Validation of intravascular ultrasound in arteriosclerotic peripheral vessels

In this in vitro-study, we validated intravascular ultrasound for the detection of irregular luminal contours, intraarterial structures, intimal thickening in peripheral arteriosclerotic human vessel segments and we compared sonographic criteria to the composition of arteriosclerotic lesions. Sixty-nine post-mortem segments of human peripheral arteries (6 patients) were fixed in formalin, examined with intravascular ultrasound and morphologically evaluated. Specificity, sensitivity, both positive and negative predictive value and accuracy of intravascular ultrasound for the detection of irregular luminal contours, intra-arterial structures and intimal thickening were determined for each of four quadrants. Ultrasonic features (echogeneity, homogeneity, shadowing of echoes) were also compared to the composition of lesions. Intravascular ultrasound detected regular (normal) luminal contours with a high specificity of 96.5%, a sensitivity of 65.0% and an accuracy of 88.4%. Intra-arterial structures were detected with a sensitivity of 88.6%, a specificity of 97.8% and an accuracy of 96.4%. Arteriosclerotic lesions could be localized with a sensitivity of 86.1%, a specificity of 99.1% and an accuracy of 86.9%. Intimal thickening was detectable with a sensitivity of 85.9%, a specificity of 87.8% and an accuracy of 86.2%. Meanwhile, fibrous, atheromatous and combined lesions without calcification did not show shadowing of echoes. The majority of fibrous or atheromatous lesions presented with homogeneous echoes showing hypo-, hyper- and normal density echoes. Using a 20-MHz transducer, homogeneity and echogeneity of echo patterns cannot accurately predict the different components of combined arteriosclerotic lesions.

Post-infarction depression and incomplete recovery 6 months after acute myocardial infarction

Patients who suffer from post-infarction depression are a high risk group with an increased mortality risk. The reasons for this are not known although it may be because such patients cannot cope with the chronic condition of cardiac disease. We designed a profile of clinical and behavioural outcome measurements representing recovery after myocardial infarction. 552 male survivors of acute myocardial infarction (29-65 years; mean = 53) were grouped at study entry according to their depression status. 377 patients were reassessed after 6 months and were divided into the following subgroups: 50 (13.3%) patients had severe depression; 85 (22.5%) moderate depression and 242 (64.2%) low degrees of depression in the initial study. There were no substantial differences in baseline characteristics between the index group and the drop-out group. The unadjusted relative risk for follow-up angina pectoris among patients with depression (severe versus low) was 3.12 (95% CI 1.58 to 6.16) and was 5.55 (CI 2.87 to 10.71) for emotional instability. The relative risk for maintenance of smoking habits was 2.63 (CI 1.23 to 5.60) and was for work resumption 0.39 (CI 0.18 to 0.88). There was no association between depression and the occurrence of late potentials. After adjustment for univariate variables (age, social class, recurrent infarction, helplessness) only small and nonsignificant changes in the relative risks were found. However the inverse association of depression and work resumption was lost after adjustment. The investigation revealed that persistent postinfarction depression is an independent and important source of subsequent morbidity and long-acting reduced quality of life. Depression has adverse effects on illness behaviour and pain perception.

[Intravascular ultrasound in peripheral calcified vascular lesions: comparison with direct magnification radiography]

Intravascular ultrasound can detect calcified peripheral arteriosclerotic lesions by hyperdense echo patterns and shadowing of subintimal layers. Nevertheless, 20 MHz ultrasound systems have not been validated for the detection of peripheral calcifications; besides, it is unknown whether the depiction of calcified lesions by intravascular ultrasound depends on the morphology of the calcification. Histological evaluation of severely calcified arteries is difficult because the preparation of those specimens often causes artefacts, e.g., fracture of calcified structures. Direct magnification radiography, currently used in forensic medicine or skeleton examination, is based on a minimized focus and enables the edge-enhanced views of calcifications with high discrimination. In this in-vitro-study direct radiological magnification was used to validate intravascular ultrasound. Forty-nine segments of human peripheral arteries were fixed in formalin, examined with intravascular ultrasound and, as a reference, radiographically magnified using a newly developed microfocus x-ray tube. Sensitivity, specificity, positive and negative predictive value, and accuracy of intravascular ultrasound for the detection of calcified wall areas were determined and compared to the appearance (configuration, circumferential and areal expansion, density, number of fragments) of these calcifications. Thicknesses of 110 single calcified structures were estimated on sonograms and radiograms. The overall sensitivity of the 20 MHz intravascular ultrasound system for the detection of calcification in 913 sectors was 70%, specificity 53%, positive predictive value 66%, negative value 58% and accuracy 62%. The depiction of calcified regions by direct magnification radiography showed that the sensitivity strongly depended on the density of the calcification. Sensitivity was 81% with calcified lesions of high density, but only 51% with lesions of low density.(ABSTRACT TRUNCATED AT 250 WORDS)

