Studies of the laser thermal probe in cardiovascular disease

The initial use of optical fibres to transmit laser energy intravascularly was accompanied by a high rate of perforations and the production of inadequate vascular channels when used for recanalisation. The laser thermal probe - in which all laser energy is converted into heat by a metal cap at the tip of the fibre, prior to tissue application - was one of the earliest modifications designed to overcome these problems. The studies in this thesis were concerned with the application of the laser thermal probe to percutaneous peripheral and coronary artery angioplasty and His bundle ablation. In vitro studies were commenced in March 1987 when the first (argon) laser generator was installed in the cardiac catheterisation laboratory at Guy's Hospital and these were followed by clinical studies in three groups of patients: nine with peripheral artery occlusions, three with coronary artery stenoses and four with supraventricular arrhythmias using either argon or Nd-YAG energies. Suggestions that enhanced safety might be possible with on-line monitoring and/or control of the probe temperature were studied by recording the temperature responses in simulated circulations at flow rates observed clinically. The highly variable temperatures recorded in blood indicate that these measures are unlikely to contribute to improvements in either efficacy or clinical safety. An earlier report of successful peripheral artery recanalisation using the laser thermal probe was confirmed in the patients studied here, though a learning curve was evident. Coronary laser angioplasty had also been performed in a few patients with a similar device but without as much success. A more flexible "over the wire" laser probe was assessed here, first in cadaver coronary arteries and then in three patients undergoing coronary angioplasty. The lack of success seen with this laser thermal probe relates to the considerable differences found between peripheral and coronary arteries: percutaneous accessibility, vessel size and the susceptibility to thermal injury being the most important. These aspects and subsequent developments in coronary laser angioplasty are discussed further. The final chapter considers a hitherto new area for laser thermal probe application the interruption of arrhythmia circuits. Cadaver and electrophysiological studies indicated that ablation of the bundle of His might be possible with this device - without the need for a general anaesthetic. The course of the first patient ever to undergo this procedure is described, as well as the implications for percutaneous His bundle ablation using other energy sources

Measurement and monitoring of atheromatous lesions of the femoral artery by duplex ultrasound.

In Western Societies atheromatous stenosis and occlusion of the superficial femoral artery cause intermittent claudication in up to 5% of the population over 55 years of age, and the associated morbidity and disability are considerable. A foreknowledge of impending lesion progression might allow prevention of clinical deterioration by early intervention. However, the natural history of these lesions needs to be more fully evaluated. Critical to the monitoring of early lesions is the need for accurate, repeatable and non-invasive investigations. The role of duplex ultrasound in this area is largely unexplored. In this thesis clinical and laboratory data demonstrate the accuracy and repeatability of duplex ultrasound in the measurement of femoral stenoses. A prospective study was carried out to determine the incidence of progression from stenosis to occlusion. There has been an enormous increase in the use of percutaneous transluminal angioplasty (PTA) in the treatment of patients with claudication. However, the relative benefits of PTA over conventional treatment have not been established. A study to determine the role of duplex in screening patients with claudication prior to PTA was carried out. The results demonstrate its accuracy and the consequent clinical benefits. A randomised controlled trial of PTA for patients with intermittent claudication has been established and the early patient data at trial entry are presented

Laser coronary revascularization: an evaluation of metal-capped optical fibres

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Current Approach to the Diagnosis and Treatment of Femoral-Popliteal Arterial Disease. A Systematic Review

Peripheral arterial disease (PAD) is a common manifestation of atherosclerosis affecting 5 million adults in the United States, with an age-adjusted prevalence of 4% to 15% and increasing up to 30% with age and the presence of cardiovascular risk factors. In this article we focus on lower extremity PAD and specifically on the superficial femoral and proximal popliteal artery (SFPA), which are the most common anatomic locations of lower extremity atherosclerosis. We summarize current evidence and perform a systematic review on the diagnostic evaluation as well as the medical, endovascular and surgical management of SFPA disease

The effect of percutaneous transluminal angioplasty of superficial femoral artery on pulse wave features

