Exercise Heat Acclimation With Dehydration Does Not Affect Vascular and Cardiac Volumes or Systemic Hemodynamics During Endurance Exercise

Permissive dehydration during exercise heat acclimation (HA) may enhance hematological and cardiovascular adaptations and thus acute responses to prolonged exercise. However, the independent role of permissive dehydration on vascular and cardiac volumes, ventricular-arterial (VA) coupling and systemic hemodynamics has not been systematically investigated. Seven males completed two 10-day exercise HA interventions with controlled heart rate (HR) where euhydration was maintained or permissive dehydration (-2.9 ± 0.5% body mass) occurred. Two experimental trials were conducted before and after each HA intervention where euhydration was maintained (-0.5 ± 0.4%) or dehydration was induced (-3.6 ± 0.6%) via prescribed fluid intakes. Rectal (Tre) and skin temperatures, HR, blood (BV) and left ventricular (LV) volumes, and systemic hemodynamics were measured at rest and during bouts of semi-recumbent cycling (55% V̇O2peak) in 33°C at 20, 100, and 180 min. Throughout HA sweat rate (12 ± 9%) and power output (18 ± 7 W) increased (P < 0.05), whereas Tre was 38.4 ± 0.2°C during the 75 min of HR controlled exercise (P = 1.00). Neither HA intervention altered resting and euhydrated exercising Tre, BV, LV diastolic and systolic volumes, systemic hemodynamics, and VA coupling (P > 0.05). Furthermore, the thermal and cardiovascular strain during exercise with acute dehydration post-HA was not influenced by HA hydration strategy. Instead, elevations in Tre and HR and reductions in BV and cardiac output matched pre-HA levels (P > 0.05). These findings indicate that permissive dehydration during exercise HA with controlled HR and maintained thermal stimulus does not affect hematological or cardiovascular responses during acute endurance exercise under moderate heat stress with maintained euhydration or moderate dehydration.

Impact of age, sex, and cardiac size on the diagnostic performance of myocardial perfusion single-photon emission computed tomography: insights from the REFINE SPECT registry

Background Single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI) is a well-validated non-invasive method for detecting coronary artery disease (CAD). Variations in diagnostic performance due to age and sex have been thoroughly investigated in the literature yet have demonstrated conflicting results. Several studies have associated female sex with reduced accuracy, although others have discovered no significant difference (1). Similarly, while SPECT MPI in the elderly has shown prognostic utility, cardiac event rates are elevated compared to younger patients despite a normal study (2). Additional analyses have suggested that cardiac chamber size may contribute to these observed differences due to its relationship with spatial resolution; however, the interaction of age, sex, and cardiac size remains unknown. Purpose We aimed to leverage a large, multicenter, international registry to assess the impact of age, sex, and left ventricular size on the diagnostic accuracy of contemporary SPECT MPI. Methods In 9 centers, 2067 patients (67% male, 64.7±11.2 years) in the REFINE SPECT database (REgistry of Fast Myocardial Perfusion Imaging with NExt Generation SPECT) underwent MPI with new generation solid-state scanners followed by invasive coronary angiography within 6 months (3). Stress total perfusion deficit was quantified automatically, and obstructive CAD was defined as >70% stenosis or >50% for left main. Receiver-operating characteristic curves and corresponding areas under the curve (AUC) were computed to compare diagnostic performance between cohorts created based on age (<75 vs. ≥75 years), sex, and end-diastolic volume (EDV; ≥20th vs. <20th sex-specific percentile). Results Female and elderly patients had a significantly lower EDV than male and younger patients respectively (p<0.001, Figure 1). Diagnostic accuracy of SPECT was similar by sex (p=0.63). Elderly patients (AUC 0.72 vs. 0.78, p=0.025) and patients with reduced volumes (AUC 0.72 vs. 0.79, p=0.009) exhibited significantly worse performance. When isolating male patients with reduced volumes, a significant difference in accuracy was observed (AUC 0.69 vs. 0.79, p=0.001; Figure 2A), while female patients trended towards significance (p=0.32). Likewise, SPECT performed poorly for elderly patients with reduced volumes (AUC 0.64 vs. 0.78, p=0.01; Figure 2B). If patients possessed any two characteristics of male sex, age ≥75, or low EDV, prediction of CAD with SPECT was significantly decreased (p=0.002; Figure 2C). Conclusions Our findings suggest that men with reduced cardiac volumes display worse diagnostic SPECT performance, although it is uncertain whether a pathophysiologic reason exists or further investigation is required for female patients. Patients age ≥75 tended to have lower cardiac volumes as well as lower diagnostic performance. Given these results, alternative diagnostic modalities may better diagnose CAD in patients with these characteristics. FUNDunding Acknowledgement Type of funding sources: None. Figure 1 Figure 2

