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G Schreier

Publications and source records attributed to G Schreier.

At least 19 recordsLinked to original sources
PubMed2002

Correlation between changes in stroke volume and the paced intracardiac electrogram.

AIM: The aim of this study was to examine the relation between cardiac haemodynamics and parameters extracted from the intracardiac electrogram obtained during pacing, i.e. ventricular evoked response. METHODS AND RESULTS: In the course of routinely scheduled right heart catheterization, intracardiac electrograms and cardiac haemodynamics were monitored simultaneously in ten heart transplant patients (two females, aged 48 +/- 12 (18-59) years), using pacemaker telemetry and Swan-Ganz thermodilution techniques. Different haemodynamic states were induced by pacemaker programming (pacing rate changes) and table tilting (postural changes). Forty different haemodynamic states were assessed, with an average of three (2.4) haemodynamic variations in each patient. Linear regression analysis between relative stroke volume changes and relative changes in the R wave slew rate as extracted from the evoked responses revealed a strong, inverse, and highly significant correlation (r= - 0.93, P<0.0001) between those parameters. Similar results were obtained for pacing rate and postural variations alone, respectively. CONCLUSIONS: The strong correlation between changes in stroke volume and R slew rate indicates that paced intracardiac electrograms reflect changes in the size and geometry of the heart. Telemetrically recorded intracardiac electrograms may thus be used non-invasively to assess key aspects of cardiac haemodynamics.

Adolescent↗
PubMed2000

Non-invasive graft monitoring after heart transplantation: rationale to reduce the number of endomyocardial biopsies.

The endomyocardial biopsy is invasive, reduces quality of life and cannot be repeated daily. Initial studies on noninvasive cardiac graft monitoring have been presented recently. During the heart transplant procedure, we implanted wideband telemetric pacemakers and fractally coated, epimyocardial electrodes. On biopsy days and during each follow-up, intramyocardial electrogram sequences were obtained. The maximum T-slew rate from the ventricular evoked response (VER) was automatically calculated and compared to the biopsy results (n = 331, ISHLT grading). The VER T-slew rate was significantly lower during rejection grade 2 or higher. The negative predictive value to exclude rejection was 98%. Using a single threshold diagnosis model, 74% of the biopsies could have been avoided. Noninvasive cardiac graft monitoring can reduce the need for surveillance biopsies and may offer a tool to optimize immunosuppressive therapy after heart transplantation.

Adolescent↗
PubMed2000

Non-invasive cardiac allograft monitoring: the graz experience.

Based on previous reports by our group, initial studies on non-invasive cardiac graft monitoring have been presented recently. In this study we define new parameters to monitor rejection and infection after heart transplantation (HTX) the ventricular evoked response (VER) T-slew rate parameter is defined as the maximum negative slope in the descending part of the repolarization phase of the VER. We calculated the VER duration parameter in milliseconds and defined it as the time between the pacemaker spike and the cross-over of the baseline, with the slope line used to calculate the VER T-slew rate. During the HTX procedure, we implant wide-band telemetric pacemakers and fractally coated, epimyocardial electrodes (Physios CTM 01 and ELC 54-UP, Biotronik; Berlin, Germany). During each follow-up and on biopsy days, intramyocardial electrogram sequences were obtained and sent via the Internet to the central data-processing unit in Graz. We scored the infection status of the patients before data acquisition. The VER parameters were automatically calculated and send back within a few minutes. We prospectivly compared 1,613 follow-ups from 42 patients with biopsy (International Society of Heart and Lung Transplantation grading) and infection classification. The VER duration parameter did not change during rejection; however, we found an increase during clinically apparent infection. The VER T-slew rate parameter was lower during rejection grade 2 or higher, as well as during clinically apparent infection. The negative predictive value to rule out rejection was 99%. Our results indicate that rejection and infection cause different, reproducible effects on the electrical activity of the transplanted heart. Non-invasive cardiac graft monitoring may reduce the need for surveillance biopsies and may offer a tool to optimize immunosuppressive therapy after HTX.

Action Potentials↗
PubMed2000

Heart graft monitoring by the ventricular evoked response.

