Biomedical subjects

R Candinas

Publications and source records attributed to R Candinas.

At least 55 records · Page 3Linked to original sources

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

Within-patient comparison of effects of different dosages of enalapril on functional capacity and neurohormone levels in patients with chronic heart failure.

BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors are established as first-line therapy in chronic heart failure (CHF). However, conflicting results exist regarding the dose-effect relation of ACE inhibitors. METHODS: We investigated 45 patients (age 55 +/- 10 years) with stable CHF who presented with a maintenance dosage of enalapril of either 5 mg given twice daily (E10; n = 16), 10 mg given twice daily (E20; n = 18), or 20 mg given twice daily (E40; n = 11). This dosage was changed 3 times to treat all patients with lower, higher, and the initial dosages for 4 weeks each. Neurohormones (atrial natriuretic peptide [ANP], brain natriuretic peptide [BNP], and norepinephrine) and enalaprilat trough levels were measured, and ergospirometry was performed. RESULTS: Changes in enalapril dose and enalaprilat level were concordant in 82% of patients, indicating good compliance. After augmentation of enalapril to 40 mg daily, patients in the E10 group showed an increase in maximal oxygen consumption and a decrease in neurohormonal stimulation, whereas the opposite changes were observed after reduction of enalapril to 10 mg daily in patients in the E20 and E40 groups (maximal oxygen consumption: Delta1.1 +/- 2.0 vs -1.0 +/- 1.9 mL. kg(-1). min(-1), P <.01; ANP: Delta-63 +/- 106 vs 19 +/- 54 pg/mL, P <.01; BNP: Delta-62 +/- 104 vs 18 +/- 89 pg/mL, P <.05; norepinephrine: Delta-1.3 +/- 2.9 vs 0.6 +/- 1.8, P <.05). Within-patient comparison showed that neurohormone levels were higher and exercise capacity lower while patients were receiving 10 mg of enalapril per day than when they were receiving 40 mg per day (ANP: 172 +/- 148 vs 139 +/- 122 pg/mL, P <.01; BNP: 193 +/- 244 vs 152 +/- 225 pg/mL, P <.005; norepinephrine: 4.2 +/- 2.2 vs 3.5 +/- 1. 6 nmol/L, P <.05; maximal oxygen consumption 22.0 +/- 4.4 vs 21.3 +/- 4.3 mL. kg(-1). min(-1) P <.05). Similar differences were observed when comparing these variables, and patients had lowest and highest enalaprilat trough levels. CONCLUSIONS: High doses of enalapril resulted in an improvement of exercise capacity and reduction of neurohumoral stimulation, whereas these parameters worsened after reduction of enalapril dose. Thus patients with congestive heart failure may benefit from increasing dosage of ACE inhibitors.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1999

Oxygen uptake to work rate relation throughout peak exercise in normal subjects: relevance for rate adaptive pacemaker programming.

The oxygen uptake to work rate (VO2/WR) relationship observed throughout peak exercise testing is already being applied for rate adaptive pacemaker programming. However, the detailed curve design of VO2/WR with respect to the anaerobic threshold (AT) has not yet been investigated. It was the purpose of this study to determine the VO2/WR slope below and above the AT in a healthy control group. Seventy-eight healthy control subjects (45.9 +/- 17.4 years; 34 women: 49.9 +/- 18.6 years 44 men: 43.6 +/- 16.6 years) were exercised on a treadmill with "breath-by-breath" gas exchange monitoring using the symptom limited "ramping incremental treadmill exercise" (RITE) protocol. The slope of the VO2/WR relationship from rest to peak exercise (r-p), rest to AT (slope A), and AT to peak exercise (slope B) in mL oxygen uptake per watt of external treadmill work was determined by linear regression analysis. [table: see text] The oxygen uptake to work rate relationship throughout peak exercise in the entire study group generated a significant slope change at the AT (31%, P < 0.0001) with a decreasing slope during higher work load intensities. Female subjects demonstrated a greater percentage of slope change at AT (43%), as compared to men (22%, P < 0.01). When using the oxygen uptake to work rate relationship for the programming of the pacemaker's rate response to exercise, the significant slope change at the AT should be considered to more appropriately pace during higher work intensities supported by anaerobic metabolism. Female pacemaker patients should be programmed to generate a steeper VO2/WR slope below AT with a greater slope change at AT, as compared to men. Abnormally high oxygen uptake to work rate ratios above the AT may be possibly used as an indicator of overpacing.

