Clinical Profile, Management, and Outcome in Patients With Out-of-Hospital Cardiac Arrest and ST Segment Elevation Myocardial Infarction: Insights From a 20-Year Registry.

AIM OF THE STUDY: We studied the clinical profile, management, and outcomes of patients with out-of-hospital cardiac arrest (OHCA) with and without ST-elevation myocardial infarction (STEMI). METHODS: Retrospective analysis of the 20-year registry data (January 1991- June 2010) was conducted on patients with cardiac disease hospitalized at Hamad General Hospital and Qatar Heart Hospital, Doha, Qatar. RESULTS: A total of 987 patients with OHCA were admitted to the cardiology department during the study period; among them, 296 (30%) patients had STEMI. Compared to the patients with OHCA without STEMI, the patients who had OHCA with STEMI were younger (53 ± 13 vs 58 ± 16 years; P = .001), more likely to be male (78% vs 34%; P = .001), smokers (35% vs 14%) but less likely to have hypertension (30% vs 48%; P = .001), diabetes (32% vs 47%, P = .001), and chronic renal failure (3.4% vs 9%; P = .002). The use of thrombolytic treatment in patients with STEMI increased from 21.6% (period 1991-1095) to 44.4% (period 2006-2010); P = .04. CONCLUSION: Percutaneous coronary intervention had increased significantly during the last quarter of the study. There was a decline in the in-hospital mortality among patients with STEMI during the last quarter of the study.

Mortality Trends in Patients Hospitalized with the Initial Acute Myocardial Infarction in a Middle Eastern Country over 20 Years.

We aimed to define the temporal trend in the initial Acute Myocardial Infarction (AMI) management and outcome during the last two decades in a Middle Eastern country. A total of 10,915 patients were admitted with initial AMI with mean age of 53 ± 11.8 years. Comparing the two decades (1991-2000) to (2001-2010), the use of antiplatelet drugs increased from 84% to 95%, ß -blockers increased from 38% to 56%, and angiotensin converting enzyme inhibitors (ACEI) increased from 12% to 36% (P < 0.001 for all). The rates of PCI increased from 2.5% to 14.6% and thrombolytic therapy decreased from 71% to 65% (P < 0.001 for all). While the rate of hospitalization with Initial MI increased from 34% to 66%, and the average length of hospital stay decreased from 6.4 ± 3 to 4.6 ± 3, all hospital outcomes parameters improved significantly including a 39% reduction in in-hospital Mortality. Multivariate logistic regression analysis showed that higher utilization of antiplatelet drugs, ß -blockers, and ACEI were the main contributors to better hospital outcomes. Over the study period, there was a significant increase in the hospitalization rate in patients presenting with initial AMI. Evidence-based medical therapies appear to be associated with a substantial improvement in outcome and in-hospital mortality.

Clinical presentation and cardiovascular risk profiles in patients with left main coronary artery disease in a middle eastern country.

We evaluated the prevalence and clinical profile of patients with left main coronary artery disease (LMCA) in Qatar between 2006 and 2010. Patients were divided into 2 groups: patients with LMCA and patients without LMCA but had severe 3-vessel disease (VeD) eligible for surgical revascularization. Among 7000 patients who underwent coronary angiography, 210 patients had significant LMCA and 200 patients with severe 3VeD were matched for age and sex. Diabetes mellitus and hypertension were comparable in the 2 groups. Presentations with myocardial infarction or heart failure were comparable in both groups. Isolated LMCA was 4-fold higher in women (P = .02). Dyslipidemia and smoking were more prevalent in patients with distal and proximal lesions, respectively. Renal failure was independent predictor of LMCA (adjusted odds ratio: 2.6; 95% confidence interval: 1.43-4.69). One-year mortality was higher in LMCA (P = .01). The LMCA carries high mortality. Certain cardiovascular risk factors were important predictors of stenosis site.

Prevalence of unrecognized diabetes mellitus in patients admitted with acute coronary syndrome.

