Increased myocardial oxygen consumption rates are associated with maladaptive right ventricular remodeling and decreased event-free survival in heart failure patients

Extrarenal Benefits of SGLT2 Inhibitors in the Treatment of Cardiomyopathies

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have emerged as pivotal medications for heart failure, demonstrating remarkable cardiovascular benefits extending beyond their glucose-lowering effects. The unexpected cardiovascular advantages have intrigued and prompted the scientific community to delve into the mechanistic underpinnings of these novel actions. Preclinical studies have generated many mechanistic theories, ranging from their renal and extrarenal effects to potential direct actions on cardiac muscle cells, to elucidate the mechanisms linking these drugs to clinical cardiovascular outcomes. Despite the strengths and limitations of each theory, many await validation in human studies. Furthermore, whether SGLT2 inhibitors confer therapeutic benefits in specific subsets of cardiomyopathies akin to their efficacy in other heart failure populations remains unclear. By examining the shared pathological features between heart failure resulting from vascular diseases and other causes of cardiomyopathy, certain specific molecular actions of SGLT2 inhibitors (particularly those targeting cardiomyocytes) would support the concept that these medications will yield therapeutic benefits across a broad range of cardiomyopathies. This article aims to discuss the important mechanisms of SGLT2 inhibitors and their implications in hypertrophic and dilated cardiomyopathies. Furthermore, we offer insights into future research directions for SGLT2 inhibitor studies, which hold the potential to further elucidate the proposed biological mechanisms in greater detail.

QCard-NM: Developing a semiautomatic segmentation method for quantitative analysis of the right ventricle in non-gated myocardial perfusion SPECT imaging

BACKGROUND

Recent studies have shown that the right ventricular (RV) quantitative analysis in myocardial perfusion imaging (MPI) SPECT can be beneficial in the diagnosis of many cardiopulmonary diseases. This study proposes a new algorithm for right ventricular 3D segmentation and quantification.

METHODS

The proposed Quantitative Cardiac analysis in Nuclear Medicine imaging (QCard-NM) algorithm provides RV myocardial surface estimation and creates myocardial contour using an iterative 3D model fitting method. The founded contour is then used for quantitative RV analysis. The proposed method was assessed using various patient datasets and digital phantoms. First, the physician's manually drawn contours were compared to the QCard-NM RV segmentation using the Dice similarity coefficient (DSC). Second, using repeated MPI scans, the QCard-NM's repeatability was evaluated and compared with the QPS (quantitative perfusion SPECT) algorithm. Third, the bias of the calculated RV cavity volume was analyzed using 31 digital phantoms using the QCard-NM and QPS algorithms. Fourth, the ability of QCard-NM analysis to diagnose coronary artery diseases was assessed in 60 patients referred for both MPI and coronary angiography.

RESULTS

The average DSC value was 0.83 in the first dataset. In the second dataset, the coefficient of repeatability of the calculated RV volume between two repeated scans was 13.57 and 43.41 ml for the QCard-NM and QPS, respectively. In the phantom study, the mean absolute percentage errors for the calculated cavity volume were 22.6% and 42.2% for the QCard-NM and QPS, respectively. RV quantitative analysis using QCard-NM in detecting patients with severe left coronary system stenosis and/or three-vessel diseases achieved a fair performance with the area under the ROC curve of 0.77.

CONCLUSION

A novel model-based iterative method for RV segmentation task in non-gated MPI SPECT is proposed. The precision, accuracy, and consistency of the proposed method are demonstrated by various validation techniques. We believe this preliminary study could lead to developing a framework for improving the diagnosis of cardiopulmonary diseases using RV quantitative analysis in MPI SPECT.

Work and oxygen consumption of isolated right ventricular papillary muscle in experimental pulmonary hypertension

