Extracorporeal driveline vibrations to detect left ventricular assist device thrombosis - A porcine model study.

BACKGROUND: Pump thrombosis (PT) and related adverse complications contributed to the HeartWare Ventricular Assist Device (HVAD) market withdrawal. Many patients still receive lifelong support, with deficient PT surveillance based on pump power trends. Analysis of pump vibrations is better for detecting PT. Here, we investigated the feasibility of an extracorporeal accelerometer to detect PT from pump vibrations propagated out on the driveline. METHODS: In a porcine HVAD model (n = 6), an accelerometer was attached to the pump as a reference and another to the driveline for comparisons of signals. In total, 59 thrombi were injected into the heart to induce PT, followed by intermittent thrombus washout maneuvers. Signals were compared visually in spectrograms and quantitatively in third harmonic saliences (S3H) by correlation analysis. Receiver operating characteristic curves expressed the method's outcome in sensitivity vs specificity, with the overall diagnostic performance in the area under the curve (AUC) score. RESULTS: Five experiments had good driveline signal strength, with clear spectrographic relationships between the 2 accelerometers. Third harmonic driveline vibrations were visible 20 vs 30 times in the reference. The comparison in S3H showed a strong correlation and yielded an AUC of 0.85. Notably, S3H proved robust regarding noise and false PT detections. CONCLUSIONS: An extracorporeal accelerometer on the driveline can be a readily available method for accurate HVAD PT detection before an accelerometer integration with left ventricular assist device is feasible.

AAPM Medical physics practice guideline 15.A: Peer review in clinical physics.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning. Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Resource Allocations for Common Radiation Oncology Procedures.

PURPOSE: Radiation Oncology is a complex, resource-intensive discipline. The complexity of the radiation oncology treatment process has increased significantly in recent years with the introduction of more advanced imaging, planning, and treatment delivery technology and enhanced use of multidisciplinary care paths. We conducted a multi-institutional study to estimate the average time by functional unit for a wide range of modern radiation oncology treatment regimens. METHODS AND MATERIALS: Structured process mapping was performed for 24 treatment categories, and average time estimates for 6 functional groups were obtained for each process step through consultation with the full clinical team at each institution. Six geographically dispersed institutions participated in the study. Significant effort was invested in aggregate data analysis and clarification of assumptions. RESULTS: The findings show significant variability in the resources expended for many treatment categories as well as the distribution of workload between functional units. Major factors in the variability include the rate of adoption of hypofractionation in external beam therapy, adoption of automation tools and standardization, and the transition to multimodality image-based planning in brachytherapy. CONCLUSIONS: The data obtained from this study may be useful in designing institution-specific staffing models appropriate to the scope of radiation therapy services provided at each institution.

Detection of inflow obstruction in left ventricular assist devices by accelerometer: A porcine model study.

BACKGROUND: Left ventricular assist devices (LVAD) provide circulatory blood pump support for severe heart failure patients. Pump inflow obstructions may lead to stroke and pump malfunction. We aimed to verify in vivo that gradual inflow obstructions, representing prepump thrombosis, are detectable by a pump-attached accelerometer, where the routine use of pump power (PLVAD) is deficient. METHOD: In a porcine model (n = 8), balloon-tipped catheters obstructed HVAD inflow conduits by 34% to 94% in 5 levels. Afterload increases and speed alterations were conducted as controls. We computed nonharmonic amplitudes (NHA) of pump vibrations captured by the accelerometer for the analysis. Changes in NHA and PLVAD were tested by a pairwise nonparametric statistical test. Detection sensitivities and specificities were investigated by receiver operating characteristics with areas under the curves (AUC). RESULTS: NHA remained marginally affected during control interventions, unlike PLVAD. NHA elevated during obstructions within 52-83%, while mass pendulation was most pronounced. Meanwhile, PLVAD changed far less. Increased pump speeds tended to amplify the NHA elevations. The corresponding AUC was 0.85-1.00 for NHA and 0.35-0.73 for PLVAD. CONCLUSION: Elevated NHA provides a reliable indication of subclinical gradual inflow obstructions. The accelerometer can potentially supplement PLVAD for earlier warnings and localization of pump.

