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Biomedical subjects

F Duru

Publications and source records attributed to F Duru.

At least 55 records · Page 3Linked to original sources
PubMed2000

Effect of exercise training on heart rate variability in patients with new-onset left ventricular dysfunction after myocardial infarction.

BACKGROUND: Cardiac rehabilitation with exercise training alters sympathovagal control of heart rate variability (HRV) toward parasympathetic dominance in patients after acute myocardial infarction (MI). However, its effects on HRV in patients after MI with new-onset left ventricular dysfunction are yet unknown. We aimed to investigate the effects of 8 weeks of supervised, high-intensity exercise training on time- and frequency-domain measures of HRV in this selected patient population. METHODS AND RESULTS: Twenty-five men with an acute MI and a low ejection fraction were randomly assigned to enter or not to enter a training program in a regional rehabilitation center. HRV was evaluated before and after 1 and 2 months of training and at 12 months. Maximal exercise testing with respiratory gas exchange was performed at baseline and after training. Resting heart rate decreased (P <. 01) and the percentage of R-R intervals differing >50 ms from the preceding one (pNN50) increased (P <.05) after training. The standard deviation of R-R intervals (SDRR) tended to increase, but frequency-domain indexes remained unchanged. There was a significant decrease in SDRR (P <.05) and high-frequency power (P <.01) at 12 months in untrained patients. Exercise time increased by 38% and maximal oxygen uptake increased by 29% in the training group (P <. 01). CONCLUSIONS: Despite beneficial effects on clinical variables, exercise training did not markedly alter HRV indexes. A significant decrease in SDRR and high-frequency power in the control group suggests an ongoing process of sympathovagal imbalance in favor of sympathetic dominance in untrained patients after MI with new-onset left ventricular dysfunction.

Aged↗
PubMed2000

Parvovirus B19 infection reminiscent of myelodysplastic syndrome in three children with chronic hemolytic anemia.

The authors have seen transient pancytopenia with erythroid hypoplasia and striking trilineage myelodysplasia reminiscent of true myelodysplastic syndrome (MDS) in 3 children, 1 with thalassemia intermedia and the other 2 with previously undiagnosed hereditary spherocytosis. In these 3 children transient pancytopenia and myelodysplasia coincided with serological evidence of acute parvovirus-B19 (PV-B19) infection, strongly suggesting their relevance. It is of interest that these 3 cases were encountered within a period of 6 months. This might be an incidental event, but it might also be concluded that acute PV-B19 infection associated transient pancytopenia with morphological appearance of MDS may occur more frequently than reported in the literature. So, PV-B19-associated nonclonal MDS should be considered in the differential diagnosis of true clonal MDS.

Child↗
PubMed2000

Importance of ventricular rate after mode switching during low intensity exercise as assessed by clinical symptoms and ventilatory gas exchange.

Automatic mode switching from DDD(R) to DDI(R) or VVI(R) pacing modes has improved dual chamber pacing in patients at high risk for supraventricular tachyarrhythmias. However, little is known about the effect of ventricular pacing rate adaptation after mode switching. We conducted a single-blinded, crossover study in 15 patients (58 +/- 21 years) with a DDD pacemaker who had AV block and normal sinus node function to investigate the influence of pacing rate adaptation to intrinsic heart rate during low intensity exercise. Patients performed two tests (A/B) of low intensity treadmill exercise (0.5 W/kg) in randomized order. They initially walked for 6 minutes while paced in DDD mode. The pacing mode was then switched to VVI with a pacing rate of either 70 beats/min (test A) or matched to the intrinsic heart rate (95 +/- 11 beats/min test B). Respiratory gas exchange variables were determined and patients classified the effort before and after mode switching on a Borg scale from 6 to 20. Percentage changes of respiratory gas exchange measurements were significantly larger (O2 consumption: -8.2 +/- 5.0% vs. -0.6 +/- 7.2%; ventilatory equivalent of CO2 exhalation: 5.3 +/- 4.9% vs. 1.5 +/- 4.3%; respiratory exchange ratio: 7.0 +/- 2.2% vs. 3.5 +/- 3.0%; end-tidal CO2: -5.7 +/- 2.9% vs. -1.8 +/- 2.7%; all P < 0.01) and the increase in subjective assessment of the effort tended to be higher (mean increase on Borg scale: 1.6 +/- 1.9 vs. 1.1 +/- 1.8, P = 0.07) after heart rate unadjusted than after adjusted mode switching. Mode switching from DDD to VVI pacing is better tolerated and gas exchange measurements are less influenced if ventricular pacing rate is adjusted to the level of physical activity. Thus, pacing rate adjustment should be considered as part of automatic mode switch algorithms.