201Tl reinjection predicts improvement of left ventricular function following revascularization

The aim of this study was to evaluate the correlation between improved Tl uptake in reinjection imaging with improvements in regional wall motion and global ejection fraction following PTCA or aorto-coronary bypass surgery. 19 patients with CHD were investigated and divided into two groups according to their thallium uptake in the reinjection studies. Group I showed additional uptake on reinjection imaging compared to the redistribution image, whereas group II showed no additional uptake. Both groups had a similar number and distribution of affected vessels and location of the leading stenosis. Stress, redistribution and reinjection images were obtained prior to revascularization and evaluated semiquantitatively from a bulls eye scheme. There was a postoperative increase in regional wall motion in group 1 from 5.3 to 8.8% whereas group II did not show a relevant change (6.3 vs 6.0%). The ejection fraction increased II from 55.0 to 66.7% in group I and dit not increase in group II (59.8 vs 58.7%). The overall predictive value of the reinjection image for improvement in wall motion (> 10%) was 91% and for the redistribution image 58%. Increased uptake in reinjection imaging predicts improved ventricular function following revascularization and indeed indicates viable myocardium with reversible functional impairment.

Factors which provoke post-infarction depression: results from the post-infarction late potential study (PILP)

Symptoms of depression in the majority of patients immediately following acute myocardial infarctions (AMI) resolve rapidly; they are an adjustment reaction. However, in a group of 552 male patients there were 80 (14.5%) patients with persistent major depressive symptoms during a finite period after AMI. Infarction size was assessed by maximum creatine kinase levels, the QRS-complex and the occurrence of late potentials. These measures did not correlate with the degree of depressed moods in these groups. An arrhythmic event in the early hospitalization phase, a recurrent infarction, dyspnoea, and persistent angina pectoris before the AMI were significantly related to more profound degrees of depression. Patients who reported serious life-events in the last 2 yr before AMI, or who suffered from exhaustion and fatigue in the prehospital phase were subject to significantly higher levels of depression. A prodromal phase prior to hospitalization free of bodily symptoms and the use of denial were related to low levels of depression. The logistic regression model incorporating all univariate significant variables revealed that symptoms of exhaustion and fatigue prior to AMI had the strongest independent correlation with post AMI depression.

[Does anginal pain influence the medical care-seeking behavior of patients in the prodromal phase prior to an acute myocardial infarction. Results of a post-infarction late potential study.]

The aim of the study was to determine the proportion of high-risk patients who received appropriate antianginal therapy in the prodromal phase prior to a myocardial infarction, as an indicator of medical care seeking behavior. To this end, 606 male infarct patients aged 29-65 years were retrospectively interviewed 17-21 days after acute myocardial infarct. It was found that 77% of all patients (465/606) suffered from anginal pain, but only 32% of the patients with angina pectoris were receiving antianginal therapy in the prodromal period before acute myocardial infarction. Patients not taking medication were significantly younger than those with antianginal medication; they were more often smokers; they were less often suffering from high blood pressure; they expressed more pronounced nonacceptance of the risk; their history of anginal pain was significantly shorter; and they belonged more often to the patient group with a first myocardial infarction. In stepwise logistic regression analysis, high blood pressure, older age and exhaustion were found to be associated with medical treatment before infarction in the patient group with first myocardial infarction. In patients with recurrent infarction, continued smoking and denial of the risk remained predictive of nonmedication.

