crossover trial

Background

There are no current recommendations for oxygen titration in patients with stable coronary artery disease. This study investigates the effect of iatrogenic hyperoxia on cardiac function in patients with coronary artery disease undergoing general anaesthesia.

Methods

Patients scheduled for elective coronary artery bypass graft surgery were prospectively recruited into this randomised crossover clinical trial. All patients were exposed to inspired oxygen fractions of 0.3 (normoxaemia) and 0.8 (hyperoxia) in randomised order. A transoesophageal echocardiographic imaging protocol was performed during each exposure. Primary analysis investigated changes in 3D peak strain, whereas secondary analyses investigated other systolic and diastolic responses.

Results

There was no statistical difference in systolic function between normoxaemia and hyperoxia. However, the response in systolic function to hyperoxia was dependent on ventricular function at normoxaemia. Patients with a normoxaemic left ventricular (LV) global longitudinal strain (GLS) poorer than the derived cut-off (>-15.4%) improved with hyperoxia (P<0.01), whereas in patients with normoxaemic LV-GLS <-15.4%, LV-GLS worsened with transition to hyperoxia (P<0.01). The same was seen for right ventricular GLS with a cut-off at -24.1%. Diastolic function worsened during hyperoxia indicated by a significant increase of averaged E/e' (8.6 [2.6]. vs 8.2 [2.4], P=0.01) and E/A ratio (1.4 (0.4) vs 1.3 (0.4), P=0.01).

Conclusions

Although the response of biventricular systolic variables is dependent on systolic function at normoxaemia, diastolic function consistently worsens under hyperoxia. In coronary artery disease, intraoperative strain analysis may offer guidance for oxygen titration.

Clinical trial registration

NCT04424433.

Performance of the Dexcom G6 Continuous Glucose Monitoring System During Cardiac Surgery Using Hypothermic Extracorporeal Circulation

OBJECTIVE

Continuous glucose monitoring (CGM) may be challenged by extreme conditions during cardiac surgery using hypothermic extracorporeal circulation (ECC).

RESEARCH DESIGN AND METHODS

We evaluated the Dexcom G6 sensor in 16 subjects undergoing cardiac surgery with hypothermic ECC, of whom 11 received deep hypothermic circulatory arrest (DHCA). Arterial blood glucose, quantified by the Accu-Chek Inform II meter, served as reference.

RESULTS

Intrasurgery mean absolute relative difference (MARD) of 256 paired CGM/reference values was 23.8%. MARD was 29.1% during ECC (154 pairs) and 41.6% immediately after DHCA (10 pairs), with a negative bias (signed relative difference: -13.7%, -26.6%, and -41.6%). During surgery, 86.3% pairs were in Clarke error grid zones A or B and 41.0% of sensor readings fulfilled the International Organization for Standardization (ISO) 15197:2013 norm. Postsurgery, MARD was 15.0%.

CONCLUSIONS

Cardiac surgery using hypothermic ECC challenges the accuracy of the Dexcom G6 CGM although recovery appears to occur thereafter.

Perioperative Fully Closed-Loop Insulin Delivery in Patients Undergoing Elective Surgery: An Open-Label, Randomized Controlled Trial

OBJECTIVE

Perioperative management of glucose levels remains challenging. We aimed to assess whether fully closed-loop subcutaneous insulin delivery would improve glycemic control compared with standard insulin therapy in insulin-requiring patients undergoing elective surgery.

RESEARCH DESIGN AND METHODS

We performed a single-center, open-label, randomized controlled trial. Patients with diabetes (other than type 1) undergoing elective surgery were recruited from various surgical units and randomly assigned using a minimization schedule (stratified by HbA1c and daily insulin dose) to fully closed-loop insulin delivery with fast-acting insulin aspart (closed-loop group) or standard insulin therapy according to local clinical practice (control group). Study treatment was administered from hospital admission to discharge (for a maximum of 20 days). The primary end point was the proportion of time with sensor glucose in the target range (5.6-10.0 mmol/L).

