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Biomedical subjects

M Block

Publications and source records attributed to M Block.

At least 37 records · Page 2Linked to original sources
PubMed1996

Biphasic defibrillation using a single capacitor with large capacitance: reduction of peak voltages and ICD device size.

The volume of current implantable cardioverter defibrillators (ICD) is not convenient for pectoral implantation. One way to reduce the size of the pulse generator is to find a more effective defibrillation pulse waveform generated from smaller volume capacitors. In a prospective randomized crossover study we compared the step-down defibrillation threshold (DFT) of a standard biphasic waveform (STD), delivered by two 250-microF capacitors connected in series with an 80% tilt, to an experimental biphasic waveform delivered by a single 450-microF capacitor with a 60% tilt. The experimental waveform delivered the same energy with a lower peak voltage and a longer duration (LVLD). Intraoperatively, in 25 patients receiving endocardial (n = 12) or endocardial-subcutaneous array (n = 13) defibrillation leads, the DFT was determined for both waveforms. Energy requirements did not differ at DFT for the STD and LVLD waveforms with the low impedance (32 +/- 4 omega) endocardial-subcutaneous array defibrillation lead system (6.4 +/- 4.4 J and 5.9 +/- 4.2 J, respectively) or increased slightly (P = 0.06) with the higher impedance (42 +/- 4 omega) endocardial lead system (10.4 +/- 4.6 J and 12.7 +/- 5.7 J, respectively). However, the voltage needed at DFT was one-third lower with the LVLD waveform than with the STD waveform for both lead systems (256 +/- 85 V vs 154 +/- 51 V and 348 +/- 76 V vs 232 +/- 54 V, respectively). Thus, a single capacitor with a large capacitance can generate a defibrillation pulse with a substantial lower peak voltage requirement without significantly increasing the energy requirements. The volume reduction in using a single capacitor can decrease ICD device size.

Adult↗
PubMed1996

Improved sensing signals after endocardial defibrillation with a redesigned integrated sense pace defibrillation lead.

Adequate sensing is a basic requirement for appropriate therapy with ICDs. Integrated sense pace defibrillation leads, which facilitate ICD implantation, show a close proximity of sensing and defibrillation electrodes that might affect the sensing signal amplitude by the high currents of internal defibrillation. In 99 patients, we retrospectively examined two integrated sense pace defibrillation leads, either both with a distance of 6 mm between the tip of the lead (sensing cathode) and the right ventricular defibrillation electrode (sensing anode) or one with a distance of 12 mm. Three seconds after a shock of 20 J, mean sensing signal amplitude during sinus rhythm (SR) decreased from 10.5 +/- 4.3 mV to 5.1 +/- 3.7 mV (P < 0.001) for the 6-mm lead, but showed no significant decrease for the 12-mm lead. The degree of signal reduction was inversely related to the time passed since defibrillation. Significant differences in reduction of sensing signal amplitude concerning monophasic and biphasic shocks could not be observed. Mean sensing signal amplitude of VF after shocks that failed to terminate it decreased in the same order as during SR (from 8.3 +/- 4.1 mV to 4.1 +/- 3.2 mV), but resulted in no failure of redetection during ongoing VF. DFTs did not differ for the 6-mm and the 12-mm lead. In conclusion, close proximity of the right ventricular defibrillation coil to the sensing tip of an integrated sense pace defibrillation lead causes energy and time related reduction in sensing signal amplitude after defibrillation, and might cause undersensing in the postshock period. A new lead design with a more proximal position of the right ventricular defibrillation coil avoids these problems without impairing DFTs.

Defibrillators, Implantable↗
PubMed1996

Cardiac output is not affected during intraoperative testing of the automatic implantable cardioverter defibrillator.