Adolescent↗
PubMed2000

Importance of AV synchronous pacing during low intensity exercise evaluated by oxygen kinetics.

It has been shown that dual chamber pacing with preservation of AV synchrony (DDD) is superior to fixed rate ventricular (VVI) or rate responsive ventricular (VVIR) pacing modes, as evaluated by ventilatory response to exercise. Previous studies have focused on the benefits of maintained AV synchrony at maximal exercise. However, there are limited data comparing O2 kinetics in different pacing modes during low intensity exercise, representing the majority of daily activities. This study aimed to provide an evaluation of different pacing modes using O2 kinetics during low intensity exercise. Nineteen patients (age 61 +/- 18 years) with complete AV block underwent low intensity treadmill exercise (35 W) with simultaneous evaluation of symptoms and O2 kinetics in three pacing modes. The first test was performed in DDD mode followed by a second test in VVIR mode with a programmed heart rate corresponding to the sinus rate during the first test. After 6 minutes of each test, the mode was switched from DDD to VVIR and vice versa. The third test was performed in VVI mode at 70 beats/min. O2 kinetics were defined as O2 deficit (time [rest to steady state] x delta VO2-sigma VO2 [rest to steady state]) and mean response time (MRT) of oxygen consumption (O2 deficit/delta VO2). The O2 deficit was 551 +/- 134 mL in DDD pacing, 634 +/- 139 mL in VVIR pacing, and 648 +/- 179 mL in VVI pacing (P = 0.001). MRT was 49 +/- 7.8 seconds in DDD pacing, 54.7 +/- 9.5 seconds in VVIR pacing, and 57.4 +/- 11.0 seconds in VVI pacing (P = 0.002). Ten (53%) patients developed symptoms during switch from DDD to VVIR mode whereas the switch from VVIR to DDD mode was not perceived by any patient (P < 0.001). In conclusion, our study shows an impact of AV synchronous pacing and heart rate adaptation on O2 kinetics during low intensity exercise that correspond to casual daily life activities. Our observations may have clinical implications for the management of patients with complete AV block.

Atrioventricular Node↗
PubMed2000

Influence of acute exposure to high altitude and hypoxemia on ventricular stimulation thresholds in pacemaker patients.

Cardiac stimulation threshold of implanted pacemakers may be influenced by a variety of endogenous and exogenous factors. High altitude provokes hypoxemia, which may change stimulation thresholds, besides causing other important physiological changes. The aim of our study was to investigate the influence of high altitude on ventricular stimulation thresholds in pacemaker patients. Thirteen patients (10 men; aged 65.5 +/- 4.8 years) with implanted single chamber pacemakers (nine with Pacesetter Regency SR+ with the Autocapture feature) were exposed to an altitude of 4,000 m above sea level, as simulated in a hypobaric chamber. Stepwise ascension was performed with a speed of 5 m/s starting at 450 m above sea level. A 5-minute rest was performed every 500 m to measure stimulation threshold at each step. After a stay of 30 minutes at 4,000 m stimulation threshold was measured, followed by a stepwise descent. Pacemaker interrogation and arterial blood gas analysis were performed at 450 and at 4,000 m, and a strength-duration curve was determined. Blood pressure, heart rate, and oxygen saturation were monitored continuously during the study. Ascent to 4,000 m above sea level induced a significant decrease in arterial pO2 (10.7 +/- 1.1 vs 5.5 +/- 0.3 kPa), pCO2 (5.3 +/- 0.3 vs 4.7 +/- 0.4 kPa), oxygen saturation measured by arterial blood gas analysis (95.5% +/- 1.2% vs 79.1% +/- 2.5%), and increase in pH (7.39 +/- 0.02 vs 7.45 +/- 0.04) (P < 0.0001). Stimulation thresholds and the strength-duration curve remained unchanged in all patients throughout the study. In conclusion, exposure to an altitude of 4,000 m above sea level with resultant hypobaric hypoxemia has no impact on ventricular stimulation thresholds. Therefore, in regard to the safety of pacing, pacemaker patients can safely be exposed to this altitude.