RESULTS

Forty-five patients were enrolled and assigned to the closed-loop (n = 23) or the control (n = 22) group. One patient (closed-loop group) withdrew from the study before surgery and was not analyzed. Participants underwent abdominal (57%), vascular (23%), orthopedic (9%), neuro (9%), or thoracic (2%) surgery. The mean proportion of time that sensor glucose was in the target range was 76.7 ± 10.1% in the closed-loop and 54.7 ± 20.8% in the control group (mean difference 22.0 percentage points [95% CI 11.9; 32.0%]; P < 0.001). No episodes of severe hypoglycemia (<3.0 mmol/L) or hyperglycemia with ketonemia or any study-related adverse events occurred in either group.

CONCLUSIONS

In the context of mixed elective surgery, the use of fully closed-loop subcutaneous insulin delivery improves glucose control without a higher risk of hypoglycemia.

Diagnostic performance of cardiac magnetic resonance segmental myocardial strain for detecting microvascular obstruction and late gadolinium enhancement in patients presenting after a ST-elevation myocardial infarction

Background

Microvascular obstruction (MVO) and Late Gadolinium Enhancement (LGE) assessed in cardiac magnetic resonance (CMR) are associated with adverse outcome in patients with ST-elevation myocardial infarction (STEMI). Our aim was to analyze the diagnostic performance of segmental strain for the detection of MVO and LGE.

Methods

Patients with anterior STEMI, who underwent additional CMR were enrolled in this sub-study of the CARE-AMI trial. Using CMR feature tracking (FT) segmental circumferential peak strain (SCS) was measured and the diagnostic performance of SCS to discriminate MVO and LGE was assessed in a derivation and validation cohort.

Results

Forty-eight STEMI patients (62 ± 12 years old), 39 (81%) males, who underwent CMR (i.e., mean 3.0 ± 1.5 days) after primary percutaneous coronary intervention (PCI) were included. All patients presented with LGE and in 40 (83%) patients, MVO was additionally present. Segments in all patients were visually classified and 146 (19%) segments showed MVO (i.e., LGE+/MVO+), 308 (40%) segments showed LGE and no MVO (i.e., LGE+/MVO–), and 314 (41%) segments showed no LGE (i.e., LGE–). Diagnostic performance of SCS for detecting MVO segments (i.e., LGE+/MVO+ vs. LGE+/MVO–, and LGE–) showed an AUC = 0.764 and SCS cut-off value was –11.2%, resulting in a sensitivity of 78% and a specificity of 67% with a positive predictive value (PPV) of 30% and a negative predictive value (NPV) of 94% when tested in the validation group. For LGE segments (i.e., LGE+/MVO+ and LGE+/MVO– vs. LGE–) AUC = 0.848 and SCS with a cut-off value of –13.8% yielded to a sensitivity of 76%, specificity of 74%, PPV of 81%, and NPV of 70%.

Conclusion

Segmental strain in STEMI patients was associated with good diagnostic performance for detection of MVO+ segments and very good diagnostic performance of LGE+ segments. Segmental strain may be useful as a potential contrast-free surrogate marker to improve early risk stratification in patients after primary PCI.

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.

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

BACKGROUND

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).

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Reproducibility and its confounders of CMR feature tracking myocardial strain analysis in patients with suspected myocarditis

Objectives

Cardiovascular magnetic resonance feature tracking (CMR-FT) is an emerging technique for assessing myocardial strain with valuable diagnostic and prognostic potential. However, the reproducibility of biventricular CMR-FT analysis in a large cardiovascular population has not been assessed. Also, evidence of confounders impacting reader reproducibility for CMR-FT in patients is unknown and currently limits the clinical implementation of this technique.