[Patient-specific determinants of delay in goal-oriented patient behavior in acute myocardial infarct. Results of the post-infarct late potential study]

369 (63%) of 586 consecutive patients with confirmed myocardial infarction were admitted to hospital within 6 h of symptom onset. Patients' arrival to hospital followed a characteristic circadian distribution with a marked morning increase between 0600 and 1200 hours, and a corresponding decrease in the late night hours. There were no differences in the occurrence of late potentials and in ECG data between early and late arrival group. The early group (less than 5.9 h) was, however, characterized by significantly higher cardiac enzyme levels than the late group (greater than 6.0 h); they also experienced more arrhythmic events in the acute phase (16.0% vs. 9.7%; p less than 0.032). Catecholamines were significantly more often necessary (26.4% vs. 10.3%; p less than 0.0001). Six-month prognosis after AMI was markedly worse. The time between symptom onset and hospital arrival was not affected by age and risk factors. In univariate analysis, pain history and recurrent infarction also had no influence on delay of admission to hospital. The time interval was, however, significantly shorter when the acute event occurred during the night (18.4% vs. 8.3%; p less than 0.0001). Absence of prodromi in the prehospital phase (18.5% vs. 12.0%; p less than 0.04) and a higher socio-economic level (68.3% vs. 61.0%; p less than 0.077) also shortened the admission time, whereas a hyperactive behavioral pattern prolonged the delay time (21.1% vs. 28.9%; p less than 0.05).

[Non-pharmacological treatment of arrhythmia using the method of trans-catheter ablation]

Trans-catheteral ablation is an important therapeutic method for nonpharmacological management of various types of cardiac arrhythmias. Since its introduction into clinical practice in 1982, it has proved its efficacy in disturbance or change of the type of atrioventricular conduction and conduction along accessory abnormal atrioventricular conduction pathways. Positive results have also been attained in the treatment of some patients with ventricular tachycardia. The energy sources used for ablation include direct current pulses possessing large energy, high-frequency currents, and laser energy. Ablation with direct current and high-frequency current is already used successfully in patients, while the use of laser energy for ablation of myocardial arrhythmogenic tissue is limited mainly to operations on the open heart. The use of alternating high-frequency current has attracted particular attention in the last years. Trans-coronary chemical ablation is another recently introduced method which is not connected with the use of electric current. Only experimental and a small clinical experience with this new method has been gained to date. This survey systemasizes the current knowledge of the biophysical bases of the various method of ablation from the standpoint of the mechanisms of treatment, the methodology and the main types of tissue response. Clinical experience with trans-catheteral treatment of cardiac arrhythmias is analysed.

Acute and long-term efficacy of oral propafenone in patients with ventricular tachyarrhythmias

The class Ic antiarrhythmic agent propafenone was studied by repeated electrophysiologic testing in 54 patients (43 male, aged 54 +/- 10 years, mean ejection fraction of 37.3 +/- 16.9%) with ventricular tachyarrhythmias. Forty patients (74%) had coronary artery disease. Programmed ventricular stimulation (S2, S2S3 during sinus rhythm and/or during S1S1 = 500, 430, 370, and 330 ms) off antiarrhythmic drugs induced sustained ventricular tachycardia, flutter, or fibrillation in all patients. After 450-900 mg of oral propafenone/day for 4-7 days, 51 patients were restudied. In the remaining three patients, spontaneous ventricular tachycardia occurred on drug therapy. Tachycardia induction was suppressed in 9 of 51 patients restudied (18%) and rendered more difficult to induce (basic stimulation drive greater than or equal to 40 beats/min higher than at control study) in another 7 patients (14%) (overall efficacy of 31%). The tachycardia rate decreased from 220 +/- 43 to 177 +/- 44 beats/min (p less than 0.01). The right ventricular effective refractory period increased from 232 +/- 22 to 252 +/- 22 ms (p less than 0.001). Responders to propafenone therapy had higher rates of inducible ventricular tachycardia at control (greater than 230 beats/min: 43%; less than or equal to 230 beats/min: 21%; p less than 0.05), higher ejection fractions, and lower left ventricular end-diastolic pressures than nonresponders. Eleven of the 16 patients showing a positive response to propafenone therapy in electrophysiologic testing were discharged on propafenone alone. During follow-up (17 +/- 12 months), nine patients remained free from ventricular tachycardia, one patient had a relapse, and one patient died of noncardiac death.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of Ca2(+)-release-dependent inward current reveals two distinct components of Ca2+ release from sarcoplasmic reticulum in guinea-pig atrial myocytes

