Usman Jaffer

Resolving Ambiguities in the LF/HF Ratio: LF-HF Scatter Plots for the Categorization of Mental and Physical Stress from HRV

It is generally accepted that the activities of the autonomic nervous system (ANS), which consists of the sympathetic (SNS) and parasympathetic nervous systems (PNS), are reflected in the low- (LF) and high-frequency (HF) bands in heart rate variability (HRV)—while, not without some controversy, the ratio of the powers in those frequency bands, the so called LF-HF ratio (LF/HF), has been used to quantify the degree of sympathovagal balance. Indeed, recent studies demonstrate that, in general: (i) sympathovagal balance cannot be accurately measured via the ratio of the LF- and HF- power bands; and (ii) the correspondence between the LF/HF ratio and the psychological and physiological state of a person is not unique. Since the standard LF/HF ratio provides only a single degree of freedom for the analysis of this 2D phenomenon, we propose a joint treatment of the LF and HF powers in HRV within a two-dimensional representation framework, thus providing the required degrees of freedom. By virtue of the proposed 2D representation, the restrictive assumption of the linear dependence between the activity of the autonomic nervous system (ANS) and the LF-HF frequency band powers is demonstrated to become unnecessary. The proposed analysis framework also opens up completely new possibilities for a more comprehensive and rigorous examination of HRV in relation to physical and mental states of an individual, and makes possible the categorization of different stress states based on HRV. In addition, based on instantaneous amplitudes of Hilbert-transformed LF- and HF-bands, a novel approach to estimate the markers of stress in HRV is proposed and is shown to improve the robustness to artifacts and irregularities, critical issues in real-world recordings. The proposed approach for resolving the ambiguities in the standard LF/HF-ratio analyses is verified over a number of real-world stress-invoking scenarios.

Impaired Hyperaemic and Rhythmic Vasomotor Response in Type 1 Diabetes Mellitus Patients: A Predictor of Early Peripheral Vascular Disease

OBJECTIVES The smooth muscle of distal vascular networks exhibits periodical contraction and relaxation known as rhythmical vasomotion. The nature of microvascular vasomotion has been shown to correlate with severity of peripheral vascular disease. We present basal and post-ischaemic hyperaemic laser doppler flowmetry vasomotion in control and type 1 adult diabetic patients. DESIGN Prospective case control study. METHODS Laser Doppler flowmetry was used to measure vasomotion and hyperaemic responses in age and body mass index matched male subjects (25 type 1 Diabetes Mellitus and 13 controls), all with ankle/brachial pressure index (ABPI) >1.0 but <1.2. RESULTS The frequency of resting vasomotion was raised in diabetics compared to controls 8 (5-9)min(-1) vs. 5 (4-6)min(-1) (median (range); p<0.0001). The post ischaemic hyperaemia response was significantly higher in the diabetic group compared to the controls 11 (7-12)min(-1) vs. 6 (5-7)min(-1) (median (range); p<0.05). Post ischaemic hyperaemic flux (expressed as percent increase from resting) was significantly lower in the diabetic group compared to controls (234+/-62 vs. 453+/-155%, p<0.01). The time to achieve peak post ischaemic response was also significantly increased in the diabetic group compared to control: 21.4+/-0.4 vs. 12.8+/-5.4sec (mean+/-SD, p<0.05). CONCLUSIONS Vasomotion frequency and its change during hyperaemic insult is significantly different in Type 1 Diabetes Mellitus subjects compared to controls. The results are similar to patients with macrovascular atherosclerosis. Long term studies of these groups of patients will be required to determine the significance of these findings and whether these changes could be used as a non invasive screening test to predict peripheral early vascular disease in type 1 diabetic patients.

Variation in duplex peak systolic velocity measurement in a multi-site vascular service

Objective: Duplex US (DUS) is increasingly utilised as a first-line investigation for the assessment of carotid disease. For clinical decision-making, DUS assessment must be accurate and reproducible to ensure reliability. We aimed to investigate the variability in peak systolic velocity (PSV) measurement in a multi-site vascular network. Methods: DUS measurements of PSV were taken from continuous and pulsatile flow, generated by a high fidelity phantom, by 12 experienced vascular scientists across four hospitals. Participants were blinded to the actual PSV value (50 cm/s). Results: We observed an average error of 13.2% (± 8.3) and 11.6% (± 7.5) in PSV measurements taken from pulsatile and continuous waveforms, respectively. Measurements of PSV using the pulsatile waveform demonstrated statistically significant variation across all hospitals; ((hospital/mean) A 43.9 cm/s, B 61.7 cm/s, C 57.4 cm/s, D 47.7 cm/s, p=0.001). Further analysis demonstrated statistically significant variation in 4 instrumentation-related factors when measuring from a pulsatile waveform (Doppler angle, angle of insonation, velocity range, scale range). Conclusion: We observed a significant level of error and variation in PSV measurements across four sites within our vascular network. Variation in instrumentation-related factors may be accountable for this. In light of the centralisation of vascular services, it is increasingly important to unify and implement scanning protocols in order to reduce error and inter-site variability.