Methods

From a dual-center database of patients referred to CMR for suspected myocarditis, 125 patients were randomly selected to undergo biventricular CMR-FT analysis for 2-dimensional systolic and diastolic measures, with additional 3-dimensional analysis for the left ventricle. All image analysis was replicated by a single reader and by a second reader for intra- and inter-reader analysis (Circle Cardiovascular Imaging). Reliability was tested with intraclass correlation (ICC) tests, and the impact of imaging confounders on agreement was assessed through multivariable analysis.

Results

Left and right ventricular ejection fractions were reduced in 34% and 37% of the patients, respectively. Good to excellent reliability was shown for 2D (all ICC > 0.85) and 3D (all ICC > 0.70) peak strain and early diastolic strain rate for both ventricles in longitudinal orientation as well as circumferential orientations for the left ventricle. An increased slice number improved agreement while the presence of pericardial effusion compromised diastolic strain rate agreement, and arrhythmia compromised right ventricular agreement.

Conclusion

In a large clinical cohort, we could show CMR-FT yields excellent inter-reader and intra-reader reproducibility. Multi-parametric CMR-FT of the right and left ventricles appears to be a robust tool in cardiovascular patients referred to CMR.

Clinical trial registration.

ClinicalTrials.gov Identifier: NCT03470571, NCT04774549.

Key Points

• Cardiovascular magnetic resonance feature tracking (CMR-FT) is an emerging technique to measure myocardial strain in cardiovascular patients referred for CMR; however, the evaluation of its reproducibility in a large cohort has not yet been performed.

• In a large clinical cohort, CMR-FT yields excellent inter-reader and intra-reader reproducibility for both left and right ventricular systolic and diastolic parameters.

• Arrhythmia and pericardial effusion compromise agreement of select FT parameters, but poor ejection fraction does not.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-08416-5.

Assessment of Myocardial Function During Blood Pressure Manipulations Using Feature Tracking Cardiovascular Magnetic Resonance

Background: Coronary autoregulation is a feedback system, which maintains near-constant myocardial blood flow over a range of mean arterial pressure (MAP). Yet in emergency or peri-operative situations, hypotensive or hypertensive episodes may quickly arise. It is not yet established how rapid blood pressure changes outside of the autoregulation zone (ARZ) impact left (LV) and right ventricular (RV) function. Using cardiovascular magnetic resonance (CMR) imaging, measurements of myocardial tissue oxygenation and ventricular systolic and diastolic function can comprehensively assess the heart throughout a range of changing blood pressures.

Design and methods: In 10 anesthetized swine, MAP was varied in steps of 10–15 mmHg from 29 to 196 mmHg using phenylephrine and urapidil inside a 3-Tesla MRI scanner. At each MAP level, oxygenation-sensitive (OS) cine images along with arterial and coronary sinus blood gas samples were obtained and blood flow was measured from a surgically implanted flow probe on the left anterior descending coronary artery. Using CMR feature tracking-software, LV and RV circumferential systolic and diastolic strain parameters were measured from the myocardial oxygenation cines.

Results: LV and RV peak strain are compromised both below the lower limit (LV: Δ1.2 ± 0.4%, RV: Δ4.4 ± 1.2%, p < 0.001) and above the upper limit (LV: Δ2.1 ± 0.4, RV: Δ5.4 ± 1.4, p < 0.001) of the ARZ in comparison to a baseline of 70 mmHg. LV strain demonstrates a non-linear relationship with invasive and non-invasive measures of oxygenation. Specifically for the LV at hypotensive levels below the ARZ, systolic dysfunction is related to myocardial deoxygenation (β = −0.216, p = 0.036) in OS-CMR and both systolic and diastolic dysfunction are linked to reduced coronary blood flow (peak strain: β = −0.028, p = 0.047, early diastolic strain rate: β = 0.026, p = 0.002). These relationships were not observed at hypertensive levels.

