Aman Mahajan

University of California, Los Angeles, Los Angeles, California, United States

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Publications (107)319.13 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Vagal nerve stimulation (VNS) has been proposed as a cardio-protective intervention. However, regional ventricular electrophysiological effects of VNS are not well characterized. The purpose of this study was to evaluate effects of right and left VNS on electrophysiological properties of the ventricles and hemodynamic parameters. In Yorkshire pigs, a 56-electrode sock was used for epicardial (n=12) and a 64-electrode catheter for endocardial (n=9) activation recovery interval (ARI) recordings at baseline and during VNS. Hemodynamic recordings were obtained using a conductance catheter. Right and left VNS decreased heart rate (84±5 to 71±5 bpm, and 84±4 to 73±5 bpm), LV pressure (89±9 to 77±9 mmHg, and 91±9 to 83±9 mmHg), dP/dt max (1660±154 to 1490±160 mmHg/s, and 1595±155 to 1416±134 mmHg/s) and prolonged ARI (327±18 to 350±23 ms, and 327±16 to 347±21 ms), respectively, p < 0.05 vs. baseline for all parameters, p = NS for right vs. left VNS. No anterior-posterior-lateral regional differences in prolongation of ARI during right or left VNS were found. However, endocardial ARI prolonged more than epicardial, and apical ARI more than basal ARI during both right and left VNS. Changes in dP/dt max showed the strongest correlation with ventricular ARI effects (R(2) = 0.81, p < 0.0001) than either heart rate (R(2) = 0.58, p < 0.01), or LV pressure (R(2)=0.52, p < 0.05). Therefore, right and left VNS have similar effects on ventricular ARI in contrast to sympathetic stimulation that shows regional differences. Decrease in inotropy correlates best with ventricular electrophysiological effects.
    AJP Heart and Circulatory Physiology 07/2014; · 4.01 Impact Factor
  • Anesthesia and analgesia. 07/2014; 119(1):35-40.
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    ABSTRACT: The current commonly used cardiac ischemic preconditioning (IPC) protocol, involving three 5-min cycles of ischemia-reperfusion (I/R), may not be clinically beneficial because of its acutely deleterious effects on hemodynamics. This study attempted to assess the effects of a novel stepwise IPC scheme on cardiac function, infarct size, and arrhythmogenesis in a rabbit model of prolonged I/R. Anesthetized open-chest rabbits were subjected to 60-min occlusion of a proximal branch of the left coronary artery followed by 180-min reperfusion. Animals were divided into five groups (n = 6 each): (1) control group (no IPC); (2) 2-min IPC group (three cycles of 2-min IPC); (3) 5-min IPC group (three cycles of 5-min IPC); (4) 10-min IPC group (three cycles of 10-min IPC); and (5) stepwise IPC group (2-, 5-, and 10-min I/R). Compared with control group, 2-, 5-, and 10-min IPC decreased arrhythmia score by 16%, 67%, and 33%, respectively. Remarkably, stepwise IPC resulted in a 78% reduction of arrhythmias. Stepwise IPC also produced the least ventricular infarct size when compared with 2-, 5-, and 10-min IPC groups (16.4% versus 39.3%, 28.1%, and 38.5%, P < 0.05). These results suggest that stepwise IPC has better cardioprotective effects against prolonged I/R injury and may serve as an acceptable approach to clinical revascularization procedures on the heart, including catheter-based and surgical approaches.