7-Tesla Functional Cardiovascular MR Using Vectorcardiographic Triggering—Overcoming the Magnetohydrodynamic Effect

Objective: Ultra-high-field B0 ≥ 7 tesla (7T) cardiovascular magnetic resonance (CMR) offers increased resolution. However, electrocardiogram (ECG) gating is impacted by the magneto-hydrodynamic effect distorting the ECG trace. We explored the technical feasibility of a 7T magnetic resonance scanner using an ECG trigger learning algorithm to quantitatively assess cardiac volumes and vascular flow. Methods: 7T scans were performed on 10 healthy volunteers on a whole-body research MRI MR scanner (Siemens Healthineers, Erlangen, Germany) with 8 channel Tx/32 channels Rx cardiac coils (MRI Tools GmbH, Berlin, Germany). Vectorcardiogram ECG was performed using a learning phase outside of the magnetic field, with a trigger algorithm overcoming severe ECG signal distortions. Vectorcardiograms were quantitatively analyzed for false negative and false positive events. Cine CMR was performed after 3rd-order B0 shimming using a high-resolution breath-held ECG-retro-gated segmented spoiled gradient echo, and 2D phase contrast flow imaging. Artefacts were assessed using a semi-quantitative scale. Results: 7T CMR scans were acquired in all patients (100%) using the vectorcardiogram learning method. 3,142 R-waves were quantitatively analyzed, yielding sensitivity of 97.6% and specificity of 98.7%. Mean image quality score was 0.9, sufficient to quantitate both cardiac volumes, ejection fraction, and aortic and pulmonary blood flow. Mean left ventricular ejection fraction was 56.4%, right ventricular ejection fraction was 51.4%. Conclusion: Reliable cardiac ECG triggering is feasible in healthy volunteers at 7T utilizing a state-of-the-art three-lead trigger device despite signal distortion from the magnetohydrodynamic effect. This provides sufficient image quality for quantitative analysis. Other ultra-high-field imaging applications such as human brain functional MRI with physiologic noise correction may benefit from this method of ECG triggering.

Imaging myocardial ischemia: from emerging techniques to state-of-the-art

The widespread clinical use of cardiovascular imaging inspires constant improvement in imaging technology and post-processing applications. Recent advances in hardware and software have brought about important developments in the assessment of myocardial ischemia such as the rapid evaluation of cardiac volumes and function, ability for detection of subtle myocardial changes, and the combination of anatomic and functional assessment of a coronary artery stenosis via a single modality, which was previously not possible in a noninvasive fashion. These milestones indicate the start of a new era, a paradigm shift that broadens the role of noninvasive imaging. The thematic series Myocardial tissue characterization in ischemic heart disease introduces a set of narrative review and original articles by world renowned authors demonstrating such novel advancements and the state-of-the-art techniques in cardiac imaging.

