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Biomedical subjects

M Manz

Publications and source records attributed to M Manz.

At least 55 records · Page 3Linked to original sources
PubMed1994

Heart rate during exercise: what is the optimal goal of rate adaptive pacemaker therapy?

The objective of minute ventilation (MV)-controlled pacemaker algorithms is to simulate the physiologic relationship of the sensed signal and the sinus node response during exercise. In our study we determined the relationship between heart rate and MV in healthy middle-aged subjects by measuring breath-by-breath gas exchange throughout peak exercise. Regarding several clinical limitations of peak exercise testing, we additionally evaluated whether a 35 W low-intensity treadmill exercise (LITE) protocol can be used as a substitute for peak exercise testing to determine the physiologic heart rate to MV slope. The results demonstrated that the heart rate to MV relationship is not linear throughout peak exercise but is curvilinear with a smooth logarithmic-type profile. To simulate this relationship, MV-based rate adaptive pacemakers should generate a decreasing heart rate to MV slope during higher levels of work. The heart rate to MV slope determined during the early, dynamic phase of low-intensity exercise represents the same slope derived from peak exercise below the anaerobic threshold. The low-intensity treadmill exercise protocol, with minimal patient effort, can thus be used as a substitute for peak exercise to optimize rate adaptive slope programming of MV-controlled pacemakers.

Algorithms↗
PubMed1994

Complications of pacemaker-defibrillator devices: diagnosis and management.

Treatment of resuscitated patients with implantable cardioverter defibrillators has become increasingly more common as a method for the prevention of sudden cardiac death. Major complications such as perioperative death (incidence 2% to 8%), infection (2% to 11%); and lead-related problems (3% to 27%) have been described in previous trials. In our experience with 140 patients, problems were related to leads (n = 11), the device (n = 2), pacing (n = 1), sensing (n = 13), and defibrillation function (n = 5). Additional problems that occurred during the perioperative period included infection (n = 11), hematoma, and seroma (n = 2). Thrombus formation along endocardial leads was observed in 13 of 62 (21%) patients. Different arrhythmias (n = 10), such as sinus tachycardia, atrial fibrillation, and nonsustained, slow or incessant ventricular tachycardia with shock delivery, were also detected. Surgical management (predominantly for the major problems) was used in 31 (48%) patients, drug treatment in 25 (39%), and reprogramming of the device in 24 (38%) patients. All of these problems can result in an increase in mortality rates. This article provides an overview of the complications of cardioverter defibrillator treatment and is based on both published data and our series.

Arrhythmias, Cardiac↗
PubMed1994

Predictors of outcome in patients with implantable transvenous cardioverter defibrillators.

The identification of patients who benefit most from implantable cardioverter defibrillator (ICD) therapy is of great interest. To find out if clinical variables, the signal-averaged electrocardiogram, and electrophysiologic study predict occurrence of appropriate ICD discharges and death, we followed-up on 76 patients after implantation of a transvenous ICD. During a mean follow-up period of 18.2 +/- 6.4 months, 29 patients (38.6%) experienced at least one appropriate episode. When these patients were compared with those who had either no therapy or inappropriate episodes, three variables were found to be significant in the identification of patients who experienced appropriate discharges: (1) The mean ejection fraction of patients who received appropriate discharges was 35.4% +/- 13.5% versus 45.1% +/- 15.3% in the other group (p < 0.05); (2) patients with appropriate therapy had sustained monomorphic ventricular tachycardia that was more likely to be inducible (75.9% vs 21.2%, p < 0.01); and (3) in patients with appropriate therapy ventricular fibrillation was less likely to be inducible (10.3% vs 25.5%, p < 0.05). The signal-averaged electrocardiograms were more often abnormal, but the differences were not significant. The total mortality rate in our patient group was 7.8%, with nonsudden cardiac death in four patients, noncardiac death in one patient, and sudden death in one patient. In our patient group a lower ejection fraction and inducible sustained monomorphic ventricular tachycardia were predictors of future ICD discharge after implantation. The survival rate after transvenous ICD implantation is excellent; a longer follow-up period is necessary to further define predictors of total mortality rate.