INTRODUCTION: Perioperative mortality of patients undergoing implantation of automatic implantable cardioverter defibrillators (ICDs) has been reduced dramatically following the availability of transvenous-subcutaneous defibrillation leads. However, patients with severely reduced left ventricular function show a substantial rate of nonsudden cardiac mortality within the first year. Whether repeated intraoperative inductions of ventricular tachycardia/fibrillation (VT/VF) during implantation lead to hemodynamic deterioration and thus might contribute to development of end-stage heart failure in these patients is unknown. The purpose of the present study was to determine cardiac output and hemodynamic performance during transvenous-subcutaneous ICD implantation in patients with severe left ventricular dysfunction. METHODS AND RESULTS: In 11 patients with a left ventricular ejection fraction (EF) < or = 0.35, cardiac output was measured automatically with a combined continuous cardiac output/mixed venous oxygen saturation pulmonary artery catheter system. ICD implantation was performed during standardized general anesthesia. In the 11 patients (EF = 27 +/- 2% [mean +/- SEM]) a total of 95 episodes of VT/VF followed by defibrillation were induced (episodes per patient = 9 +/- 1; range 6 to 11). Cardiac index was 2.2 +/- 0.2 L.min-1.m-2 after induction of anesthesia (before start of surgery), and 1.9 +/- 0.1 L.min-1.m-2 immediately before first induction of VT/VF. After the last episode of VT/VF, cardiac index was 2.1 +/- 0.2 L.min-1.m-2. Cardiac index measured 1, 2, and 3 minutes after induction of VT/VF was not significantly different when compared to the preinduction value during any episode of VT/VF induction. Similarly, stroke volume index was 39 +/- 5 mL.m-2 immediately before first induction of VT/VF and 36 +/- 3 mL.m-2 after the last episode of VT/VF (NS). At the end of surgery, hemodynamic parameters did not exhibit any significant difference when compared to the data obtained before start of ICD implantation and testing. CONCLUSION: Extensive defibrillation tests during transvenous-subcutaneous ICD implantation in patients with severe left ventricular dysfunction are not associated with acute deterioration of cardiac performance.

Cardiac Output↗
PubMed1996

Implantable cardioverter-defibrillator: present and future indications.

Indications for of automatic cardioverter-defibrillators of automatic in patients with ventricular tachyarrhythmias have changed since the publications of first guidelines in 1991. Less invasive surgical approaches reduced the perioperative mortality. Tiered therapy devices improved the quality of life by reducing appropriate and inappropriate shocks. A low annual incidence of sudden death with implantable cardioverter defibrillators and frustrating results with antiarrhythmic drugs caused an extension of implantable cardioverter-defibrillator indications. Despite the absence of prospective studies implantable cardioverter-defibrillators have become a first line treatment for patients with ventricular tachyarrhythmias which are not due to acute myocardial infarction. In cardiac arrest survivors implantable cardioverter-defibrillator therapy has become the gold standard due to the low annual incidence of sudden death seen in implantable cardioverter-defibrillator patients. The results of ongoing prospective studies comparing implantable cardioverter-defibrillator therapy to antiarrhythmic drugs have to be awaited and will influence tomorrow's indications for implantable cardioverter-defibrillator therapy in patients with documented ventricular tachyarrhythmias. Additionally, studies evaluating prophylactic implantable cardioverter-defibrillator implantations in patients at high risk for ventricular tachyarrhythmias might expand indications for implantable cardioverter-defibrillator therapy.

Cardiac Pacing, Artificial↗
PubMed1996

[Intravascular sonographic findings after orthotopic heart transplantation: comparison with clinical factors].