    Journal of Surgical Research 01/2014; · 2.02 Impact Factor
  • Journal of cardiothoracic and vascular anesthesia 11/2013; · 1.06 Impact Factor
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    ABSTRACT: Left and bilateral CSD have been shown to reduce burden of ventricular arrhythmias acutely in a small number of patients with VT storm. The effects of this procedure beyond the acute setting are unknown. The purpose of this study was to evaluate the intermediate and long-term effects of left and bilateral cardiac sympathetic denervation (CSD) in patients with cardiomyopathy and refractory ventricular tachy-arrhythmias (VT) or VT storm. Retrospective analysis of medical records for patients who underwent either left or bilateral cardiac sympathetic denervation for VT storm or refractory VT between April 2009 and December 2012 was performed. Forty one patients underwent CSD (left CSD: n = 14; bilateral CSD: n = 27). There was a significant reduction in the burden of ICD shocks during follow up as compared to the 12 months prior to the procedure. The number of ICD shocks was reduced from a mean of 19.6±19 pre-procedure to 2.3±2.9 post-procedure, P<0.001, with 90% of patients experiencing a reduction in ICD shocks. At a mean follow up of 367±251 days post-procedure, survival free of ICD shock was 30% of in the left CSD group and 48% in the bilateral CSD group. Shock free survival was greater in the bilateral group than in the left CSD group, P=0.04. In patients with VT storm, bilateral CSD is more beneficial than left CSD. The beneficial effects of bilateral CSD extend beyond the acute post-sympathectomy period, with continued freedom from ICD shocks in 48% of patients and a significant reduction in ICD shocks in 90% of patients.
    Heart rhythm: the official journal of the Heart Rhythm Society 11/2013; · 4.56 Impact Factor
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    ABSTRACT: The aim of this study was to determine the pertinent anesthetic considerations for patients undergoing surgical sympathectomy for electrical storm (incessant ventricular tachycardia (VT) refractory to traditional therapies). This is a retrospective review of a prospective database. This single-center study took place in a university hospital setting. Twenty-six patients were enrolled. Fifteen patients underwent left-sided sympathectomy, whereas 11 patients underwent bilateral sympathectomy. Anesthetic management of these patients was quite complex, requiring invasive monitoring, transesophageal echocardiography, one-lung ventilation, programming of cardiac rhythm management devices, and titration of vasoactive medications. Paired t test of hemodynamic data before, during, and after surgery showed no significant difference between preoperative and postoperative blood pressure values, regardless of whether the patient underwent unilateral or bilateral sympathectomy. Eight patients remained free of VT, three patients responded well to titration of oral medications, and one patient required 2 radiofrequency ablations after sympathectomy to control his VT. Three patients continued to have VT episodes, although reduced in frequency compared with before the procedure. Four patients were lost to followup. Overall, five patients within the cohort died within 30 days of the procedure. No patients developed any anesthetic complications or Horner's syndrome. The overall perioperative mortality (within the first 7 days of the procedure) was 2 of 26, or 7.7%. The anesthetic management of patients undergoing surgical sympathectomy for electrical storm can be quite complex, because these patients often present in a moribund and emergent state and cannot be optimized using current ACC/AHA guidelines. Expertise in invasive monitoring, transesophageal echocardiography, one-lung ventilation, cardiac rhythm device management, and pressor management is crucial for optimal anesthetic care.
    Journal of cardiothoracic and vascular anesthesia 11/2013; · 1.06 Impact Factor
  • Journal of cardiothoracic and vascular anesthesia 10/2013; · 1.06 Impact Factor
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    ABSTRACT: Although rotational parameters by speckle tracking echocardiography (STE) have been previously compared to sonomicrometry and cardiac magnetic resonance imaging, few have examined the relationship between left ventricular (LV) rotational mechanics and intraventricular measures of load-independent contractility, LV stiffness, or ventriculoarterial coupling. The aim of this study was to compare the changes in LV rotational indices to intraventricular pressure-volume (PV) relationships under a range of inotropic states induced by pharmacological interventions, acute ischemia, and changes in preload. In nine pigs, simultaneous echocardiographic imaging and LVPV measurements were performed during pharmacologically induced high or low inotropy and during acute ischemia by ligation of the left anterior descending coronary artery (LAD). Maximal ventricular elastance (Emax), arterial elastance (Ea), ventricular-arterial coupling (Emax/Ea), dP/dt, tau, and other hemodynamic parameters were determined. Dobutamine and esmolol infusions led to inversely correlated changes in hemodynamic measurements of LV function. Apical but not basal rotation and diastolic rotation rate were decreased by esmolol and increased by dobutamine. The LV twist correlates well with Emax (r = 0.83) and Emax/Ea (r = 0.80). Apical diastolic rotation rate also correlates with dP/dtmin (r = -0.63), τ (r = -0.81), and LV stiffness (r = -0.52). LAD ligation decreased systolic and diastolic LV rotation in apical (P < 0.05), but not basal myocardium. Occlusion of the inferior vena cava, to reduce preload, increased apical rotation in systole and diastole. LV rotational parameters measured by STE provide quantitative and reproducible indices of global LV systolic and diastolic function during acute changes in hemodynamics.