Computed tomography characteristics of patients with functional MR receiving MitraClip

Funding Acknowledgements Type of funding sources: None. Background Percutaneous leaflet repair with the MitraClip device (Abbott Vascular, Menlo Park, CA) is safe and effective in patients with severe functional mitral regurgitation (FMR). Residual or recurrent MR may occur in up to 40% of patients and is associated with persistent symptoms and impaired survival. The anatomical characteristics associated with residual or recurrent MR after MitraClip are not well defined by computed tomography angiography (CTA) in FMR population. Methods A retrospective analysis of patients with significant FMR, who underwent retrospective-gated CTA at Minneapolis Heart Institute between July 2015 to January 2020, identified those who underwent percutaneous leaflet repair with MitraClip. Anatomical and functional parameters were assessed by pre-procedure CTA and compared between those with and without residual (≥2) MR. Results A total of 25 patients were included (median[Q1, Q3]; age, 80[75, 85]; 44% men) and classified into ventricular FMR (V-FMR, n = 12) and atrial FMR (A-FMR, n = 13) according to anatomical and functional characteristics by CTA. 50% of V-FMR and 38% of A-FMR had residual/worsening MR. Among V-FMR patients with residual/worsening MR, shorter coaptation length was observed (2.2[2, 2.3] mm vs. 3.5[3, 4], p = 0.006) (Figure). No differences in anatomical or functional characteristics were seen in A-FMR patients. Conclusion Longer coaptation length in V-FMR is predictive of successful MitraClip procedure, whereas mitral annulus size and cardiac volumes are not. <Ventricular FMR> Total (N = 12) No residual/no worsening MR (N = 6) Residual/worsening MR (N = 6) P value Septal-lateral diameter, mm 31.9 (30.5, 37.9) 32.2 (30.1, 39.8) 31.9 (29.5, 35) 0.749 Annulus area, cm² 11.2 (10.4, 13.6) 11.3 (10.1, 14.6) 11.1 (9.6, 12.6) 0.631 Tenting area, cm² 1.6 (1.3, 2.1) 1.6 (1.2, 2.2) 1.7 (1.2, 2.3) 0.873 Tenting height, mm 8.5 (6.5, 9.7) 8.5 (6.6, 9.3) 8.3 (6.3, 10.1) 0.749 Coaptation length, mm 2.6 (2.1, 3.5) 3.5 (3.0, 4.0) 2.2 (2.0, 2.3) 0.006 <Atrial FMR> Total (N = 13) No residual/no worsening MR (N = 8) Residual/worsening MR (N = 5) P value Septal-lateral diameter, mm 32.3 (29.5, 39.0) 32.0 (29.2, 39.9) 34.3 (30.8, 39.02) 0.464 Annulus area, cm² 10.3 (9.2, 14.7) 10.2 (9.0, 14.6) 12.4 (9.4, 14.7) 0.661 Tenting area, cm² 1.2 (0.8, 1.8) 1.1 (0.7, 2.2) 1.3 (0.7, 1.8) 0.884 Tenting height, mm 5.5 (4.1, 6.9) 6.3 (4.1, 8.7) 4.6 (3.7, 5.8) 0.213 Coaptation length, mm 2.3 (1.5, 2.8) 2.5 (1.4, 3.5) 1.9 (1.5, 2.6) 0.464 Comparison of baseline CT parameters between no residual/ no worsening MR and residual/ worsening MR Abstract Figure.

Nitrate induced vasoplegia depletes cardiac energy reserves: a model for acute cardiomyopathy in septic shock?