30 patients (mean age 51.4 +/- 11.6 years; female n = 6) were studied early after orthotopic heart transplantation (11.6 +/- 5.5 weeks). Twelve recipients had undergone specific treatment for biopsy proven rejection. Using a mechanical intravascular ultrasound device (3.5-F catheter), 153 coronary artery segments (16 left coronary main stem, 122 left anterior descending artery, 15 left circumflex artery) were studied. Intimal index and circumferential extension of a three-layer appearance of the vessel wall were assessed. In all segments, systolic-diastolic changes in area (delta A) with respect to vessel area and pressure (delta P) were used to study normalized compliance (normalized compliance = [delta A/A]/delta P [mm Hg-1 x 10(3)]). Intravascular ultrasound findings were correlated to perioperative ischemia time, LDL/HDL-ratio, Lp(a) and donor age. In a subgroup of 13 recipients, intravascular ultrasound investigation was repeated after an interval of 67.4 +/- 10.2 weeks. At first investigation, mean intimal index of all coronary segments was 0.07 +/- 0.10. Mean circumferential extension of a three-layer appearance of the vessel wall was 84 +/- 112 degrees. Normalized compliance was 2.43 +/- 1.90 mm Hg-1 in the left main stem 2.45 +/- 1.47 mm Hg-1 within the left anterior descending artery, and 2.66 +/- 1.72 mm Hg-1 within the circumflex artery (differences n.s.). No correlation was found between intimal index and normalized compliance (r = -0.322), nor between circumferential extension of intimal thickening and normalized compliance (r = -0.362). Furthermore, there was no correlation between normalized compliance and donor age. Normalized compliance was significantly lower in recipients with proven rejection than in those without (1.76 +/- 0.81 versus 2.95 +/- 1.22 mm Hg-1, p = 0.005). Both, intimal index and circumferential extension of intimal thickening, were significantly higher in recipients following rejection periods (p < 0.05). The extent of coronary vessel wall alterations on ultrasound correlated to donor age but not to perioperative ischemia time, LDL/HDL-ratio and Lp(a). Re-investigation of a subgroup of 13 recipients 67.4 +/- 10.2 weeks after the first study showed an insignificant increase of the intimal index (from 0.03 to 0.09) and of the circumferential extension of intimal thickening (from 40 to 111 degrees). Normalized compliance changed from 2.53 +/- 1.48 to 2.87 +/- 1.33 mm Hg-1 (differences n.s.). Early after orthotopic heart transplantation, a significant correlation between atherosclerotic coronary vessel wall alterations assessed by intravascular ultrasound and donor age can be confirmed. Heart recipients following rejection periods present with significantly more atherosclerotic vessel wall alterations and a severely reduced compliance of the coronary vessels.

Adult↗
PubMed1996

[Inadequate therapies with implantable cardioverter-defibrillators--incidence, etiology, predictive factors and preventive strategies].

Patients with implantable cardioverter defibrillators (ICD) often suffer inappropriate ICD-therapies. The incidence, causes and risk factors of ICD-therapies for a rhythm other than ventricular tachyarrhythmias (VT) were determined retrospectively in 462 consecutive patients (pts). Inappropriate ICD-therapies were identified based on stored R-R intervals and/or electrograms. Eighty-two pts (18%) had inappropriate ICD-therapies. Actuarial rates for inappropriate ICD-therapies were 13%, 20%, 24% and 29% at 1, 2, 3 and 4 years after ICD-implantation, respectively. Atrial fibrillation with rapid ventricular response was the most common cause (34 pts, 39%). In 26 pts (30%), sinus tachycardia triggered inappropriate ICD-therapies, in 21 pts (24%) overseeing, mostly due to fractures and insulation failures of the leads, in three pts atrial flutter, in two pts non-sustained VT, in one pt supra-ventricular tachycardia and in another pt T-wave double sensing caused inappropriate ICD-therapies. In order to prevent recurrences of inappropriate ICD-therapies due to atrial fibrillation or sinus tachycardia, a rate stability (n = 19) or onset (n = 15) criterion was programmed, 41 pts additionally received beta-blocking agents and/or digoxin. In pts with overseeing an operative revision of lead system was performed. During further follow-up (15 +/- 13 months), 15 pts had recurrences of inappropriate ICD-therapies (eight pts due to atrial fibrillation, three due to sinus tachycardia and four due to overseeing). On multivariate analysis (Cox regression), history of atrial fibrillation, maximum heart rate during exercise and low cut-off rate for VT-detection were predictors of inappropriate ICD-therapies. Thus, inappropriate ICD-therapies are frequent, especially in the first year after implantation. Additional detection criteria, beta-blocking agents and/or digoxin prevent recurrences in most patients. In patients with a history of atrial fibrillation, high heart rate during exercise or a low cut-off rate for VT-detection, activation of additional detection criteria should be considered directly after ICD-implantation.

Adult↗
PubMed1996

[Pharmacologic therapy of ventricular tachyarrhythmias: value of class III anti-arrhythmia drugs].