    Physiological reports. 10/2013; 1(5):e00110.
  • Annemarie Thompson, Aman Mahajan
    Anesthesia and analgesia 09/2013; 117(3):748. · 3.08 Impact Factor
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    ABSTRACT: Background Myocardial infarction (MI) induces neural and electrical remodeling at the scar border zones. The impact of focal MI on global functional neural remodeling is not well understood. Methods and Results Sympathetic stimulation (SS) was performed in swine with antero-apical infarcts (MI) (n=9), and controls (n=9). A 56-electrode sock was placed over both ventricles to record electrograms (EGMs) at baseline (BL), and during left, right, and bilateral stellate ganglia (LSG, RSG, & BSG, respectively) stimulation. Activation recovery intervals (ARIs) were measured from EGMs. Global and regional ARI shortening, dispersion of repolarization (DOR), and activation propagation were assessed before and during SS. At BL, mean ARI was shorter in MI hearts than controls (365±8ms vs. 436±9ms, p<0.0001), DOR was greater in MI vs. control hearts (734±123ms(2) vs. 362±32ms(2), p=0.02), and the infarcted region in MI hearts showed longer ARIs than non-infarcted regions (406±14ms vs. 365±8ms p=0.027). In controls, percent ARI shortening was greater on anterior than posterior wall during RSG stimulation (p=0.0001), while, LSG stimulation showed the reverse (p=0.0003). In infarcted animals, this pattern was completely lost. In 50% of the animals studied, SS compared to baseline, significantly altered the direction of activation propagation emanating from intra-myocardial scar during pacing. Conclusion: Focal distal anterior MI alters regional and global pattern of sympathetic innervation, resulting in shorter ARIs in infarcted hearts, greater repolarization dispersion and altered activation propagation. These conditions may underlie the mechanisms by which arrhythmias are initiated when sympathetic tone is enhanced.
    AJP Heart and Circulatory Physiology 07/2013; · 4.01 Impact Factor
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    ABSTRACT: Left stellate or right stellate ganglia stimulation (L/R SGS) is associated with ventricular tachyarrhythmias(VT/VF); however, the electrophysiological mechanisms remain unclear. We assessed (1) regional dispersion of myocardial repolarization during RSGS and LSGS, and (2) regional electrophysiological mechanisms underlying T wave changes, including Tp-e, that are associated with VT/VF. In 10 pigs, a 56-electrode sock was placed around the heart and both stellate ganglia were exposed. Unipolar electrograms, to asses activation recovery interval (ARI) and repolarization time (RT), and 12-lead ECG were recorded pre and during RSGS and LSGS. Both LSGS and RSGS increased dispersion of repolarization; with LSGS, greatest regional dispersion occurred on the LV anterior wall and LV apex, while with RSGS, greatest regional dispersion occurred on RV posterior wall. Baseline, LSGS and RSGS dispersion correlated with Tp-e. The increase in RT dispersion, which was due to increase in ARI dispersion, correlated with the increase in Tp-e intervals (R(2)=0.92 LSGS, R(2)=0.96 RSGS). During LSGS, the ARIs and RTs on the lateral and posterior walls were shorter than the anterior LV wall (P<0.01), and on the apex versus base (P<0.05), explaining the T wave vector shift posteriorly/inferiorly. RSGS caused greater ARI and RT shortening on anterior versus lateral or posterior walls (P<0.01), and on base versus apex (P<0.05), explaining the T wave vector shift anteriorly/superiorly. LSGS and RSGS cause differential effects on regional myocardial repolarization, explaining the ECG T-wave morphology. Sympathetic stimulation, in line with its pro-arrhythmic effects, increases Tp-e interval, which correlates with increases in myocardial dispersion of repolarization.