Cardiac Pacing, Artificial↗
PubMed1994

Patient acceptance of implantable cardioverter defibrillator devices: changing attitudes.

Clinical experience suggests that the implantable cardioverter defibrillator (ICD) can reduce sudden cardiac death and total mortality in patients with malignant ventricular arrhythmia who meet the selection criteria for implantation. In addition to surgical problems, patients are faced with psychological and social adjustments. Patient acceptance for such therapy is marked by perceived concerns regarding device discharge, life-style alterations, and complications. We included 57 patients with ICDs in a study of their acceptance of the device. Results of a specially designed questionnaire (state-trait personality inventory) showed that 47 of 57 patients felt that their symptoms improved with the ICD system, 32 were constantly aware of the device, and 24 patients acclimated to the ICD system within less than 2 months. With respect to the need for battery replacement, only 27 patients requested a repeat electrophysiologic evaluation, 20 patients stated fear of ICD discharges, 12 patients revealed physical discomfort from the device, and limited quality of life occurred in eight patients. Fifty-five of 57 patients answered that it was worth having an ICD device implanted, 30 (53%) patients returned to active life, and 56 (98%) would advise another patient to have an ICD implantation if necessary. In conclusion, in general, the acceptance of the ICD as a tool for management of life-threatening ventricular tachyarrhythmias is very high. Quality of life and patient acceptance are important criteria for successful ICD therapy in addition to the improved survival rate.

Attitude to Health↗
PubMed1994

Reduction of cerebral blood flow with induced tachycardia in rats and in patients with coronary artery disease and premature ventricular contractions.

A reduction of cerebral blood flow (CBF) was observed in experimental studies in rats immediately after the onset of parasystolic rhythm or with stable, but haemodynamically compromising, tachycardias. Based on these data and with a view to studying the effects of premature ventricular contractions (PVCs) on the cerebral circulation in humans, CBF was measured using the 133-Xenon inhalation method in 24 age matched human controls (group A1: age 58.5 +/- 6.2 years; group A2: 52.2 +/- 7.8 years) in nine coronary artery disease (CAD) patients without PVCs (B), in 11 CAD patients with frequent PVCs (> 300.h-1) (C) and in nine patients, after exclusion of CAD by angiography, also with frequent PVCs (> 300.h-1) (D). Holter monitoring was performed during the CBF measurement. CBF determined in the human control groups A1 and A2 was 79.9 +/- 9.9 ml.100 g.-1 min-1 and 81.5-13.0 ml. 100 g-1 min-1, respectively. CBF was 74.1 +/- 13.6 ml . 100 g.-1 min-1 (P = 0.267 vs A1) in group B, 65.8 +/- 11.8 ml.100 g-1 min-1 (P = 0.004 vs A1) in group C and 74.2 +/- 15.6 ml.100 g.-1 min-1 (P = 0.218 vs A2) in group D. The significant reduction of CBF in CAD patients with frequent PVCs suggests that arrhythmias have a significant impact on CBF. Non-CAD patients with frequent PVCs did not show significant CBF decreases in comparison with controls. One can hypothetize that an impairment of electrical postextrasystolic potentiation, due to premature ventricular depolarization, and hence myocardial dysfunction leads to CBF reduction in CAD patients. The CBF reduction with CAD could also reflect concomitant coronary and cerebral arteriosclerosis.

Aged↗
PubMed1994

Loss of late potentials after radiofrequency catheter ablation of recurrent ventricular tachycardia in a patient with right bundle branch block.