Acute Disease↗
PubMed2000

Morphology discriminator feature for enhanced ventricular tachycardia discrimination in implantable cardioverter defibrillators.

The morphology discriminator (MD) feature is an electrogram template matching algorithm that intends to improve tachycardia discrimination in implantable cardioverter defibrillators (ICDs). The aim of this study was to evaluate the performance of this feature during spontaneously occurring ventricular and supraventricular tachyarrhythmias and exercise induced sinus tachycardia. Twenty-three patients (20 men, 3 women; mean age 54.3 +/- 13.8 years) with pectorally implanted Ventritex Contour MD, Angstrom MD, and Profile MD ICDs were studied. The stability of the acquired morphology template and performance of the algorithm during spontaneous tachyarrhythmias were evaluated at follow-up. A treadmill exercise test was performed in 16 patients along with continuous telemetric monitoring of matching scores. A satisfactory template could be acquired at baseline in 22 (96%) patients. Variations in electrogram morphology necessitated new template acquisition in seven (30%) patients at first follow-up (6-8 weeks postimplant). During a mean follow-up of 9.1 +/- 3.7 months, 56 ventricular tachycardia (VT) and 15 supraventricular tachycardia episodes (sinus tachycardia in two-thirds) in 11 patients were all appropriately discriminated by the MD feature. Exercise testing showed appropriate discrimination of sinus tachycardia in 15 (94%) of 16 patients. A common observation was postshock changes in electrogram morphology that resulted in transient mismatch with the template. In conclusion, the recently introduced MD feature in ICDs has a high sensitivity for detection of VT and high specificity for rejection of sinus tachycardia. Postshock changes in electrogram morphology have been observed that may cause inappropriate redetection. Marked variations of electrogram morphology over time may be a concern in some patients, especially during lead maturation.

Adult↗
PubMed2000

Influence of posture, breathing pattern, and type of exercise on minute ventilation estimation by a pacemaker transthoracic impedance sensor.

Previous studies have shown a high correlation between transthoracic impedance minute ventilation (IMV) determined by a pacemaker sensor and actual minute ventilation (VE) measured by standard methods. We hypothesized that several factors (e.g., posture, breathing pattern, and exercise type) could potentially affect the calibration between IMV and VE. In patients with Medtronic Kappa 400 pacemakers, VE (L/min) was monitored using a standard cardiopulmonary metabolic gas analysis system with simultaneous recording of IMV (ohms/min) using DR-180 extended telemetry monitors. Effects of posture and of breathing pattern at rest (19 patients; age 60 +/- 13 years) were evaluated by monitoring each patient under three conditions: (a) slow breathing, supine, (b) slow breathing, sitting, and (c) shallow breathing, supine. Calibration at rest was defined as the ratio of IMV to VE. Effect of type of exercise on calibration compared treadmill versus graded bicycle ergometer exercise (18 patients; age 62 +/- 14 years). Calibration during exercise was defined as: (a) "Begin" (the IMV to VE ratio at VE = 10 L/min, the typical VE value at beginning of exercise), and (b) slope of the IMV/VE regression line. Calibration of IMV/VE was significantly smaller for sitting versus supine position (0.7130.177, P < 0.001) and for shallow versus slow breathing (0.7210.373, P < 0.001), and larger for treadmill versus bicycle exercise (Begin: 1.240.43, P = 0.018; Slope: 1.260.42, P = 0.013). In conclusion, posture, breathing pattern, and type of exercise affect the IMV estimation of the actual VE, possibly by altering the static or dynamic geometry (thus, the impedance) of the intrathoracic viscera.

Arrhythmias, Cardiac↗
PubMed2000

The impact of automatic threshold tracking on pulse generator longevity in patients with different chronic stimulation thresholds.