    AJP Heart and Circulatory Physiology 07/2013; · 4.01 Impact Factor
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    ABSTRACT: -Radiofrequency ablation for ventricular tachycardia (VT) is an established therapy. Use of chemical agents for scar homogenization represents an alternative approach. The purpose of this study was to characterize the efficacy of collagenase (CLG) application on epicardial ventricular scar homogenization. -Myocardial infarcts were created in Yorkshire pigs (n=6) by intra-coronary microsphere injection. After 46.6±4.3 days, CLG type 2, type 4, and purified CLG were applied in vitro (n=1) to myocardial tissue blocks containing normal myocardium, border-zone (BZ) and dense scar (DS). Histopathological studies were performed to identify the optimal CLG subtype. In-vivo high-density electroanatomic mapping of the epicardium was also performed, and BZ and DS surface area, and LPs were quantified before and after CLG-4 application (n=5). Of the CLG subtypes tested in vitro, CLG-4 provided the best scar modification, and least damage to normal myocardium. During in vivo testing, CLG-4 application decreased BZ area (21.3±14.3mm(2) to 17.1±11.1 mm(2), p=0.043) and increased DS area (9.1±10.3 mm(2) to 22.0±20.6 mm(2), p=0.043). The total scar area before and after CLG application was 30.4±23.4mm(2) and 39.2±29.5 mm(2), respectively, p=0.08). LPs were reduced by CLG-4 application (28.8±21.8 to 13.8±13.1, p=0.043). During CLG-4 application (50.0±15.5 min), systolic blood pressure and heart rate were not significantly changed (68.0±7.7mmHg vs. 61.8±5.3mmHg, p=0.08; 77.4±7.3 beats per minute (BPM) vs. 78.8±6.0BPM, p=0.50, respectively). -Ventricular epicardial scar homogenization by CLG-4 application is feasible and effective. This represents the first report on bioenzymatic ablation of arrhythmogenic tissue as an alternative strategy for lesion formation.
    Circulation Arrhythmia and Electrophysiology 07/2013; · 5.95 Impact Factor
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    ABSTRACT: While right ventricular (RV) dysfunction has long been known to affect the performance of left ventricle (LV), the mechanisms remain poorly defined. Recently, speckle-tracking echocardiography (STE) has demonstrated that preservation of strain and rotational dynamics is crucial to both LV systolic and diastolic function. We hypothesized that alteration in septal strain and rotational dynamics of the LV occurs during acute RV pressure overload (RVPO), and leads to decreased cardiac performance. Seven anesthetized pigs underwent median sternotomy and placement of intraventricular pressure-volume (PV) conductance catheters. 2D-echocardiographic images and LV PV loops were acquired for offline analysis at baseline and after banding of the pulmonary artery to achieve RVPO (>50 mmHg) induced RV dysfunction. RVPO resulted in a significant decrease (p<0.05) in LV end systolic elastance (50%), +dP/dtmax (19%), EDV (22%), and cardiac output (37%) that correlated with decrease in LV global circumferential strain (58%), LV apical rotation (28%), peak untwisting (reverse rotation) rate (27%) and prolonged time to peak rotation (17%), while basal rotation was not significantly altered. RVPO reduced septal radial and circumferential strain, while no other segment of the LV midpapillary wall was affected. RVPO decreased septal radial strain on LV side by 27% and induced a negative radial strain from 28±5% to -16±2% on the RV-side of the septum. The septal circumferential strain on both LV and RV-side decreased by 46% and 50%, respectively following RVPO (p<0.05). Our results suggest that acute RVPO impairs LV performance by primarily altering septal strain and apical rotation.