The case of a patient with a history of myocardial infarction and recurrent ventricular tachycardia undergoing attempted radiofrequency catheter ablation with loss of late potentials is described. Prior to energy delivery fractionated, late activation could be found using the signal-averaged ECG despite the presence of a right bundle branch block. After successful catheter ablation, the clinical ventricular tachycardia was no longer inducible and the signal-averaged ECG, recorded the next day, showed marked changes indicating loss of late potentials. Our report emphasizes the possibility of late potential recordings despite the presence of bundle branch block.

Aged↗
PubMed1994

Myocardial and cerebral hemodynamics during tachyarrhythmia-induced hypotension in the rat.

BACKGROUND: The different vulnerabilities of heart and brain to hypotension and hypoxia have been discussed. Hemorrhagic or cardiogenic hypotension appears to cause greater cerebral lesions than drug-induced hypotension. The present model was established to evaluate myocardial blood flow (MBF) and function of the heart and cerebral blood flow (CBF) during tachyarrhythmias and to characterize the capacity of blood flow regulation in the heart and brain during tachycardia-induced borderline hypotension. METHODS AND RESULTS: MBF and CBF were determined with radiolabeled microspheres. Coronary and central venous oxygen tensions were measured to estimate myocardial and cerebral oxygen consumption (MVO2 and CVO2). Measurements were performed in 62 Sprague-Dawley rats during sinus rhythm and high-rate left ventricular pacing and after hemorrhage. In control rats, MBF and CBF were 5.08 +/- 1.07 and 1.09 +/- 0.29 mL.g-1.min-1. MBF increased (7.21 +/- 1.98 mL.g-1.min-1, P < .05), whereas CBF decreased (0.99 +/- 0.29 mL.g-1.min-1, P = NS) during normotensive high-rate pacing. MBF and CBF dropped to 4.27 +/- 2.24 mL.g-1.min-1 (P = NS) and 0.68 +/- 0.29 mL.g-1.min-1 (P < .05) during pacing-induced borderline hypotension and decreased further during severe hypotension (1.77 +/- 0.81 mL.g-1.min-1, P < .01; 0.45 +/- 0.18 mL.g-1.min-1, P < .01). During borderline hypotension due to hemorrhage, MBF and CBF were 4.05 +/- 0.95 mL.g-1.min-1 (P = NS) and 0.71 +/- 0.23 mL.g-1.min-1 (P < .05). MVO2 and CVO2 were 72.7 +/- 15.4 and 12.7 +/- 3.3 mL.100 g-1.min-1 in control rats. MVO2 increased during normotensive pacing (100.3 +/- 27.4 mL.100 g-1.min-1, P = NS). Mean MVO2 was reduced during pacing-induced borderline hypotension (64.1 +/- 35.6 mL.100 g-1.min-1, P = NS) and severe hypotension (29.8 +/- 15.4 mL.100 g-1.min-1, P < .05). CVO2 decreased in correlation to CBF. Coronary and cerebrovascular resistance and autoregulation indexes indicated a maintenance of MBF regulation and a failure of CBF regulation during borderline hypotensive tachycardias. These results show a dissociation of MBF and CBF after onset of hypotensive tachycardias. Thus, brain tissue appears to be jeopardized at an earlier stage than myocardial muscle during tachyarrhythmias. CONCLUSIONS: The proposed hypotension model is suitable to analyze tachyarrhythmia-induced hemodynamic changes and end-organ perfusion in the presence of myocardial dysfunction. It has the potential to test therapeutic strategies in the treatment of tachycardias.

Animals↗
PubMed1994

[Intermittent focal cerebral ischemia in hypotension due to pacemaker syndrome].