Conclusion: In an animal model, biventricular function is compromised outside the coronary autoregulatory zone. Dysfunction at pressures below the lower limit is likely caused by insufficient blood flow and tissue deoxygenation. Conversely, hypertension-induced systolic and diastolic dysfunction points to high afterload as a cause. These findings from an experimental model are translatable to the clinical peri-operative environment in which myocardial deformation may have the potential to guide blood pressure management, in particular at varying individual autoregulation thresholds.

Study design for a randomized crossover study investigating myocardial strain analysis in patients with coronary artery disease at hyperoxia and normoxemia prior to coronary artery bypass graft surgery (StrECHO-O2)

BACKGROUND

Supplemental oxygen (O₂) is used routinely during anesthesia. In the treatment of acute myocardial infarction, it has been established that hyperoxia is to be avoided, whereas information on benefit and risk of hyperoxia in patients with stable coronary artery disease (CAD) remain scarce, especially in the setting of general anesthesia. This study will compare the immediate effects of normoxemia and hyperoxia on cardiac function, with a primary focus on changes in peak longitudinal left-ventricular strain, in anesthetized stable chronic CAD patients using peri-operative transesophageal echocardiography (TEE).

METHODS

A single-center randomized cross-over clinical trial will be conducted, enrolling 106 patients undergoing elective coronary artery bypass graft surgery. After the induction of anesthesia and prior to the start of surgery, cardiac function will be assessed by 2D and 3D TEE. Images will be acquired at two different oxygen states for each patient in randomized order. The fraction of inspired oxygen (F_IO₂) will be titrated to a normoxemic state (oxygen saturation of 95-98%) and adjusted to a hyperoxic state (F_IO₂ = 0.8). TEE images will be analyzed in a blinded manner for standard cardiac function and strain parameters.

CONCLUSION

By using myocardial strain assessed by TEE, early and subtle signs of biventricular systolic and diastolic dysfunction can be promptly measured intraoperatively prior to the onset of severe signs of ischemia. The results may help anesthesiologists to better understand the effects of F_IO₂ on cardiac function and potentially tailor oxygen therapy to patients with CAD undergoing general anesthesia.

Diastolic function assessed my CMR feature tracking is a predictor for outcomes in patients with suspected myocarditis and preserved left ventricular ejection fraction

Funding Acknowledgements

Type of funding sources: None.

Diastolic function assessed my CMR feature tracking is a predictor for outcomes in patients with suspected myocarditis and preserved left ventricular ejection fraction

Background

Impairment of left ventricular (LV) systolic function was reported to be a valuable predictor for outcomes in patients with myocarditis. However, in patients with myocarditis and preserved LV systolic function, prediction of outcomes remains challenging. So far, minimal data exists about the prognostic role of diastolic function, as assessed by cardiac magnetic resonance imaging (CMR) in the clinical setting of suspected myocarditis.

Purpose

To determine the predictive value of LV diastolic function in patients with suspected myocarditis and preserved LV ejection fraction (LVEF).

Methods

In patients referred for CMR with clinically suspected myocarditis and LVEF≥50%, diastolic function was assessed by CMR feature tracking (FT). The primary endpoint was defined as a composite of major adverse cardiovascular events (MACE) including hospitalization for heart failure, recurrent myocarditis, sustained ventricular tachycardia and all-cause death.

Results

Of 381 patients included with clinically suspected myocarditis (216, 56.7% male, mean age 45.7 ± 16.4 years) late gadolinium enhancement (LGE) was present in 124 (32.4 %) of patients (mean LGE extent 4.9 ± 5.0 g). MACE occurred in 25 (6.6%) individuals at a median follow-up time of 4.5 years. In a univariate cox-regression model, radial, circumferential and longitudinal early diastolic strain rate (EDSR) and circumferential late diastolic strain rate were significantly associated with MACE. After adjustment for age, gender and extent of LGE, radial EDSR remained an independent predictor for MACE (HR = 2.26, 95% CI 1.06 to 4.8; p = 0.034).