    Journal of Applied Physiology 05/2013; · 3.48 Impact Factor
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    ABSTRACT: BACKGROUND: Assessment of left ventricular rotational mechanics and myocardial deformation may provide new insight into both systolic and diastolic function. However, the effects of increasing afterload on these measures of cardiac function are poorly understood. The aim of this study was to identify the changes in left ventricular function and rotational mechanics during increasing pharmacologic afterload. METHODS: In 14 anesthetized rabbits, two-dimensional speckle-tracking echocardiographic images and left ventricular pressure-volume loops were acquired at baseline and during norepinephrine, phenylephrine, and vasopressin infusion at increasing doses. Maximal ventricular elastance, arterial elastance, ventricular-arterial coupling, dP/dt, the time constant of relaxation, and other hemodynamic parameters were determined. RESULTS: An increase in dP/dtmax with norepinephrine and phenylephrine and a decrease with vasopressin at escalating doses were detected. Ventricular-arterial coupling was preserved with norepinephrine and phenylephrine but decreased with vasopressin (P < .05). Apical rotation, rotational rate, and strain were preserved during the norepinephrine and phenylephrine infusions but were reduced with vasopressin (P < .05). Apical rotation and circumferential strain were significantly correlated with both ventricular-arterial coupling (r = 0.84 and r = 0.81) and dP/dtmax (r = -0.81 and r = -0.77). High-dose vasopressin decreased the diastolic time constant of relaxation and dP/dtmin while reducing apical untwisting rate. CONCLUSIONS: Pharmacologic increases in afterload with vasopressin resulted in greater derangements in ventricular-arterial coupling and cardiac performance compared with norepinephrine and phenylephrine. Rotation and strain correlated well with invasively determined measures and can be used to assess afterload-induced alteration in cardiac function.
    Journal of the American Society of Echocardiography: official publication of the American Society of Echocardiography 04/2013; · 2.98 Impact Factor
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    ABSTRACT: BACKGROUND:Red blood cell (RBC) transfusions are associated with increased morbidity. Children receiving heart transplants constitute a unique group of patients due to their risk factors. Although previous studies in nontransplant patients have focused primarily on the effects of postoperative blood transfusions, a significant exposure to blood occurs during the intraoperative period, and a larger percentage of heart transplant patients require intraoperative blood transfusions when compared with general cardiac surgery patients. We investigated the relationship between clinical outcomes and the amount of blood transfused both during and after heart transplantation. We hypothesized that larger amounts of RBC transfusions are associated with worsening clinical outcomes in pediatric heart transplant patients.METHODS:A database comprising 108 pediatric patients undergoing heart transplantation from 2004 to 2010 was queried. Preoperative and postoperative clinical risk factors, including the amount of blood transfused intraoperatively and 48 hours postoperatively, were analyzed. The outcome measures were length of hospital stay, duration of tracheal intubation, inotrope score, and major adverse events. Bivariate and multivariate analyses were performed to control for simultaneous risk factors and determine outcomes in which the amount of blood transfused was an independent risk factor.RESULTS:Ninety-four patients with complete datasets were included in the final analysis. Eighty-eight percent received RBC transfusions, with a median transfusion amount of 38.7 mL/kg. A multivariate analysis correcting for 8 covariate risk factors, including the Index for Mortality Prediction After Cardiac Transplantation, age, weight, United Network for Organ Sharing status, warm and cold ischemia time, repeat sternotomy, and pretransplant hematocrit, showed RBC transfusions were independently associated with increased length of intensive care unit stay (means ratio = 1.34; 95% confidence interval, 1.03-1.76; P = 0.03), and increased inotrope score in the first postoperative 24 hour (mean ratio = 1.26; 95% confidence interval, 1.04-1.52; P = 0.04). Patients suffering major adverse events received significantly larger median amounts of blood RBC transfusions (P = 0.002). Transfusions >60 mL/kg were also associated with increased risk of major adverse events (accuracy 76%) including postoperative sepsis, extracorporeal membrane oxygenation, open chest, dialysis, and graft failure.CONCLUSION:The majority of pediatric patients undergoing orthotropic heart transplantation receive RBC transfusions, with the largest amount transfused in the operating room. Escalating amounts of RBC transfusions are independently associated with increased length of intensive care unit stay, inotrope scores, and major adverse events. Since heart allografts are a limited resource, improvement in the blood transfusion and conservation practices can enhance clinical outcomes in pediatric heart transplant patients.