Automatic adjustment of the stimulation output of pacemakers to changing stimulation thresholds using the Autocapture feature increases patient safety and decreases energy consumption. This study examined the impact of Autocapture on pulse generator longevity in patients with different chronic stimulation thresholds. Eighty patients (mean age 79 +/- 9 years; 37 men, 43 women) with Pacesetter Regency SR+ pacemakers were included in the study. Data were collected before discharge of the patients from the hospital, 6-12 weeks postimplant, and then every 6-12 months. Pulse generator longevity was calculated theoretically, assuming 100% stimulation with a stable threshold, at a pacing rate of 65 +/- 6 beats/min and 1% backup pulses. Theoretical pulse generator longevity was calculated for low (< 1 V), intermediate (> or = 1 V and < 2 V), and high (> or = 2 V) stimulation thresholds. Pulse generator longevity was compared among three groups: (A) Autocapture programmed On, (B) Autocapture programmed Off, (C) theoretical calculations using thresholds of patients in group A with the stimulation voltage programmed at twice pacing threshold, or at a minimum of 2.4 V. The mean follow-up time since implantation was 19 +/- 8 months. The calculated longevity benefits for patients in group A were 36%, 59%, and 30% compared to group B, and 19%, 32%, and 49% compared to group C in patients with low, intermediate, and high chronic stimulation thresholds, respectively. Theoretical calculations based on chronic stimulation thresholds in our patient population with Regency SR+ pacemakers suggest that Autocapture may markedly prolong pulse generator longevity in patients with a broad range of long-term pacing thresholds.

Aged↗
PubMed2000

High prevelance of chronic magnesium deficiency in T cell lymphoblastic leukemia and chronic zinc deficiency in children with acute lymphoblastic leukemia and malignant lymphoma.

Magnesium and zinc are the elements having essential roles in regulation of cell growth, division and differentiation. There have been some studies in the literature suggesting an association between the deficiency of these elements and the development of malignant disorders. In this study hair and serum zinc and magnesium levels were investigated in children with acute lymphoblastic leukemia (ALL) and malignant lymphoma (ML) at the time of initial diagnosis. Ten children with T-cell ALL, 10 children with B-precursor ALL, 5 children with Burkitt's Lymphoma (BL), 11 children with Hodgkin's lymphoma (HL), 10 children with non-Burkitt non-Hodgkin's lymphoma (NBNHL) and 12 age and sex matched healthy children as a control group were included in the study. Mean hair magnesium levels in all of the groups of the patients were lower than the levels in the control group but the difference was statistically significant only in the children with T cell ALL comparable to the controls (28.9+/-3.9 microg/g and 87.6+/-18.5 microg/g respectiveley, p<0,05). Mean serum magnesium levels in all the cohorts were not significantly different than those in controls (p>0.05 in each comparison). Mean hair zinc levels in the patients with T-cell, B-precursor ALL, BL, HL, NBNHL were 103.4+/-14.6 microg/g, 100.9+/-7.8 microg/g, 91.1+/-19 microg/g, 72.5+/-9.1 microg/g, 103.2+/-12.2 microg/g respectively. Each of these levels were significantly lower than the mean hair zinc levels of the control group (141.2+/-9.6 microg/g, p<0.05 in each comparison). Although mean serum zinc levels in all of the groups were also decreased, the differences were statistically significant only in the groups with B-precursor ALL, HL and NBNHL (75.9+/-5.29 microg/dl, 68.6+/-7.3 microg/dl, 85.7+/-5.5 microg/dl respectively) when compared with controls (105.1+/-9.9 microg/dl, p<0.05 in each comparison). Hair magnesium and zinc levels showed a positive correlation with each other in all the groups (r congruent with 0.5). No significant difference was found in the mean hair/serum magnesium and zinc levels between malnourished and nonmalnourished patients. In conclusion, regarding the results of our study and previous data in the literature chronic magnesium and zinc deficiency seems to be associated with the development of ALL and malignant lymphoma in a group of patients.

Child↗
PubMed1999

[Heart failure and treatment of ventricular arrhythmias].