We assessed the prevalence of unrecognized diabetes mellitus (DM) in patients with acute coronary syndrome (ACS) as determined by elevated glycosylated hemoglobin (HbA1c), fasting plasma glucose (FPG), and random plasma glucose (RPG) levels. This prospective study recruited 583 patients admitted with ACS without previous diagnosis of DM during 1-year period. Glycosylated hemoglobin was checked for most patients especially those with high values of FPG and or RPG. Patients were classified according to their glycemic state into 123 (21.1%) with DM, 82 (14.1%) with prediabetes, and 57(9.8%) with stress hyperglycemia, while 321 (55%) were classified as nondiabetics. Glycosylated hemoglobin estimation in the setting of ACS was helpful in the diagnosis of DM to eliminate the effect of stress-induced hyperglycemia that might accompany this condition.

Study of shift work and risk of coronary events.

BACKGROUND: The effects of shift work on coronary heart diseases (CHD) are well described. Most of the studies on coronary events in shift workers are supportive of the hypothesis that they are at increased risk. OBJECTIVE: The objective of this study was to investigate the relation shift work has to risk of CHD in a cohort of men from different Asian races working in a fertilizer plant in the Middle East. DESIGN: This is a case series of cohort study. SUBJECTS: The medical records for 2562 staff employed at the plant, from the start of the company in 1972 till 2003, were surveyed. Of these, 648 were shift workers and 1914 were daytime workers. A total of 223 employees had cardiovascular event. METHODS: For each case we recorded the date and age at start of employment, and the age at the time of diagnosis. Data from their last medical examination in the company were used to calculate their BMI, and to register whether they were smokers, had diabetes, or were senior or intermediate staff. Univariate and multivariate statistical analyses were performed. RESULTS: The incidence of CHD is significantly higher in shift workers (13.5%) compared with the daytime workers (7.1%). Also, there was a statistically significant difference between shift workers and daytime workers concerning hypertension and cerebrovascular incidents. CONCLUSION: Our results suggest the possibility of an overall relationship between shift work and cardiovascular diseases.

Does the circadian pattern for acute cardiac events presentation vary with fasting?

BACKGROUND: Over one billion Muslims fast worldwide during the month of Ramadan. The impact of fasting on circadian presentation with acute cardiac events is unknown. AIM: To determine if fasting has any effect on the circadian presentation of acute cardiac events. SETTING AND DESIGN: A prospective study in a general hospital. MATERIALS AND METHODS: Patients with acute coronary events were divided into two groups based on the history of fasting. Information about age, gender, cardiovascular risk factor profiles and outcome was collected. The relationship of time of presentation of initial symptoms with fasting was evaluated using Student's t-test, Mann-Whitney U-test and chi2 analysis. RESULTS: Of the 1019 patients hospitalized during the study period, 162 were fasting. Although, fasting patients were more likely to present to the emergency department in the time periods 5-6 AM (10.5% vs 6.3%) and 11 PM (11.1% vs 7.1%) and were less likely to present in the time periods 1-2 PM (3.7% vs 7.2%) and 5-6 PM (3.7% vs 7.0%); these differences were not statistically significant. Fasting patients were less likely to have their symptoms start between 5 and 8 AM (11.1% vs 19.4%) and more likely to have symptoms between 5 and 6 PM (11.1% vs 6.0%) and 3 and 4 AM (11.1% vs 6.9%). These differences for time of initial symptoms were statistically significant (P=0.002). CONCLUSION: Exogenous factors associated with fasting, namely, the changes in food intake and/or sleep timings, affect the circadian rhythm and influence the timing of presentation of acute coronary events.

Myocardial infarction with normal coronary angiography compared with severe coronary artery disease without myocardial infarction: the crucial role of smoking.

