Gopal Sivagangabalan

University of Sydney, Sydney, New South Wales, Australia

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Publications (47)202.45 Total impact

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    ABSTRACT: XXXX: Steam pop is an explosive rupture of cardiac tissue due to tissue overheating above 100°C resulting in steam formation, predisposing to serious complications associated with radiofrequency (RF) ablations. However, there are currently no reliable techniques to predict the occurrence of steam pops. We propose the utility of acoustic signals emitted during RF ablation as a novel method to predict steam pop formation and potentially prevent serious complications. Radiofrequency generator parameters (power, impedance and temperature) were temporally recorded during ablations performed in an in vitro bovine myocardial model. The acoustic system consisted of HTI-96-min hydrophone, microphone preamplifier and sound card connected to a laptop computer. The hydrophone has the frequency range of 2Hz to 30kHz and nominal sensitivity in the range -240 to -165dB. The sound was sampled at 96kHz with 24-bit resolution. Output signal from the hydrophone was fed into the camera audio input to synchronize the video stream. An automated system was developed for the detection and analysis of acoustic events. Nine steam pops were observed. Three distinct sounds were identified as warning signals each indicating rapid steam formation and its release from tissue. These sounds had a broad frequency range up to 6kHz with several spectral peaks around 2-3kHz. Subjectively, these warning signals were perceived as separate loud clicks, a quick succession of clicks or continuous squeaking noise. Characteristic acoustic signals were identified preceding 80% of pops occurrence. Six Cardiologists were able to identify 65% of acoustic signals accurately preceding the pop. An automated system identified the characteristic warning signals in 85% of cases. The mean time from the first acoustic signal to pop occurrence was 46 ± 20 seconds. The automated system had 72.7% sensitivity and 88.9% specificity for predicting pops. Easily identifiable characteristic acoustic emissions predictably occur before imminent steam popping during RF ablations. Such acoustic emissions can be carefully monitored during an ablation and may be useful to prevent serious complications during RF delivery. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Journal of Cardiovascular Electrophysiology 12/2014; · 2.88 Impact Factor
  • Circulation 11/2014; 130(20):e179. · 14.95 Impact Factor
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    ABSTRACT: In recent years, there has been a shift away from performing electrophysiologic study (EPS) to guide implantable cardioverter-defibrillator (ICD) implantation with a reliance on left ventricular ejection fraction (LVEF) alone.
    Journal of Interventional Cardiac Electrophysiology 09/2014; · 1.55 Impact Factor
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    ABSTRACT: -Cardiac and respiratory movements cause catheter instability. Lateral catheter sliding over target endocardial surface can lead to poor tissue contact and unpredictable lesion formation. We describe a novel method of overcoming the effects of lateral catheter sliding movements by using an electrogram-gated pulsed power ablation.
    Circulation Arrhythmia and Electrophysiology 08/2014; · 5.95 Impact Factor
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    ABSTRACT: -Inducible Ventricular tachycardia (VT) is a strong predictor of spontaneous ventricular tachyarrhythmia following ST elevation myocardial infarction (STEMI). Reduced left ventricular ejection fraction (LVEF) predisposes patients to inducible ventricular tachycardia post STEMI. However the role of right ventricular (RV) dysfunction in predisposing to inducible VT has not been described previously.
    Circulation Arrhythmia and Electrophysiology 08/2014; · 5.95 Impact Factor
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    ABSTRACT: Aims: Radiofrequency renal artery denervation has been used effectively to treat resistant hypertension. However, comparison of lesion and thermodynamic characteristics for different systems has not been previously described. We aimed to assess spatiotemporal lesion growth and ablation characteristics of Symplicity and EnligHTN systems. Methods and results: A total of 39 ablations were performed in a phantom renal artery model using Symplicity (n=17) and EnligHTN (n=22) systems. The phantom model consisted of a hollowed gel block surrounding a thermochromic liquid crystal (TLC) film, exhibiting temperature sensitivity of 50-78°C. Flow was simulated using 37°C normal saline with impedance equal to blood. Radiofrequency ablations with each system were delivered with direct electrode tip contact to the TLC. Lesion size was interpreted from the TLC as the maximum dimensions of the 51°C isotherm. Mean lesion depth was 3.82 mm±0.04 versus 3.44 mm±0.03 (p<0.001) for Symplicity and EnligHTN, respectively. Mean width was 7.17 mm±0.08 versus 6.23 mm±0.07 (p<0.001), respectively. With EnligHTN, steady state temperature was achieved 20 sec earlier, and was 15°C higher than Symplicity. Conclusions: In this phantom model, Symplicity formed larger lesions compared to EnligHTN with lower catheter-tip temperature. The clinical significance of our findings needs to be explored further.