Conclusion

Diastolic strain rate, as assessed by CMR-FT, can be useful in the prediction of outcomes in patients with myocarditis and preserved LVEF.

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.

Visualizing myocardial injury from elective cardioversion with CMR

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Association of Cardiothoracic Anaesthesiologists Research Grant

Background

Despite everyday use of electrical interventions in cardiovascular care, the extent and type of concomitant myocardial injury is not fully understood. Current literature disagrees about the question whether and how cardioversion or defibrillation damage the myocardium, especially when serologic markers are used. Such markers are not always cardiac-specific, nor diagnostic for type and region of myocardial injury. These limitations may be overcome by parametric T1 and T2 mapping. We aimed to investigate whether the acute and long-term impact of electrical cardioversion on myocardial structure and function is detectable using CMR imaging.

Methods

Patients scheduled for elective cardioversion were enrolled to undergo three CMR exams (3 Tesla): on the morning prior to cardioversion to assess pre-existing injury; two to five hours after cardioversion to assess the acute response; and six to ten weeks later to investigate chronic injury. The CMR exam studied left ventricular (LV) function, T2 mapping to measure edema, and extracellular volume (ECV) from T1 maps to measure diffuse fibrosis. Both the degree of injury and proportion (%) of myocardial area affected were analysed.

Results

Eight patients completed the study, requiring 1-2 shocks (totalling 120-300 J biphasic energy) to achieve sinus rhythm. LV ejection fraction increased after cardioversion from 47 ± 13% to 55 ± 15% (p = 0.020), and was 52 ± 16% at the third exam (p = 0.199). Even prior to intervention, some patients showed edema (baseline T2 &gt; 40ms) afflicting 49 ± 23% of their LV myocardium. Area affected by edema expanded to 72 ± 18% after cardioversion (p = 0.002) and returned to 54 ± 24% by the third exam. T2 rose from baseline (40.4 ± 1.8ms) after cardioversion acutely to 44.1 ± 5.2ms (p = 0.028) and normalized until the late exam (40.8 ± 3.1ms). Myocardial area affected by diffuse fibrosis (ECV &gt; 30%) was 28.3 ± 9.4% at baseline and 38.8 ± 18.9% late after cardioversion (p = 0.018). Pathologic T2 increases (indicative of edema) were not observed in all patients, but individuals with higher baseline ECV also experienced greater T2 increase after cardioversion (r = 0.840, p = 0.036).

Conclusion

Elective cardioversion improves LV systolic function, but also aggravates myocardial edema and possibly adds to diffuse fibrosis during several weeks thereafter. Such sequelae of cardioversion were observed mainly in patients with a greater burden of pre-existing myocardial injury. More data is needed to corroborate these preliminary findings and to study whether this type of myocardial injury predicts worse outcome. Moreover, changes in CMR markers caused by electrical interventions including defibrillation, may have the potential to confound diagnostic assessments of the underlying cardiac injury.

Abstract Figure

Changes in right ventricular deformation during hyperoxia versus normoxaemia in patients with stable coronary artery disease and healthy controls

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): Local research funds of the Department of Anaesthesiology and Pain medicine, Bern University Hospital, Inselspital

Background

During anaesthesia, emergency and critical care treatment, patients with coronary artery disease (CAD) are often exposed to supraphysiologic arterial oxygen tensions. The balance between benefits and risks of hyperoxia (HO) in patients with stable CAD is controversial, with reports about reduced left ventricular contractility or increased morbidity and mortality. Effects of HO on right ventricular (RV) function in CAD are less well described. Advanced cardiovascular magnetic resonance (CMR) feature tracking software allows assessment of myocardial deformation, which may serve as early marker of ventricular dysfunction. In a CMR study we quantified the effect of HO on RV function and deformation in awake healthy participants and CAD patients.