BACKGROUND: Why do some patients suffer acute myocardial infarction (MI) despite angiographically normal coronary arteries (NL + MI) whereas others enjoy an acute MI-free life despite extensive three-vessel disease (3VD-MI)? The present study contrasts these two groups to identify some differences in the risk profile. METHODS: In 10,000 patients admitted to the cardiology service, a first MI was confirmed in 2356 patients, of whom 1609 underwent coronary angiography. In 77 patients with MI, coronary angiography was found to be entirely normal (NL + MI, 77/1609, 4.1%). These were contrasted to 123 patients with severe three-vessel coronary disease but no MI (3VD-MI). RESULTS: Patients with NL + MI were 13 years younger (42 +/- 8.3 vs 55 +/- 10.5, P < 0.05), with 33 patients (43%) under the age 40 years, in contrast to only 9 patients (7.3%) in the 3VD group being this age. Patients with NC + MI were more often current smokers (80.5% vs 29% in the 3VD group; P < 0.01). Patients with 3VD-MI were, on the other hand, more often diabetic (54% vs 9% in the NL + MI group; P < 0.01) and had a higher cholesterol level (5.6 +/- 1.1 vs 4.9 +/- 1.0 Mmol/l, P < 0.01) as well as a higher incidence of chronic stable angina (52% vs 22%; P < 0.01) and heart failure (6% compared with 0% in the NL + MI group). Sixty-one out of 77 (79%) NL + MI patients had a single risk factor, and in 87%, this was smoking alone. Diabetes mellitus was rare and never occurred alone in this group. CONCLUSION: In patients who suffer MI despite normal coronary angiography, smoking is a major risk factor: In contrast, in patients with extensive coronary artery disease on angiography but no MI, diabetes rather than smoking is the dominant risk factor. The findings of this study support the view that the risk factors for stable and unstable coronary artery disease are different, as reflected by the contrast of the above groups at the extremes of the spectrum. Smoking appears to be a major risk factor for acute MI (even with normal coronary angiography), whereas diabetes is a major risk factor for more severe but more stable coronary artery disease.

Can rotational atherectomy cause thermal tissue damage? A study of the potential heating and thermal tissue effects of a rotational atherectomy device.

PURPOSE: Thermal tissue damage (TTD) is customarily associated with some lasers. The thermal potential of rotational atherectomy (RA) devices is unknown. We investigated the temperature profile and potential TTD as well as the value of fluid flushing of an RA device. METHODS: We used a high-resolution infrared imaging system that can detect changes as small as 0.1 degree C to measure the temperature changes at the tip of a fast RA device with and without fluid flushing. To assess TTD, segments of porcine aorta were subjected to the rotating tip under controlled conditions, stained by a special histochemical stain (picrisirius red) and examined under normal and polarized light microscopy. RESULTS: There was significant heating of the rotating cam. The mean "peak" temperature rise was 52.8 +/- 16.9 degrees C. This was related to rotational speed; thus the "peak" temperature rise was 88.3 +/- 12.6 degrees C at 80,000 rpm and 17.3 +/- 3.8 degrees C at 20,000 rpm (p < 0.001, t-test). Fluid flushing at 18 ml/min reduced, but did not abolish, heating of the device (11.8 +/- 2.9 degrees C). A crater was observed in all segments exposed to the rotating tip. The following features were most notable: (i) A zone of "thermal" tissue damage extended radially from the crater reaching adventitia in some sections, especially at high speeds. This zone showed markedly reduced or absent birefringence. (ii) Fluid flushing of the catheter reduced the above changes but increased the incidence and extent of dissections in the media, especially when combined with high atherectomy speeds. (iii) These changes were observed in five of six specimens exposed to RA without flushing, but in only one of six with flushing (p < 0.05). (iv) None of the above changes was seen in control segments. CONCLUSION: RA is capable of generating significant heat and potential TTD. Fluid flushing reduced heating and TTD. These findings warrant further studies in vivo, and may influence the design of atherectomy devices.

Fast rotating atherectomy catheter tip inhibits platelet aggregation and ATP release: a study using platelet-rich plasma.