Monitoring of the negative slew rate of the evoked T wave has been proposed as a noninvasive diagnostic tool to follow heart transplant recipients. The clinical contribution of this measurement on telemetrically recorded, paced unipolar ventricular electrograms was evaluated in the detection of grade 3 acute allograft rejection. Thirteen patients undergoing heart transplantation received a DDD pacemaker connected to two epimyocardial leads. Electrograms were recorded and digitized after each endomyocardial biopsy (EMB). The maximum slew rate of the descending slope of the repolarization phase (RSP) was extracted and normalized. A 20% downward shift of RSP from the reference value was considered abnormal. Results of signal processing were blinded during the first 6 months. Eleven patients completed the 6 months blinded period and two patients died. A total of 101 EMB were graded according to the International Society for Heart and Lung Transplantation classification. Grade 3 was assigned to 9 EMB. A significant difference was found between RSP values measured during grade 3 rejection episodes and other RSP values (P < 0.001). A diagnostic model consisting of a single threshold test confirmed the ability of RSP to predict significant signs of rejection on EMB (P < 0.0001). The sensitivity of RSP in detecting grade 3 rejections was 100%, specificity was 81%, negative predictive value 100%, and positive predictive value 35%. The use of RSP as a noninvasive monitoring tool to pose the indication for a biopsy would avoid 73% of EMB. Monitoring of transplanted hearts based on the analysis of the ventricular evoked response is promising and may markedly reduce the number of EMB.

Biopsy↗
PubMed1999

Ventricular evoked response in patients with hypertrophic obstructive cardiomyopathy treated with DDD pacing.

OBJECTIVE: To assess the changes in ventricular evoked responses (VER) produced by the decrease in left ventricular outflow tract gradient (LVOTG) in patients with hypertrophic obstructive cardiomyopathy (HOCM) treated with dual-chamber (DDD) pacing. METHODS: A pulse generator Physios CTM (Biotronik, Germany) was implanted in 9 patients with severe drug-refractory HOCM. After implantation, the following conditions were assessed: 1) Baseline evaluation: different AV delay (ranging from 150 ms to 50 ms) were sequentially programmed during 5 to 10 minutes, and the LVOTG (as determined by Doppler echocardiography) and VER recorded; 2) standard evaluation, when the best AV delay (resulting in the lowest LVOTG) programmed at the initial evaluation was maintained so that its effect on VER and LVOTG could be assessed during each chronic pacing evaluation. RESULTS: LVOTG decreased after DDD pacing, with a mean value of 59 +/- 24 mmHg after dual chamber pacemaker, which was significantly less than the gradient before pacing (98 + 22 mmHg). An AV delay > 100 ms produced a significantly lower decrease in VER depolarization duration (VERDD) when compared to an AV delay < or = 100 ms. Linear regression analyses showed a significant correlation between the LVOTG values and the magnitude of VER (r = 0.69; p < 0.05) in the 9 studied patients. CONCLUSION: The telemetry obtained intramyocardial electrogram is a sensitive means to assess left ventricular dynamics in patients with HOCM treated with DDD pacing.

Adolescent↗
PubMed1998

Intramyocardial electrograms for non-invasive rejection monitoring: initial experience with an infection-specific parameter.

Non-invasive rejection monitoring based on the analysis of paced intramyocardial electrograms enables repeated or even daily graft surveillance. The rejection-sensitive parameter is calculated from the maximum slope of the descending part of the t wave. Biopsy-proven rejection grade 2 or higher (ISHLT classification) can safely be detected. Nevertheless, infection influences the rejection-sensitive parameter in the same manner as does rejection (99% negative predictive value for rejection grade 2 or higher, 17% positive predictive value). We defined the infection-specific parameter as the time on the O line between the pacemaker stimulus and the crossover with the maximum slope of the descending part of the t wave. Patients were classified prospectively according to infection status: patients without infection and those with clinically apparent infection. Patients with clinically apparent infections had a significantly longer infection-specific parameter. A simultaneous decrease of the rejection-sensitive parameter and an increase in the infection-specific parameter was observed during clinical infection: a decrease in the rejection-sensitive parameter and no changes in the infection-specific parameter were observed during rejection. This preliminary analysis revealed that discrimination of rejection and infection might be possible by the analysis of intramyocardial electrograms.

Diagnosis, Differential↗
PubMed1998

Noninvasive rejection monitoring of cardiac transplants using high resolution intramyocardial electrograms: initial US multicenter experience.