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

Oxygen uptake kinetics during low level exercise in patients with heart failure: relation to neurohormones, peak oxygen consumption, and clinical findings.

OBJECTIVE: To investigate whether oxygen uptake (VO2) kinetics during low intensity exercise are related to clinical signs, symptoms, and neurohumoral activation independently of peak oxygen consumption in chronic heart failure. DESIGN: Comparison of VO2 kinetics with peak VO2, neurohormones, and clinical signs of chronic heart failure. SETTING: Tertiary care centre. PATIENTS: 48 patients with mild to moderate chronic heart failure. INTERVENTIONS: Treadmill exercise testing with "breath by breath" gas exchange monitoring. Measurement of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and noradrenaline. Assessment of clinical findings by questionnaire. MAIN OUTCOME MEASURES: O2 kinetics were defined as O2 deficit (time [rest to steady state] x DeltaVO2 -sigmaVO2 [rest to steady state]; normalised to body weight) and mean response time of oxygen consumption (MRT; O2 deficit/DeltaVO2). RESULTS: VO2 kinetics were weakly to moderately correlated to the peak VO2 (O2 deficit, r = -0.37, p < 0.05; MRT, r = -0.49, p < 0.001). Natriuretic peptides were more closely correlated with MRT (ANF, r = 0.58; BNP, r = 0.53, p < 0.001) than with O2 deficit (ANF, r = 0.48, p = 0.001; BNP, r = 0.37, p < 0.01) or peak VO2 (ANF, r = -0.40; BNP, r = -0.31, p < 0.05). Noradrenaline was correlated with MRT (r = 0. 33, p < 0.05) and O2 deficit (r = 0.39, p < 0.01) but not with peak VO2 (r = -0.20, NS). Symptoms of chronic heart failure were correlated with all indices of oxygen consumption (MRT, r = 0.47, p < 0.01; O2 deficit, r = 0.39, p < 0.01; peak VO2, r = -0.48, p < 0. 01). Multivariate analysis showed that the correlation of VO2 kinetics with neurohormones and symptoms of chronic heart failure was independent of peak VO2 and other variables. CONCLUSIONS: Oxygen kinetics during low intensity exercise may provide additional information over peak VO2 in patients with chronic heart failure, given the better correlation with neurohormones which represent an index of homeostasis of the cardiovascular system.

Adult↗

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

Myocardial amiodarone concentrations after short- and long-term treatment in patients with end-stage heart failure.