The interaction of atherectomy devices with the arterial wall is the focus of many studies, but their effect on the surrounding blood is largely unknown. This is a detailed investigation on the effects of a rotational atherectomy device with a fast rotating tip on platelet structure and function. Platelet-rich plasma (PRP) was obtained from six volunteers, divided into 5 mL samples, and subjected to the atherectomy tip rotating at 20, 40, or 80 thousand rpm for 30 or 60 seconds. Platelet aggregation to collagen or adenosine diphosphate (ADP) was obtained in all samples by means of a dual-chamber optical aggregometer. The fast rotating catheter tip caused marked inhibition of platelet aggregation to both collagen and ADP. The maximum extent of aggregation was reduced from 85% +/-2.8 in control to 46% +/-4.8 with collagen (p<0.01) and from 86.1% +/-6.9 to 25.1% +/-4.3 with ADP (p<0.01). The rate of aggregation (measured at 4 minutes) dropped from 81.3% +/-2.7 to 40% +/-4.5 and from 73.9% +/-8.5 to 12.5% +/-2.6 (p<0.005) with collagen and ADP, respectively. These effects were related to rotating speed and duration of exposure. ATP release in response to collagen fell from 2.63 +/-0.13 nMol in control to 0.7 +/-0.1 nMol, p<0.001 after exposure to the rotating tip. There was no significant change in platelet count, nor was there formation of platelet aggregates (platelet aggregate ratio remained unchanged) to account for these phenomena. Furthermore, transmission electron microscopy showed no significant platelet disruption or release of granules, and little signs of activation were seen even after addition of collagen. This is the first study to demonstrate that exposure to a fast rotating catheter tip inhibits in vitro platelet aggregation and ATP release. There were no apparent loss of integrity of platelet structure, release of granules, or formation of platelet aggregates. This phenomenon and its clinical implication justify further investigation.

Coronary angiography in Qatar: the first ten years.

Cardiac catheterization in Qatar was initiated in July 1982. In ten years, a total of 3900 procedures were performed at Hamad General Hospital. Computerized data registry has been maintained since 1982. Isolated coronary angiography was done in 2911 patients; of these, 2635 (90.5%) were men, and 276 (9.5%) were women, the average age of the patients was 47+/-9.2 years (range, twenty-five to eighty-eight). Patients' nationality was Qatari in 492 (17%), and other Arabs in 610 (21%), and 1512 (52%) were from the Asian subcontinent. Myocardial infarction was the most common indication (43%). Single-vessel disease was found in 638 (22%), two-vessel disease in 630 (22%), three-vessel disease in 950 (33%), and nonsignificant coronary artery disease in 693 (24%) patients. Morbidity related to the coronary angiography was reported in 147 (5%) patients, but there was no mortality related to the procedure. In 822 (28%) patients, the age was forty years or younger. The angiographic findings of these younger patients were compared with those of the older ones. Younger patients were usually men of Asian subcontinental origin with a recent myocardial infarction (MI). Often, they had normal coronary arteries or single-vessel disease. Patients of Asian subcontinent origin were usually young male patients with a recent MI, who receive streptokinase, and have single-vessel disease.

Percutaneous laser recanalisation of femoropopliteal occlusions using continuous wave Nd-YAG laser and sapphire contact probe delivery system.

A conventional continuous wave Nd-YAG medical laser system delivered by transparent sapphire tipped optical fibres was used for percutaneous recanalisation of 32 chronic femoropopliteal occlusions in 27 patients (19 men, eight women; median age 68 years, range 46-83 years). Twenty-four patients had severe intermittent claudication and three had critical ischaemia. The median occlusion length was 8 cm (range 3-35 cm) and lesions were not negotiable by guidewire. Laser energy was delivered at powers of 10-15 Watts using intermittent 1 second emissions (mean total energy 315 Joules, range 30-1015]). The sapphire tips used were 1.8 to 3.0 mm diameter. After laser recanalisation adjunctive balloon dilatation was necessary to widen the resulting lumen. All patients received anti-platelet therapy. Initial clinical success was achieved in 22 limbs (69%) with symptomatic relief and increase in mean (+/- S.D.) ankle-brachial pressure ratio from 0.52 (+/- 0.25) to 0.80 (+/- 0.21) [Mann-Whitney U, p < 0.001]. Recanalisation was unsuccessful in all calcified lesions (four cases). There was a high incidence of vessel perforation (28%) and wall dissection (25%). Emergency surgery was not required after failed procedures. The median follow-up was 12 months (range 6-20 months). By 6 months, 15 of 22 successfully recanalised lesions (68%) had reoccluded. The cumulative primary patency at 1 year was only 12%. These disappointing results do not support routine use of this system. Clearly, modifications of the laser/delivery system or the technique, or both, are required. The aim should be to achieve sole laser recanalisation without concomitant balloon dilatation.