A pacemaker syndrome manifested as transient sensoric aphasia in a 68-year-old woman with a VVI-pace-maker implanted after SA-block. The attack occurred during long-term blood pressure recording and Holter monitoring. Borderline hypotension was documented during ventricular pacing which induced a retrograde excitation of the atrium. Clinical investigations excluded any intracranial abnormality, any source of embolism or stenosis of extra- and intracranial cerebral arteries. Cerebral blood flow measurements revealed a significant increase during pacing at elevated heart rate. Therefore, a device for AV-sequential pacing was implanted and basic pacing rate was elevated. The present case report indicates that focal and not only global cerebral ischemia can be produced by an impairment of systemic hemodynamics due to hypotension and a pacemaker syndrome. Improvement of cerebral blood flow during pacing is an unexpected finding contrasting with the concept of autoregulation. In addition, pacemaker implantation should be discussed in patients with transient cerebral perfusion deficits if an improvement of cerebral blood flow is documented along with rising heart rate.

Aged↗
PubMed1994

[Non-pharmacologic therapy of atrial fibrillation].

Since patients with recurrent atrial fibrillation are prone to recurrences, even under treatment with antiarrhythmic agents, alternative treatment modalities are being sought. Today, the non-pharmacological treatment modalities such as modification or ablation of the AV node or the operative procedures ("maze" or "corridor" operation) do not cure these patients. The non-pharmacological therapies are indicated if severe symptoms are due to high ventricular rate with hemodynamic compromise. In such cases, His bundle ablation followed by rate adaptive pacing can achieve control of symptoms in the majority of patients. In the future, more refined techniques for ablation or the introduction of automatic atrial cardioverters will extend therapeutic options.

Anti-Arrhythmia Agents↗
PubMed1994

[The value of magnesium in intensive care medicine].

UNLABELLED: In the management of severely ill patients it has been suggested that magnesium might protect the heart muscle and prevent lift-threatening irregularities of heart rhythm. 1) Cardiac arrhythmias: The mechanism of action of magnesium in monomorphic ventricular tachycardia is not known. Magnesium does not affect the effective refractory period of ventricular structures. It alters the inward rectifying potassium channel in experimental animal models. Though magnesium may exhibit negative inotropic effects in animal studies, an increase of the cardiac index during ventricular tachycardia could be documented in recent investigations. The application of magnesium is usually well tolerated. Magnesium (i.v.) is indicated in Torsade de pointes tachycardia Digitalis-induced cardiac arrhythmias Monomorphic ventricular tachycardia (efficacy ca. 30%) Multifocal atrial tachyarrhythmias. 2) Myocardial infarction: In the past, several trials of intravenous infusions of magnesium have indicated a considerable mortality reduction following myocardial infarction. More recently, the LIMIT-2 (Leicester Intravenous Magnesium Intervention Trial) of a 24-h magnesium infusion in about 2000 patients indicated a benefit of about 25%. Now, the ISIS-4 (International Study of Infarct Survival)-trial has tested magnesium in 58,000 patients. In ISIS-4 there was no evidence of a beneficial effect of magnesium on mortality--neither in all patients nor in any particular type of patient. Overall, there was no beneficial effect on morbidity. According to these data, there seems only a limited role for magnesium in the routine treatment of cardiac infarction patients. IN CONCLUSION: Intravenous magnesium can terminate Torsade de pointes tachycardia and, in selected patients, monomorphic ventricular tachycardia regardless of the serum magnesium concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Arrhythmia Agents↗
PubMed1994

[The effect of the impulse form of the defibrillation shock on its effectiveness and device technology of the implantable cardiac defibrillator].