Methods

Ten healthy participants and 26 patients with stable one- or two-vessel obstructive CAD were included. In a CMR study, a short-axis function stack of both ventricles was obtained first at room air (RA), then during HO induced by breathing oxygen at 10L/min for 5 minutes via a non-rebreathing facemask. RV strain was analysed by a blinded reader who manually traced epicardial and endocardial contours of the RV for determining peak global circumferential strain (RVGCS), time to peak strain, systolic and diastolic strain rate parameters.

Results

RV ejection fraction did not change with O2 breathing in the healthy control group (RA, 56 ± 12% vs. HO, 55 ± 10%, p = 0.999) nor in the CAD group (RA, 60 ± 8% vs. HO, 60 ± 9%, p = 0.609). RV cardiac index decreased significantly in CAD patients from RA (2.62 ± 0.88 L/min/m2) to HO (2.42 ± 0.77L/min/m2, p = 0.002). The decrease in the control group was not significant (RVCI: RA 3.28 ± 1.29 vs HO 3.04 ± 1.27L/min/m2 p = 0.068).

In the healthy control group, RVGCS, time to peak strain, and systolic strain rate did not change significantly with HO (RVGCS: RA, -14.6 ± 3.9% vs. HO, -13.1 ± 4.5%, p = 0.353; time to peak strain: 282 ± 45ms vs. 286 ± 29ms, p = 0.540; and systolic strain rate: -0.85 ± 0.27/s vs. -0.67 ± 0.28, p = 0.055).

In CAD patients RVGCS worsened from -14.8 ± 3.3% on RA to -13.9 ± 3.6% at HO (p = 0.040). Time to peak strain became significantly prolonged from 319 ± 40ms on RA to 329 ± 49ms at HO (p = 0.046). This was accompanied by a reduction of systolic strain rate from -0.79 ± 0.27/s to -0.75 ± 0.22/s (p = 0.037). Diastolic strain parameters did not differ significantly between RA and HO in either group.

Conclusion

In our cohort of CAD patients HO significantly reduced RV cardiac index and impaired systolic deformation as determined by CMR feature tracking. Studies are required in a larger patient cohort with regional analysis and assessment of longitudinal and radial deformation to assess the role of hyperoxia in CAD.

Abstract Figure. Change in RV Peak Circumferential Strain

Resolution of Strain Abnormalities During Extracorporeal Rewarming From Accidental Hypothermic Cardiac Arrest Following Avalanche Burial

A hypothermic avalanche victim underwent, during extracorporeal warming from asystolic arrest, 3-dimensional transesophageal echocardiography. At 33°C core temperature, left ventricular ejection fraction had recovered, whereas myocardial strain still demonstrated significant dysfunction until 36°C. Deformation analysis seems more sensitive than global assessment during myocardial recovery from hypothermic cardiac arrest. (Level of Difficulty: Intermediate.)

Feature Tracking Myocardial Strain Incrementally Improves Prognostication in Myocarditis Beyond Traditional CMR Imaging Features

OBJECTIVES

This study investigated the association of cardiovascular cardiac magnetic resonance (CMR) feature tracking (FT) with outcome in a patient cohort with myocarditis and evaluated the possible incremental prognostic benefit beyond clinical features and traditional CMR features.

BACKGROUND

CMR is used to diagnose and risk stratify patients with myocarditis. CMR-FT allows quantitative strain analysis of myocardial function; however, its prognostic benefit in myocarditis is unknown.

METHODS

Consecutive patients with clinically suspected myocarditis and presence of midmyocardial or epicardial late gadolinium enhancement (LGE) and/or myocardial edema in CMR were included. Clinical and CMR features were analyzed with regard to major adverse cardiovascular events (MACE) (i.e., hospitalization for heart failure, sustained ventricular tachycardia, and all-cause mortality).