We aimed to analyze the effects of percutaneous transluminal angioplasty (PTA) of the superficial femoral artery (SFA) on arterial pulse waves (PWs). Altogether 24 subjects i.e. 48 lower limbs were examined including 26 treated lower limbs having abnormal ankle-to-brachial pressure index (ABI) (ABI1.3) and 22 non-treated lower limbs. The measurements were conducted in pre-, peri- and post-treatment phases as well as in follow-up visit after 1 month. Both ABI and toe pressures measured by standard equipment were used as reference values. PW-derived parameters include ratios of different peaks of the PW and time differences between them as well as aging index. Both treated and non-treated limbs were compared in pre- and post-treatment as well as follow-up visit conditions. The results were evaluated in terms of statistical tests, Bland-Altman-plots, free-marginal multirater κ-analysis and multiple linear regression analysis. PTA was found to cause small changes to the studied PW-derived parameters of the treated limb which were observed immediately after the treatment, but the changes were more pronounced in the follow-up visit. In addition, we observed that the endovascular instrumentation itself does not cause significant changes to the PW-derived parameters. The results show that PW-analysis could be a useful tool for monitoring the treatment-effect of the PTA. However, because the pre-treatment differences of the treated and non-treated limb were small, further studies with subjects having no arterial diseases are required. The study demonstrates the potential of the PW analysis in monitoring vascular abnormalities.acceptedVersionPeer reviewe

Influence of endovascular treatment on the vascular endothelium in patients with peripheral arterial disease: a systematic review

Peripheral arterial disease (PAD) is a major public health problem. Endothelial dysfunction represents an important mechanism in the development and progression of atherosclerosis, in part attributable to inflammation, platelet and smooth muscle activation, and arterial stiffening. The aim of this study was to explore the impact of lower limb revascularization on endothelial function in patients with PAD. We performed a comprehensive search of the academic literature using the PubMed and Embase databases to screen suitable records. Following the application of our search strategies, a total of eight studies were included in this review. Despite the limited available evidence, the dearth of academic literature suggests that revascularization has a positive effect on endothelial functioning. The effects of endovascular revascularization on endothelial functioning in patients with PAD are subject to further research

The computation of blood flow waveforms from digital X-ray angiographic data

This thesis investigates a novel technique for the quantitative measurement of pulsatile blood flow waveforms and mean blood flow rates using digital X-ray angiographic data. Blood flow waveforms were determined following an intra-arterial injection of contrast material. Instantaneous blood velocities were estimated by generating a 'parametric image' from dynamic X-ray angiographic images in which the image grey-level represented contrast material concentration as a function of time and true distance in three dimensions along a vessel segment. Adjacent concentration-distance profiles in the parametric image of iodine concentration versus distance and time were shifted along the vessel axis until a match occurred. A match was defined as the point where the mean sum of the squares of the differences between the two profiles was a minimum. The distance translated per frame interval gave the instantaneous contrast material bolus velocity. The technique initially was validated using synthetic data from a computer simulation of angiographic data which included the effect of pulsatile blood flow and X-ray quantum noise. The data were generated for a range of vessels from 2 mm to 6 mm in diameter. Different injection techniques and their effects on the accuracy of blood flow measurements were studied. Validation of the technique was performed using an experimental phantom of blood circulation, consisting of a pump, flexible plastic tubing, the tubular probe of an electromagnetic flowmeter and a solenoid to simulate a pulsatile flow waveform which included reverse flow. The technique was validated for both two- and three-dimensional representations of the blood vessel, for various flow rates and calibre sizes. The effects of various physical factors were studied, including the distance between injection and imaging sites and the length of artery analysed. Finally, this method was applied to clinical data from femoral arteries and arteries in the head and neck

Volume 27, issue 4

The mission of CJS is to contribute to the effective continuing medical education of Canadian surgical specialists, using innovative techniques when feasible, and to provide surgeons with an effective vehicle for the dissemination of observations in the areas of clinical and basic science research. Visit the journal website at http://canjsurg.ca/ for more.https://ir.lib.uwo.ca/cjs/1197/thumbnail.jp