The Effect of a Simulation Training Package on Skill Acquisition for Duplex Arterial Stenosis Detection

OBJECTIVES In vascular surgery, duplex ultrasonography is a valuable diagnostic tool in patients with peripheral vascular disease, and there is increasing demand for vascular surgeons to be able to perform duplex scanning. This study evaluates the role of a novel simulation training package on vascular ultrasound (US) skill acquisition. MATERIALS AND METHODS A total of 19 novices measured predefined stenosis in a simulated pulsatile vessel using both peak systolic velocity ratio (PSVR) and diameter reduction (DR) methods before and after a short period of training using a simulated training package. The training package consisted of a simulated pulsatile vessel phantom, a set of instructional videos, duplex ultrasound objective structured assessment of technical skills (DUOSATS) tool, and a portable US scanner. Quantitative metrics (procedure time, percentage error using PSVR and DR methods, DUOSAT scores, and global rating scores) before and after training were compared. RESULTS Subjects spent a median time of 144 mins (IQR: 60-195) training using the simulation package. Subjects exhibited statistically significant improvements when comparing pretraining and posttraining DUOSAT scores (pretraining = 17 [16-19.3] vs posttraining = 30 [27.8-31.8]; p < 0.01), global rating score (pretraining = 1 [1-2] vs posttraining = 4 [3.8-4]; p < 0.01), percentage error using both the DR (pretraining = 12.6% [9-29.6] vs posttraining = 10.3% [8.9-11.1]; p = 0.03) and PSVR (pretraining = 60% [40-60] vs posttraining = 20% [6.7-20]; p < 0.01) methods. CONCLUSION In this study, subjects with no previous practical US experience developed the ability to both acquire and interpret arterial duplex images in a pulsatile simulated phantom following a short period of goal direct training using a simulation training package. A simulation training package may be a valuable tool for integration into a vascular training program. However, further work is needed to explore whether these newly attained skills are translated into clinical assessment.

Randomized study of teaching ultrasound-guided vascular cannulation using a phantom and the freehand versus needle guide-assisted puncture techniques.

The task of ultrasound‐guided vessel cannulation can be technically difficult. Needle guides have been designed to facilitate vessel puncture. We aimed to identify and compare the learning curves of participants performing vessel puncture with conventional freehand (FH) and needle guide–assisted (NG) techniques.

Evaluation of rapid training in ultrasound guided tourniquet application skills.

Tourniquet application has been widely accepted to improve survival for major limb trauma. Colour duplex ultrasound (US) can be used as a non-invasive method of confirming cessation of arterial flow. Participants with no or limited experience of ultrasound were taught to apply the Combat Application Tourniquet with ultrasound guidance. Following this, participants were tested in effective tourniquet application: Blind and with ultrasound guidance. US guidance improved abolition of limb perfusion from 22 to 93 per cent in upper limb; from 25 to 100 per cent in lower limb (p=0.0027 and <0.0001). No significant difference was found in application time for the lower limb; less time was taken for application with US guidance in the upper limb 8.1 (7.1, 8.6) vs 4.5 s (4.0, 5.3; median (IQR)), p=0.002. Tourniquet ultrasound skills are rapidly acquired by novice operators. Accuracy improves with ultrasound guidance, this may have a role in improving survival.

Bilateral Internal Carotid Artery Occlusion, External Carotid Artery Stenosis, and Vertebral Artery Kinking: May It Be Asymptomatic?

The clinical spectrum of internal carotid artery occlusion ranges from being a completely asymptomatic occlusion to a devastating stroke or death. The prevalence of asymptomatic internal carotid artery occlusion is unknown, particularly for bilateral occlusion. The distal branches of the external carotid artery anastomose with distal branches of the internal carotid artery provide important sources of collateral circulation to the brain. Stenosis of the external carotid artery with ipsilateral/bilateral internal occlusion may result in ischemic sequelae. Coiling or kinking of the vertebral artery is a rare morphological entity that is infrequently reported because it remains asymptomatic and has no clinical relevance. Currently, there is little evidence to support management strategies for this disease entity and no official recommendations for asymptomatic bilateral carotid artery occlusion. We present a case of a 62-year-old female with asymptomatic bilateral internal carotid artery occlusion, bilateral external carotid artery stenoses, and bilateral kinking of the vertebral artery at the V2 segment, who has been successfully managed conservatively for over 5 years. An individualized approach to management of patients with bilateral internal carotid artery occlusion, especially in combination with external carotid artery stenosis and elongation malformations of the vertebral artery is key to a successful strategy.