RESULTS

Of 740 patients with clinically suspected myocarditis, 455 (61%) met our final diagnostic criteria based on CMR tissue characterization. At a median follow-up of 3.9 years, MACE occurred in 74 (16%) patients. In the univariable analysis, CMR-FT global longitudinal peak strain (GLS) was significantly associated with MACE. In a multivariable model adjusting for clinical variables (age, sex, body mass index, and acuteness of symptoms) and traditional CMR features (left ventricular ejection fraction [LVEF] and LGE extent), GLS remained independently associated with outcome (GLS hazard ratio: 1.21; 95% confidence interval: 1.08 to 1.36; p = 0.001) and incrementally improved prognostication (chi-square increases from 42.6 to 79.8 to 88.5; p < 0.001).

CONCLUSIONS

Myocardial strain using CMR-FT provides independent and incremental prognostic value over clinical features, LVEF, and LGE in patients with myocarditis. CMR-FT may serve as a novel marker to improve risk stratification in myocarditis. (CMR Features in Patients With Suspected Myocarditis [CMRMyo]; NCT03470571).

Effect of Hyperoxia on Myocardial Oxygenation and Function in Patients With Stable Multivessel Coronary Artery Disease

Background

The impact of hyperoxia, that is, supraphysiological arterial partial pressure of O₂, on myocardial oxygen balance and function in stable multivessel coronary artery disease (CAD) is poorly understood. In this observational study, we assessed myocardial effects of inhalational hyperoxia in patients with CAD using a comprehensive cardiovascular magnetic resonance exam.

Methods and Results

Twenty‐five patients with stable CAD underwent a contrast‐free cardiovascular magnetic resonance exam in the interval between their index coronary angiography and subsequent revascularization. The cardiovascular magnetic resonance exam involved T1 and T2 mapping for tissue characterization (fibrosis, edema) as well as function imaging, from which strain analysis was derived, and oxygenation‐sensitive cardiovascular magnetic resonance imaging. The latter modalities were both acquired at room air and after breathing pure O₂ by face mask at 10 L/min for 5 minutes. In 14 of the 25 CAD patients (56%), hyperoxia induced poststenotic myocardial deoxygenation with a subsequent oxygenation discordance across the myocardium. Extent of deoxygenation was correlated to degree of stenosis (r=−0.434, P=0.033). Hyperoxia‐associated poststenotic deoxygenation was accompanied by ipsiregional reduction of diastolic strain rate (1.39±0.57 versus 1.18±0.65; P=0.045) and systolic radial velocity (37.40±17.22 versus 32.88±13.58; P=0.038). Increased T2, as well as lower cardiac index, and defined abnormal strain parameters on room air were predictive for hyperoxia‐induced abnormalities (P<0.05). Furthermore, in patients with prolonged native T1 (>1220 ms), hyperoxia reduced ejection fraction and peak strain.

Conclusions

Patients with CAD and pre‐existent myocardial injury who respond to hyperoxic challenge with strain abnormalities appear susceptible for hyperoxia‐induced regional deoxygenation and deterioration of myocardial function.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02233634.

Association of ECG parameters with late gadolinium enhancement and outcome in patients with clinical suspicion of acute or subacute myocarditis referred for CMR imaging

BACKGROUND

Risk stratification of myocarditis is challenging due to variable clinical presentations. Cardiovascular magnetic resonance (CMR) is the primary non-invasive imaging modality to investigate myocarditis while electrocardiograms (ECG) are routinely included in the clinical work-up. The association of ECG parameters with CMR tissue characterisation and their prognostic value were investigated in patients with clinically suspected myocarditis.

