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Biomedical subjects

O J Ohm

Publications and source records attributed to O J Ohm.

At least 55 records · Page 3Linked to original sources
PubMed1987

Assessment of the work capacity and relationship between rate response and exercise tolerance associated with activity-sensing rate-responsive ventricular pacing.

The relationship between rate response and exercise tolerance was studied by measuring the symptom-limited maximum treadmill time (MTT)both during fixed rate VVI pacing and during VVI + activity mode pacing (RRP) in 15 patients (mean age, 73 years) who had received rate-responsive ventricular pacemakers. Their indications were atrioventricular block, sino-atrial block, and atrial fibrillation with slow ventricular response. Basic rate was programmed to 60 ppm in both pacing modes; rate response and activity threshold were programmed to 5 and medium, respectively. The order in which the two pacing modes were tested was randomly determined. The MTT was, on average, 29% longer in RRP than in VVI mode with a mean of 12 minutes in VVI and 14.8 minutes in RRP (p less than 0.001). For the subgroup of eight patients with paced-only rhythm the average increase in MTT was 38% with a mean of 9.5 minutes in VVI and 12.8 minutes in RRP (p less than 0.01). Seven patients who showed episodes of spontaneous rhythm, increased their average MTT by 17% (mean in VVI, 14.9 minutes; in RRP, 17.1 minutes; p less than 0.02). During RRP, a significant positive correlation existed between MTT and the increase in heart rate (N = 15; r = 0.83; p less than 0.001). In 12 patients with paced-only rhythm, the pacing rate remained at the programmed basic rate when the patients were lying, sitting, and standing and increased to 86 +/- 4 ppm during casual walking, and to 101 +/- 4 ppm during jumping up and down with the pacemaker programmed to the above-mentioned parameters. The maximum pacing rate during jumping corresponded with the maximum pacing rates measured from Holter recordings during normal daily activities.

Aged↗
PubMed1987

Noninvasive assessment by Doppler and M-mode echocardiography of hemodynamic responses to temporary pacing and to ventriculoatrial conduction.

A new, dual-chamber temporary pacing lead was introduced via the subclavian vein in 20 patients who needed a temporary pacemaker. Stroke volume (SV) was measured continuously by combining M-mode and noninvasive Doppler echocardiography during spontaneous rhythm (SR), AV sequential pacing at a positive AV interval (DP), ventricular pacing (VP) and AV sequential pacing at a negative AV interval (VA pacing). The valvular functions were determined by Doppler echocardiography. Left ventricular dimensions and function, and left atrial size were measured by M-mode echocardiography. In the nine patients with no valvular heart disease and with no ventriculoatrial (VA) conduction (group I) the CO increased 83 +/- 11% during DP and 42 +/- 9% during VP as compared to during SR when the heart rate (HR) was increased from 34 +/- 3 to 72 +/- 1 beats/min. The CO was 29 +/- 3% higher during DP than that during VP. In the seven patients with valvular heart disease and with no VA conduction (group II), the increment in CO compared to that during SR was 53 +/- 12% during DP and 31 +/- 11% during VP; the CO was 17 +/- 4% higher during DP than that during VP. In the four patients with spontaneous VA conduction (group III), the CO during DP was 35 +/- 10% greater than that during VP, which did not result in an increase in the CO compared to that during SR in spite of an increase in HR from 52 +/- 8 to 74 +/- 2 beats/min. The study demonstrated that DP is the preferred temporary pacing mode and also that VA conduction during VP resulted in a mean decrease of 20% in CO compared to that during VP without VA conduction. The hemodynamic benefit from DP compared to SR seems to decrease when the left ventricular end-diastolic dimension increases. Furthermore, patients with large left ventricular end-systolic dimensions seem to have a lower increase in stroke index during DP as compared to that during VP than patients with smaller end-systolic dimensions.

