Emergence of tick-borne encephalitis in new endemic areas in Austria: 42 years of surveillance

Human infections with tick-borne encephalitis (TBE)virus are a public health concern in certain regions of Europe, central and eastern Asia. Expansions of endemic areas and increased incidences have been associated with different factors including ecological changes supporting tick reproduction, socioeconomic changes increasing human outdoor activities and climatic changes favouring virus circulation in natural foci. Austria is among the most strongly affected countries in Central Europe, but the annual number of cases has strongly declined due to vaccination. Here,we have analysed changes of the incidence of TBE in the unvaccinated population of all federal states of Austria over a period of 42 years. The overall incidence in Austria has remained constant, but new strongly affected endemic regions have emerged in alpine valleys in the west of Austria. In parallel, the incidence in low-land regions in the north-east of the country is decreasing. There is no evidence for a shift to higher altitudes of infection sites in the traditional TBE zones,but the average altitudes of some newly established endemic areas in the west are significantly higher. Our analyses underscore the focal nature of TBE endemic areas and the potential of TBE virus to emerge in previously unaffected regions.

Temperature and SAR measurement errors in the evaluation of metallic linear structures heating during MRI using fluoroptic probes

The purpose of this work is to evaluate the error associated with temperature and SAR measurements using fluoroptic temperature probes on pacemaker (PM) leads during magnetic resonance imaging (MRI). We performed temperature measurements on pacemaker leads, excited with a 25, 64, and 128 MHz current. The PM lead tip heating was measured with a fluoroptic thermometer (Luxtron, Model 3100, USA). Different contact configurations between the pigmented portion of the temperature probe and the PM lead tip were investigated to find the contact position minimizing the temperature and SAR underestimation. A computer model was used to estimate the error made by fluoroptic probes in temperature and SAR measurement. The transversal contact of the pigmented portion of the temperature probe and the PM lead tip minimizes the underestimation for temperature and SAR. This contact position also has the lowest temperature and SAR error. For other contact positions, the maximum temperature error can be as high as -45%, whereas the maximum SAR error can be as high as -54%. MRI heating evaluations with temperature probes should use a contact position minimizing the maximum error, need to be accompanied by a thorough uncertainty budget and the temperature and SAR errors should be specified.

MRI-induced heating of selected thin wire metallic implants-- laboratory and computational studies-- findings and new questions raised

We performed experiments and computer modeling of heating of a cardiovascular stent and a straight, thin wire by RF fields in a 1.5 T MRI birdcage coil at 64 MHz. We used ASTM F2182-02a standard and normalized results to 4 W/kg whole body average. We used a rectangular saline-gel filled phantom and a coiled, double stent (Intracoil by ev3 Inc) 11 cm long. The stent had thin electrical insulation except for bare ends (simulating drug eluting coating). The stent and phantom were placed close to the wall of the RF Coil and had approximately 0.5 degrees C initial temperature rise at the ends (local SAR = 320 W/kg). We exposed a wire (24.1 cm, 0.5 mm diameter) with 0.5 mm insulation and saw an 8.6 degrees C temperature rise (local SAR = 5,680 W/kg) at the bare ends. All heating was within 1 mm3 of the ends, so the position of our fiber optic temperature probe was critical for repeatability. Our computational study used finite difference time domain software with a thermodynamics solver. We modeled a coiled bare-wire stent as a spiral with a rectangular cross section and found a maximum increase of 0.05 degrees C induced at the tips for plane wave exposures. A maximum local SAR of up to 200 W/kg occurred in a volume of only 8 x 10(-3) mm. We developed improved computational exposure sources-- optimized birdcage coils and quasi-MRI fields that may eliminate the need to model an RF coil. We learned that local (point) SAR (initial linear temperature rise) is the most reliable indicator of the maximum heating of an implant. Local SAR depends greatly on implant length, insulation and shape, and position in the MRI coil. Accurate heating must be measured with sensors or software having millimeter resolution. Many commercially available fiber optic temperature probes do meet this requirement.