Endomyocardial biopsy (EMB) remains the mainstay for the diagnosis of acute cellular rejection in cardiac transplant patients. A noninvasive alternative that would supplant or reduce the number of EMBs would be a highly desirable and cost-effective tool. To evaluate one potential alternative, a pacemaker with high resolution telemetry capabilities and two fractally coated epimyocardial leads were implanted in 30 patients at five transplant centers during the heart transplant procedure. Ventricular electrograms were recorded during intrinsic and paced activity and digitized to a laptop-based data acquisition device. Electrograms were recorded at frequent intervals and systematically on days when EMBs were performed. The electrogram data were then transferred via the Internet to a central data processing site. Clinical patient management was blinded to the electrogram results and varied considerably among the five centers. Using EMB together with clinical assessment of the transplant revealed 18 cases of clinically significant rejection beyond postoperative day 27 that required antirejection therapy. The normalized parameter values extracted from the electrogram recordings during pacing (the ventricular evoked response) that were associated with significant rejection were statistically lower (86% +/- 16% versus 96% +/- 22%, P < 0.005). The application of a single-threshold diagnosis model to the parameter values allowed detection of significant rejection with a negative predictive value of 98%. This analysis also showed that as many as 55% of the routine surveillance EMBs could have been eliminated had the pacemaker monitoring technique been used as a screening tool prior to EMB. A prospective study should further define the role of this technique in the detection and management of cardiac transplant patients.

Electrocardiography↗
PubMed1998

Intramyocardial electrogram variability in the monitoring of graft rejection after heart transplantation.

The ventricular evoked response is a well-standardized electrophysiological signal that can be used for noninvasive, long-term cardiac transplant monitoring. Rejection-sensitive and infection-specific parameters extracted from intramyocardial electrograms correlate with clinical results. The influences of pacing rate, transition from intrinsic to paced rhythm and positional changes on the diagnostic parameters were studied. Increasing the pacing rate shortened the ventricular evoked response and directly influenced the infection specific parameter. The rejection-sensitive parameter remained stable at pacing rates between 100 and 120 beats/min. Measurements made immediately after the patient assumed a supine position and after switching to paced rhythm showed a decrease in the rejection-sensitive parameter. A change in position from supine to upright did not influence the rejection-sensitive parameter, but higher values were measured after returning to the supine position. In conclusion, noninvasive recordings of the ventricular evoked response for monitoring of cardiac allograft should be done at the same time of day, at the same pacing rate, and with the patient resting for at least 5 minutes before measurements are made.

Adolescent↗
PubMed1996

Evoked epimyocardial electrogram for rejection diagnosis after heart transplantation.

An endomyocardial electrogram (ECG) was reported to be a sensitive and practicable method for rejection monitoring after heart transplantation. Long-term follow up was limited, however, by variations of signals. The repolarization part of ECG signals vary with changes of heart rate. Both can be avoided by using pacemaker-induced signals. For stimulation and sensing of the ventricular-evoked response, a new type of electrode with fractal surface structure was used. Twenty patients undergoing heart transplantation were evaluated. Amplitudes of the depolarization and repolarization part of the ventricular-evoked response signals were analyzed and related to the degree of acute rejection according to histological findings from endomyocardial biopsy. Signals were transferred by Internet and analyzed automatically. In the case of focal moderate rejection (grade 2, International Society for Heart Transplantation grading) and higher degrees of rejection, a significant amplitude decrease was found. This sensitive non-invasive method for rejection monitoring with a high level of reliability provides the possibility of reducing the number of endomyocardial biopsies.

Adult↗
PubMed1996

Definitions of cytomegalovirus disease after heart transplantation: antigenemia as a marker for antiviral therapy.

In this prospective study, cytomegalovirus (CMV) antigenemia was defined as the marker for initiation and episodes of antigenemia as the indicator for the duration of antiviral therapy (CMV hyperimmune globulin and ganciclovir). The CMV antigenemia assay and CMV-specific IgM and IgG antibody tests were used to monitor CMV infection in 22 heart transplant recipients who, between October 1992 and July 1994, were followed up for 6 months. A total of 178 out of 627 antigenemia assays tested positive. The highest number of positive cells was greater after primary infection than after either reactivation (43.3 vs 0.3; P < 0.01) or reinfection (43.3 vs 9.3; P = NS). Sixty episodes of antigenemia were observed. More episodes of antigenemia were seen after primary infection than after either reactivation (4.6 vs 0.2; P < 0.01) or reinfection (4.6 vs 2.2; P = NS). The detection of antigenemia indicated the initiation of antiviral therapy within 24 h after the blood sample was harvested. Therapy was stopped immediately after a subsequent negative result became available. Our experience indicates that antigenemia directed antiviral therapy prevents CMV disease after primary and secondary infection in heart transplant recipients.

Adolescent↗