Intensive Simulation Training in Lower Limb Arterial Duplex Scanning Leads to Skills Transfer in Real-World Scenario

OBJECTIVES To train novices to perform an abbreviated duplex lower limb ultrasound scan using simulation training and assess real-world skills transference. METHODS Novices undertook 3 days of simulation training. Their progress was assessed using the Duplex Ultrasound Objective Structured Assessment of Technical Skills (DUOSATS) for simulation and Cumulative Imaging Score (CIS). A final assessment day was held to assess DUOSATS for simulation and real patient scanning, CIS, cumulative diagnostic accuracy, and sections A and B of the Society of Vascular Technology examination. MSc students in vascular ultrasound were also assessed for comparison. RESULTS A total of 17 novices and 7 MSc students with 3-month training participated. Novices improved DUOSATS for simulation scores between days 1, 3, and 4: 18 (17-19) vs 27 (25-28) vs 30 (28-32), (median [interquartile range], p < 0.001). Novices improved in CIS between days 1 and 3: 10 (10-13) vs 21 (19-21), p < 0.001, with a decline on day 4: 15.3 (11.3-18.3), p < 0.001. On the final assessment day, there were no significant differences between novices and MSc students in: DUOSATS for simulation scores (30 [28-32] vs 31 [6-31.5], p = 0.85); DUOSATS for patient assessment (31 [28.7-33.7] vs 26.7 [24.5-35.7], p = 0.41); CIS (15.3 [11.3-18.7] vs 20.7 [12.3-22.2], p = 0.2), respectively. However, novices performed better in section B of the Society of Vascular Technology examination compared with MSc students (72.9% vs 54.3%, p < 0.001). Novices also demonstrated a higher diagnostic accuracy when compared with MSc students (65.7% of arterial segments correctly assessed vs 47.6%, respectively [p = 0.044]). CONCLUSIONS Intensive simulation of 3-day training achieved real patient-based assessments that were comparable to MSc students who were 3 months into their traditional training program.

Venous Reflux Duplex Ultrasound Objective Structured Assessment of Technical Skills (V-DUOSATS)

Background: Treatment of a symptomatic incompetent saphenous vein is routinely accomplished using radiofrequency ablation (RFA). Treatment efficacy is dependent upon, among other factors, effective exsanguination of the target vein. Trendelenburg positioning is often used to facilitate emptying the vein. However, the angle of torso inversion is limited to approximately 15 due to patient stability in a head down position. In November 2007, our clinic implemented a technique whereby the patient’s leg was elevated to a consistent 30 angle while maintaining the torso horizontal, thus achieving enhanced vein emptying. Methods: Patient records for treatments prior to (May-October 2007; Group 1) and subsequent to (November 2007-December 2012; Group 2) implementing the enhanced vein drainage technique were retrospectively analyzed for outcomes. The VNUS Medical Technologies (Covidien, San Jose, Calif) ClosureFast catheters were used for all treatments. Results: Table I summarizes the patient demographics. Incomplete vein obliteration at first postoperative ultrasound was observed in one of 105 (1.0%) treatments in Group 1 (G1), compared with two of 895 (0.2%) in Group 2 (G2; P 1⁄4 NS). Documentation of an early first postoperative ultrasound was lacking for one G2 patient. For outcome analysis, treatments for which an ultrasound follow-up examination was not performed beyond 1 month were excluded. Results are shown in Table II. As would be expected since the G2 patients were treated more recently than the G1 patients, the months of follow-up were skewed toward a shorter interval in G2. In November 2009, we altered our technique from performing two heating passes in the proximal vein segment to a single pass. In comparing G2 treatments that received proximal vein double heating (n 1⁄4 161) to the G1 technique having a similar proximal heating protocol, it was found that one of the six G2 recanalizations occurred in this sub-group (P 1⁄4 .0404). The difference in outcomes between the G2 sub-groups, 1/161 (0.6%) vs 5/ 356 (1.4%), was not significant. Conclusions: An analysis of our clinical experience, although retrospective in nature, suggests that using enhanced leg elevation during saphenous vein RFA, by facilitating exsanguination, may be an effective technique to achieve durable vein obliteration.

Validation of an assessment tool for pre-operative EVAR planning

Introduction: Current methods of teaching endovascular aortic aneurysm repair (EVAR) planning involve non-criteria-based observations that lack validity. The primary aim of this study was to validate an EVAR Planning Objective Structured Assessment of Skill (EpOSAS) tool for the assessment of pre-operative EVAR planning skills. Methods: Content analysis was performed in order to inform the formulation of EpOSAS domains. Thirty-five participants planned two cases of infra-renal abdominal aortic aneurysm for EVAR, using the OsiriX 7 platform. EVAR planning measurements, with accompanying screenshots, were uploaded onto an electronic data collection sheet. Performance was assessed by three blinded assessors using the EpOSAS tool. Construct and concurrent validity were evaluated. Results: Inter-observer reliability for the three assessors for total EpOSAS scores was high (Cronbach’s α 0.89). There were statistically significant differences in total EpOSAS scores between the different experience groups, demonstrating construct validity (Novice (5.3, IQR 5-5.3), Intermediate (15.3, IQR 14.8-16.8) and Experts (17.5, IQR 17-17.7), p<0.001). A statistically significant correlation was found between total EpOSAS scores and percentage error in measurements, demonstrating concurrent validity (Spearman’s rank correlation coefficient: R=-0.250, p<0.001). Receiver-operator characteristics analysis established a cut-off point of 16 out of 18 for determining competence. Conclusion: We have developed and validated a tool that can be used for the assessment of pre-operative EVAR planning skills.