Introduction The healthy heart is at its most efficient when contractile filaments are stretched with preload. To produce the same cardiac output, oxygen requirement rises are proportionally greater with increased inotropy or heart rate than with increased preload. We hypothesized that in vasoplegia, loss of preload (owing to dilation of capacitance veins) and compensatory rises in heart rate and contractility would compromise the efficiency of the heart. We speculated that this may be one factor impairing cardiac function in conditions of distributive shock such as sepsis and looked to model the effects. We used cardiac magnetic resonance imaging to capture changes in cardiac volumes and contractility and magnetic resonance spectroscopy to investigate changes in ATP metabolism within the myocardium in healthy volunteers given GTN as a vasodilator. Methods We recruited 7 healthy volunteers (mean age 40 years, range 28–62 years; mean BMI 21.9, range 18.5–24.5) and measured their baseline cardiac volumes and function, PCr/ATP ratio and Creatine Kinase first order rate constant (CKkf), using cardiac magnetic resonance imaging and magnetic resonance spectroscopy and saturation transfer at 3 Tesla. At the same visit, they received a glyceryl trinitrate (GTN) infusion to induce vasoplegia and the measurements were repeated. We targeted GTN infusion rate to a fall in mean arterial pressure of 15mmHg. Results The GTN infusion brought about a fall in mean arterial pressure (from a baseline of 79±7mmHg to 64±7 mmHg, p<0.0001) and a fall in LV end diastolic volume (169±57 ml vs 148±58 ml, p=0.003) indicating a reduction in preload. As expected, there was a compensatory rise in heart rate (61±7 bpm vs 69±10bpm, p=0.0005) and ejection fraction (62±3% vs 67±3%, p=0.001), however cardiac output remained unchanged (6.72±1.49 L/min vs 6.68±1.48 L/min, p=0.87). Cardiac work (calculated as stroke volume x MAP x heart rate) fell (477±123 vs 424±119 L.mmHg/min, p=0.03). There was a fall in PCr/ATP ratio on GTN (2.18±0.25 vs 1.91±0.2, p 0.03) while CKkf more than doubled (0.14±0.06 s-1 vs 0.23±0.08 s-1, p=0.02) and creatine kinase flux also showed a significant increase (1.65±0.78 μmol/g/s vs 2.28±0.71 μmol/g/s, p=0.05). Conclusions What is novel here is that we show a fall in PCr/ATP ratio: as ATP concentrations in the cell are strictly maintained, this suggests phosphocreatine pool depletion occurs when preload is lost and cardiac output is maintained by an increase in inotropy and chronotropy. The rise in CKkf and CK flux confirm the increased energy demand. Progressive energetic depletion during high demand may give rise to contractile dysfunction over time as the heart is unable to keep up with increased requirements for ATP, and progressively becomes more starved of energy. This could be a mechanism of cardiac dysfunction in septic shock and other vasoplegic states. Figure 1 Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): British Heart Foundation

3D Hermite Transform Optical Flow Estimation in Left Ventricle CT Sequences

Heart diseases are the most important causes of death in the world and over the years, the study of cardiac movement has been carried out mainly in two dimensions, however, it is important to consider that the deformations due to the movement of the heart occur in a three-dimensional space. The 3 D + t analysis allows to describe most of the motions of the heart, for example, the twisting motion that takes place on every beat cycle that allows us identifying abnormalities of the heart walls. Therefore, it is necessary to develop algorithms that help specialists understand the cardiac movement. In this work, we developed a new approach to determine the cardiac movement in three dimensions using a differential optical flow approach in which we use the steered Hermite transform (SHT) which allows us to decompose cardiac volumes taking advantage of it as a model of the human vision system (HVS). Our proposal was tested in complete cardiac computed tomography (CT) volumes ( 3 D + t ), as well as its respective left ventricular segmentation. The robustness to noise was tested with good results. The evaluation of the results was carried out through errors in forwarding reconstruction, from the volume at time t to time t + 1 using the optical flow obtained (interpolation errors). The parameters were tuned extensively. In the case of the 2D algorithm, the interpolation errors and normalized interpolation errors are very close and below the values reported in ground truth flows. In the case of the 3D algorithm, the results were compared with another similar method in 3D and the interpolation errors remained below 0.1. These results of interpolation errors for complete cardiac volumes and the left ventricle are shown graphically for clarity. Finally, a series of graphs are observed where the characteristic of contraction and dilation of the left ventricle is evident through the representation of the 3D optical flow.