    EuroIntervention: journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology 06/2014; 10(2):277-84. · 3.76 Impact Factor
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    ABSTRACT: The prognostic significance of a second programmed ventricular stimulation (PVS) at electrophysiology study (EPS), when the first PVS is negative for inducible ventricular tachycardia (VT), in patients following myocardial infarction (MI) is unknown. Consecutive ST-elevation MI patients with left ventricular ejection fraction ≤40% following revascularization underwent early EPS. An implantable cardioverter defibrillator (ICD) was implanted for a positive (inducible monomorphic VT) but not a negative (no arrhythmia or inducible ventricular fibrillation [VF]/flutter) EPS. The combined primary end point of death or arrhythmia (sudden death, resuscitated cardiac arrest, and spontaneous VT/VF) was assessed in EPS-positive patients grouped according to if VT was induced on the first PVS application, or the second PVS application, when the first was negative. EPS performed a median 8 days post-MI in 290 patients was negative in 70% (n = 203) and positive in 30% (n = 87). In patients with a positive EPS, VT was induced on the first PVS in 67% (n = 58) and the second PVS, after the first was negative, in 33% (n = 29). Predischarge ICD was implanted in 79 of 87 patients with a positive EPS. Three-year primary end point occurred in 20.9 ± 5.6% and 38.3 ± 9.7% of patients with VT induced by the first and second PVS, respectively (P = 0.042) and in 6.3 ± 1.9% of electrophysiology-negative patients (P < 0.001). In patients with post-MI left ventricular dysfunction, VT can be induced in a significant proportion with a second PVS when negative on the first. These patients have a similar higher risk of death or arrhythmia compared to patients with VT induced on the first PVS.
    Pacing and Clinical Electrophysiology 03/2014; · 1.75 Impact Factor
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    ABSTRACT: The optimal left ventricular ejection fraction (LVEF) to select patients early post myocardial infarction (MI) for risk stratification for prevention of sudden cardiac death (SCD) in the era of primary percutaneous coronary intervention (PPCI) is unknown.METHODS AND RESULTS: Consecutive patients (n = 1722) treated with PPCI for ST-elevation MI underwent early (median 4 days) LVEF assessment. An electrophysiological study (EPS) was performed if LVEF ≤40% and a prophylactic implantable-cardioverter defibrillator (ICD) implanted for a positive [inducible monomorphic ventricular tachycardia (VT)], but not a negative, result. According to an early LVEF, a primary endpoint of inducible VT at EPS and a secondary endpoint of death or arrhythmia (SCD, resuscitated cardiac arrest or ECG-documented VT/ventricular fibrillation) were determined. The proportion of patients with early LVEF >40, 36-40, 31-35, and ≤30% were 75% (n = 1286), 7% (n = 128), 8% (n = 136), and 10% (n = 172), respectively. Inducible VT occurred in 22, 25, and 40% of patients with LVEF 36-40, 31-35, and ≤30%, respectively (P = 0.014). Three-year death or arrhythmia occurred in 6.6 ± 0.8, 8.1 ± 2.6, 18.0 ± 3.4, and 37.4 ± 3.9% of patients with LVEF >40, 36-40, 31-35, and ≤30%, respectively (overall P<0.001; LVEF 36-40% vs. LVEF > 40% P = 0.265). The number of EPS-positive patients implanted with an ICD to treat one or more arrhythmic event (95% confidence interval) was 18.3 ± 2.4, 11.5 ± 3.0, and 4.2 ± 5.6 if LVEF is 36-40, 31-35, and ≤30%, respectively.CONCLUSION: A cut-off LVEF of ≤40% selects patients with a high incidence of inducible VT post-PPCI. Patients with LVEF ≤35% and inducible VT appear to derive a greater benefit from prophylactic ICD implantation due to their higher risk of death or arrhythmia.