Development and multi-institutional validation of a convolutional neural network to detect vertebral body mis-alignments in 2D x-ray setup images.

BACKGROUND: Misalignment to the incorrect vertebral body remains a rare but serious patient safety risk in image-guided radiotherapy (IGRT). PURPOSE: Our group has proposed that an automated image-review algorithm be inserted into the IGRT process as an interlock to detect off-by-one vertebral body errors. This study presents the development and multi-institutional validation of a convolutional neural network (CNN)-based approach for such an algorithm using patient image data from a planar stereoscopic x-ray IGRT system. METHODS: X-rays and digitally reconstructed radiographs (DRRs) were collected from 429 spine radiotherapy patients (1592 treatment fractions) treated at six institutions using a stereoscopic x-ray image guidance system. Clinically-applied, physician approved, alignments were used for true-negative, "no-error" cases. "Off-by-one vertebral body" errors were simulated by translating DRRs along the spinal column using a semi-automated method. A leave-one-institution-out approach was used to estimate model accuracy on data from unseen institutions as follows: All of the images from five of the institutions were used to train a CNN model from scratch using a fixed network architecture and hyper-parameters. The size of this training set ranged from 5700 to 9372 images, depending on exactly which five institutions were contributing data. The training set was randomized and split using a 75/25 split into the final training/ validation sets. X-ray/ DRR image pairs and the associated binary labels of "no-error" or "shift" were used as the model input. Model accuracy was evaluated using images from the sixth institution, which were left out of the training phase entirely. This test set ranged from 180 to 3852 images, again depending on which institution had been left out of the training phase. The trained model was used to classify the images from the test set as either "no-error" or "shifted", and the model predictions were compared to the ground truth labels to assess the model accuracy. This process was repeated until each institution's images had been used as the testing dataset. RESULTS: When the six models were used to classify unseen image pairs from the institution left out during training, the resulting receiver operating characteristic area under the curve values ranged from 0.976 to 0.998. With the specificity fixed at 99%, the corresponding sensitivities ranged from 61.9% to 99.2% (mean: 77.6%). With the specificity fixed at 95%, sensitivities ranged from 85.5% to 99.8% (mean: 92.9%). CONCLUSION: This study demonstrated the CNN-based vertebral body misalignment model is robust when applied to previously unseen test data from an outside institution, indicating that this proposed additional safeguard against misalignment is feasible.

Quality management, quality assurance, and quality control in medical physics.

The historic and ongoing evolution of the practice, technology, terminology, and implementation of programs related to quality in the medical radiological professions has given rise to the interchangeable use of the terms Quality Management (QM), Quality Assurance (QA), and Quality Control (QC) in the vernacular. This White Paper aims to provide clarification of QM, QA, and QC in medical physics context and guidance on how to use these terms appropriately in American College of Radiology (ACR) Practice Parameters and Technical Standards, generalizable to other guidance initiatives. The clarification of these nuanced terms in the radiology, radiation oncology, and nuclear medicine environments will not only boost the comprehensibility and usability of the Medical Physics Technical Standards and Practice Parameters, but also provide clarity and a foundation for ACR's clinical, physician-led Practice Parameters, which also use these important terms for monitoring equipment performance for safety and quality. Further, this will support the ongoing development of the professional practice of clinical medical physics by providing a common framework that distinguishes the various types of responsibilities borne by medical physicists and others in the medical radiological environment. Examples are provided of how QM, QA, and QC may be applied in the context of ACR Practice Parameters and Technical Standards.

Detection of inflow obstruction in left ventricular assist devices by accelerometer: An in vitro study.