Aged↗
PubMed1987

Ventricular tachyarrhythmia initiation in a canine model of recent myocardial infarction. Comparison of unipolar cathodal, anodal and bipolar stimulation.

Ventricular tachyarrhythmia initiation was compared using unipolar cathodal, anodal and bipolar programmed stimulation at 21 sites in 5 normal adult mongrel dogs and 67 noninfarct sites in 16 dogs 3-5 days after experimental myocardial infarction. For this purpose, the minimum number of extrastimuli required for tachyarrhythmia initiation was determined in each pacing mode using twice cathodal threshold current for the drive beats and all extrastimuli except the last. The current and pacing mode were varied for the last extrastimulus (S2, S3 or S4). In the 5 normal dogs, ventricular fibrillation was reproducibly inducible from only 1/21 sites, and only in the cathodal mode. In 15/16 (94%) of the myocardial infarction dogs, a sustained ventricular tachycardia or ventricular fibrillation could be reproducibly initiated with either one (4 dogs), two (5 dogs) or three extrastimuli (6 dogs). Diastolic excitability thresholds were 0.08 +/- 0.03, 0.30 +/- 0.17, and 0.09 +/- 0.04 mA (median +/- SD) for unipolar cathodal, anodal and bipolar pacing, respectively (p less than 0.001 for anodal vs. cathodal and bipolar). The median absolute current required for ventricular tachyarrhythmia initiation was also highest with anodal pacing (0.72 +/- 0.77 mA), versus both the cathodal and anodal modes (0.18 +/- 0.28 and 0.20 +/- 0.28 mA, respectively, each p less than 0.001) but was comparable in all three modes relative to the threshold current (2.0, 2.4 and 2.6 mA for cathodal, anodal and bipolar pacing, respectively) required for initiation. Overall, ventricular tachyarrhythmia initiation was concordant in all three modes at 58/67 (87%) sites and discordant at only 9/67 (13%) sites (p less than 0.001). Moreover, there was no difference in either the pattern of arrhythmia initiated in each of the pacing modes with respect to ventricular tachycardia versus ventricular fibrillation, or in the median current required to initiate ventricular tachycardia (0.30 +/- 0.36 mA) versus ventricular fibrillation (0.31 +/- 0.44 mA; p greater than 0.1). Thus, ventricular tachyarrhythmia initiation was comparable in all three pacing modes with respect to overall success rate, number of ventricular extrastimuli required and the pattern of ventricular tachyarrhythmia initiated. Bipolar pacing with similar size anodal and cathodal electrodes appear to be appropriate for electrophysiologic ventricular tachyarrhythmia studies and are not likely to induce spurious arrhythmias resulting from stimulation at the anodal pole.

Animals↗
PubMed1986

Hypertrophic cardiomyopathy in three generations of a large Norwegian family. A clinical, echocardiographic, and genetic study.

Hypertrophic cardiomyopathy is a heart muscle disease with an obscure aetiology. Data from four generations of a large family (71 members) are presented. The occurrence of hypertrophic cardiomyopathy among members of the two oldest generations was compatible with a pattern of autosomal dominant inheritance. Seven out of 14 siblings in the second generation had definite signs of or were clinically suspected of having hypertrophic cardiomyopathy. The severity and distribution of left ventricular hypertrophy varied, but three (21%) brothers in generation II showed the classic picture of left ventricular outflow obstruction. Four siblings (29%) died suddenly aged 11, 22, 38, and 40 years. A high incidence of the disease would have been expected in the two younger generations (41 members, aged 1-31 years), but only two, a 16 year old boy and a 17 year old girl had signs of asymmetric septal hypertrophy. Current diagnostic procedures, including M mode and cross sectional echocardiography, are not sufficiently sensitive to identify young family members who may have preclinical hypertrophic cardiomyopathy. No evidence for close genetic linkage between a postulated locus for hypertrophic cardiomyopathy and the major histocompatibility complex (antigens HLA-A, HLA-B, and HLA-DR) was found.