    Europace 03/2014; · 3.05 Impact Factor
  • Global Heart. 03/2014; 9(1):e5.
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    ABSTRACT: Current conventional ablation strategies for ventricular tachycardia (VT) aim to interrupt reentrant circuits by creating ablation lesions. However, the critical components of reentrant VT circuits may be located at deep intramural sites. We hypothesized that bipolar ablations would create deeper lesions than unipolar ablation in human hearts.METHODS AND RESULTS: Ablation was performed on nine explanted human hearts at the time of transplantation. Following explant, the hearts were perfused by using a Langendorff perfusion setup. For bipolar ablation, the endocardial catheter was connected to the generator as the active electrode and the epicardial catheter as the return electrode. Unipolar ablation was performed at 50 W with irrigation of 25 mL/min, with temperature limit of 50°C. Bipolar ablation was performed with the same settings. Subsequently, in a patient with an incessant septal VT, catheters were positioned on the septum from both the ventricles and radiofrequency was delivered with 40 W. In the explanted hearts, there were a total of nine unipolar ablations and four bipolar ablations. The lesion depth was greater with bipolar ablation, 14.8 vs. 6.1 mm (P < 0.01), but the width was not different (9.8 vs. 7.8 mm). All bipolar lesions achieved transmurality in contrast to the unipolar ablations. In the patient with a septal focus, bipolar ablation resulted in termination of VT with no inducible VTs.CONCLUSION: By using a bipolar ablation technique, we have demonstrated the creation of significantly deeper lesions without increasing the lesion width, compared with standard ablation. Further clinical trials are warranted to detail the risks of this technique.
    Europace 02/2014; · 3.05 Impact Factor
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    ABSTRACT: Structural differences between ventricular regions may not be the sole determinant of local ventricular fibrillation (VF) dynamics and molecular remodeling may play a role. To define regional ion channel expression in myopathic hearts compared to normal hearts, and correlate expression to regional VF dynamics. High throughput real-time RT-PCR was used to quantify the expression patterns of 84 ion-channel, calcium cycling, connexin and related gene transcripts from sites in the LV, septum, and RV in 8 patients undergoing transplantation. An additional eight non-diseased donor human hearts served as controls. To relate local ion channel expression change to VF dynamics localized VF mapping was performed on the explanted myopathic hearts right adjacent to sampled regions. Compared to non-diseased ventricles, significant differences (p<0.05) were identified in the expression of 23 genes in the myopathic LV and 32 genes in the myopathic RV. Within the myopathic hearts significant regional (LV vs septum vs RV) expression differences were observed for 13 subunits: Nav1.1, Cx43, Ca3.1, Cavα2δ2, Cavβ2, HCN2, Na/K ATPase-1, CASQ1, CASQ2, RYR2, Kir2.3, Kir3.4, SUR2 (p<0.05). In a subset of genes we demonstrated differences in protein expression between control and myopathic hearts, which were concordant with the mRNA expression profiles for these genes. Variability in the expression of Cx43, hERG, Na(+)/K(+) ATPase ß1 and Kir2.1 correlated to variability in local VF dynamics (p<0.001). To better understand the contribution of multiple ion channel changes on VF frequency, simulations of a human myocyte model were conducted. These simulations demonstrated the complex nature by which VF dynamics are regulated when multi-channel changes are occurring simultaneously, compared to known linear relationships. Ion channel expression profile in myopathic human hearts is significantly altered compared to normal hearts. Multi-channel ion changes influence VF dynamic in a complex manner not predicted by known single channel linear relationships.