Inflow obstruction in left ventricular assist devices (LVAD) may lead to embolic stroke and pump malfunction. We investigated if an accelerometer detected graded LVAD inflow obstructions. Detection performances were compared to the current continuous surveillance routine based on the pump power consumption (PLVAD). In ten mock circuit experiments, four different-sized pendulating balloons obstructed HVAD™ inflow conduits cross-section areas by 14%-75%. Nonharmonic amplitudes (NHA) of continuous signals from a triaxial accelerometer attached to the LVAD were compared against single-point PLVAD values, using load and speed alterations as control interventions. We analyzed the NHA band power with a pairwise nonparametric statistical test. The detection performances were analyzed by receiver operating characteristics with areas under the curves (AUC). The NHA remained unaffected during load alterations. In contrast, NHA increased significantly from the 27% obstruction level (AUC≥0.82), an effect amplified by increased pump speed. PLVAD did not change significantly below the maximal 75% obstruction level (AUC≤0.36). In conclusion, NHA detected the inflow obstructions much better than PLVAD. The technique may provide a future monitoring modality of any pendulating obstructive inflow pathology.

Improved Detection Of Thromboembolic Complications In Left Ventricular Assist Device By Novel Accelerometer-Based Analysis.

We have previously demonstrated that accelerometer-based vibration analysis detects thromboembolism and pump thrombosis in HeartWare Left Ventricular Assist Device (HVAD) using the third harmonic frequency (pump_speedx3). Thromboembolism also affected the amplitude of the nonharmonic frequencies. The aim of this study was to determine whether nonharmonic-amplitude (NHA) analysis can improve the diagnosis of thromboembolic complications. An accelerometer was attached to HVAD in three in vitro and seven in vivo experiments. Control interventions, including load and pump speed alternations (n = 107), were followed by thromboembolic events (n = 60). A sliding fast-Fourier-transform was analyzed, and changes in NHAs were quantified in the acute phase and in a steady state. Receiver operating characteristic curves were constructed with cutoff values of NHA to detect thromboembolic events. Positive predictive values were calculated on the basis of a specificity of 1. In the acute phase, NHA change was 6.5 times higher under thromboembolism than under control interventions (p < 0.001). Most thromboembolic events lead to concomitant changes in both NHA and third-harmonic amplitude. Combining the two methods improved the PPV by 8.3%. At steady state, signal changes predominantly demonstrated either NHA or third-harmonic changes. Combined signal analysis improved the PPV by 36%. This method enhanced the detection of thromboembolism and pump thrombosis in the HVAD.

Randomized, open-label, crossover trial comparing the pharmacokinetic profile of a novel oral aspirin solution and a chewed aspirin tablet.

OBJECTIVES: The primary objective of this study was to assess the pharmacokinetic profiles of acetylsalicylic acid (ASA) and salicylic acid (SA) after administration of two different formulations of aspirin under fasting and fed conditions. MATERIALS AND METHODS: The study was a randomized, open-label, parallel-group, 2-arm crossover study conducted at a single center. Healthy subjects were randomized to receive 300 mg of aspirin in either a 15-mL oral solution (pre-packaged vial containing powder and solvent that are combined at the time of administration) or a single solid tablet to be chewed and swallowed with 150 mL of water. Treatment visits were separated by a 10-day wash-out period. RESULTS: At 3 minutes, ASA concentrations for the oral solution fed state and fasting state arms exceeded those for the chewed tablet (fed 299 vs. 139 ng/mL; fasting 356 vs. 204 ng/mL). Compared to the chewed tablet, the mean plasma ASA concentration was 74% greater with the oral solution under fasting conditions, and 115% greater under fed conditions. Similarly, at 3 minutes, the mean SA plasma concentration with the oral solution under fed and fasting conditions exceeded those for the chewed tablet (fed 310 vs. 160 ng/mL; fasting 330 vs. 185 ng/mL). Under fasting conditions, the mean plasma ASA AUC0-last, with the oral solutions was 168,076.8 min.ng/mL compared to 163,726.3 min.ng/mL with the chewed tablet. Under fed conditions, the mean plasma ASA AUC0-last, with the oral solutions was 179,116.7 min.ng/mL compared to 164,704.3 min.ng/mL with the chewed tablet. CONCLUSION: This phase 1 study showed that use of an aspirin oral solution provided more rapid exposure to higher plasma concentration levels of ASA and SA than chewing a solid tablet.