BACKGROUND: Pharmacokinetics and tissue concentrations of amiodarone may vary considerably in end-stage heart failure, but may be crucial for treatment efficiency and antiarrhythmic drug therapy. OBJECTIVE: This study was undertaken to determine plasma amiodarone and desethylamiodarone concentrations and to determine whether they correlate with myocardial concentrations in explanted hearts from patients with end-stage heart failure. PATIENTS AND METHODS: Eight patients with idiopathic dilated cardiomyopathy and normal coronary arteries were included in the present study. Myocardial tissue samples (seven sites) and epicardial fat were taken from each explanted heart, and drug concentrations of amiodarone and desethylamiodarone were determined. In addition, plasma drug levels were measured and compared with the myocardial amiodarone/desethylamiodarone concentrations. RESULTS: The mean cumulative amiodarone dose was 91 g and the mean plasma concentrations of amiodarone and desethylamiodarone were 0.68 and 0.84 microg.ml(-1), respectively. The tissue concentrations of amiodarone amounted to 13.2 and 28.3 microg.g(-1), respectively, in the atria and to 13.0 and 40.8 microg.g(-1), respectively, in the ventricles. The distribution of the drug and its metabolite were similar in the right and left ventricles. There was a good correlation between myocardial concentration of amiodarone and desethylamiodarone and the cumulative ingested dose of amiodarone. Tissue drug concentrations correlated only poorly with plasma amiodarone or desethylamiodarone levels. The highest drug levels were measured in the epicardial fat tissue, where the ratio of amiodarone 105 microg.g(-1) to desethylamiodarone 32 microg.g(-1) was reversed (3.3 compared with 0.29 in the ventricles). Thus, amiodarone concentrations in epicardial fat were approximately 10 times higher than myocardial and 150 times higher than plasma levels. CONCLUSIONS: Our data confirm the slow equilibrium of amiodarone and desethylamiodarone concentrations between plasma and myocardium. Myocardial tissue concentrations of desethylamiodarone and, to a lesser degree, amiodarone correlate with the cumulative ingested dose of amiodarone. Monitoring of the total cumulative dose may be more relevant clinically than monitoring plasma levels. These results support the clinical practice of reducing the maintenance dose of amiodarone in patients who are on long-term treatment.

Amiodarone↗

PubMed1998

Systolic and diastolic function with alternate and combined site pacing in the right ventricle.

UNLABELLED: We hypothesized that pacing at two ventricular sites simultaneously would activate the myocardium more rapidly and improve ventricular function. We studied the effect of pacing at the right ventricular outflow tract (RVOT) and the RV apex (RVA) on systolic and diastolic function. In 14 patients with a reduced systolic ejection fraction < 40% (mean EF 32% +/- 4%) we measured RV pressures, left ventricular pressures, EF, cardiac output, peak dP/dt, peak negative dP/dt, and the time constant of relaxation, Tau, during intrinsic rhythm, atrial pacing and DVI pacing at the RVA, the RVOT, and both RV sites combined in random order. Repeated measures analysis of variance showed no significant differences in any of these parameters. The highest absolute values of dP/dt were observed during sinus rhythm and the lowest with RVA pacing. This parameter tended to improve progressively with pacing in the RVOT and at both sites. Peak negative dP/dt showed a similar nonsignificant trend. CONCLUSION: These data suggest that in patients with poor LV function, there may be subtle improvements in diastolic and systolic function with pacing in the RVOT and at combined sites in the RV compared to traditional RVA pacing.

Analysis of Variance↗

PubMed1998

Activity-controlled circadian base rate.

The current pacing rates are clustered around a fixed base rate since pacemaker patients are usually sedentary, resting, or sleeping most of the time. This fixed base rate is either too low for daytime hemodynamic support or too high for nighttime rest and recovery. Multiple Holter studies involving normal individuals have suggested that the resting base rate fluctuates during the course of the day. The circadian base rate (CBR) algorithm was designed to provide patients with a circadian change in paced resting rate and a normal rate distribution. The CBR algorithm, using a sophisticated accelerometer sensor, was developed and tested using the downloaded activity data from patients implanted with Trilogy DR+ pacemakers. Twenty-five patients (19 men, 6 women, age 72 +/- 9 years) were studied. Trilogy DR+ is able to record the detailed sensor and system behavior data for a week. During outpatient visits, the pacemaker was interrogated and the data accumulated in the pacemaker memory were downloaded. The CBR algorithm was applied to the activity variance histogram to calculate the base rate and to construct its histogram. The base rates in the CBR histogram are generally below 100 ppm with a distribution that mimics the natural sinus rate distribution of normal subjects. The CBR algorithm provides the highest daytime rates for hemodynamic support and the lowest nighttime rates for cardiac recovery, with a smoothly changing base rate modeling the normal circadian variation in heart rate.