    PLoS ONE 01/2014; 9(1):e82179. · 3.53 Impact Factor
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    ABSTRACT: A negative electrophysiology study (EPS) may delineate a sub-group of patients with severely impaired left ventricular ejection fraction (LVEF) who are safe long-term without an implantable-cardioverter defibrillator (ICD). Consecutive patients treated with primary percutaneous coronary intervention for ST-elevation myocardial infarction (STEMI) underwent early (median 4 days) LVEF assessment. Patients with LVEF≤40% underwent EPS. A prophylactic ICD was implanted for a positive [inducible monomorphic ventricular tachycardia (VT)] but not a negative (no inducible VT or inducible ventricular fibrillation (VF)/flutter) EPS result. Patients who would have become eligible for a late primary prevention ICD with LVEF≤30% or ≤35% with NYHA class II/III heart failure (HF) were included and analysed according to EPS result. Patients with LVEF>40%, ineligible for EPS, were followed as controls (n=1,286). The primary endpoint was survival free of death or arrhythmia (resuscitated cardiac arrest or sustained VT/VF). EPS performed in 128 patients with LVEF≤30%/≤35% & HF was negative in 63% (n=80) and positive in 37% (n=48). ICDs were implanted in <0.1%, 4% and 90% of control, EPS-negative and EPS-positive patients, respectively. The distribution of time to death or arrhythmia was comparable in control patients and EPS-negative patients with LVEF≤30%/≤35% & HF (P=0.738); who both differed significantly from EPS-positive patients (P<0.001). At 3 years 91.8±3.2%, 93.4±1.0% and 62.7±7.5% of control, EPS-negative and EPS-positive patients were free of death or arrhythmia, respectively. Re-vascularised STEMI patients with severely impaired LV function but no inducible VT have favourable long term prognosis without the protection of an ICD.
    Circulation 12/2013; · 14.95 Impact Factor
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    ABSTRACT: Collagen has been attributed as the principle structural substrate of ventricular tachycardia (VT) post-myocardial infarction (MI) even though adiposity of myocardium post-MI is well recognised histologically. We investigated the association of intramyocardial adiposity in comparison to collagen on electrophysiological (EP) properties, connexin-43 (Cx43) expression, and VT induction post-MI. Simultaneous, left ventricular (LV) plunge-needle, and noncontact mapping was performed in sheep (a) without MI (MI-, n=5), (b) with MI and inducible VT (MI+VT+, n=7) and (c) with MI and no inducible VT (MI+VT-, n=8). Histological intramyocardial quantity of adipose, collagen, and degree of discontinuity was co-registered with EP parameters (MI+, 290 specimens). Additional assessment of Cx43 expression was performed. LV scar contained a body-mass-independent abundance of adipocytes (adipose:collagen=0.8). Increased adipose density, and discontinuity contributed to a greater inverse correlation (r) with conduction velocity (CV, r: adipose=0.39, discontinuity=0.45, collagen=0.26), and electrogram amplitude (Vpp, r: adipose=0.73, contiguity=0.77, collagen=0.68), compared to collagen. Collagen density was similar between MI+ groups (p>0.29). However the MI+VT+ group demonstrated a significant (all p<=0.01) increase of adipose (8%) and discontinuity (qualitative); and decrease of CV (13%), and Vpp (21%) at MI borders compared to the MI+VT- group. In scar, myocytes adjacent to fibro-fatty interfaces demonstrated increased Cx43 lateralization. A gradient increase in adipose was observed at sites that supported preferential presystolic VT activation, and exhibited attenuation of excitation wavelength (p<0.001). Intramyocardial adiposity, in association with myocardial discontinuity within LV scar borders is a significant factor associated with altered EP properties, aberrant Cx43 expression, and increased propensity for VT post-MI.