Ca2+ current (L-type) and inward current caused by Ca2+ release from the sarcoplasmic reticulum and carried by electrogenic Na+/Ca2+ exchange have been measured in cultured atrial myocytes from hearts of adult guinea-pigs using whole-cell voltage clamp techniques. The pipette solution, used for internal dialysis of the cells, contained a high concentration, 60 mM or 25 mM, of citrate as a non-saturable low-affinity Ca2(+)-chelating compound. It has been shown previously that Ca2(+)-release-dependent inward current under these conditions is carried by electrogenic Na+/Ca2+ exchange. Furthermore, Ca2(+)-release-dependent inward current (the release signal) can be completely separated from triggering Ca2+ current if brief depolarizations for activating ICa are used. In the majority of cells that did not produce spontaneous Ca2+ release, conditions could be found that caused the release signal to be split into two components: an early component of variable amplitude and a late component of rather constant amplitude. The delay of the late component with regard to triggering ICa was inversely related to the amplitude of the first one. Below a certain amplitude of the first component, the second one failed to be elicited. This suggests the second component to be triggered by the first one. Weakly Ca2(+)-buffered cells produced spontaneous Ca2+ release, resulting in irregular "transient inward currents" at constant membrane-holding potential. Synchronization by trains of step depolarizations unmasked two components also in the spontaneous release signals. In none of the cells studied was any indication of more than two components of the release signal detected. The results are discussed in terms of two distinct compartments of sarcoplasmic reticulum with different properties of Ca2+ release.

Implantable cardioverter/defibrillators (ICD): a new lead-system using transvenous-subcutaneous approach in patients with prior cardiac surgery

The current approach in cardioverter-defibrillator implantation requires placement of epicardial leads which may lead to pericardial and/or pleural effusion and pneumonia during the perioperative period. Although ICD implantation is less invasive than other surgical techniques for the treatment of rhythm disturbances, the perioperative mortality must be considered. Minimizing the operative procedure could lead to a reduction in perioperative mortality. Therefore, we investigated an approach without the need for thoracotomy using a transvenous/subcutaneous lead system. In nine patients with prior cardiac surgery, defibrillator implantation was performed by a transvenous/subcutaneous approach. There was no perioperative mortality. In all patients, a sufficient defibrillation threshold was achieved. The defibrillation pulses were delivered as two sequential pulses between a right ventricular electrode (cathode) and a coronary sinus or superior caval vein electrode (anode 1) and a subcutaneous patch electrode (anode 2). Intubation of the coronary sinus was necessary in 4 patients in order to obtain satisfactory defibrillation thresholds. These data demonstrate that a transvenous/subcutaneous approach is feasible in patients with prior cardiac surgery obviating the need for thoracotomy. Sensing function of the RV-electrode, intubation of the coronary sinus and the intraoperative use of an epicutaneous patch electrode are current problems of this new technique.

[Catheter ablation in ventricular tachycardia]