Value of a radionuclide limb blood flow technique in the assessment of percutaneous balloon and dynamic angioplasty.

In a prospective study, a radionuclide technique was used to evaluate the limb blood flow (LBF) changes in 30 patients undergoing dynamic (n = 15) or balloon (n = 15) angioplasty for arterial occlusions or stenoses, respectively. The results were compared with Doppler Ankle Brachial Index (DABI) and treadmill exercise tests. Whilst LBF values (ml of blood flow per 100 ml of limb volume per min) were significantly lower in limbs with arterial occlusion than stenosis (4.5 +/- 0.46 and 6.4 +/- 0.74, respectively; P less than 0.05). DABI provided no discrimination. Immediately after balloon angioplasty, there was a fall in DABI, from 0.60 +/- 0.05 to 0.47 +/- 0.04 (P less than 0.05), which rose 24 h later to 0.73 +/- 0.02 (P less than 0.01). Following dynamic angioplasty, DABI improved from 0.60 +/- 0.05 to 0.66 +/- 0.02 (P less than 0.05). At 3 weeks, the LBF improved from 4.6 +/- 0.66 to 11.1 +/- 0.53 (P less than 0.001) following dynamic angioplasty and from 6.2 +/- 0.68 to 8.53 +/- 0.81 (P less than 0.001) following balloon angioplasty. "Normal" LBF (greater than 10 ml/100 ml per min) was achieved in 80% of patients who underwent successful dynamic angioplasty but in only 36% of the balloon group (P less than 0.05, chi 2-test). Reproducibility of repeated LBF measurements in control limbs was superior to that of DABI. This was indicated by a lower coefficient of variation, 13.8% compared with 25.2%, and a higher correlation coefficient, r = 0.79 compared with 0.27. Treadmill exercise tests were invalid or impossible in 30% of all occasions.(ABSTRACT TRUNCATED AT 250 WORDS)

Does the Kensey catheter keep a coaxial position inside the arterial lumen? An in-vitro angioscopic study.

Angioscopy was used to evaluate the "self-centering" ability of three Kensey catheters (KC) with different flexibility: one 8Fr "peripheral" and two 5Fr "coronary" (I & II). Angioscopic observations were made inside arteries, 5-18 mm in diameter. There was a good correlation between flexibility and self-centering of the KC [r = 0.83, p less than 0.05]. Increasing the flow rate of rinsing solution from 18 to 60 ml/min prolonged coaxial position from 8.9 +/- 3.3 to 36 +/- 2.2 sec/min of activation [p less than 0.001]. A smaller effect on coaxial position was exerted by increasing cam speed from 5.2 +/- 0.7 to 19.2 +/- 1.6 sec/min (p less than 0.001). In conclusion, angioscopy showed that the KC has a limited ability to maintain a coaxial position inside the arterial lumen and operators cannot rely on its self-centering property.

Isotope limb blood flow measurement in patients undergoing peripheral laser angioplasty.

A technique of isotope limb blood flow (ILBF) measurement employing Technetium-labelled human albumin and a gamma camera, was used to assess limb perfusion in 19 patients undergoing percutaneous laser angioplasty, both before and one month after treatment. Twenty-three limbs with femoro-popliteal occlusions ranging in length from 3-35 cm (median 8 cm) were recanalized using an Nd-YAG laser and sapphire tipped optical fibre. Primary angiographic success was achieved in 19 lesions of which 6 re-occluded within the first month, and 13 remained patent with relief of symptoms. Clinically successful procedures were associated with a large increase in ILBF. However, normal blood flow was restored in only 54% of limbs. There was a slight decrease in limb perfusion after failed laser angioplasty but this was not statistically significant in this small series. Furthermore, there was no clinically apparent circulatory compromise, or need for urgent surgical bypass in failed cases. We conclude that ILBF is a useful means of assessing patients undergoing laser angioplasty, particularly for detecting small flow changes in patients who are unable to complete a standard exercise test. Its use can be recommended for assessing blood flow changes following other forms of limb revascularization.

Experimental and clinical percutaneous angioscopy experience with dynamic angioplasty.