The impact of different techniques used for coronary angiography and percutaneous coronary intervention on the occurrence of procedure-related ischemic cerebral complications

Background Coronary angiography (CA) is the gold standard in diagnosing and determining the treatment of patients with coronary heart disease. Procedure-related neurological complications are rare; 0.1-0.4% for CA and percutaneous coronary intervention (PCI). In contrast, the incidence of procedure-related silent cerebral lesions, shown with diffusion-weighted magnetic resonance tomography, is considerably higher (2-35%). Cerebral microemboli have been observed during different vascular procedures and are related to new silent cerebral lesions but their clinical impact is debated. CA and PCI can be performed with different techniques, i.e. with the radial or the femoral access. As procedure-related stroke is associated with high mortality, considerable morbidity and suffering it is important to study which technique entails the lowest risk for patient injury. Methods and results Study I: Fifty-one patients with stable angina pectoris were randomised to CA with the radial or the femoral access and the number of cerebral microemboli was assessed with bilateral transcranial Doppler technique of the middle cerebral arteries (MCAs). The number of particulate cerebral microemboli was signifiantly higher with the radial compared to the femoral access. The number of cerebral microemboli was higher for both access sites during catheter exchanges compared with other specifi procedural steps during CA, with most cerebral microemboli detected in the right MCA in the radial group. This indicates a causal anatomical link, as the catheter is advanced from the right radial artery through the brachiocephalic trunk before it bends into the ascending aorta to reach the coronary ostia. Study II: Forty-one patients with stable angina pectoris or non-ST-segment-elevation myocardial infarction scheduled for CA were randomised to two different guidewire techniques with the femoral access involving catheter advancement with or without a leading guidewire over the aortic arch. After the CA was completed, including contrast injections, the opposite technique was used on the same patient without further contrast injections. At the same time, the number of cerebral microemboli was registered using bilateral transcranial Doppler technique. The number of cerebral microemboli was higher when the catheter was advanced with, rather than without a leading guidewire over the aortic arch, independent of whether a complete CA was performed or if a catheter was placed in the vicinity of the coronary ostia only. Study III: All CAs and PCIs reported between 2003 and 2011, n= 336,836, to the Swedish Coronary Angiography and Angioplasty Register with information on access site were retrospectively analysed regarding the association between access site and procedure-related stroke or transient ischemic attack (TIA). After cross-checking the reported neurological complications with the corresponding medical records the incidence of procedure-related stroke or TIA was 0.16%. After multivariable adjustment, the radial access was associated with a higher risk for procedure-related stroke or TIA (risk ratio 1.30, 95% confience interval 1.04-1.62) compared with the femoral access. Parallel to the increased use of the radial access over time, the risk for procedure-related stroke or TIA also increased, although there was no signifiant interaction between the different time intervals observed. Study IV: Ninety-three patients with suspected or stable angina pectoris scheduled for CA or PCI were tested with Montreal Cognitive Assessment (MoCA) before and twice after the coronary procedure to study postprocedural cognitive impairment. A subgroup was monitored with bilateral transcranial Doppler technique to explore the relationship between cerebral microemboli and cognitive function. The patients were also randomised to radial or femoral vascular access site to study if the access site used was related to postprocedural cognitive impairment. Cognitive function assessed with the MoCA test was not impaired after the coronary procedure. There was no signifiant correlation between the results of the MoCA test and cerebral microemboli or vascular access site. Conclusions The choice of access site and guidewire technique used for CA and PCI had an impact on the occurrence of cerebral microemboli. There may be an association between the radial access and increased risk for procedure-related stroke or TIA, which should be studied further. Earlier studies have shown that cerebral microemboli are related to new silent cerebral lesions, but we found no cognitive impairment after coronary procedures using the MoCA test. Further studies are needed to explore the clinical impact of cerebral microemboli and to minimise or prevent the occurrence of procedure-related ischemic cerebral lesions in patients undergoing CA and PCI