The basis for management of ventricular tachycardia (VT) is pharmacologic treatment which is effective, however, in only about 20 to 30% of the patients. With respect to this problem, alternative therapeutic modes have been developed which include, in addition to antitachycardia stimulation, electrical, palliative therapy such as the implantable automatic defibrillator, definitive measures such as map-guided antitachycardia surgery and catheter ablation. The goal of catheter ablation is the selective destruction of heart structures which are the morphologic correlate for initiation of propagation of VT. Catheter ablation was discovered by chance by Fontaine after a defibrillation during an electrophysiologic study in which a defibrillating electrode in the proximity of a catheter at the His bundle induced complete AV-block. This effect of destruction in the AV-conduction system by direct current as a therapeutic measure was further developed by Gallagher and Scheinman. The mechanism held responsible is coagulation by the electrode of neighboring tissue and barotrauma. The technique, which was initially used for ablation of the His bundle in supraventricular tachycardia, can also be used for ablation of accessory pathways or the site of origin of VT which generally lies endocardially in marginal regions of myocardial infarctions. CATHETER MAPPING: In sinus rhythm and induced VT, endocavity catheter mapping is carried out after heparinization with electrocardiograms recorded from at least six to ten sites in the right and left ventricles. At the site of early activation, detailed mapping is used for identification of the site of earliest activation, then pace-mapping is performed during sinus rhythm and VT. The morphology of the stimulated QRS complexes is compared with that of the spontaneous VT. In patients in whom VT cannot be induced, localization is carried out by pace-mapping alone. CATHETER ABLATION: After localization, in intubation narcosis and with continuously monitored arterial blood pressure, the suspected site of origin of the VT is subjected to an initial shock during sinus rhythm by means of a distal electrode of a catheter in stable contact with the endocardium. For mapping and ablation, the same catheter is used. After each subsequent shock, assessment is performed to determine if the distal electrode pair still conducts local ventricular signals and if ventricular stimulation is possible. The shock energy delivered is 100, 200 or 400 Joules. At the time of shock discharge, the remaining electrodes or catheters are disconnected. In the case of bradycardia or tachycardia after the shock, immediate connection to an external stimulation generator is established. At the time of the shocks, relaxation is provided by succinylcholine. All shocks are delivered from the anode. The integrity of the catheter is tested after each shock, no catheter is used more than three or four times. At the earliest, ten minutes after shock delivery, induction of clinical VT is attempted with programmed stimulation and if induction is possible, at the same site a maximum of two more shocks are delivered or, after renewed mapping, another shock is delivered to a different site. Induced non-clinical VT is not subjected to ablation.(ABSTRACT TRUNCATED AT 400 WORDS)

Radiofrequency coagulation of ventricular myocardium: improved prediction of lesion size by monitoring catheter tip temperature

To assess the importance of voltage, current, impedance and catheter tip temperature for the prediction of the size of tissue injury induced by transcatheter radiofrequency application, radiofrequency pulses (500 kHz) were delivered both in vitro and in vivo to isolated ventricular preparations and the intact canine heart, respectively. Radiofrequency coagulations were performed using unipolar electrode configuration. Besides measurements of current and voltage which were used to calculate the delivered power and tissue impedance, the catheter tip temperature was monitored during each application using specially designed 6F USCI catheters with a built-in nickel/chromium-nickel thermoelement. Lesion dimensions were measured and the correlation between lesion volume and delivered radiofrequency energy, maximum changes in catheter tip temperature and the integral of the temperature curve were calculated. First, in a pilot in vitro investigation, 50 radiofrequency coagulations (3.2 W-22.4 W, pulse duration 10 s) were performed in ventricular preparations from freshly excised dog hearts. The correlation between applied radiofrequency energy and lesion volume was 0.87; the correlation between maximal catheter tip temperature and lesion volume was 0.82; the correlation between temperature integral and lesion volume was 0.9. In the intact dog heart, 44 radiofrequency pulses were delivered to the left and right ventricular endocardium in 12 anaesthetized dogs (exposure time: 10 s). Delivered power ranged between 5.6 W and 24.6 W; tissue impedance varied between 92 omega and 364 omega; lesion volume measured 0-273 mm3; developed peak temperatures ranged from 16.25 degrees C to 196 degrees C. The calculated integral beneath temperature curves measured 126-1971 degrees C.s. The correlation between applied radiofrequency energy and lesion volume was 0.32; the correlation between maximal catheter tip temperature and lesion volume was 0.61. Temperature integral correlated best with the assessed volume of myocardial necrosis (r = 0.7). No significant arrhythmogenic or haemodynamic side-effects were observed. Macroscopic examination showed a central depression surrounded by a zone of homogeneous coagulation. Vaporization and crater formation up to a depth of 4 mm were observed following three radiofrequency discharges. In two of these cases, rapid changes and oscillation of catheter tip temperature were observed. Thus, monitoring of catheter tip temperature during radiofrequency energy application improves the prediction of lesion size. In addition, temperature monitoring might improve the safety of the procedure with respect to the risk of perforation.

