Alexander Kushnir - Academia.edu (original) (raw)

Papers by Alexander Kushnir

Nature, Jan 22, 2020

Increased cardiac contractility during fight-or-flight response is caused by β-adrenergic augment... more Increased cardiac contractility during fight-or-flight response is caused by β-adrenergic augmentation of Ca V 1.2 channels 1-4. In transgenic murine hearts expressing fully PKA phosphorylation-site-deficient mutant Ca V 1.2 α 1C and β subunits, this regulation persists, implying involvement of extra-channel factors. Here, we identify the mechanism by which β-adrenergic agonists stimulate voltage-gated Ca 2+ channels. We expressed α 1C or β 2B subunits conjugated to ascorbate-peroxidase 5 in mouse hearts and used multiplexed, quantitative proteomics 6,7 to track hundreds of proteins in proximity of Ca V 1.2. We observed that the Ca 2+ channel inhibitor Rad 8,9 , a monomeric G-protein, is enriched in the Ca V 1.2 micro-environment but is depleted during β-adrenergic stimulation. PKA-catalyzed phosphorylation of specific Ser residues on Rad decreases its affinity for auxiliary β-Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Acta Neuropathologica Communications, 2021

The type 1 ryanodine receptor (RyR1) is an intracellular calcium (Ca 2+ ) release channel on the ... more The type 1 ryanodine receptor (RyR1) is an intracellular calcium (Ca 2+ ) release channel on the sarcoplasmic/endoplasmic reticulum that is required for skeletal muscle contraction. RyR1 channel activity is modulated by ligands, including the activators Ca 2+ and ATP. Patients with inherited mutations in RyR1 may exhibit muscle weakness as part of a heterogeneous, complex disorder known as RYR1 -related myopathy ( RYR1 -RM) or more recently termed RYR1-related disorders (RYR1-RD). Guided by high-resolution structures of skeletal muscle RyR1, obtained using cryogenic electron microscopy, we introduced mutations into putative Ca 2+ and ATP binding sites and studied the function of the resulting mutant channels. These mutations confirmed the functional significance of the Ca 2+ and ATP binding sites identified by structural studies based on the effects on channel regulation. Under normal conditions, Ca 2+ activates RyR1 at low concentrations (µM) and inhibits it at high concentrations ...

Prior studies have shown that addition of posterior wall isolation (PWI) may reduce atrial fibril... more Prior studies have shown that addition of posterior wall isolation (PWI) may reduce atrial fibrillation recurrence in patients with persistent atrial fibrillation. No data on PWI in paroxysmal AF (pAF) patients with normal left atrial voltage is available, to date. This study sought to evaluate the efficacy of PWI in addition to pulmonary vein isolation (PVI) in patients presenting with pAF and normal left atrial voltage. Consecutive patient registry analysis was performed on all patients with pAF and normal left atrial voltage undergoing initial radiofrequency ablation from November 1, 2018 to November 15, 2019. Primary endpoint was recurrence of atrial arrhythmia including AF, atrial tachycardia (AT) or atrial flutter (AFL). A total of 321 patients were studied, 214 in the PVI group and 107 in the PWI+PVI group. Recurrence of any atrial arrhythmia occurred in 18.2% of patients in the PVI group and 16.8% in the PVI+PWI cohort (p=0.58). At one year, recurrence was 14.0% in the PVI group and 15.0% in the PWI+PVI group (p=0.96). There was a lower AT/AFL recurrence in the PVI+PWI group, not reaching significance (3.7% in the PWI+PVI group vs. 7.9% in PVI group, p=0.31). Need for carina lesions predicted recurrence in the PVI-only group. Addition of PWI to PVI in pAF patients undergoing their first ablation did not reduce the frequency of atrial arrhythmia recurrence. This warrants further study in a prospective trial. This article is protected by copyright. All rights reserved.

HeartRhythm Case Reports, 2022

Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical ro... more Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical roles in global ecosystems and serve as essential biotechnology models. Recent work has demonstrated that both marine and freshwater cyanobacteria produce extracellular vesicles-small membrane-bound structures released from the outer surface of the microbes. While vesicles likely contribute to diverse biological processes, their specific functional roles in cyanobacterial biology remain largely unknown. To encourage and advance research in this area, a detailed protocol is presented for isolating, concentrating, and purifying cyanobacterial extracellular vesicles. The current work discusses methodologies that have successfully isolated vesicles from large cultures of Prochlorococcus, Synechococcus, and Synechocystis. Methods for quantifying and characterizing vesicle samples from these strains are presented. Approaches for isolating vesicles from aquatic field samples are also described. Finally, typical challenges encountered with cyanobacterial vesicle purification, methodological considerations for different downstream applications, and the trade-offs between approaches are also discussed.