    Anesthesia and analgesia 04/2013; · 3.08 Impact Factor
  • Annemarie Thompson, Aman Mahajan
    Anesthesia and analgesia 02/2013; 116(2):276-7. · 3.08 Impact Factor
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    ABSTRACT: Sympathetic neural activation directly modulates cardiac function. However, left ventricular (LV) twist mechanics and regional strain during sympathetic efferent activation are poorly understood. The purpose of this study was to identify the effects of cardiac sympathetic activation on cardiac twist mechanics and regional strain by stimulation of the left and right stellate ganglia (LSG and RSG). In nine pigs, echocardiographic imaging and LV pressure-volume measurements were performed before and during unilateral and bilateral stellate ganglion stimulation. LSG and RSG stimulation significantly augmented LV end systolic pressure by 24% and 22% (P<0.01), dP/dtmax by 167% and 165% (P<0.01), and time constant of LV relaxation by 20% and 12% (P<0.01), respectively. RSG stimulation resulted in a greater chronotropic response than LSG stimulation (RSG 68% vs.LSG 12%, P<0.01). Both LSG and RSG stimulation significantly increased global epicardial and endocardial LV rotation and diastolic untwisting rate, while reducing the time to peak rotation (P<0.05). However, LSG stimulation predominantly increased radial and circumferential strain in the LV inferoseptal, inferior, posterior and lateral regions, while RSG stimulation primarily increased radial and circumferential strain in the anteroseptal, anterior and lateral LV regions. Stimulation of both stellate ganglia led to a uniform increase in all LV segments. LSG and RSG stimulation caused a global increase in LV twist, driven by distinct regional strain heterogeneity that may result from myocardial innervation from the left and right stellate ganglia. These findings provide insight into role of sympathetic innervation from the LSG and RSG in modulating regional and global cardiac function.
    AJP Heart and Circulatory Physiology 01/2013; · 4.01 Impact Factor
  • Zhou W, So E, Yamakawa K, Mahajan A
    Journal of Diabetes & metabolism. 01/2013;
  • Chua J, Zhou W, Ho J, Ko Y, Mahajan A
    Journal of applied physiology 01/2013; · 3.73 Impact Factor
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    ABSTRACT: Background: Increased cardiac sympathetic activation worsens dispersion of repolarization and is pro-arrhythmic. The functional differences between intrinsic nerve stimulation, and adrenergic receptor activation remain incompletely understood. This study was undertaken to determine the functional differences between efferent cardiac sympathetic nerve stimulation and direct adrenergic receptor activation in porcine ventricles. Methods: Female Yorkshire pigs (n=13) underwent surgical exposure of the heart and stellate ganglia. A 56-electrode sock was placed over the ventricles to record epicardial electrograms. Animals underwent bilateral sympathetic stimulation (BSS) (n=8) or norepinephrine (NE) administration (n=5). Activation recovery intervals (ARIs) were measured at each electrode before and during BSS or NE. The degree of ARI shortening during BSS or NE administration was used as a measure of functional nerve or adrenergic receptor density. Results: During BSS, ARI shortening was non-uniform across the epicardium (F value 9.62, p=0.003), with ARI shortening greatest in the mid-basal lateral right ventricle (RV) and least in the mid posterior left ventricle (LV) (mean normalized values: 0.9±0.08 vs. 0.56±0.08, p=0.03). NE administration resulted in greater ARI shortening in the LV apex than basal segments (0.91±0.04 vs 0.63±0.05 (averaged basal segments), p = 0.003). Dispersion of ARIs increased in 50% & 60% of the subjects undergoing BSS and NE respectively, but decreased in the others. Conclusion: There is non-uniform response to cardiac sympathetic activation of both porcine ventricles, which is not fully explained by adrenergic receptor density. Different pools of adrenergic receptors may mediate the cardiac electrophysiological effects of efferent sympathetic nerve activity and circulating catecholamines.
    AJP Heart and Circulatory Physiology 12/2012; · 4.01 Impact Factor

Publication Stats

829 Citations
319.13 Total Impact Points

Institutions

  • 2002–2014
    • University of California, Los Angeles
      • • Department of Anesthesiology
      • • Cardiac Arrhythmia Center
      • • Division of Cardiology
      • • Division of Cardiothoracic Surgery
      Los Angeles, California, United States
  • 2013
    • University of Southern California
      Los Angeles, California, United States
  • 2009–2012
    • University of California, Davis
      • Department of Biomedical Engineering
      Davis, CA, United States
  • 2007–2010
    • Stanford University
      • E. L. Ginzton Laboratory
      Stanford, CA, United States
    • Oregon Health and Science University
      Portland, Oregon, United States
  • 2006
    • Harbor-UCLA Medical Center
      Torrance, California, United States