Pathophysiological mechanisms of ventricular tachyarrhythmias

The pathophysiological background for ventricular tachyarrhythmias based on experimental and clinical evidence is presented. Sudden cardiac death may occur as the first manifestation of coronary artery disease without antecedent complaints or it may occur in patients with a previous myocardial infarction. In the latter situation, a circumscribed area of cardiac tissue may be responsible for the genesis and maintenance of a ventricular tachyarrhythmia which may be called the 'arrhythmogenic substrate'. This zone of electrically abnormal ventricular myocardium is usually located at the border of a previous myocardial infarction, and is characterized by islands of relatively viable muscle alternating with areas of necrosis and, later, fibrosis. The consequent fragmentation of the propagating electromotive forces leads to the development of high-frequency components that can be recorded directly or non-invasively using signal-averaging techniques. These signals have been called ventricular late potentials. The 'arrhythmogenic substrate' may be present permanently or may rise acutely and be present only transiently in the case of extensive ischaemia or acute myocardial infarction. In the setting of a chronic 'arrhythmogenic substrate', this electrically abnormal tissue may be triggered by spontaneously occurring ventricular ectopic beats or salvoes or by programmed ventricular stimulation, as well as by transient episodes of ischaemic causing spontaneous arrhythmias. These trigger factors modify the 'arrhythmogenic substrate' in such a way that ventricular tachyarrhythmias are sustained. It is apparent that sudden cardiac death is due to a wide spectrum of pathophysiological mechanisms which may be interrelated. There is obviously no single parameter that helps the clinician to predict the propensity for sudden cardiac death in the individual patient.

Catheter ablation of ventricular tachycardia using defibrillator pulses: electrophysiological findings and long-term results

Catheter ablation of ventricular tachycardia (VT) was attempted in 24 patients (mean age 49 +/- 15.1 years) with a history of recurrent sustained VT resistant to previous antiarrhythmic drug therapy. 14 patients (58.3%) had also failed to respond to long-term administration of amiodarone alone and in combination with class I antiarrhythmic drugs. Endocardial catheter mapping during induced or spontaneous VT and/or pacemapping were performed to identify the site of origin of VT. Direct-current high-energy anodal shocks were delivered from a conventional cardioverter with stored energies of 100, 200 or 400 J via the distal electrode of conventional catheters. A total of 139 shocks was delivered during the ablation procedure. One patient died from wall perforation. Within 1 week of ablation, nine patients developed spontaneous recurrences of monomorphic sustained VT, identical to the clinical VT, and one patient developed a VT with a new morphology. In addition, four patients had a recurrence of their clinical VT after several weeks. In seven of 14 patients with spontaneous recurrences after the first ablation procedure and in three patients in whom VT was again inducible at the end of the first week, a second ablation procedure was performed. One patient with inducible VT after the first and second ablation sessions was given a third ablation procedure, and was discharged from hospital on anti-arrhythmic drugs which were successful despite being previously ineffective. After a mean follow-up period of 14.1 +/- 9.1 months, there were no spontaneous recurrences of sustained VT in 17 patients (71%) (nine without antiarrhythmic drugs and eight on antiarrhythmic drugs). In the remaining patients, incessant non-sustained VT (n = 2) or recurrent sustained VT (n = 2) occurred, and two patients died suddenly (at 2 and 21 months). There was no correlation between catheter mapping data or the results of pre-discharge electrophysiological study and clinical outcome during long-term follow-up. Complications related to catheter ablation included pulmonary oedema, cardiac tamponade, femoral artery occlusion, multiple episodes of ventricular tachycardia/fibrillation and thrombus formation, each in one patient (major complications; n = 7,29.1%), as well as transient third degree AV block, transient right or left bundle branch block, transient marked ST elevation or transient atrial tachycardia (minor complications; n = 8, 33.3%). The results suggest that catheter ablation might become an effective procedure for the non-pharmacological treatment of sustained VT.(ABSTRACT TRUNCATED AT 400 WORDS)

Bidirectional transvenous/subcutaneous defibrillation of ventricular fibrillation in dogs: success rates, energy requirements, currents, voltages and impedance