MRI induced heating of pacemaker leads: effect of temperature probe positioning and pacemaker placement on lead tip heating and local SAR

The radio frequency field used in magnetic resonance imaging (MRI) procedures leads to temperature and local absorption rate (SAR) increase for patients with implanted pacemakers (PM). In this work a methodological approach for temperature and SAR measurements using fluoroptic probes is presented. Experimental measures show how the position of temperature probes affects the temperature and SAR value measured at the lead tip. The transversal contact between the active portion of the probe and the lead tip is the configuration associated with the highest values for temperature and SAR, whereas other configurations may lead to an underestimation close to 11% and 70% for temperature and SAR, respectively. In addition measurements were performed on a human-shaped phantom inside a real MRI system, in order to investigate the effect of the PM placement and of the lead geometry on heating and local SAR.

Electromagnetic compatibility of electronic implants--review of the literature

The aim of the article was to provide an overview of published studies regarding the electromagnetic compatibility (EMC) of electronic implants. The available literature was sorted according to combinations of implant types and sources of interference. Several experiments concerning the susceptibility of pacemakers to mobile phones have been performed. The results of these experiments suggest measures that may be used to prevent the disturbance of pacemakers. For instance, instead of carrying the activated mobile phone in the breast pocket it is recommended that a distance of 30 cm be maintained between the pacemaker and the mobile phone, and that the mobile phone be used on the contralateral side of the pacemaker's location. Similar measures may be recommended for patients with implantable cardioverter defibrillators when using mobile phones. Patients with electronic implants should walk rapidly through anti theft-devices because some of these devices are liable to disturb implants. Patients with cardiac pacemakers should not be subjected to magnetic resonance imaging as far as possible. For a variety of combinations of implants and interference sources, e.g. cardiac pacemakers and base station antennas, no studies were found in the literature. It is strongly recommended that trials be carried out to evaluate the potential risk for patients in these settings.

[Sick sinus syndrome indication: AAI/R versus DDD/R]

Numerous studies demonstrated the superiority of atrial based pacing modes (AAI/R, DDD/R) in the pacemaker therapy of sinus node disease. They reduce mortality, the incidence of atrial fibrillation and the risk for heart failure and increase quality of life, but there is still debate about the most appropriate mode of pacing. The AAI-mode carries the risk of high degree AV-block and the possible occurence of atrial fibrillation with slow ventricular response, demanding ventricular stimulation. DDD-pacemakers, however, are more complex and expensive and the stimulation in the apex of the right ventricle results in the loss of the normal activation sequence of the ventricles and can cause hemodynamic deterioration. Despite the lack of prospective randomized studies comparing the long term performance of the two pacing modes (AAI/R and DDD/R) many arguments plead in favour of a preferential use of AAI/R in patients eligible for permanent atrial pacing.

Application of pulsed-Doppler tissue imaging in patients with dual chamber pacing: the importance of conduction time and AV delay on regional left ventricular wall dynamics

Pulsed-Doppler tissue imaging (pDTI) is able to measure myocardial wall velocities (systolic: S; early diastolic: E; late diastolic: A) and their timings. Relationships have been demonstrated between the pre-ejection period and indexes of left ventricular systolic function. This study was designed to examine with pDTI the effects of variations in atrioventricular delay (AVD) (100 ms, 150 ms, 200 ms) on myocardial dynamics and on their timings at the basal interventricular septum (IVS) from an apical approach and at the posterior wall (PW) from the parasternal view. These data were compared with stroke volume measurements recorded from the left ventricular outflow tract. Seventeen patients with dual chamber pacemakers (7 because of complete heart block, 10 with sick sinus syndrome and first-degree AV block) were studied; full atrial and ventricular capture was present at any AVD. These data were also compared with those obtained in 10 age-matched healthy volunteers with comparable heart rates.