METHODS AND RESULTS

Consecutive patients with suspected myocarditis who underwent CMR and ECG were analysed. Major adverse cardiovascular event (MACE) included all-cause death, hospitalisation for heart failure, heart transplantation, documented sustained ventricular arrhythmia, or recurrent myocarditis. A total of 587 patients were followed for a median of 3.9 years. A wide QRS-T angle, low voltage and fragmented QRS were significantly associated with late gadolinium enhancement. Further, a wide QRS-T angle, low voltage and prolonged QTc duration were associated with MACE in the univariable analysis. In a multivariable model, late gadolinium enhancement (HR: 1.90, 95%CI: 1.17-3.10; p = 0.010) and the ECG parameters of a low QRS voltage (HR: 1.86, 95%CI: 1.01-3.42; p = 0.046) and QRS-T-angle (HR: 1.01, 95%CI: 1.00-1.01; p = 0.029) remained independently associated with outcome. The cumulative incidence of MACE was incrementally higher when findings of both CMR and ECG were abnormal (p<0.001).

CONCLUSION

In patients with clinically suspected myocarditis, abnormal ECG parameters are associated with abnormal tissue characteristics detected by CMR. Further, ECG and CMR findings have independent prognostic implications for morbidity and mortality. Integrating both exams into clinical decision-making may play a role in risk stratification in this heterogeneous patient population.

Hyperventilation-induced heart rate response as a potential marker for cardiovascular disease

An increase of heart rate to physical or mental stress reflects the ability of the autonomous nervous system and the heart to respond adequately. Hyperventilation is a user-controlled breathing maneuver that has a significant impact on coronary function and hemodynamics. Thus, we aimed to investigate if the heart rate response to hyperventilation (HRRHV) can provide clinically useful information. A pooled analysis of the HRRHV after 60 s of hyperventilation was conducted in 282 participants including healthy controls; patients with heart failure (HF); coronary artery disease (CAD); a combination of both; or patients suspected of CAD but with a normal angiogram. Hyperventilation significantly increased heart rate in all groups, although healthy controls aged 55 years and older (15 ± 9 bpm) had a larger HRRHV than each of the disease groups (HF: 6 ± 6, CAD: 8 ± 8, CAD+/HF+: 6 ± 4, and CAD-/HF-: 8 ± 6 bpm, p < 0.001). No significant differences were found between disease groups. The HRRHV may serve as an easily measurable additional marker of cardiovascular health. Future studies should test its diagnostic potential as a simple, inexpensive pre-screening test to improve patient selection for other diagnostic exams.

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.

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

BACKGROUND

Breathing 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 FINDINGS

In 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.

CONCLUSION

In 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.

Evidence for Acute Myocardial and Skeletal Muscle Injury after Serial Transthoracic Shocks in Healthy Swine

Background

Previous serological studies have shown controversial results whether defibrillation or cardioversion can cause myocardial injury. Cardiovascular Magnetic Resonance (CMR) can be used to detect myocardial edema, hyperemia and capillary leak as features of acute myocardial injury. The aim of this study was to assess for myocardial and skeletal muscle injury in swine following transthoracic shocks.

Methods

Seventeen anaesthetized swine were examined, with 11 undergoing five synchronized transthoracic shocks (200J). Myocardial and skeletal muscle injury were assessed at baseline and up to 5h post-shock employing T1 mapping, T2 mapping, early and late gadolinium enhancement. Serologic markers (cFABP, TnI, CK, and CK-MB) and myocardial tissue were assessed by standard histology methods.

Results

In myocardial regions within the shock path, T1 and T2 were significantly increased compared to remote myocardium in the same animals. The early gadolinium enhancement ratio between the left-ventricular myocardium and the right pectoral muscle was also increased compared to control animals. After the shocks cFABP and CK were significantly elevated. After shock application, the regions identified as abnormal by CMR showed significantly increased interstitial and myocardial cell areas in histological analysis. This increased cell area suggests significant cellular and interstitial edema.

Conclusion

Our pilot study data indicate that serial defibrillator shocks lead to acute skeletal muscle and myocardial injury. CMR is a useful tool to detect and localize myocardial and skeletal muscle injury early after transthoracic shocks in vivo. In the future the technique could potentially be used as an additional tool for quality control such as verifying insufficient local shock application in non-responders after cardioversion or to develop safer shock forms.

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.