Aged↗

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↗

PubMed1997

Temporary loss of cardiac autonomic innervation after the maze procedure.

OBJECTIVE: Blunted sinus node response to exercise has been reported after the maze operation. We suggested the autonomic vegetative function of the heart to be disturbed after the maze procedure. METHODS: 17 patients, mean age 63 +/- 15 years, with chronic atrial fibrillation for 49 +/- 46 months (range 5-65) underwent the maze procedure during mitral valve surgery. Bicycle stress test, 24-h electrocardiography and heart rate variability were analysed in 11 patients after three and in six after 14 +/- 3 months. Spectral analysis within two frequency bands, vector analysis of the main circular resultant and influence of orthostasis and Valsalva manoeuvre on different R-R intervals were calculated. RESULTS: One patient died from a perioperative ischaemic stroke. At follow-up, all patients were in sinus rhythm. Heart rate reached 84 +/- 14%, the mean circular resultant was 60 +/- 48%, the ratio of the longest to the shortest R-R interval during the Valsalva manoeuvre was 92 +/- 8% and the ratio of maximal to minimal R-R interval after orthostasis was 98 +/- 4% of the age-adjusted normal value. Maximal workload was 116 +/- 31 watts. All patients had abnormal heart rate variability. Heart rate variability was significantly more blunted after three months, than after 14 months (P < 0.05). The minimal heart rate and the difference between the maximal and the minimal heart rate during the 24-h electrocardiography were significantly correlated to the number of normal physiological tests (r = -0.52; P < 0.05; r = 0.71; P < 0.005); for the maximal heart rate, there was a positive trend only (r = 0.44; P = 0.07). CONCLUSIONS: Early after the maze procedure, a nearly total denervation of the sinus node is present, similar as seen after heart transplantation, with partial restoration of the autonomic function after one year. The exercise capacity of the patients was satisfactory.

Adult↗

PubMed1997

High thresholds may alter end-of-life behavior in a dual chamber pacemaker.

We noted a series of 12 consecutive patients with a DDD Genisis pacemaker that showed an unexpected and a relatively rapid fall in battery voltage and output as these devices approached end-of-life (EOL). Twenty-one of 24 leads were Vitatron Helifix leads and there was a relatively high mean threshold (atrial 2.5 +/- 0.94 V; ventricular 2.9 +/- 0.65 V). These devices were replaced after 65 +/- 12 months. During the 9.3 +/- 3.5 months before replacement, a striking fall in voltage from 2.7 +/- 0.04 V to 2.49 +/- 0.05 V was seen. Battery impedance rose from 3 +/- 1.2 K omega to 10.2 +/- 4.3 K omega during this same period. We unexpectedly observed a marked difference between programmed and telemetered output for both atrial (50%) and ventricular leads (30%). A discrepancy between measured and telemetered magnet rate was also seen. Despite this relatively rapid fall in battery voltage, several of these devices did not meet the manufacturer's recommended replacement time (RRT) criteria by magnet rate or according to the projected RRT determined by the relationship of battery impedance to current drain. These data have implications for the selection of RRT and EOL criteria for this device. Magnet rate measured by surface ECG was the safest indicator for RRT. Follow-up for this pulse generator should be increased to every 2 months when battery impedance is > 2 KOhms or if there is a difference between programmed and measured output amplitude of more than 15%. The data also highlight the effect of combining high threshold leads with modern pacemakers with relatively "small" batteries as well as certain problems with telemetered data.

Cardiac Pacing, Artificial↗

PubMed1997

Vibration, acceleration, gravitation, and movement: activity controlled rate adaptive pacing during treadmill exercise testing and daily life activities.