Four hundred and thirteen defibrillations of alternating current-induced ventricular fibrillation were performed in 10 halothane-anaesthetized dogs (body weight: 24.5-30.5 kg). Success rates, energy demands, currents, peak voltages and impedance were determined. A transvenous catheter electrode system (Medtronic 6880, right ventricular apex and superior vena cava, distance 100 or 150 mm) and subcutaneous patch electrodes (Intec 67 L, 2nd/3rd and/or 3rd/4th left intercostal space) were used for bidirectional defibrillation. Loading voltages ranged from 600 to 850 V. With an electrode distance of 100 mm and a pulse duration of 2 ms separated by 1 ms, success rates were 100%, 40% and 0% for 850.650 and 600 V, respectively. With a 3-ms pulse duration, the corresponding rates were 100%, 60% and 50%. With a 2-ms pulse duration, successful defibrillation was achieved with energies lower than 15 J in 27%, with energies between 15 and 20 J in 77%, and 100% with energies higher than 20 J. Defibrillation currents were 4.4-9.3 A for pulse 1 (superior vena cava/ventricular apex) and 6.3-13.4 A for pulse 2 (patch/ventricular apex), respectively. Effective peak voltages ranged from 510 to 787 V and from 514 to 777V and averaged 89.6% of the loading voltages. Impedance values (peak voltage/current) were 75.5-117.7 (pulse 1) and 51.7-94.9 Ohms (pulse 2). Fifty consecutive defibrillations in one animal resulted in a decrease of impedance (114.6 to 84.9 Ohms, pulse 1:75.4 to 53.0 Ohms, pulse 2). Defibrillation of ventricular fibrillation can be achieved with acceptably low energies using a bidirectional transvenous/subcutaneous system, avoiding thoracotomy and general anaesthesia for implantation of the defibrillation system.

Influence of the cycle length of basic drive on induction of sustained ventricular tachycardia associated with coronary artery disease

The relation between the cycle length of basic drive during programmed ventricular stimulation and the coupling intervals at which sustained monomorphic ventricular tachycardia (VT) was initiated was analyzed in patients with coronary artery disease and documented sustained VT. The study included 28 patients in whom hemodynamically tolerable, monomorphic sustained VT was inducible at different cycle lengths of basic drive during the same electrophysiologic study. The stimulation protocol included single or double premature stimuli during paced ventricular rhythms at different cycle lengths of basic drive. The coupling intervals of premature stimuli for induction of VT (considered the outer margin of the echo zone) during step 1 of the stimulation protocol (basic drive at cycle lengths of 500 or 430 ms) were compared with those during step 2 (basic drive at cycle lengths of 370 or 330 ms). The mean cycle length of induced sustained VT was 370 +/- 79 ms. The mode of induction of VT remained the same in 23 patients (single or double premature stimuli); in 5 patients, fewer premature stimuli were required during step 2 than step 1. By moving from step 1 to step 2, VT could be induced at longer coupling intervals of the premature stimuli in 23 patients (82.1%). The mean increase in the sum of the coupling intervals was 52 +/- 37 ms. In 5 patients, the coupling intervals either did not change from step 1 to step 2 (n = 1) or decreased by an average of -40 +/- 14.1 ms. The results suggest that inducibility of VT is favored by a decrease in the cycle length of basic drive.(ABSTRACT TRUNCATED AT 250 WORDS)

[Possibilities and limitations of catheter ablation of tachycardia arrhythmia]

Catheter ablation has become an alternative to other non-pharmacological forms of antiarrhythmic therapy. Since supraventricular arrhythmias were first treated by ablation of the AV-conduction system, the clinical use of the technique has recently been extended to treat accessory pathways or ventricular tachycardias. The results of experiences from a number of clinical centers are available. To improve clinical applicability and to avoid complications, besides direct-current ablation, new technologies have been tested experimentally and in some cases already applied to patients. Whereas catheter ablation with radio-frequency alternating current has already been used in patients, the application of laser technology to ablation of arrhythmogenic myocardium has been limited to open heart surgery. Both techniques may offer improvements regarding precision and safety aspects of the method. To perform catheter ablation, a multitude of prerequisites concerning organisatory and safety aspects has to be fulfilled. Thus far, catheter ablation should only be performed in clinical centers with the facilities for cardiac surgery.