Automatic Detection of Aortic Valve Events Using Deep Neural Networks on Cardiac Signals From Epicardially Placed Accelerometer.

BACKGROUND: Miniaturized accelerometers incorporated in pacing leads attached to the myocardium, are used to monitor cardiac function. For this purpose functional indices must be extracted from the acceleration signal. A method that automatically detects the time of aortic valve opening (AVO) and aortic valve closure (AVC) will be helpful for such extraction. We tested if deep learning can be used to detect these valve events from epicardially attached accelerometers, using high fidelity pressure measurements to establish ground truth for these valve events. METHOD: A deep neural network consisting of a CNN, an RNN, and a multi-head attention module was trained and tested on 130 recordings from 19 canines and 159 recordings from 27 porcines covering different interventions. Due to limited data, nested cross-validation was used to assess the accuracy of the method. RESULT: The correct detection rates were 98.9% and 97.1% for AVO and AVC in canines and 98.2% and 96.7% in porcines when defining a correct detection as a prediction closer than 40 ms to the ground truth. The incorrect detection rates were 0.7% and 2.3% for AVO and AVC in canines and 1.1% and 2.3% in porcines. The mean absolute error between correct detections and their ground truth was 8.4 ms and 7.2 ms for AVO and AVC in canines, and 8.9 ms and 10.1 ms in porcines. CONCLUSION: Deep neural networks can be used on signals from epicardially attached accelerometers for robust and accurate detection of the opening and closing of the aortic valve.

Myocardial electrophysiological and mechanical changes caused by moderate hypothermia-A clinical study.

Moderate hypothermia has been used to improve outcomes in comatose out-of-hospital cardiac arrest survivors during the past two decades, although the effects remain controversial. We have recently shown in an experimental study that myocardial electrophysiological and mechanical relationships were altered during moderate hypothermia. Electromechanical window positivity increased, and electrical dispersion of repolarization decreased, both of which are changes associated with decreased arrhythmogenicity in clinical conditions. Mechanical dispersion, a parameter also linked to arrhythmic risk, remained unaltered. Whether corresponding electrophysiological and mechanical changes occur in humans during moderate hypothermia, has not been previously explored. Twenty patients with normal left ventricular function were included. Measurements were obtained at 36 and 32°C prior to ascending aortic repair while on partial cardiopulmonary bypass and at 36°C after repair. Registrations were performed in the presence of both spontaneous and comparable paced heart rate during standardized loading conditions. The following electrical and mechanical parameters were explored: (1) Electromechanical window, measured as time difference between mechanical and electrical systole, (2) dispersion of repolarization from ECG T-wave, and (3) mechanical dispersion, measured as segmental variation in time to peak echocardiographic strain. At moderate hypothermia, mechanical systolic prolongation (425 ± 43-588 ± 67 ms, p < 0.001) exceeded electrical systolic prolongation (397 ± 49-497 ± 79 ms, p < 0.001), whereby, electromechanical window positivity increased (29 ± 30-86 ± 50 ms, p < 0.001). Dispersion of repolarization and mechanical dispersion remained unchanged. Corresponding electrophysiological and mechanical relationships were present at comparable paced heart rates. After rewarming, the increased electromechanical window was reversed in the presence of both spontaneous and paced heart rates. Moderate hypothermia increased electromechanical window positivity, while dispersion of repolarization and mechanical dispersion remained unchanged. This impact of hypothermia may be clinically relevant for selected groups of patients after cardiac arrest.

