Myopotontial interference (MPI) can inhibit or trigger single and dual chamber unipolar pacemakers while bipolar pacemakers are resistant. Twenty units of two different models of dual chamber pacemaker, each capable of being programmed to single chamber or dual chamber and unipolar or bipolar function were tested to provoke myopotential interference. No patient had evidence of myopotential interference at any sensitivity setting in the bipolar configuration either in atrium or in ventricle. All patients (20/20) interfered with pacemaker function at the highest atrial or ventricular sensitivity settings in the unipolar configuration. T wave sensing occurred at the 0.25 mV sensitivity setting in four patients in pacemaker model 925, in both bipolar and unipolar configurations. Tiventy‐five percent of patients had myopotential interference at the unipolar atrial sensing threshold and did not allow a setting which would reject myopotential interfercnce while providing satisfactory atrial sensing. Twenty percent (2/10) had myopotential caused ventricular inhibition at the least sensitive ventricular channel setting in model 240G so that myopotential interference could not be avoided in that unit no matter how large the electrogram.
Automatic discrimination between antegrade and retrograde atrial electrograms would prevent endless loop tachycardia and contribute to tachycardia detection algorithms. We tested its feasibility by comparing antegrade and retrograde atrial electrograms in 129 patients at the time of atrial lead implantation. Only unipolar, passive‐fixation, endocardial, right atrial appendage leads were included. The mean antegrade amplitude was 4.2 ± 2.2 mV, and retrograde 2.4 ± 1.5 mV (P < 0.001); the mean antegrade slew rate was 2.6 ± 2.1 mV/ms, and retrograde 1.3 ± 1.1 mV/ms (P < 0.001). Morphology was similar in 84 patients (65%). The antegrade amplitude exceeded the retrograde by 1.0 mV in 67%, and by 0.5 mV in 81% of patients. Morphology and slew rate contributed little to the discriminating power of amplitude alone. Thus, amplitude criteria reliably distinguish antegrade from retrograde atrial activity.
Relatively limited contemporary information is available about the magnitude of, and factors associated with, the metabolic syndrome in adult men and women. The purpose of our observational study was to describe the prevalence and predictors of the metabolic syndrome in a sample of employed adults attending a worksite cardiovascular screening program. The study sample consisted of 871 men and women between the ages of 21 and 77 years from 6 locations of the parent company. These individuals attended an employer-sponsored cardiovascular screening and wellness program during 2003. A standardized questionnaire was administered to all study participants and a number of different coronary risk factors were measured. Approximately 27% of the study sample was classified as having the metabolic syndrome. Men, persons with a history of hypertension, heart disease, or stroke, sedentary individuals, and those with an increased heart rate and higher levels of C-reactive protein were associated with presence of the metabolic syndrome. A relatively similar risk factor profile was noted in persons without a self-reported history of prior cardiovascular disease. The results of our cross-sectional observational study suggest that the prevalence of the metabolic syndrome is considerable. A number of demographic, comorbid, and other factors are associated with this syndrome. Increased attention to the metabolic syndrome, and modification of predisposing factors, remains of considerable public health and clinical importance.
DDD pacemakers sense and pace right-sided cardiac chambers. The relationship of atrial to ventricular systole on the left side of the heart is of importance for systemic hemodynamics. Effective atrioventricular synchrony is partially determined by interatrial conduction time (IACT). At the time of DDD pacemaker implantation, interatrial conduction was measured using an intraesophageal pill electrode in 25 patients who were on no cardiac medications. Mean interatrial conduction time for all patients prolonged from 95 +/- 18 ms during sinus rhythm to 122 +/- 30 ms during right atrial pacing (p less than 0.001). In 16 patients with P wave duration less than 110 ms interatrial conduction prolonged from 85 +/- 10 ms during sinus rhythm to 111 +/- 9 ms during right atrial pacing (p less than 0.01) compared to 114 +/- 20 ms prolonging to 111 +/- 19 ms (p less than 0.01) in 9 patients with P wave duration greater than 110 ms. In each patient, while atrioventricular conduction prolonged with incremental right atrial pacing, interatrial conduction times did not vary. Interatrial conduction prolongs from baseline during atrial pacing and remains constant at all paced rates from 60-160 beats per minute. In addition to longer interatrial conduction times during sinus rhythm, patients with electrocardiographic P wave prolongation have longer interatrial conduction times during right atrial pacing than do normals (p less than 0.001). Based on interatrial conduction times alone, the AV interval during DDD cardiac pacing should be approximately 25 ms longer during AV pacing as compared to atrial tracking.