Supplemental Material, Supp_data_3-Data_beyond_24h for Improving Fluid Output Monitoring in the I... more Supplemental Material, Supp_data_3-Data_beyond_24h for Improving Fluid Output Monitoring in the Intensive Care Unit by Alexander Kushnir, Eytan Palte, Nadia Morris, Zoha A. Shahabuddin, Jeffrey Hammond, Sinisa Vukelic and LeRoy E. Rabbani in Journal of Intensive Care Medicine

Supplemental Material, Supplemental_2 for Improving Fluid Output Monitoring in the Intensive Care... more Supplemental Material, Supplemental_2 for Improving Fluid Output Monitoring in the Intensive Care Unit by Alexander Kushnir, Eytan Palte, Nadia Morris, Zoha A. Shahabuddin, Jeffrey Hammond, Sinisa Vukelic and LeRoy E. Rabbani in Journal of Intensive Care Medicine

Journal of Intensive Care Medicine, 2020

Purpose: To assess the potential clinical impact of an automated urine output (UOP) monitoring sy... more Purpose: To assess the potential clinical impact of an automated urine output (UOP) monitoring system in the intensive care unit. Methods: Frequency of UOP documentation during a 20-month period was assessed in records of inpatients on the medicine floor, cardiac intensive care (CCU), and cardiothoracic-intensive care units (CTICU). Documentation timeliness (time between expected and observed UOP recording) was assessed over a 3-month period. A novel reusable device that monitors UOP based on continuous analysis of the weight of a urine collection container was tested in the CCU/CTICU. Results: A total of 165,363 UOP measurements were recorded for 2,039 CCU/CTICU admissions. Sixty percent of CCU/CTICU admissions had UOP recorded in the electronic medical record (EMR) less than every 2 hours. One-third of CCU/CTICU measurements were documented more than 2 hours late, and only 10% were recorded less than 20 minutes late. Half of these patients had fewer than 2 measurements recorded pe...

Cardiac Electrophysiology: From Cell to Bedside, 2018

Heart Rhythm, 2021

BACKGROUND Coronary sinus (CS) ostial atresia/anomalies prevents access to the CS from the right ... more BACKGROUND Coronary sinus (CS) ostial atresia/anomalies prevents access to the CS from the right atrium (RA) for left ventricular (LV) lead implantation. Some patients with CS ostial anomalies also have a small persistent left superior vena cava (sPLSVC). OBJECTIVE Describe CS ostial anomalies and sPLSVC as an opportunity for LV lead implantation and unrecognized source of stroke. METHODS Twenty patients with CS ostial anomalies and sPLSVC were identified. Clinical information, imaging methods, LV lead implantation techniques and complications were summarized. RESULTS Forty percent had at least one previously unsuccessful LV lead placement. In 70%, sPLSVC was identified by catheter manipulation and contrast injection in the left brachiocephalic vein, and in 30% by levophase CS venography. In 30%, sPLSVC were associated with drainage from the CS into the left atrium (LA). When associated with CS ostial anomalies, sPLSVC diameter averaged 5.6±3mm. sPLSVC was used for successful LV lead implantation in 90% of cases. In 80%, LV lead was implanted down sPLSVC and in 20% sPLSVC was used to access the CS from the RA. Presumably due to unrecognized drainage from CS to LA, one patient experienced a stroke during implantation via sPLSVC. CONCLUSION When CS ostial anomalies prevent access to CS from RA, sPLSVC can be used to successfully implant LV leads. In some, CS partially drains into the LA and stroke can occur spontaneously or during lead intervention. It is important to distinguish sPLSVC associated with CS ostial anomalies from isolated PLSVC.