Treatment strategies in patients with life-threatening ventricular tachyarrhythmias (i.e. sustained ventricular tachycardia, ventricular fibrillation, aborted sudden cardiac death) are changing. Amiodarone and d,l-sotalol, chosen by electrophysiologic study guidance, can be considered as drugs of choice for the pharmacological treatment. Compared to these agents, which both have additional electrophysiologic effects, the new pure class III agents seem to be less effective. With regard to antiarrhythmic efficacy, clinical trials comparing the long-term efficacy of antiarrhythmic agents and the implantable cardioverter/defibrillator are under way. Preliminary results indicate that the implantable cardioverter/defibrillator may provide superior outcome with regard to sudden cardiac death compared to the use of class III agents.

Amiodarone↗
PubMed1995

Radiofrequency catheter ablation of sustained ventricular tachycardia in idiopathic dilated cardiomyopathy.

BACKGROUND: The feasibility of radiofrequency (RF) catheter ablation for the treatment of sustained ventricular tachycardia (VT) in patients with coronary artery disease and remote myocardial infarction has recently been demonstrated. At present, therapeutic options for VT in patients with idiopathic dilated cardiomyopathy (DCM) include antiarrhythmic drugs and implantable cardioverter/defibrillators (ICD). The purpose of the present study was to investigate the feasibility of RF catheter ablation in patients with idiopathic DCM who could not be adequately treated by conventional treatment modalities because of incessant or frequent, recurrent VT. METHODS AND RESULTS: RF current application for ablation of 9 VTs (mean cycle length, 402 +/- 78 ms) was attempted in 8 patients with idiopathic DCM (4 men, 4 women; mean age, 54 +/- 6 years; mean left ventricular ejection fraction, 30 +/- 9%). Inclusion criteria for ablation were incessant VT (n = 4) or frequent, recurrent VT reproducibly inducible with programmed electrical stimulation (n = 5). Three patients had suffered aborted sudden cardiac death, and 2 had experienced syncope. Two patients were artificially ventilated and catecholamine dependent for hemodynamic reasons at the time of attempted ablation. Potential target sites for RF current application were identified by detailed endocardial mapping during sinus rhythm, activation and entrainment mapping during VT, and pace mapping. After 7 +/- 5 RF pulses (range, 2 to 18 pulses; median, 6 pulses) applied with 32 +/- 7 W for 39 +/- 9 seconds, 6 of the 9 target VTs (67%) were rendered noninducible (4 of 4 incessant VTs and 2 of 5 chronic recurrent VTs). In 6 patients, VTs with ECG morphologies other than the target VTs were inducible after RF catheter ablation. Seven patients were on antiarrhythmic drugs during the ablation procedure and during the follow-up period of 8 +/- 5 months (range, 2 to 17 months). One patient received an ICD before RF ablation, 4 patients after RF ablation, and 1 patient after ablation of an incessant VT and before attempted ablation of frequent, recurrent VTs. One patient underwent heart transplantation 5 months after ablation in end-stage heart failure. There were no acute complications during the mapping and ablation procedure. During the follow-up period, 1 patient had been resuscitated from ventricular fibrillation 6 weeks after ablation and finally died of congestive heart failure 2 weeks later. No further episodes of incessant VT occurred in the patients who had undergone RF current application for ablation of incessant VT. A complete prevention of VT could be achieved in 2 of 8 patients, whereas in 5 patients, VT episodes were stored in the ICD devices during follow-up. CONCLUSIONS: The results of the present study indicate that RF current application for ablation of VT in a select group of patients with idiopathic DCM is feasible. The efficacy of RF ablation may be high in patients presenting with incessant VT, whereas the success rate seems to be only moderate in patients with chronic recurrent VT. In all patients, additional treatment options, including antiarrhythmic drugs, ICDs, and/or heart transplantation, were applied after RF ablation, indicating that RF ablation for this indication may be an adjunctive and not a curative treatment option.

Anti-Arrhythmia Agents↗
PubMed1995

Optimizing defibrillation through improved waveforms.