Adolescent↗
PubMed1986

Splanchnic extraction of oestrone and oestradiol and production of oestrone sulphate in man.

The plasma concentrations of oestrone (Oe1), oestradiol (Oe2) and oestrone sulphate (Oe1S) were measured in the femoral artery (FA), femoral vein (FV) and hepatic vein (HV) in seven men and three postmenopausal women undergoing catheterization for the evaluation of cardiac arrhythmias. None of the persons had congestive heart failure; conventional liver function tests were normal, and they were without any medication. The plasma concentration (mean +/- SD) for Oe1 was 34.6 +/- 19.5 pM in HV, 134 +/- 71.6 pM in FV and 93.4 +/- 48.5 pM in FA. The plasma concentration of Oe2 was 29.9 +/- 19.7 pM in HV, 80.3 +/- 42.7 pM in FV and 55.2 +/- 28.1 pM in FA. The results support the concept of peripheral formation of Oe1 and Oe2 and hepatic removal. The plasma concentration of Oe1S was 980 +/- 469 pM in HV, 945 +/- 463 pM in FV and 937 +/- 461 pM in FA. The small difference in plasma level of Oe1S between FA and FV was insignificant. In all persons the plasma level of Oe1S was higher in HV than in FA and FV (2P less than 0.01) indicating a net formation of Oe1S in the splanchnic area.

Adult↗
PubMed1985

Importance of the pacing mode in the initiation of ventricular tachyarrhythmia in a canine model of chronic myocardial infarction.

The use of unipolar anodal or bipolar pacing, as compared with unipolar cathodal pacing, purportedly increases the likelihood of inducing inadvertent ventricular fibrillation in susceptible patients. In this study, the ability to initiate sustained ventricular tachycardia or fibrillation with unipolar cathodal, unipolar anodal and bipolar pacing modes was compared using programmed ventricular stimulation at 82 subendocardial periinfarction sites in 11 dogs with chronic myocardial infarction. The late diastolic excitability threshold was significantly higher and the ventricular refractory period was significantly shorter (p less than 0.001) with anodal pacing (mean 0.62 mA, 156 ms, respectively) than with pacing in either the cathodal (0.12 mA, 174 ms) or the bipolar (0.13 mA, 173 ms) mode. At a current intensity twice that of the excitability threshold, the introduction of one or two extrastimuli induced ventricular tachycardia and ventricular fibrillation comparably among the three pacing modes. However, when three extrastimuli were used, ventricular fibrillation was induced with anodal pacing twice as frequently (50 [61%] of 82 sites) as with either of the other two pacing modes (each 23 [28%] of 82 sites, p less than 0.001), whereas the induction of ventricular tachycardia remained comparable with anodal pacing (15 [18%] of 82 sites) and cathodal and bipolar pacing (each 14 [17%] of 82 sites). Furthermore, a similarly high incidence of inducibility of ventricular fibrillation was observed with both cathodal pacing (56 [68%] of 82 sites) and bipolar pacing (40 [49%] of 82 sites) when an increased current equal to twice the anodal excitability threshold (1.23 mA) was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

A time-related study of the hemodynamic benefit of atrioventricular synchronous pacing evaluated by Doppler echocardiography.

We have used Doppler echocardiography to estimate the stroke volume (SV) in a study of 13 patients equipped with DDD pacemakers. SV was measured both during DDD and VVI pacing after observation times of 1,3,6, and 12 months of DDD pacing. SV was also measured at seven atrioventricular (AV) intervals (75-250 ms) in the search for optimal AV intervals. Mitral flow velocity was investigated to see if DDD pacing resulted in synchronous atrial contraction, and if mitral insufficiency existed at any of the pacing modes. Compared with the VVI mode, DDD pacing resulted in a mean increase in SV of 21 +/- 2% for the four observation periods. Two patients with severe left ventricular failure had no significant increase in SV during DDD vs VVI pacing. In each patient, an optimal AV interval ranging between 100-250 ms for the SV was found. Velocity profiles of mitral flow showed synchronous atrial contraction during DDD pacing, but not during VVI pacing. Mitral insufficiency was not seen in any pacing mode. DDD pacing resulted in a reduction in SV during the first 6 months, and was constant thereafter. Doppler echocardiography can be used repeatedly to evaluate the hemodynamic response of DDD pacing vs VVI pacing, and to find which AV interval gives the highest SV in the individual patient. Our study further shows that the hemodynamic benefit of DDD pacing is present after short-term as well as after long-term DDD pacing.