    Circulation 09/2013; · 14.95 Impact Factor
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    ABSTRACT: Implantable cardioverter-defibrillator therapy in the form of high-energy shock (HES) is associated with adverse effects. This study evaluated an alternative therapy to HES, including antitachycardia pacing (ATP) for very fast ventricular tachycardia (VFVT) and low-energy shock (LES) ≤5 J for ventricular tachycardia (VT) of any cycle length (CL). This multicenter study recruited 602 patients with standard indications for an implantable cardioverter-defibrillator. Programming was standardized into 3 zones: (1) ventricular fibrillation (VF) CL of <200 ms treated with HES; (2) VFVT defined within the VF zone (CL, 200 to 250 ms) treated with 2 ATP bursts, LES, and HES; and (3) fast ventricular tachycardia (CL, 251 to 320 ms) and slow VT (CL, >320 ms) treated with 3 ATP bursts, LES, and HES. The primary end point was ATP and LES efficacy and safety. After a mean follow-up of 19 ± 8 months, 2,815 device activations were recorded in 152 patients. Of 67 VFVT episodes, 34 reverted with combined ATP and LES (success rate 50.7%) with first and second ATPs successful in 36% and 13.8%, respectively. LES was used in 39 fast ventricular tachycardia and 60 slow VT episodes with success rates of 53.8% and 73.3%, respectively. Syncope occurred in 19.4%, 16.2%, and 1% of episodes because of VFVT, VF, and VT CL >250 ms, respectively. In conclusion, tiered ATP and LES therapy terminates >50% of VFVT episodes (CL, 200 to 250 ms), which otherwise would fall within the VF zone and be treated exclusively with HES. LES is efficacious and safe in patients with VT CL >250 ms with extremely low syncope rates. Limitation of ATP to a single burst in VFVT is recommended to minimize syncope.
    The American journal of cardiology 07/2013; · 3.58 Impact Factor
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    ABSTRACT: BACKGROUND: Radiofrequency (RF) ablation causes thermal mediated irreversible myocardial necrosis. This study aimed to (i) characterize the thermal characteristics of RF ablation lesions with high spatial resolution using a thermochromic liquid crystal (TLC) myocardial phantom; and (ii) compare the thermochromic lesions with in vivo and in vitro ablation lesions. The myocardial phantom was constructed from a vertical sheet of TLC film, with color change between 50 °C (red) to 78 °C (black), embedded within a gel matrix, with impedance titrated to equal that of myocardium. Saline, with impedance titrated to blood values at 37 °C, was used as supernatant. A total of 51 RF ablations were performed. This comprised 17 ablations in the thermochromic gel phantom, bovine myocardial in vitro targets and ovine in vivo ablations, respectively. There was no difference in lesion dimensions between the thermochromic gel and in vivo ablations (lesion width 10.2 ± 0.2 vs 10.2 ± 2.4, P = 0.93; and depth 6.3 ± 0.1 vs 6.5 ± 1.7, P = 0.74). The spatial resolution of the thermochromic film was tested using 2 thermal point-sources that were progressively opposed and was demonstrated to be <300 μm. High spatial resolution thermal mapping of in vitro RF lesions with spatial resolution of at least 300 μm is possible using a thermochromic liquid crystal myocardial phantom model, with a good correlation to in vivo RF ablations. This model may be useful for assessing the thermal characteristics of RF lesions created using different ablation parameters and catheter technologies. http://www.ee.usyd.edu.au/people/alistair.mcewan/UserFiles/File/High%20Spatial%20Resolution%20Thermal%20Mapping%20of%20Radiofrequency%20Ablation%20Lesions%20Using%20a%20Novel%20Thermochromic%20Liquid%20Crystal%20Myocardial%20Phantom.pdf
    Journal of Cardiovascular Electrophysiology 06/2013; · 3.48 Impact Factor