Defibrillation of the heart is achieved if an electrical current depolarizes the majority of the unsynchronized fibrillating myocardial cells. The applied current or the corresponding voltage described as a function of time is called the waveform. In pacing, to stimulate myocardial cells close to the electrode, a relatively low voltage is needed for a relatively brief duration. However, in defibrillation, approximately a 100-fold higher voltage is needed and achieved by the use of capacitors. The exponential voltage decay of a capacitor during its discharge determines the basic waveform for defibrillation. In an attempt to lower the energy needed for defibrillation, the steepness of the decay (different capacitances), the duration (fixed duration waveforms) or tilt (fixed tilt waveforms), or the initial polarity can be changed. Additionally, the polarity of the electrodes can be reversed during the discharge of the capacitor once (biphasic waveform) or twice (triphasic waveform). If two capacitors and defibrillation pathways are available, bidirectional defibrillation pulses can be delivered sequentially. In humans, the original standard waveform used with endocardial leads was a single monophasic pulse delivered by a 125-microF capacitor using the endocardial right ventricular electrode as cathode. It is now known that a reversal of the initial polarity and a reversal of polarity during capacitor discharge may significantly lower the energy needed for defibrillation, thereby preventing formerly frequent failures of defibrillation with endocardial lead systems. The use of sequential pulses showed no or only slight reductions of energy requirements and was abandoned due to the additional electrode needed. The use of a smaller capacitance (60-90 microF reduced maximum energy output but generally did not reduce energy requirements for defibrillation. However, with more efficient electrodes, smaller capacitances that will help to reduce the size of the defibrillator might be used. Thus, today defibrillation is optimized with respect to energy, capacitor size, and ease of implantation if an approximately 90-microF capacitor is used to deliver a biphasic pulse via a bipolar lead system using the right ventricular electrode as anode.

Animals↗
PubMed1995

Bipolar transvenous defibrillation: efficacy of two different positions of the anode.

For most nonthoracotomy defibrillation lead systems, the transvenous anode can positioned independently of the right ventricular (RV) cathode. Usually a vertical position in the superior vena cava (SVC) is chosen. However, it is unknown if this position yields the optimal defibrillation threshold (DFT). Therefore, in 15 patients undergoing defibrillator implantation the SVC position was compared in a crossover study design with a horizontal position in the left brachiocephalic vein (BCV). Mean DFT was not different for SVC and BCV (19.2 +/- 9.6 J vs 18.5 +/- 9.1 J) but DFT of individual patients differed by up to 12 joules. A positive correlation between impedance and DFT in the BCV position (r = 0.6; P < or = 0.05) indicated that the improved geometry of the defibrillation field with the BCV position is opposed by a higher impedance found for this position (63 +/- 15 omega vs 52 +/- 7 omega). Thus, defibrillation is not improved in general although individual patients might benefit.

Aged↗
PubMed1995

Erroneous discharge of an implantable cardioverter defibrillator caused by an electric razor.

We report an unusual case of the erroneous discharge of a third-generation multiprogrammable implantable cardioverter defibrillator in a 64-year-old patient with a history of recurrent ventricular tachycardias caused by electromagnetic interference while shaving with an electric razor. Electromagnetic interference was related to a defect in the electrode's insulation and could not be provoked in an intact electrode.

Defibrillators, Implantable↗
PubMed1995

Internal defibrillation with smaller capacitors: a prospective randomized cross-over comparison of defibrillation efficacy obtained with 90-microF and 125-microF capacitors in humans.

INTRODUCTION: The size of current implantable cardioverter defibrillators (ICD) is still large in comparison to pacemakers and thus not convenient for pectoral implantation. One way to reduce ICD size is to defibrillate with smaller capacitors. A trade-off exists, however, since smaller capacitors may generate a lower maximum energy output. METHODS AND RESULTS: In a prospective randomized cross-over study, the step-down defibrillation threshold (DFT) of an experimental 90-microF biphasic waveform was compared to a standard 125-microF biphasic waveform. The 90-microF capacitor delivered the same energy faster and with a higher peak voltage but provided only a maximum energy output of 20 instead of 34 J. DFTs were determined intraoperatively in 30 patients randomized to receive either an endocardial (n = 15) or an endocardial-subcutaneous array (n = 15) defibrillation lead system. Independent of the lead system used, energy requirements did not differ at DFT for the experimental and the standard waveforms (10.3 +/- 4.1 and 9.5 +/- 4.9 J, respectively), but peak voltages were higher for the experimental waveform than for the standard waveform (411 +/- 80 and 325 +/- 81 V, respectively). For the experimental waveform the DFT w as 10 J or less using an endocardial lead-alone system in 10 (67%) of 15 patients and in 12 (80%) of 15 patients using an endocardial-subcutaneous array lead system. CONCLUSIONS: A shorter duration waveform delivered by smaller capacitors does not increase defibrillation energy requirements and might reduce device size. However, the smaller capacitance reduces the maximum energy output. If a 10-J safety margin between DFT and maximum energy output of the ICD is required, only a subgroup of patients will benefit from 90-microF ICDs with DFTs feasible using current defibrillation lead systems.