Efforts have been focussed on the development of implantable cardioverter-defibrillator systems that reduce the size of the devices, simplify the methods of electrode implantation, and increase device longevity. The size of implantable units is predominantly determined by the capacitors and batteries, and this is dependent on the output energy requirements. The energy required for defibrillation and therefore the size of the devices can be reduced by utilizing optimal lead systems and waveforms. This report describes our experience with various shock waveforms in 86 consecutive patients undergoing implantation of a cardioverter-defibrillator with a nonthoracotomy approach. Table 1 provides information on the demographic characteristics of the study population, the various shock waveforms and lead configurations tested. In 20 patients, a bidirectional lead configuration was tested using simultaneous and sequential monophasic waveforms. In 18 patients, simultaneous monophasic and biphasic waveforms with a fixed pulse duration of 6.3 ms were employed utilizing a bidirectional lead system. In 31 patients, a undirectional lead configuration was used, and simultaneous monophasic and biphasic shocks with a constant tilt were delivered. In 17 patients, the defibrillation efficacy of biphasic and triphasic shock waveforms with a fixed pulse duration of 10 ms was evaluated. The study design was an open, randomized and prospective evaluation in all patients. Defibrillation threshold was determined in a randomized sequence using a step down protocol. The defibrillation threshold was defined as the lowest energy required for effective defibrillation on two occasions. In the 20 patients using a bidirectional lead configuration, there was no significant difference in defibrillation energy requirements between simultaneous and sequential monophasic shock waveforms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Echocardiographic profile of the normally functioning Omnicarbon valve.

Transthoracic echocardiography was performed in 141 patients with 90 Omnicarbon valves in the aortic and 66 in the mitral position. Additionally, 53 of them were investigated by transesophageal echocardiography comparing monoplane and multiplane facilities. The opening direction of the disc and the location of the pivot axis could be correctly determined by transthoracic, monoplane, and multiplane transesophageal echocardiography, respectively, in 100%, 80%, and 100% of the mitral and in 53%, 21%, and 82% of the aortic prostheses. Small regurgitation jets were detected in 90% of the aortic valves (1.6 +/- 0.4 cm2) by transthoracic and in all mitral prostheses (2.3 +/- 0.8 cm2) by transesophageal echocardiography. Based on morphological identification of the pivot points structures, origins of leakage jets were clearly identified as "design-related" in 12% (transthoracic echocardiography of aortic valves) to 100% (multiplane transesophageal echocardiography of mitral valves). In the aortic position, values obtained for transprosthetic forward flow velocity measurements exhibited wide scatter which did not allow a firm separation between valve sizes. No better differentiation was possible by using the calculated Doppler gradients or the velocity time integrals, either. Mean gradients and velocity time integrals showed even smaller differences between groups in the mitral valve patients. It is concluded that the Omnicarbon valve has a suitable design for morphological echocardiographic examination, and multiplane transesophageal technique expands the diagnostic capability. Forward flow measurements do not appear to be suited for detecting a beginning obstruction of this mechanical prosthesis.

Adult↗
PubMed1994

[Effect of nisoldipine and diltiazem on systolic and diastolic function of the left ventricle in patients with coronary heart disease].

OBJECTIVES AND BACKGROUND: Calcium channel blockers have a negative inotropic effect and protract the relaxation of the normal myocardium. These effects may vary in patients with coronary artery disease (CAD) and with the different kinds of calcium antagonists. In the present study we therefore compared the hemodynamic effects of intravenously given equihypotensive dosages of diltiazem (D) and nisoldipine (N) in patients with CAD. METHODS AND RESULTS: Each group contained 10 patients. After administration of a bolus of 300 micrograms/kg (D) and 5 micrograms/kg (N) respectively and following continuous infusion of 5.4 micrograms/kg/min (D) and 0.2 micrograms/kg/min (N) respectively, the mean arterial pressure was reduced by 15.5 +/- 6.0 (D) and 16.6 +/- 4.1 (N) mm Hg. Atrial pacing was performed in all patients to avoid reflectory heart rate effects. The pulmonary artery pressure decreased slightly with both drugs, whereas the cardiac index increased only with the use of N from 3.44 l/min x m2 to 3.93 l/min x m2. A significant change in the maximal rate of rise of left ventricular pressure (dP/dt max) as an index for inotropy was not detected for N or for D. The parameters of the diastolic function (the time constant of ventricular relaxation (tau) and the maximum rate of left ventricular isovolumic pressure decline (dP/dt min)) also did not indicate unequivocal drug effects. Doppler echocardiography of the mitral valve flow was performed simultaneously with invasive pressure measurements. The flow propagation derived from the color-M-mode correlated significantly with tau and was slightly improved by D.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

[Adenosine in prediction of the success of radiofrequency ablation in Wolff-Parkinson-White syndrome].