Chronic heart failure (CHF) is generally associated with a poor prognosis with an annual mortality rate ranging between 15-50% depending on the severity of cardiac dysfunction thus presenting a major health problem in our society. Drugs for the treatment of CHF include vasodilators (ACE-inhibitors, angiotensin II receptor blockers), diuretics, digoxin and beta-blockers. However, antiarrhythmic drugs are not currently recommended in the management of CHF with the exception of beta-blockers for which a favorable effect on the prognosis could be shown. Amiodarone is effective in the suppression of ventricular arrhythmias without a significant effect on total mortality. Implanted defibrillators are superior to antiarrhythmic drug therapy in prolonging survival among survivors of sudden cardiac death. They should be offered as firstline therapy in case of life-threatening ventricular tachy-arrhythmias.

Anti-Arrhythmia Agents↗
PubMed1999

Potential proarrhythmic effects of implantable cardioverter-defibrillators.

Implantable cardioverter-defibrillator (ICD) interventions have the potential to be proarrhythmogenic. New arrhythmias can occur in the setting of clinically appropriate therapies, as well as during a cardiac rhythm for which therapy is not intended. Cardioversion/defibrillation therapies, antitachycardia pacing, and antibradycardia pacing are potential triggers for the development of new arrhythmias. Newer ICDs allow better recognition and interpretation of the arrhythmias that are induced by delivered therapies. Two cases of ICD-induced proarrhythmias are described. Based on the course of these patients and review of previous reports, proarrhythmic effects of ICD interventions along with prevention and management strategies are discussed.

Adult↗
PubMed1999

The potential for inappropriate ventricular tachycardia confirmation using the Intracardiac Electrogram (EGM) Width Criterion.

The "Intracardiac Electrogram (EGM) Width Criterion," the first digital signal processing feature used in an implantable cardioverter defibrillator (ICD), is a detection enhancement algorithm that intends to improve ventricular tachycardia (VT) detection specificity by rejecting inappropriately detected supraventricular tachyarrhythmias. The algorithm may be activated after setting the optimal EGM source, slew, and width thresholds based on EGM width testing during sinus rhythm. This study evaluates the accuracy of the EGM width measurements during exercise testing. Twenty-one patients with Medtronic Micro Jewel II Model 7223 ICDs underwent treadmill exercise testing. EGM width testing was repeatedly performed during exercise and recovery to detect potential inappropriate measurements. In seven (33%) patients the EGM Width Criterion inappropriately confirmed VT detection. Eleven patients had inappropriately wide EGM width measurements, but did not satisfy the EGM Width Criterion. The causes of wide EGM width measurements were an actual increase in EGM width and/or inappropriate detection of the baseline irregularities as EGM onset or offset points. Based on our observations, we recommend to test the EGM Width Criterion during exercise testing for optimal ICD programming.

Adult↗
PubMed1999

Acute hemodynamic effects of alternate and combined site pacing in patients after cardiac surgery.

We hypothesized that pacing at sites other than the right ventricular (RV) apex or at two or more ventricular sites would activate the myocardium more rapidly and improve cardiac function in patients undergoing coronary revascularization or aortic valve replacement. Epicardial electrodes were placed on the right atrium (A), RV paraseptal area close to the RV apex (B), RV outflow tract (C), LV apex (D), in patients undergoing bypass surgery. At constant rate and AV delay, we measured CO during A pacing, DVI pacing at B, C, D, and various combinations of sites in random order in ten patients with EF > 50% and 27 patients with EF < or = 50%. When pacing at two sites, we made one electrode a cathode and one an anode and noted two distinct thresholds by careful observation of the 12-lead ECG. There were no significant differences in CO, systemic vascular resistance, systolic, or mean arterial pressure. Significant differences were noted in QRS duration, which increased progressively going from AAI to 3-site, 2-site, and single site pacing (P < 0.05 each comparison). Thus: (1) QRS duration correlated inversely with the number of ventricular sites paced; (2) despite this, CO did not improve irrespective of baseline EF; (3) multisite pacing produced multiple distinct thresholds which appeared to be related to the number of sites paced, and (4) unique ECG patterns confirmed multisite pacing.