Heart Rhythm, 2021

BACKGROUND Over 3 million cardiovascular implantable electronic devices (CIEDs) are implanted ann... more BACKGROUND Over 3 million cardiovascular implantable electronic devices (CIEDs) are implanted annually. There is minimal data regarding the timing of diagnosis of acute complications after implant. It remains unclear if patients can be safely discharged less than 24 hours post implantation. OBJECTIVE To determine the precise timing of acute complication diagnosis after CIED implant and optimal timing for same day discharge. METHODS A retrospective cohort analysis of adults 18 years or older who underwent CIED implant at a large urban quaternary care medical center between 6/1/2015 and 3/30/2020 was performed. Standard of care included overnight observation and chest x-ray (CXR) 6 and 24 hours post procedure. Medical records were reviewed for the timing of diagnosis of acute complications. Acute complications included pneumothorax, hemothorax, pericardial effusion, lead dislodgement and implant site hematoma requiring surgical intervention. RESULTS A total of 2421 patients underwent implantation. Pericardial effusion or cardiac tamponade was diagnosed in 13 (0.53%) patients, pneumothorax or hemothorax in 19 (0.78%) patients, lead dislodgement in 11 (0.45%) patients, and hematomas requiring surgical intervention in 5 (0.2%) patients. Of the 48 acute complications, 43 (90%) occurred either within 6 hours or greater than 24 hours post procedure. Only 3 acute complications identified between 6 and 24 hours required intervention during the index hospitalization (0.12% of all cases). CONCLUSION The majority of acute complications are diagnosed either within the first 6 hours or greater than 24 hours post implant. With rare exception, patients can be considered for discharge after 6 hours of appropriate monitoring.

Nature Reviews Cardiology, 2020

Critical Pathways in Cardiology: A Journal of Evidence-Based Medicine, 2020

The coronavirus disease 2019 crisis is a global pandemic of a novel infectious disease with far-r... more The coronavirus disease 2019 crisis is a global pandemic of a novel infectious disease with far-ranging public health implications. With regard to cardiac electrophysiology (EP) services, we discuss the "real-world" challenges and solutions that have been essential for efficient and successful (1) ramping down of standard clinical practice patterns and (2) pivoting of workflow processes to meet the demands of this pandemic. The aims of these recommendations are to outline: (1) essential practical steps to approaching procedures, as well as outpatient and inpatient care of EP patients, with relevant examples, (2) successful strategies to minimize exposure risk to patients and clinical staff while also balancing resource utilization, (3) challenges related to redeployment and restructuring of clinical and support staff, and (4) considerations regarding continued collaboration with clinical and administrative colleagues to implement these changes. While process changes will vary across practices and hospital systems, we believe that these experiences from 4 different EP sections in a large New York City hospital network currently based in the global epicenter of the coronavirus disease 2019 pandemic will prove useful for other EP practices adapting their own practices in preparation for local surges.

Nature, Jan 22, 2020

Increased cardiac contractility during fight-or-flight response is caused by β-adrenergic augment... more Increased cardiac contractility during fight-or-flight response is caused by β-adrenergic augmentation of Ca V 1.2 channels 1-4. In transgenic murine hearts expressing fully PKA phosphorylation-site-deficient mutant Ca V 1.2 α 1C and β subunits, this regulation persists, implying involvement of extra-channel factors. Here, we identify the mechanism by which β-adrenergic agonists stimulate voltage-gated Ca 2+ channels. We expressed α 1C or β 2B subunits conjugated to ascorbate-peroxidase 5 in mouse hearts and used multiplexed, quantitative proteomics 6,7 to track hundreds of proteins in proximity of Ca V 1.2. We observed that the Ca 2+ channel inhibitor Rad 8,9 , a monomeric G-protein, is enriched in the Ca V 1.2 micro-environment but is depleted during β-adrenergic stimulation. PKA-catalyzed phosphorylation of specific Ser residues on Rad decreases its affinity for auxiliary β-Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Acta Neuropathologica Communications, 2021

The type 1 ryanodine receptor (RyR1) is an intracellular calcium (Ca 2+ ) release channel on the ... more The type 1 ryanodine receptor (RyR1) is an intracellular calcium (Ca 2+ ) release channel on the sarcoplasmic/endoplasmic reticulum that is required for skeletal muscle contraction. RyR1 channel activity is modulated by ligands, including the activators Ca 2+ and ATP. Patients with inherited mutations in RyR1 may exhibit muscle weakness as part of a heterogeneous, complex disorder known as RYR1 -related myopathy ( RYR1 -RM) or more recently termed RYR1-related disorders (RYR1-RD). Guided by high-resolution structures of skeletal muscle RyR1, obtained using cryogenic electron microscopy, we introduced mutations into putative Ca 2+ and ATP binding sites and studied the function of the resulting mutant channels. These mutations confirmed the functional significance of the Ca 2+ and ATP binding sites identified by structural studies based on the effects on channel regulation. Under normal conditions, Ca 2+ activates RyR1 at low concentrations (µM) and inhibits it at high concentrations ...