Adolescent↗
PubMed1995

Benefits of treatment with implantable cardioverter-defibrillators in patients with stable ventricular tachycardia without cardiac arrest.

BACKGROUND: The availability of implantable cardioverter-defibrillators (ICD) that are capable of antitachycardia pacing may lead to an increased use of ICDs in patients with haemodynamically tolerated ventricular tachycardia without a history of cardiac arrest. The frequency of potentially life-threatening fast ventricular tachycardias (cycle length < 250 ms) was investigated in patients who had a third generation ICD with endocardial leads implanted because they had haemodynamically tolerated ventricular tachycardia without a history of cardiac arrest. METHODS: Between January 1990 and October 1993, 50 patients (age (mean (SD)) 60 (11); ejection fraction 39 (16)%; 82% with coronary artery disease and 8% with dilated cardiomyopathy) with haemodynamically tolerated ventricular tachycardia (cycle length (mean (SD)) 348 (60) ms; range 250-500 ms) and without a history of cardiac arrest were treated with third generation ICDs that were capable of antitachycardia pacing. Fast ventricular tachycardia had been induced in 14 (28%) during baseline electrophysiological study. The benefit of ICD treatment was estimated as the difference between total mortality and the occurrence of fast ventricular tachycardia that would have been fatal if it had not been terminated. RESULTS: During follow up of 17 (12) months, 33 patients (66%) had a total of 3861 episodes of ventricular tachycardia. 91% of these episodes were terminated by antitachycardia pacing. 11 patients (22%) had episodes of potentially life-threatening fast ventricular tachycardia and 3 of these also had inducible fast ventricular tachycardia. One patient died suddenly 27 months after implantation. The difference between survival without fast ventricular tachycardia and total mortality was 9%, 12%, 27%, and 27% at 6, 12, 18, and 24 months, respectively. CONCLUSIONS: About a fifth of patients who had been given an ICD to treat haemodynamically tolerated ventricular tachycardia and who had no history of cardiac arrest experienced fast ventricular tachycardia during follow up requiring immediate cardioversion. Prospective studies are needed to investigate whether the prognosis of patients with a history of haemodynamically tolerated ventricular tachycardia without cardiac arrest is improved by ICD therapy.

Cardiomyopathy, Dilated↗
PubMed1995

Control of gill filament blood flow by serotonin in the rainbow trout, Oncorhynchus mykiss.

The effects of exogenously applied serotonin [5-hydroxytryptamine (5-HT)] on the distal arterial vasculature of gill filaments were observed using an epi-illumination microscope equipped with a water-immersion objective and connected to a video camera. In addition, ventral aortic flow (Q) and celiac artery pressure (PCA) were measured. Intra-arterial injection of serotonin (100 nmol/kg) completely stopped the blood flow in the distal part of the filaments and caused a rapid decrease of PCA. Repeatedly, the flow reduction was found to coincide with a constriction of the distal portion of the efferent filamental vasculature. Because there was no concomitant reduction in Q, it is concluded that a redistribution of blood to more proximal parts of the filaments occurred. After treatment with the serotonergic receptor antagonist methysergide, the vasoconstrictor effect of serotonin on the filamental vasculature was eliminated, while a decrease in PCA was still observed. The results demonstrate a specific site(s) for the serotonergic vasoconstriction in the distal portion of the filament.

Animals↗
PubMed1995

Extensive erythrocyte deformation in fish gills observed by in vivo microscopy: apparent adaptations for enhancing oxygen uptake

The secondary lamellae of the gills are the primary sites of oxygen uptake in fish. We have used epi-illumination microscopy in vivo to observe the microcirculation directly in secondary lamellae of rainbow trout (Oncorhynchus mykiss) and roach (Rutilus rutilus). Our observations point at previously unrecognised factors in fish respiratory physiology. Erythrocytes passing through secondary lamellae became greatly deformed. We propose that this deformation plays a role in oxygen uptake by diminishing the diffusion boundary layer (adhesion layer) of fluid around the erythrocyte and possibly also by mixing intracellular haemoglobin molecules. Moreover, the erythrocytes were apparently slowed down and forced to travel over an extended path to pass through the lamella, making it tempting to speculate that plasma passes more readily than erythrocytes through the lamella, resulting in a local elevation of the haematocrit.