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    ABSTRACT: AIMS: The prognostic significance of ventricular tachycardia (VT) induced by three extrastimuli (ES) is similar to that of VT induced by one or two ES in patients with coronary disease and abnormal left ventricular (LV) function. The significance of VT inducible with four ES is unclear. To examine the prognostic significance of VT inducible with the fourth ES in patients with post-myocardial infarct (MI) LV dysfunction.METHODS AND RESULTS: Consecutive patients (n= 432) with post-MI LV ejection fraction ≤40% underwent electrophysiological (EP) studies for risk stratification. Inducible VT ≥ 200 ms cycle length (CL) with one to four ES was considered inducible. The primary endpoint of arrhythmia (sudden death or spontaneous VT/ventricular fibrillation) was compared among patients with VT inducible with less than or equal to two, three, and four ES. The incidence of inducible VT was 37.9% (n= 164). In patients with inducible VT, inducibility was with less than or equal to two, three, and four ES in 24% (n= 39), 46% (n= 75), and 30% (n= 50). Compared to VT induced with less than or equal to three ES, VT induced with the fourth ES was of shorter CL (218 vs. 256 ms, P = 0.01) and more likely to be haemodynamically unstable requiring cardioversion (77 vs. 55%, P = 0.05). After 3 years the primary endpoint occurred in 28 ± 8, 28 ± 6, and 18 ± 6% in patients with VT induced with less than or equal to two, three, and four ES, respectively (P= 0.31) and in 5 ± 2% of EP-negative patients (P< 0.01).CONCLUSION: In patients with post-MI LV dysfunction, VT can be induced in a significant proportion of patients with the fourth ES. These patients are at comparable risk of arrhythmia to patients with inducible VT with less than or equal to three ES.
    Europace 06/2012; · 3.05 Impact Factor
  • Heart Lung &amp Circulation 01/2012; 21:S3. · 1.17 Impact Factor
  • Heart Lung &amp Circulation 01/2012; 21:S123. · 1.17 Impact Factor
  • The Canadian journal of cardiology 03/2011; 27(2):263.e25-7. · 3.12 Impact Factor
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    ABSTRACT: We tested the hypothesis that exposure to concentrated ambient particles (CAP) and/or ozone (O(3)) would increase dispersion of ventricular repolarization. Elevated levels of air pollution are associated with cardiac arrhythmias through mechanisms yet to be elucidated. Each of 25 volunteers (18 to 50 years of age) had four 2-h exposures to 150 μg/m(3) CAP; 120 parts per billion O(3); CAP + O(3); and filtered air (FA). Exposure-induced changes (Δ = 5-min epochs at end-start) in spatial dispersion of repolarization were determined from continuous 12-lead electrocardiographic recording. Spatial dispersion of repolarization assessed by corrected ΔT-wave peak to T-wave end interval increased significantly for CAP + O(3) (0.17 ± 0.03, p < 0.0001) exposure only, remaining significant when factoring FA (CAP + O(3) - FA) as control (0.11 ± 0.04, p = 0.013). The influence on repolarization was further verified by a significant increase in ΔQT dispersion (for CAP + O(3) compared with FA (5.7 ± 1.4, p = 0.0002). When the low-frequency to high-frequency ratio of heart rate variability (a conventional representation of sympathetic-parasympathetic balances) was included as a covariate, the effect estimate was positive for both corrected ΔT-wave peak to T-wave end interval (p = 0.002) and ΔQT dispersion (p = 0.038). When the high-frequency component (parasympathetic heart rate modulation) was included as a covariate with corrected ΔT-wave peak to T-wave end interval, the effect estimate for high frequency was inverse (p = 0.02). CAP + O(3) exposure alters dispersion of ventricular repolarization in part by increasing sympathetic and decreasing parasympathetic heart rate modulation. Detection of changes in repolarization parameters, even in this small cohort of healthy individuals, suggests an underappreciated role for air pollutants in urban arrhythmogenesis.
    Journal of the American College of Cardiology 01/2011; 57(2):198-206. · 15.34 Impact Factor

Publication Stats

135 Citations
202.45 Total Impact Points

Institutions

  • 2014
    • University of Sydney
      Sydney, New South Wales, Australia
  • 2008–2013
    • Westmead Hospital
      • Department of Cardiology
      Sydney, New South Wales, Australia
  • 2011
    • UHN: Toronto General Hospital
      Toronto, Ontario, Canada
  • 2010
    • Ryerson University
      • Department of Electrical and Computer Engineering
      Toronto, Ontario, Canada