Left Ventricular Function Changes Induced by Moderate Hypothermia Are Rapidly Reversed After Rewarming-A Clinical Study.

OBJECTIVES: Targeted temperature management (32-36°C) is used for neuroprotection in cardiac arrest survivors. The isolated effects of hypothermia on myocardial function, as used in clinical practice, remain unclear. Based on experimental results, we hypothesized that hypothermia would reversibly impair diastolic function with less tolerance to increased heart rate in patients with uninsulted hearts. DESIGN: Prospective clinical study, from June 2015 to May 2018. SETTING: Cardiothoracic surgery operation room, Oslo University Hospital. PATIENTS: Twenty patients with left ventricular ejection fraction greater than 55%, undergoing ascending aorta graft-replacement connected to cardiopulmonary bypass were included. INTERVENTIONS: Left ventricular function was assessed during reduced cardiopulmonary bypass support at 36°C, 32°C prior to graft-replacement, and at 36°C postsurgery. Electrocardiogram, hemodynamic, and echocardiographic recordings were made at spontaneous heart rate and 90 beats per minute at comparable loading conditions. MEASUREMENTS AND MAIN RESULTS: Hypothermia decreased spontaneous heart rate, and R-R interval was prolonged (862 ± 170 to 1,156 ± 254 ms, p < 0.001). Although systolic and diastolic fractions of R-R interval were preserved (0.43 ± 0.07 and 0.57 ± 0.07), isovolumic relaxation time increased and diastolic filling time was shortened. Filling pattern changed from early to late filling. Systolic function was preserved with unchanged myocardial strain and stroke volume index, but cardiac index was reduced with maintained mixed venous oxygen saturation. At increased heart rate, systolic fraction exceeded diastolic fraction (0.53 ± 0.05 and 0.47 ± 0.05) with diastolic impairment. Strain and stroke volume index were reduced, the latter to 65% of stroke volume index at spontaneous heart rate. Cardiac index decreased, but mixed venous oxygen saturation was maintained. After rewarming, myocardial function was restored. CONCLUSIONS: In patients with normal left ventricular function, hypothermia impaired diastolic function. At increased heart rate, systolic function was subsequently reduced due to impeded filling. Changes in left ventricular function were rapidly reversed after rewarming.

Routine pretreatment patient-specific IMRT QA (PS-IMRT-QA) should be discontinued and replaced with a real-time on-board beam monitoring system (BMS).

In an era of automated measurements and analysis, the time and resource intensive process of dosimetric plan verification for intensity modulated radiation therapy treatments would seem to be ripe for improvement. In this Point-Counterpoint contribution, the authors debate benefits of methods both hypothetical and established. I offer thanks to our contributors and note that they are writing in the classic style of a debate, the opinions that they argue may or may not reflect their personal views."

AAPM medical physics practice guideline 3.b.: Levels of supervision for medical physicists in clinical training.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: (1) Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. (2) Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Modeling of kyphoplasty cement for accurate dose calculations.

We have determined the optimal method for modeling kyphoplasty cement to enable accurate dose calculations in the Eclipse treatment planning system (TPS). The cement studied (Medtronic Kyphon HV-R®) consists of 30% Barium, 68% polymethylmethacrylate (PMMA), and 2% benzoyl peroxide, formulated to be radiopaque with kV imaging systems. Neither Barium nor PMMA have a high physical density, resulting in different interaction characteristics for megavoltage treatment beams compared to kV imaging systems. This can lead to significant calculation errors if density mapping is performed using a standard CT number to density curve. To properly characterize the cement for dose calculation, we 3D printed a hemi-cylindrical container to fit adjacent to a micro-chamber insert for an anthropomorphic phantom, and filled the container with Kyphon cement. We CT scanned the combination, modeled the cement with multiple material assignments in the TPS, designed plans with different field sizes and beam geometry for five photon modes, and measured the doses for all plans. All photon energies show significant error in calculated dose when the cement is modeled based on the CT number. Of the material assignments we evaluated, polytetrafluoroethylene (PTFE) showed the best overall agreement with measurement. Calculated and measured doses agree within 3.5% for a 340-degree arc technique (which averages transmission and scatter effects) with the Acuros XB algorithm and PTFE as the assigned material. To confirm that PTFE is a reasonable substitute for kyphoplasty cement, we performed measurements in a slab phantom using rectangular inserts of cement and PTFE, showing average agreement of all photon modes within 2%. Based on these findings, we conclude that the PTFE material assignment provides acceptable dose calculation accuracy for the AAA and Acuros XB photon algorithms in the Eclipse TPS. We recommend that the cement be delineated as a structure and assigned the PTFE material for accurate dose calculation.