The authors have used ultrathin angioscopes with high optical resolution to assess the effects of dynamic angioplasty in vitro and in vivo. Experimentally, angioscopy was used to study the effects of the 5F "Kensey" catheter in "normal" porcine coronary arteries (NPCA) and postmortem human coronary arteries (PMHCA). In NPCA, the catheter keeps a coaxial position. Intimal flaps (IFs) were seen in 21/23 NPCAs. They occurred with all cam rotation speeds and were usually single and small (less than 25% of lumen). Perforations in patent arteries were rare (1/23). However, when the catheter was forced against the wall by passing through a narrowing of 5F diameter (made by a band ligature), perforations were more common at higher cam speeds. The epicardium remained intact in two thirds of perforations. Angioscopy visualized perforations in only 10% of cases (1/10), the common sign being that of large and multiple intimal flaps, which were often obstructive (5/10). In PMHCAs, angioscopy was more sensitive than angiography in detecting atheromatous lesions. The authors were able to give a better assessment of the effect of dynamic angioplasty on treated lesions, including the demonstration of intimal flaps that were not visible on angiography. In vivo, they have performed percutaneous angioscopy before and after dynamic angioplasty using 8 French Kensey catheters. Angioscopy revealed features that were not shown angiographically.

Experimental analysis of sapphire contact probes for Nd-YAG laser angioplasty.

Laser angioplasty may offer percutaneous recanalization of occluded vessels where conventional guidewire and balloon techniques fail. Metal laser thermal angioplasty probes may, however, cause excessive thermal damage due to high tip temperatures (greater than 400.C). Therefore, contact probes made from artificial sapphire crystal designed for general laser surgery are currently being evaluated for use in laser angioplasty with continuous wave Nd-YAG energy. The sapphire modifies the laser energy in various ways, and this paper examines the physical characteristics of five types of rounded sapphire probe (SMTR, MTR, MTRL, OS, LT) and how these properties are affected by clinical usage. The laser beam profile emitted by these probes demonstrates a focal spot 1-2 mm in front of the tip. However, the forward transmission of Nd-YAG energy through the sapphires varied (SMTR, 85%; MTR, 83%; MTRL, 75%; OS, 54%; LT, 69%). Probe heating occurs owing to energy absorption within the sapphire. The surface temperature of the sapphires was measured in air by infrared thermography and the hottest region within the probes localized by an isothermographic technique. At energy settings used clinically (20 J, 10 watts for 2 s) the SMTR, MTR, and MTRL probes exhibited higher temperature rises (94-112.C) than the OS and LT probes (30.C), and heating was localized to the front surface of the former probes. Peak sapphire temperatures remained lower than those of metal probes even at higher energies. After clinical use, the MTR probe demonstrated reduced transmission, beam defocusing, and increased heating, due to surface pitting. Thus, recanalization with sapphire probes occurs by a combination of photothermal and contact thermal effects that are localized to the probe tip and may reduce the degree of thermal injury associated with metal probes. Understanding these basic properties is important to the application and development of contact probes for laser recanalization.

Aneurysm formation after dynamic catheter assisted balloon angioplasty.

A male patient underwent recanalisation of a symptomatic popliteal artery occlusion using a dynamic angioplasty catheter, followed by balloon dilatation. A small subintimal dissection lead to an acute reocclusion. Repeat balloon angioplasty reopened the occlusion but was complicated by a distal embolus which was successfully treated by thrombolytic therapy followed by oral anticoagulation. Angiography 9 months later, demonstrated an aneurysm at the site of initial dissection. The artery remained patent and the patient free of claudication. A causal relationship between dynamic angioplasty and subsequent aneurysm formation is suggested and the possible predisposing factors discussed.

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty.

Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires compared with the SLT probes [P less than 0.001, one-way ANOVA]. The SLT system is, therefore, potentially safer in this respect. These results suggest that some degree of surface heating of contact probes due to energy absorption within the sapphire does occur, but is localised to the front of the probe. This effect may contribute to the process of arterial recanalisation with this device. However, variation in the thermal and optical properties of sapphires from different sources has been demonstrated. The influence of these properties on plaque ablation, and ultimately the clinical performance of different contact probe systems, requires further investigation.