High frequency alternating current ablation of an accessory pathway in humans

High frequency alternating current ablation of an accessory pathway was performed in a patient with incessant circus movement tachycardia using a right-sided, free wall accessory pathway. Antiarrhythmic drugs, antitachycardia pacing and transvenous catheter ablation using high energy direct current shocks could not control the supraventricular tachycardia. A 7F bipolar electrode catheter with an interelectrode distance of 1.2 cm was positioned at the site of earliest retrograde activation during circus movement tachycardia. At this area, two alternating current high frequency impulses were delivered with an energy output of 50 W through the distal tip of the bipolar catheter, while the patient was awake. After the first shock supraventricular tachycardia terminated and accessory pathway conduction was absent without altering anterograde conduction in the normal atrioventricular (AV) conduction system. No reports of pain or other complications were noted. In short-term follow-up of 5 months, the patient had been free of arrhythmias without antiarrhythmic medication. Thus, high frequency alternating current ablation was performed for the first time in the treatment of an arrhythmia incorporating an accessory pathway in a human. This technique may be an attractive alternative to the available transcatheter ablation techniques and to antitachycardia surgery.

[Initial experiences with high-frequency electric ablation of the AV conduction system in the human]

For the first time, radiofrequency alternating current ablation of the AV-conduction system was performed in a 49-year-old female patient with recurrent atrial tachycardia with fast atrioventricular conduction, refractory to medical therapy, and two conventional DC-shock catheter ablation procedures. Without underlying cardiac disease, the patient had experienced almost daily episodes of tachycardia with a total of 10 syncopes. An electrophysiological study had revealed an ectopic right-atrial tachycardia and fast AV conduction up to a rate of more than 180 bpm. Soon after conventional right atrial catheter ablation, tachycardia with normal AV-conduction had recurred. Therefore, after catheter positioning (Lumelec, Cordis) at the proximal His bundle, 5 alternating current high-frequency pulses with an output energy of up to 50 W were applied under general anaesthesia. After the fourth application, the ECG revealed IIIrd degree AV-block with a His-bundle escape rhythm of 50 bpm. No complications occurred. Subsequent echocardiography did not reveal any pathological changes. The patient was put on anticoagulant therapy for the following 3 months and discharged after implantation of a permanent, activity-controlled pacemaker system (Activitrax, Medtronic). AV-block was persistent within a follow-up period of 3 months.

Bacteriological assistance for optimal antibiotic therapy of endocarditis

The specific anatomical changes of the infected valvular tissue demand the best bactericidal antibiotic therapy of endocarditis. However, quantitative antibiotic sensitivity testing and determination of the bactericidal effectiveness is not sufficiently routinely practised. It is presented how appropriate bacteriological assistance to achieve the optimum antibiotic therapy for endocarditis leads to favourable clinical results. Establishment of reference laboratories for quantitative antibiotic sensitivity testing in every case of endocarditis is proposed. Active cooperation between these centres would provide excellent data for method and result comparison.

Central hemodynamics at rest and during exercise after mitral valve replacement with different prostheses

To compare the hemodynamic features of different prosthetic heart valves that have equal tissue anulus diameter (29 mm or comparable), 75 patients with isolated mitral valve replacement (19 with Björk-Shiley Standard [BS], five with Hall-Kaster [HK], seven with Ionescu-Shiley [IS], 12 with Lillehei-Kaster [LK], 12 with Starr-Edwards [type 6120, SE], and 20 with St. Jude Medical [SJ] prostheses) were reexamined approximately 1 year after operation by right and left heart catheterization while they were at rest and during bicycle exercise. Mean pulmonary artery and mean left atrial pressure were reduced significantly in all the groups postoperatively. However, pulmonary artery and left atrial pressure were somewhat lower after BS and SJ implantation than the comparable pressures in the other groups. Normal values were reached only in a small number of patients, and the cardiac index remained at the lower limit of normal. Average diastolic pressure gradients in patients at rest were 2.3 +/- 0.6 mm Hg after SJ, 4.5 +/- 1.6 after BS, 5.2 +/- 3.3 after HK, 5.3 +/- 1.6 after IS, 7.1 +/- 1.3 after LK, and 6.3 +/- 2.0 after SE implantation. Effective valve orifice areas were calculated to be 3.1 +/- 0.8 cm2 in the SJ group and 2.2 +/- 0.5 cm2 in the BS group and even smaller in the other groups. Total volume loss does not seem to be significantly different among the valve types reexamined as determined by left ventricular angiography. For hemodynamic reasons, of all those prosthetic valves we compared, the SJ prosthesis appears to perform best in terms of lowest pressure gradients and largest effective orifice areas.