Prior studies have shown that addition of posterior wall isolation (PWI) may reduce atrial fibril... more Prior studies have shown that addition of posterior wall isolation (PWI) may reduce atrial fibrillation recurrence in patients with persistent atrial fibrillation. No data on PWI in paroxysmal AF (pAF) patients with normal left atrial voltage is available, to date. This study sought to evaluate the efficacy of PWI in addition to pulmonary vein isolation (PVI) in patients presenting with pAF and normal left atrial voltage. Consecutive patient registry analysis was performed on all patients with pAF and normal left atrial voltage undergoing initial radiofrequency ablation from November 1, 2018 to November 15, 2019. Primary endpoint was recurrence of atrial arrhythmia including AF, atrial tachycardia (AT) or atrial flutter (AFL). A total of 321 patients were studied, 214 in the PVI group and 107 in the PWI+PVI group. Recurrence of any atrial arrhythmia occurred in 18.2% of patients in the PVI group and 16.8% in the PVI+PWI cohort (p=0.58). At one year, recurrence was 14.0% in the PVI group and 15.0% in the PWI+PVI group (p=0.96). There was a lower AT/AFL recurrence in the PVI+PWI group, not reaching significance (3.7% in the PWI+PVI group vs. 7.9% in PVI group, p=0.31). Need for carina lesions predicted recurrence in the PVI-only group. Addition of PWI to PVI in pAF patients undergoing their first ablation did not reduce the frequency of atrial arrhythmia recurrence. This warrants further study in a prospective trial. This article is protected by copyright. All rights reserved.

HeartRhythm Case Reports, 2022

Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical ro... more Cyanobacteria are a diverse group of photosynthetic, Gram-negative bacteria that play critical roles in global ecosystems and serve as essential biotechnology models. Recent work has demonstrated that both marine and freshwater cyanobacteria produce extracellular vesicles-small membrane-bound structures released from the outer surface of the microbes. While vesicles likely contribute to diverse biological processes, their specific functional roles in cyanobacterial biology remain largely unknown. To encourage and advance research in this area, a detailed protocol is presented for isolating, concentrating, and purifying cyanobacterial extracellular vesicles. The current work discusses methodologies that have successfully isolated vesicles from large cultures of Prochlorococcus, Synechococcus, and Synechocystis. Methods for quantifying and characterizing vesicle samples from these strains are presented. Approaches for isolating vesicles from aquatic field samples are also described. Finally, typical challenges encountered with cyanobacterial vesicle purification, methodological considerations for different downstream applications, and the trade-offs between approaches are also discussed.

Supplemental Material, Supp_data_3-Data_beyond_24h for Improving Fluid Output Monitoring in the I... more Supplemental Material, Supp_data_3-Data_beyond_24h for Improving Fluid Output Monitoring in the Intensive Care Unit by Alexander Kushnir, Eytan Palte, Nadia Morris, Zoha A. Shahabuddin, Jeffrey Hammond, Sinisa Vukelic and LeRoy E. Rabbani in Journal of Intensive Care Medicine

Supplemental Material, Supplemental_2 for Improving Fluid Output Monitoring in the Intensive Care... more Supplemental Material, Supplemental_2 for Improving Fluid Output Monitoring in the Intensive Care Unit by Alexander Kushnir, Eytan Palte, Nadia Morris, Zoha A. Shahabuddin, Jeffrey Hammond, Sinisa Vukelic and LeRoy E. Rabbani in Journal of Intensive Care Medicine

Journal of Intensive Care Medicine, 2020

Purpose: To assess the potential clinical impact of an automated urine output (UOP) monitoring sy... more Purpose: To assess the potential clinical impact of an automated urine output (UOP) monitoring system in the intensive care unit. Methods: Frequency of UOP documentation during a 20-month period was assessed in records of inpatients on the medicine floor, cardiac intensive care (CCU), and cardiothoracic-intensive care units (CTICU). Documentation timeliness (time between expected and observed UOP recording) was assessed over a 3-month period. A novel reusable device that monitors UOP based on continuous analysis of the weight of a urine collection container was tested in the CCU/CTICU. Results: A total of 165,363 UOP measurements were recorded for 2,039 CCU/CTICU admissions. Sixty percent of CCU/CTICU admissions had UOP recorded in the electronic medical record (EMR) less than every 2 hours. One-third of CCU/CTICU measurements were documented more than 2 hours late, and only 10% were recorded less than 20 minutes late. Half of these patients had fewer than 2 measurements recorded pe...