Activity-based sensors for rate adaptive pacing have been available for several years and now include several different types: vibration; acceleration; gravitation; and movement. However, a systematic comparison evaluating the relative advantages and disadvantages of these various sensors has received little study. The purpose of the present study was to compare these sensor subtypes using treadmill testing and an outdoor test circuit, which simulated daily life activities and included both uphill and downhill walking. Pacemakers were strapped on the chest of healthy volunteers and connected to one channel of an ambulatory recording device, which also recorded the subject's intrinsic heart rate. The pacemakers were programmed using an initial treadmill test to standardize the rate responsive parameters for each device. Nine different pacemaker models were studied including 3 vibration-based (Elite, Synchrony, Metros), 4 acceleration-based (Relay, Excel, Ergos, Trilogy), 1 gravitational-based (Swing), and 1 movement-based (Sensorithm) device. All devices demonstrated a prompt rate response with casual walking on flat ground. The vibration-, gravitational-, and movement-based pacemakers showed a pronounced rate decline during more strenuous work, e.g., walking uphill. This phenomenon was absent in the accelerometer-based units. In particular, the vibration- and movement-based units showed a higher rate with walking downhill compared to uphill. An optimally tuned rate behavior on the treadmill usually did not provide an optimal rate behavior during daily activities and there was a tendency to overstimulation during low workload. The development of the two newest sensors (gravitational and movement) did not result in an improved performance of rate response behavior. Overall, the accelerometer-based pacemakers simulated or paralleled sinus rate behavior the most closely.

Acceleration↗

PubMed1997

Age and sex related changes in heart rate to ventilation coupling: implications for rate adaptive pacemaker algorithms.

Minute ventilation (VE) controlled rate adaptive pacemakers determine the paced rate increase during exercise by measuring changes in transthoracic impedance that have been shown to correlate well with VE. To determine the normal coupling of heart rate (HR) to VE this relationship was evaluated in 30 younger and 25 older, healthy subjects using peak cardiopulmonary exercise testing. After determining the anaerobic threshold (AT), the linear HR to VE slope was determined both below and above the AT. In addition, the entire curve of the HR to VE relationship was assessed by a "best fit" regression analysis method. The relationship of HR to VE was more often logarithmic in younger as compared to older subjects. The HR to VE slope below the AT was always steeper than above the AT in younger subjects. Females of both age subgroups demonstrated a significantly greater slope below and above the AT. For the appropriate programming of VE controlled, rate responsive pacemakers, one should take into consideration age- and sex-specific differences in the HR to VE relationship throughout exercise. Therefore, age- and sex-specific programmable features for rate responsive parameters should be incorporated into pacemakers using VE controlled rate adaptive algorithms.

Adult↗

PubMed1997

Acute hemodynamic effects of atrioventricular pacing at differing sites in the right ventricle individually and simultaneously.

We hypothesized that pacing, which provided a rapid uniform contraction of the ventricles with a narrower QRS, would produce a better stroke volume and cardiac output (CO). We sought to study whether pacing simultaneously at two sites in the right ventricle (right ventricular apex and outflow tract) would provide a narrower QRS and improved CO in 11 patients undergoing elective electrophysiology studies. Patients were studied by transthoracic echocardiography measurement of CO using the Doppler flow velocity method in normal sinus rhythm, AOO pacing (rate 80), DOO pacing in the right ventricular apex (AV delay 100 ms), DOO pacing in the right ventricular outflow tract, and DOO pacing at both right ventricular sites simultaneously in random order. The COs were 5.42 +/- 1.83, 5.61 +/- 1.97, 5.67 +/- 1.6, 5.84 +/- 1.68, and 5.86 +/- 1.52 L/min, respectively (no significant difference by repeated measures analysis of variance [ANOVA]). The QRS durations were 0.09 +/- 0.02, 0.09 +/- 0.02, 0.13 +/- 0.027, 0.13 +/- 0.03, and 0.11 +/- 0.03 secs respectively. Repeated measures ANOVA showed that the QRS duration significantly increased with right ventricular apex or right ventricular outflow tract pacing compared to sinus rhythm and AOO pacing (P < 0.001) but then diminished with pacing at both sites (P < 0.01). QRS duration was not correlated with CO, however the change in QRS duration correlated significantly with the change in CO when pacing was performed at the two right ventricular sites simultaneously. In conclusion, during DOO pacing, there was a trend for pacing in the right ventricular outflow tract or both sites to improve the CO compared to the right ventricular apex. With simultaneous pacing at both ventricular sites, the QRS narrowed. Further studies will be required to see if this approach has value in patients with poor left ventricular function or congestive heart failure.