<i>Background:</i> Relatively limited contemporary information is available about the distribution of, and factors associated with, levels of C-reactive protein (CRP) in adult men and women. The purpose of our descriptive study was to examine the prevalence and predictors of this marker of inflammation in a sample of employed adults attending a worksite cardiovascular screening program. <i>Methods:</i> The study sample consisted of 876 men and women between the ages of 21 and 77 years from 6 locations of the parent company. These individuals attended an employer-sponsored cardiovascular screening and wellness program during 2003. A standardized questionnaire was administered to all study participants, and a number of different coronary risk factors were measured. <i>Results:</i> Approximately 25% of the study sample was classified as having elevated CRP levels (≧3 mg/l). Women, obese individuals, subjects with increasing heart rate and higher levels of serum triglycerides were more likely to have elevated concentrations of CRP than the corresponding comparison groups. Subjects who reported regularly exercising, individuals with a history of heart disease and those with lower total cholesterol levels were less likely to have elevated CRP levels. A relatively similar risk factor profile was noted in individuals without a self-reported history of prior cardiovascular disease. <i>Conclusions:</i> The results of our cross-sectional observational study suggest that the prevalence of elevated CRP levels in the general adult population is considerable. A number of demographic, comorbid and other factors are associated with this inflammatory marker of increased risk of cardiovascular disease, which demands increased attention and modification of potential predisposing factors.
Pacemaker‐mediated endless loop tachicardia is usually caused by a P wave displaced from the physiologic position preceding a QRS complex to a time of atrial channel sensitivity after the QRS. Five cases are described of endless loop tachycardia starting after a normally‐timed P wave, either spontaneous and preceding a ventricular stimulus or a P wave produced by an atrial channel stimulus followed by a ventricular stimulus and QRS complex. In each instance, the atrial refractory interval (ARI) was shorter than the retrograde conduction time. In four of the cases, prolongation of the atrial refractory interval after the ventricular event ended the tachycardias. In the fifth, in which the pulse generator could not be so programmed, the ventricular inhibited mode was required.
Although atrial synchronous and rate-responsive ventricular pacing have been compared, the importance of maintaining synchronized atrial systole in addition to rate responsiveness has been incompletely defined. That is, the effects of these two pacing modes on cardiac volumes and contractility have not been studied. Accordingly, 16 patients with normal ventricular function were studied while in the upright position and at rest with gated radionuclide ventriculography during both atrial synchronous and ventricular pacing. Twelve of these patients were also studied during low-level upright exercise (300 kilopond-meters). Rest and exercise ventricular pacing heart rates were matched to those recorded with synchronous pacing. Ventricular volumes were determined with a counts-based method. The ejection fraction and peak systolic pressure/end-systolic volumes or contractility between the two pacing modes. However, during exercise to identical heart rates, blood pressures, and workloads, although stroke volume was the same during exercise with atrial synchronous and ventricular pacing (78 +/- 13 vs 75 +/- 12 ml), end-diastolic and end-systolic volumes were lower with ventricular pacing than with atrial synchronous pacing (end-diastolic volume 101 +/- 13 vs 113 +/- 16 ml, p less than .001; end-systolic volume 26 +/- 4 vs 35 +/- 7 ml, p less than .001). Stroke volume during ventricular paced exercise was maintained at atrial synchronous pacing levels by means of increased contractility (ejection fraction of 74 +/- 4% during ventricular pacing vs 69 +/- 5% during atrial synchronous pacing, p = .002; peak systolic pressure/end-systolic volume ratio of 6.51 +/- 1 during ventricular pacing vs 4.85 +/- 1 during atrial synchronous pacing, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)