Open chest and pericardium facilitate transpulmonary passage of venous air emboli.

BACKGROUND: Transpulmonary passage of air emboli can lead to fatal brain- and myocardial infarctions. We studied whether pigs with open chest and pericardium had a greater transpulmonary passage of venous air emboli than pigs with closed thorax. METHODS: We allocated pigs with verified closed foramen ovale to venous air infusion with either open chest with sternotomy and opening of the pleura and pericardium (n = 8) or closed thorax (n = 16). All pigs received a five-hour intravenous infusion of ambient air, starting at 4-6 mL/kg/h and increased by 2 mL/kg/h each hour. We assessed transpulmonary air passage by transesophageal M-mode echocardiography and present the results as median with inter-quartile range (IQR). RESULTS: Transpulmonary air passage occurred in all pigs with open chest and pericardium and in nine pigs with closed thorax (56%). Compared to pigs with closed thorax, pigs with open chest and pericardium had a shorter to air passage (10 minutes (5-16) vs. 120 minutes (44-212), P < .0001), a smaller volume of infused air at the time of transpulmonary passage (12 mL (10-23) vs.170 mL (107-494), P < .0001), shorter time to death (122 minutes (48-185) vs 263 minutes (248-300, P = .0005) and a smaller volume of infused air at the time of death (264 mL (53-466) vs 727 mL (564-968), P = .001). In pigs with open chest and, infused air and time to death correlated strongly (r = 0.95, P = .001). CONCLUSION: Open chest and pericardium facilitated the transpulmonary passage of intravenously infused air in pigs.

Left Ventricular Function During Epinephrine Stimulation and Hypothermia: Effects at Spontaneous and Paced Heart Rates in a Porcine Model.

Postcardiac arrest patients treated with hypothermia, frequently require vasopressors and inotropic medication. The aim of this experimental study was to investigate the effect of epinephrine on left ventricular (LV) function during hypothermia. In an open-chest porcine model, seven animals were equipped with LV micromanometer and epicardial ultrasound transducers to provide LV pressure, Tau, and wall thickness and thickening velocities in systole (S') and early diastole (e'). Arterial, central venous, and pulmonal artery pressures were recorded. Cardiac output (CO) was measured by transit-time flow probe on the ascending aorta. Hypothermia was induced using a cooling catheter through the femoral vein. Pacemaker leads were attached to the right atrium for pacing. LV volumes were obtained by two-dimensional echocardiography. Measurements were made at normothermia (38°C) and hypothermia (33°C), without and with epinephrine infusion (0.03 µg/kg/min), at spontaneous and paced heart rates (HRs) 120 and 140 beats/min. Hypothermia reduced LV stroke volume (SV). Epinephrine during hypothermia increased the SV with reduced end-systolic volumes. LV dP/dtmax and wall-thickening velocity increased. During normothermia, epinephrine increased CO mainly due to accelerated HR, but during hypothermia, the increased CO resulted from augmented SV and, to a lesser degree, elevated HR. The incomplete relaxation and shortened diastolic filling time and the following reduction in SV seen in hypothermic animals, was repealed by epinephrine. The CO remained elevated also due to a shortened systolic duration, which gave time for complete relaxation during higher HRs. Epinephrine infusion improved systolic and diastolic function during hypothermia, and thereby reversed the effects induced by hypothermia considerably. Epinephrine augmented CO at hypothermia through increases in both SV and HR, in contrast to a mainly HR-dependent effect during normothermia. Systolic duration was shortened, which gave sufficient diastolic duration for complete relaxation. This allowed diastolic filling and maintained CO at elevated HRs.