Rapid bolus injection of adenosine has been shown to produce transient atrioventricular (AV) nodal block while having almost no direct effect on accessory pathway conduction. The aim of this study was to determine the efficacy of adenosine for prediction of success of catheter ablation in WPW syndrome in 31 patients (23 with preexcitation; 8 with concealed conduction) before and 30 min, 5-7 days, and 3-6 months after attempted radiofrequency catheter ablation. Before ablation 6 mg adenosine produced maximal preexcitation (QRS duration increased from 100 +/- 15 ms to 123 +/- 18 ms) in patients with manifest preexcitation, while AV block occurred in all patients (100%) with concealed conduction for 1.5 +/- 0.5 s. No patient had accessory pathway conduction unmasked by adenosine. In 30/31 (96%) of patients retrograde conduction was unchanged prior to ablation. Immediately after ablation adenosine induced AV and VA block in 29 (93%) patients. These results were also present 5-7 days and 3 months later and were confirmed by electrophysiologic study. The positive and negative predictive values are 96% and 100%, respectively. Adenosine is reliable and useful to predict short- and long-term success following radiofrequency catheter ablation.

Adenosine↗
PubMed1993

[Radiofrequency ablation of accessory pathways in pre-excitation syndrome].

Various parameters relating to the radio-frequency ablation of accessory pathways were studied in 53 patients (27 males, 26 females: mean age 38.5 [14-64] years) with a history of paroxysmal tachycardia (over 1 month to 50 years), shown to be caused by an accessory pathway (Wolff-Parkinson-White syndrome). In all patients the following values were obtained: (1) number of procedures necessary to achieve permanent blockage of the accessory pathway (1-4); (2) duration of each procedure (45-420 min); (3) duration of fluoroscopy (5-102 min); (4) number of necessary radio-frequency applications (1-48); and (5) cumulative energy per procedure. To ablate left-lateral pathways (n = 10) required fewer procedures, shorter duration per procedure, shorter fluoroscopy time, fewer current applications and less total energy than coagulation of right-sided pathways (n = 10). Those various parameters were greatest for ablation of septal and para-septal pathways (n = 9). Pathways which conducted only retrogradely (n = 15) were more difficult to ablate than those with anterograde conduction (n = 38). There were two complications. In one case a tension pneumothorax occurred after faulty puncture of the subclavian vein; in the other, the left ventricle was perforated causing an acute tamponade which required pericardiocentesis with subsequent suture closure of the perforation. It is concluded that, in principle, all accessory pathways, regardless of their conduction potential and site, can be ablated by a radio-frequency current.

Adolescent↗
PubMed1993

[The quality of life after the implantation of a cardioverter/defibrillator in malignant arrhythmias].

Quality of life after implantation of an automatic implantable cardioverter/defibrillator (ICD) was assessed by questionnaire in 43 patients (38 males, 5 females; mean age 57 +/- 16 years) with treatment-resistant symptomatic ventricular arrhythmias. 37 of the 43 patients felt better after ICD implantation. 23 were always conscious of having an ICD, but 18 had got used to it in less than 2 months. 15 patients reported being afraid of an ICD shock, while eight noted physical discomfort caused by the ICD. Limitations concerning their professional, recreational and social activities were reported by six patients. 41 of the 43 patients confirmed that the ICD had been helpful, enabling 23 to return to an active life. 42 would recommend implantation to others if indicated. These data demonstrate that there is a remarkably high degree of acceptance of the ICD. Survival rate after implantation is thus not the only criterion of success. All aspects of the quality of life should be taken into consideration before implantation is decided upon.

Adult↗