Adult↗

PubMed1997

Oxygen uptake kinetics during low intensity exercise: relevance for rate adaptive pacemaker programming.

OBJECTIVE: To establish a normal database for oxygen uptake (VO2) kinetics during low intensity treadmill exercise (LITE) testing, to be used as a guideline for programming rate adaptive pacemakers, and to determine its relation to VO2 at anaerobic threshold and peak exercise. DESIGN: VO2 kinetics during LITE were compared with VO2 at anaerobic threshold and at peak exercise. SETTING: LITE testing is applicable during ambulatory or hospital care and can even be performed by patients with reduced cardiac capacity. PATIENTS: 60 healthy subjects (23 women, 51.6 (SD 20.4) years; 37 men, 42.2 (16.2) years). INTERVENTIONS: Treadmill exercise testing with "breath by breath" gas exchange monitoring using the LITE protocol for steady state, submaximal exercise, and the ramping incremental treadmill exercise (RITE) protocol for peak exercise. MAIN OUTCOME MEASURES: Mean response time of VO2, mean oxygen deficit, and VO2 at anaerobic threshold (VO2-AT) and at peak exercise (VO2-peak) were determined. RESULTS: (1) LITE protocol: mean response time of VO2 = 35.1 (9.9) s; oxygen deficit = 418.3 (47.9) ml; oxygen deficit/VO2 time index = 54.7 (7.4). (2) RITE protocol: VO2-AT = 22.1 (5.7) ml/kg/min; heart rate at anaerobic threshold = 120.1 (3.6) beats/min; VO2-peak = 37.6 (10.7) ml/kg/min; peak heart rate = 167.8 (19.3) beats/min. The mean response time and oxygen deficit/VO2 time index were significantly correlated to VO2-peak and VO2-AT (P < 0.01). CONCLUSIONS: VO2 kinetics calculated in healthy controls may serve as a control database for assessing the rate response programming of pacemakers and its influence on VO2 during LITE. Because aerobic capacity below the anaerobic threshold is more likely to represent activity in daily life and the kinetics of VO2 are significantly related to VO2 at anaerobic threshold and peak exercise, LITE may provide a clinically useful correlate to peak exercise testing.

Adult↗

PubMed1997

[Bradycardia-induced syncope].

Bradyarrhythmias are the cause of syncope in 3 to 10% of cases. Marked bradycardia or asystole can be due to impaired function of the sinus node (sick sinus syndrome), high degree AV block or neurocardiogenic disorders (carotid sinus syndrome, vasovagal syncope). A precise history, ECG and 24-h. Holter recordings are the most helpful tools in diagnosis of bradyarrhythmia-induced syncope. An association between symptoms and documented ECG is essential for proper diagnosis. Sometimes an event-recorder may be helpful for this purpose. If a patient has normal physical examination, ECG, Holter, stress test, tilt-table test and echocardiography, no further electrophysiological investigation is needed. If the noninvasive tests show pathologic results that do not clearly explain the cause of syncope (sinus bradycardia, first-degree AV block, fascicular block, structural heart disease), then electrophysiological studies are recommended, which will also rule out ventricular tachyarrythmias in the differential diagnosis. If all diagnostic tests in a patient with syncope are normal, the prognosis is fairly good despite 30% recurrence rate. Treatment for symptomatic bradyarrhythmias is implantation of a pacemaker. The selection of an appropriate pacemaker system is very important. Dual-chamber systems (DDD) provide physiological stimulation by maintaining AV synchrony; thus, they should be preferred whenever possible.

Bradycardia↗