Safety and feasibility of dobutamine stress echocardiography in symptomatic high gradient aortic stenosis patients scheduled for transcatheter aortic valve implantation.

PURPOSE: We aimed to study the safety and feasibility of low-dose dobutamine stress echocardiography in a symptomatic high gradient aortic stenosis population scheduled for transfemoral transcatheter aortic valve implantation (TAVI) and to quantify left ventricular (LV) flow reserve. METHODS: Fifty patients underwent dobutamine stress echocardiography with 5 minutes increments of 5 µg/kg/min up to 20 µg/kg/min until the heart rate increased ≥20 beats/min from baseline or exceeded 100 beats/min. Other criteria for discontinuing the infusion were major adverse events: ventricular arrhythmia, persistent supraventricular arrhythmia, pulmonary edema, chest pain with significant ST-changes, or minor events: ST-changes, drop in systolic blood pressure >30 mmHg, mild chest pain, and/or dyspnea. LV flow reserve was defined as an increase in stroke volume ≥20% during the test. RESULTS: Of 50 patients, 45 completed the test according to protocol. No patient had major adverse event. Five patients experienced minor side effects: mild chest pain/dyspnea in three, self-terminating atrial flutter in one, and decrease in blood pressure in one. Significant LV flow reserve was observed in 20 patients (40%). CONCLUSION: Low-dose dobutamine stress test appeared safe and feasible patients with high gradient aortic stenosis, and showed LV flow reserve in a minority of them.

Continuous Estimation of Acute Changes in Preload Using Epicardially Attached Accelerometers.

OBJECTIVE: A miniaturized accelerometer can be incorporated in temporary pacemaker leads which are routinely attached to the epicardium during cardiac surgery and provide continuous monitoring of cardiac motion during and following surgery. We tested if such a sensor could be used to assess volume status, which is essential in hemodynamically unstable patients. METHODS: An accelerometer was attached to the epicardium of 9 pigs and recordings performed during baseline, fluid loading, and phlebotomy in a closed chest condition. Alterations in left ventricular (LV) preload alter myocardial tension which affects the frequency of myocardial acceleration associated with the first heart sound ( fS1). The accuracy of fS1 as an estimate of preload was evaluated using sonomicrometry measured end-diastolic volume (EDV[Formula: see text]). Standard clinical estimates of global end-diastolic volume using pulse index continuous cardiac output (PiCCO) measurements (GEDV[Formula: see text]) and pulmonary artery occlusion pressure (PAOP) were obtained for comparison. The diagnostic accuracy of identifying fluid responsiveness was analyzed for fS1, stroke volume variation (SVV[Formula: see text]), pulse pressure variation (PPV[Formula: see text]), GEDV[Formula: see text], and PAOP. RESULTS: Changes in fS1 correlated well to changes in EDV[Formula: see text] ( r2=0.81, 95%CI: [0.68, 0.89]), as did GEDV[Formula: see text] ( r2=0.59, 95%CI: [0.36, 0.76]) and PAOP ( r2=0.36, 95%CI: [0.01, 0.73]). The diagnostic accuracy [95%CI] in identifying fluid responsiveness was 0.79 [0.66, 0.94] for fS1, 0.72 [0.57, 0.86] for SVV[Formula: see text], and 0.63 (0.44, 0.82) for PAOP. CONCLUSION: An epicardially placed accelerometer can assess changes in preload in real-time. SIGNIFICANCE: This novel method can facilitate continuous monitoring of the volemic status in open-heart surgery patients and help guiding fluid resuscitation.