RESULTS

Optimal atrial contribution to left ventricular filling and, consequently, best systolic performance were achieved when AVD was programmed such that a mean interval of 77 ms was allowed between the end of the A wave and the beginning of the S wave, similar to what was measured in the healthy control group by pDTI.

CONCLUSION

The noninvasive measurement of timings of the cardiac cycle by pDTI is helpful to determine the optimal AVD in individual patients.

[Assessment of the results of aorto-coronary bypass surgery with the technetium 99m pyrophosphate scintigram (author's transl)]

In 40 patients with angiographically-documented coronary artery disease, technetium 99m pyrophosphate (99mTc-PYP) myocardial scintigrams were obtained prior to and four to six weeks after aorto-coronary bypass surgery. In the majority of patients, preoperative and postoperative exercise testing with simultaneous pulmonary artery pressure recordings was performed. In 22 of 30 patients with preoperatively increased 99mTc-PYP myocardial activity, no tracer accumulation could be found postoperatively. In the latter patients, there was also a significant increase in exercise capacity and lessening of ischemic ST-segment depression in the exercise ECG. In the remaining eight patients in whom increased tracer accumulation was found to persist postoperatively, there was no improvement in exercise capacity. In ten patients with no myocardial tracer accumulation preoperatively, unchanged myocardial scintigrams and a significant decrease of the ischemic ST-segment depression in the exercise ECG were seen postoperatively except in one patient with perioperative myocardial infarction. These results were also partially confirmed by repeated coronary angiography and ventriculography. Patent bypass grafts were associated with regional improvement in left ventricular function. The results indicate that postoperative absence of myocardial tracer accumulation appears due to amelioration of preexisting myocardial ischemia at rest. Thus, in the assessment of the results of aorto-coronary bypass surgery, the 99mTc-PYP scintigram offers an important diagnostic potential.

[Measurement of pulmonary artery pressure at rest during volume loading for assessment of ventricular function in coronary artery disease (author's transl)]

Measurements of pulmonary artery (PA) pressure at rest with volume loading of the heart was carried out in a semirecumbent position by standardized positioning of the legs (Positioning test) in 44 patients with angiographically-proven severe coronary artery disease (CAD). The patients reacted differently and were accordingly assigned to one of the three following groups: Group I (23 patients) with normal PA pressures values showed normal results on ventriculography and accordingly, a normal ejection fraction. Group II (13 patients) showed a pathological increase in PA pressure by volume loading. Ventriculography showed hypo- or akinetic areas, with accordingly reduced ejection fraction already at rest. Group III (8 patients) showed pathological PA pressure values already at rest, in accordance with the ventriculographic existence of larger akinetic areas and a marked reduction in ejection fraction. Coronary morphology per se showed no correlation with PA pressure behaviour during volume loading at rest. Therefore, PA pressure measurement in the standardized positioning test can give a relatively accurate estimation of the functional state of the left ventricle, while statements about coronary morphology in CAD are not permissible.

[Long-time follow-up scintigraphy with 99m Tc pyrophosphate after myocardial infarction (author's transl)]

Follow-up scintigraphies with 99m Tc pyrophosphate 3--4 weeks and 6--12 months after a myocardial infarction revealed the possibility of persisting a myocardial tracer activity in cases in which reinfarction can be excluded. There was a relation between the persistence of the tracer activity and the pressure in the pulmonary artery under stress conditions. The diastolic pulmonary pressure was regular in those patients whose scintiphotos showed no tracer activity in the myocardial area in the follow-up scintigraphy. Patients who showed a persisting tracer activity in the infarcted areal had elevated pressures in the pulmonary artery under stress conditions or even at rest. The elevation of the diastolic pulmonary pressure is a sign of an elevated enddiastolic pressure in the left ventricle caused by a limited left ventricular function. This could be proved by left ventriculography. The results in follow-up scintigraphy 3--4 weeks and 6--12 months after the infarction were quite similar. Therefore we believe that the results of a follow-up scintigraphy 3--4 weeks after an infarction allows to draw prognostic inferences about the further course of the disease.