Right-sided myocardial mechanical efficiency (work output/metabolic energy input) in pulmonary hypertension can be severely reduced. We determined the contribution of intrinsic myocardial determinants of efficiency using papillary muscle preparations from monocrotaline-induced pulmonary hypertensive (MCT-PH) rats. The hypothesis tested was that efficiency is reduced by mitochondrial dysfunction in addition to increased activation heat reported previously. Right ventricular muscle preparations were subjected to 5 Hz sinusoidal length changes at 37°C. Work and suprabasal oxygen consumption (V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) were measured before and after cross-bridge inhibition by blebbistatin. Cytosolic cytochrome c concentration, myocyte cross-sectional area, proton permeability of the inner mitochondrial membrane and monoamine oxidase and glucose 6-phosphate dehydrogenase activities and phosphatidylglycerol/cardiolipin contents were determined. Mechanical efficiency ranged from 23% to 11% in control (n = 6) and from 22% to 1% in MCT-PH (n = 15) and correlated with work (r2  = 0.68, P < 0.0001) but not withV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ (r2  = 0.004, P = 0.7919).V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ for cross-bridge cycling was proportional to work (r2  = 0.56, P = 0.0005). Blebbistatin-resistantV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ (r2  = 0.32, P = 0.0167) and proton permeability of the mitochondrial inner membrane (r2  = 0.36, P = 0.0110) correlated inversely with efficiency. Together, these variables explained the variance of efficiency (coefficient of multiple determination r2  = 0.79, P = 0.0001). Cytosolic cytochrome c correlated inversely with work (r2  = 0.28, P = 0.0391), but not with efficiency (r2  = 0.20, P = 0.0867). Glucose 6-phosphate dehydrogenase, monoamine oxidase and phosphatidylglycerol/cardiolipin increased in the right ventricular wall of MCT-PH but did not correlate with efficiency. Reduced myocardial efficiency in MCT-PH is a result of activation processes and mitochondrial dysfunction. The variance of work and the ratio of activation heat reported previously and blebbistatin-resistantV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ are discussed. KEY POINTS: Mechanical efficiency of right ventricular myocardium is reduced in pulmonary hypertension. Increased energy use for activation processes has been demonstrated previously, but the contribution of mitochondrial dysfunction is unknown. Work and oxygen consumption are determined during work loops. Oxygen consumption for activation and cross-bridge cycling confirm the previous heat measurements. Cytosolic cytochrome c concentration, proton permeability of the mitochondrial inner membrane and phosphatidylglycerol/cardiolipin are increased in experimental pulmonary hypertension. Reduced work and mechanical efficiency are related to mitochondrial dysfunction. Upregulation of the pentose phosphate pathway and a potential gap in the energy balance suggest mitochondrial dysfunction in right ventricular overload is a resiult of the excessive production of reactive oxygen species.

Predictive Value of Increased Perioperative Heart Rate for All-Cause Mortality After Cardiac Surgery: A Systematic Review and Meta-Analysis

Background: Accumulated studies have revealed that heart rates are associated with all-cause mortality in cardiac surgery patients, but the results remain controversial. This meta-analysis aimed to evaluate the predictive value of increased perioperative heart rate for all-cause mortality after cardiac surgery. Methods: We searched PubMed, Embase, Web of Science, and Cumulative Index of Nursing and Allied Health Literature (CINAHL) databases for studies from inception to October 11, 2021. Two researchers independently screened the studies. Titles, authors, publication years, and hazard ratios were extracted. We used a random-effects model to combine the HRs and 95% confidence intervals. Several subgroup analyses were conducted. Statistical significance was set at p < .05. Results: Eleven studies were included in the meta-analysis of 33,849 patients and 3166 (9.4%) deaths. The HR of higher perioperative heart rates was 2.09 (95% CI 1.53-2.86, p < .001, I² = 81%). The HR with a 10-bpm increase in preoperative heart rate was 1.19 (95% CI 1.11-1.26, p < .001, I² = 51%). Subgroup analysis showed patients with higher preoperative heart rates had an HR of 1.88 (95% CI 1.51-2.34, p < .001, I² = 0%), and patients with a higher postoperative heart rate had an HR of 2.29 (95% CI 1.28- 4.09, p < .0001, I² = 91%) compared to patients with lower postoperative heart rates. Conclusion: Increased perioperative heart rate is associated with all-cause mortality in patients undergoing cardiac surgery.

Focus on Autoimmune Myocarditis in Graves' Disease: A Case-Based Review

The manifestations of hyperthyroidism-related myocardial damage are multitudinous, including arrhythmia, dilated cardiomyopathy, valvular diseases, and even cardiogenic shock. Acute myocarditis induced by thyrotoxicosis had been reported in a few studies. However, attention on its prevalence and underlying mechanisms is sorely lacking. Its long-term harm is often ignored, and it may eventually develop into dilated cardiomyopathy and heart failure. We report a case of Graves' disease with a progressive elevation of hypersensitive cardiac troponin-I at several days after discontinuation of the patient's anti-thyroid drugs. Cardiac magnetic resonance imaging (CMRI) showed inflammatory edema of some cardiomyocytes (stranded enhanced signals under T2 mapping), myocardial necrosis (scattered enhanced signals under T1 late gadolinium enhancement) in the medial and inferior epicardial wall, with a decreased left ventricular systolic function (48%), which implied a possibility of acute myocarditis induced by thyrotoxicosis. The patient was then given a transient glucocorticoid (GC) treatment and achieved a good curative effect. Inspired by this case, we aim to systematically elaborate the pathogenesis, diagnosis, and treatment of hyperthyroidism-induced autoimmune myocarditis. Additionally, we emphasize the importance of CMRI and GC therapy in the diagnosis and treatment of hyperthyroidism-related myocarditis.