Cardiac Electrophysiology: From Cell to Bedside, 2018

Heart Rhythm, 2021

BACKGROUND Coronary sinus (CS) ostial atresia/anomalies prevents access to the CS from the right ... more BACKGROUND Coronary sinus (CS) ostial atresia/anomalies prevents access to the CS from the right atrium (RA) for left ventricular (LV) lead implantation. Some patients with CS ostial anomalies also have a small persistent left superior vena cava (sPLSVC). OBJECTIVE Describe CS ostial anomalies and sPLSVC as an opportunity for LV lead implantation and unrecognized source of stroke. METHODS Twenty patients with CS ostial anomalies and sPLSVC were identified. Clinical information, imaging methods, LV lead implantation techniques and complications were summarized. RESULTS Forty percent had at least one previously unsuccessful LV lead placement. In 70%, sPLSVC was identified by catheter manipulation and contrast injection in the left brachiocephalic vein, and in 30% by levophase CS venography. In 30%, sPLSVC were associated with drainage from the CS into the left atrium (LA). When associated with CS ostial anomalies, sPLSVC diameter averaged 5.6±3mm. sPLSVC was used for successful LV lead implantation in 90% of cases. In 80%, LV lead was implanted down sPLSVC and in 20% sPLSVC was used to access the CS from the RA. Presumably due to unrecognized drainage from CS to LA, one patient experienced a stroke during implantation via sPLSVC. CONCLUSION When CS ostial anomalies prevent access to CS from RA, sPLSVC can be used to successfully implant LV leads. In some, CS partially drains into the LA and stroke can occur spontaneously or during lead intervention. It is important to distinguish sPLSVC associated with CS ostial anomalies from isolated PLSVC.

Heart Rhythm, 2021

BACKGROUND Over 3 million cardiovascular implantable electronic devices (CIEDs) are implanted ann... more BACKGROUND Over 3 million cardiovascular implantable electronic devices (CIEDs) are implanted annually. There is minimal data regarding the timing of diagnosis of acute complications after implant. It remains unclear if patients can be safely discharged less than 24 hours post implantation. OBJECTIVE To determine the precise timing of acute complication diagnosis after CIED implant and optimal timing for same day discharge. METHODS A retrospective cohort analysis of adults 18 years or older who underwent CIED implant at a large urban quaternary care medical center between 6/1/2015 and 3/30/2020 was performed. Standard of care included overnight observation and chest x-ray (CXR) 6 and 24 hours post procedure. Medical records were reviewed for the timing of diagnosis of acute complications. Acute complications included pneumothorax, hemothorax, pericardial effusion, lead dislodgement and implant site hematoma requiring surgical intervention. RESULTS A total of 2421 patients underwent implantation. Pericardial effusion or cardiac tamponade was diagnosed in 13 (0.53%) patients, pneumothorax or hemothorax in 19 (0.78%) patients, lead dislodgement in 11 (0.45%) patients, and hematomas requiring surgical intervention in 5 (0.2%) patients. Of the 48 acute complications, 43 (90%) occurred either within 6 hours or greater than 24 hours post procedure. Only 3 acute complications identified between 6 and 24 hours required intervention during the index hospitalization (0.12% of all cases). CONCLUSION The majority of acute complications are diagnosed either within the first 6 hours or greater than 24 hours post implant. With rare exception, patients can be considered for discharge after 6 hours of appropriate monitoring.

Nature Reviews Cardiology, 2020

Critical Pathways in Cardiology: A Journal of Evidence-Based Medicine, 2020

The coronavirus disease 2019 crisis is a global pandemic of a novel infectious disease with far-r... more The coronavirus disease 2019 crisis is a global pandemic of a novel infectious disease with far-ranging public health implications. With regard to cardiac electrophysiology (EP) services, we discuss the "real-world" challenges and solutions that have been essential for efficient and successful (1) ramping down of standard clinical practice patterns and (2) pivoting of workflow processes to meet the demands of this pandemic. The aims of these recommendations are to outline: (1) essential practical steps to approaching procedures, as well as outpatient and inpatient care of EP patients, with relevant examples, (2) successful strategies to minimize exposure risk to patients and clinical staff while also balancing resource utilization, (3) challenges related to redeployment and restructuring of clinical and support staff, and (4) considerations regarding continued collaboration with clinical and administrative colleagues to implement these changes. While process changes will vary across practices and hospital systems, we believe that these experiences from 4 different EP sections in a large New York City hospital network currently based in the global epicenter of the coronavirus disease 2019 pandemic will prove useful for other EP practices adapting their own practices in preparation for local surges.