Journal Article↗
PubMed1995

[In vitro validation of intravascular ultrasound, computerized and magnetic resonance tomography in diagnosis of atherosclerotic vascular segments in comparison with direct magnification radiography].

The depiction of atherosclerotic vessel abnormalities is a prerequisite for percutaneous interventional therapy and long-term observations of peripheral artery disease. The aim of this in-vitro study was to determine the potentials and limitations of 12.5 and 20 MHz intravascular ultrasound, computed tomography and magnetic resonance (MR) imaging in comparison to direct magnification radiography for the localization and quantification of peripheral vessel wall calcifications. Forty-three postmortem, human iliac segments were examined by intravascular ultrasound (12.5 and 20 MHz), computed tomography and magnetic resonance tomography (gradient echo-and spin echo-technique). For comparative analysis, each segment was divided into eight sectors of 45 degrees each; using all five methods, the presence of calcified wall areas was examined in each sector, and luminal area (42 segments) and plaque area (32 isolated plaques) were quantitatively estimated. In the sonograms, the circumferential extension of the boundary between intima and media was measured. 122 of 344 sectors showed regional vessel wall calcifications. Sensitivity of 20 MHz intravascular ultrasound was 73% versus 59% with the 12.5 probe, specificity was 97% with 20 MHz, 96% with 12.5 MHz. Sensitivity of both 12.5 and 20 MHz intravascular ultrasound was higher with increased thickness of the calcified structures. 20 MHz ultrasound identified the intima-media boundary averaging 146.8 degrees of the vessel circumference; the corresponding value of 131.8 degree with 12.5 MHz did not differ significantly. Computed tomography detected calcifications with a sensitivity of 88%, specificity was 88%. With MR imaging, sensitivity of the gradient echo-technique was 94% versus a sensitivity of 86% with spin echo-technique. Quantification of luminal and plaque areas showed that luminal area was precisely estimated only by 20 MHz ultrasound (no significant difference to direct magnification radiography), whereas all other techniques showed significant overestimation. Plaque areas were markedly overestimated by computed tomography and MR imaging, too. In an in vitro set-up, intravascular ultrasound, MR tomography and computed tomography do not allow an authentic depiction of peripheral vessel wall architecture. Limited resolution, subintimal shadowing and and distortion are the main limitations of these new techniques so that details of regional vessel wall calcifications cannot be presented thoroughly. Relevant over-estimation of luminal and plaque areas must be considered.

Arteriosclerosis↗
PubMed1994

The role of implantable cardioverter defibrillators in dilated cardiomyopathy.

Depending on the severity of the disease, patients with dilative cardiomyopathy (DCM) have a poor prognosis. No definite data are available to show that complex ventricular ectopy, the presence of ventricular late potentials, or programmed electrical stimulation in patients without symptoms with DCM identify patients at risk of sudden cardiac death. Although poor left ventricular function seems to be the most potent predictor of total cardiac death, the prediction of sudden death in patients without symptoms with DCM is poor. Studies with either class I antiarrhythmic drugs or amiodarone have not yet demonstrated a reduction in total mortality rates or sudden death. The usefulness of an implantable cardioverter defibrillator (ICD) in patients without symptoms with DCM is currently under investigation. The usefulness of serial electropharmacologic testing for patients with documented sustained ventricular tachycardia or ventricular fibrillation and DCM is still controversial. Because most patients with DCM and VT or out-of-hospital cardiac arrest have either no inducible ventricular tachyarrhythmia at baseline or the reproducibility of ventricular tachycardia/ventricular fibrillation induction is poor, implantation of an ICD should be considered in most of these patients. The indication for implantation of an ICD should be made on clinical judgment of the patient's functional status and other prognosis-limiting factors, such as rapid progression of heart failure, end-stage heart failure, and age.

Anti-Arrhythmia Agents↗