Aortic Valve↗
PubMed1999

Postmortem analysis of encapsulation around long-term ventricular endocardial pacing leads.

OBJECTIVE: To analyze the site and thickness of encapsulation around ventricular endocardial pacing leads and the extent of tricuspid valve adhesion, from today's perspective, with implications for lead removal and sensor location. MATERIAL AND METHODS: Gross cardiac postmortem analysis was performed in 11 cases (8 female and 3 male patients; mean age, 78+/-7 years). None of the patients had died because of pacemaker malfunction. The mean implant time was 61+/-60 months (range, 4 to 184). RESULTS: The observations ranged from encapsulation only at the tip of the pacing lead to complete encapsulation along the entire length of the pacing lead within the right ventricle. Substantial areas of adhesion at the tricuspid valve apparatus were noted in 7 of the 11 cases (64%). The firmly attached leads could be removed only by dissection, and in some cases, removal was possible only by damaging the associated structures. No specific optimal site for sensor placement could be identified along the ventricular portion of the pacing leads; however, the fibrotic response was relatively less prominent in the atrial chamber. CONCLUSION: Extensive encapsulation is present in most long-term pacemaker leads, which may complicate lead removal. The site and thickness of encapsulation seem to be highly variable. Tricuspid valve adhesion, which is usually underestimated, may be severe. In contrast to earlier reports, our study demonstrates that the extent of fibrotic encapsulation may not be related to the duration since lead implantation. Moreover, we noted no ideal encapsulation-free site for sensors on the ventricular portion of long-term pacing leads.

Aged↗
PubMed1998

A comparison of the effect of high-dose methylprednisolone with conventional-dose prednisolone in acute lymphoblastic leukemia patients with randomization.

In this preliminary study the efficacy of high-dose methylprednisolone (HDMP) during remission-induction chemotherapy was evaluated on 166 children with acute lymphoblastic leukemia (ALL). The St. Jude Total Therapy Study XI protocol with minor modifications was used in this trial. Patients were randomized into two groups. Group A received conventional-dose (2 mg/kg/day orally) prednisolone, and group B received high-dose methylprednisolone (HDMP, Prednol-L, 900-600 mg/m2 orally) during remission-induction chemotherapy. Complete remission was achieved in 97% of the children. For the 80 patients who were followed up for 3 years, median follow-up was 44 (range 5-60) months and the 3-year event-free survival (EFS) rate was 68.5%) overall, 58.6% in group A and 78.4% in group B. The EFS among patients in group B was significantly higher than in group A (p=0.05). When we compared the 3-year EFS of groups A and B in the high-risk groups and high-risk subgroups with white blood cell (WBC) counts > or = 50 x 10(9)/l and age > or = 10 years, the survival rates were 45% versus 77.2%, 33% versus 78% and 45% versus 89%, respectively. During the follow-up of 162 patients, relapses were significantly higher in group A. Bone marrow relapses in 162 patients, and also in a subgroup of patients > or = 10 years of age were significantly higher in group A. These results suggest that HDMP during remission-induction chemotherapy improves long-term EFS, particularly for high-risk patients.

Adolescent↗
PubMed1998

Hospital pager systems may cause interference with pacemaker telemetry.

Electromagnetic interference (EMI) is a well-known cause of pacemaker dysfunction. The communication between pacemakers and programmers, enabled by telemetry, is also susceptible to EMI. We have observed that hospital pager systems have the potential to interfere with pacemaker telemetry. Measurements in our pacemaker clinic and in a technical laboratory have shown that inductive pager systems may disturb telemetry in the form of inaccurate battery voltage, current and impedance measurements, disturbances in intracardiac electrogram tracings, or total interruption of telemetric communications. The reason for EMI was an overlap of carrier frequencies of some pacemaker programmers (32-37 kHz) with those of our inductive pager system (36.11 kHz). Radiofrequency pager systems using higher frequencies (in MHZ range) are unlikely to cause such interference. Awareness of this interference potential may have practical implications in choosing the carrier frequencies of inductive hospital pager systems, as well as pacemaker programmers, and in planning the location of pacemaker clinics.

Electromagnetic Fields↗