Adult↗
PubMed1984

Permanent pacemaker treatment in older age groups.

Of 693 patients on permanent pacemaker treatment between 1962 and 1981, 282 (40.7%) were above the age of 75. Of this number, 142 patients were 75-79 years, 95 80-84 years and 45 85-93 (mean 87) years old at the time of the first pacemaker implantation. The patients were followed for 13-154 months (mean 37.1) with special attention being paid to morbidity and mortality after the implantation. Complications occurred in 65 (23%) of the elderly patients, with no significant difference between the three age groups. Excessive threshold rise with stimulation failure (6%) and infections or skin erosions (4.9%) were the most frequent complications. Mortality increased in all age groups during the first 6-12 months compared with the age- and sex-matched Norwegian population. Five-year survival rates were 56, 32 and 25% respectively. We conclude that cardiac pacemaker treatment in the elderly is a safe symptom-relieving therapeutic procedure and that the prognosis for these patients is similar to that for their fellow senior citizens after the first year of treatment.

Aged↗
PubMed1984

Heart disease in myasthenia gravis.

Patients with myasthenia gravis (MG) may develop heart disease. Our data on 108 MG patients were examined to assess the type and frequency of this. 17 of 108 patients (16%) showed signs of heart disease which could be regarded as MG-related. 11 of these, of whom 5 died suddenly, had clinical symptoms, mainly arrhythmias. Signs of heart disease were most frequent in thymoma patients (5 of 10), and all 3 microscopically examined hearts from these patients showed a focal myocarditis. 44 spinal muscular atrophy patients serving as controls showed a 16% frequency of signs of heart disease of unknown etiology. However, only 1 of 44 spinal muscular atrophy patients (2%) had clinical symptoms as compared to 11 of 108 MG patients (10%). Together with the characteristic focal nature of the myocarditis and the microscopic similarities between lesions of heart and skeletal muscle, this indicates that the heart disease is specifically related to MG.

Adolescent↗
PubMed1983

Long-term comparison of unipolar and bipolar pacing and sensing, using a new multiprogrammable pacemaker system.

Over a six-month period a comparison was made between uni- and bipolar myocardial stimulation thresholds and R-wave sensitivity in 15 consecutive pacemaker patients. The patients received a new multiprogrammable Cordis 336 A pulse generator, that could be programmed with either uni- or bipolar circuitry. In addition, rate, output, sensitivity and pacing mode could be noninvasively programmed. The occurrence of myopotential interference at different sensitivity levels was also studied. Cordis 325-161 bipolar endocardial leads were used in all patients. In one patient, the current output sometimes had to be programmed higher bipolarly than unipolarly to capture the ventricles, otherwise no differences in threshold were found. Acutely. R-wave sensitivity was superior in 9 patients (60%) in the bipolar mode. Unipolar and bipolar electrograms were equal in 4 (26.7%), whereas unipolar R-wave sensitivity was best in only 2 (13.3%) of the patients. At a six-month follow-up, the same tendency was found. In 5 patients, bipolar sensing was superior to unipolar, while anti- and bipolar sensitivity was equal in the remaining patients. Myopotential inhibition was never seen in the bipolar mode at highest sensitivity (0.8 mV) even during provocative tests (n = 15) or 24-hour Holter monitoring (n = 12). In the unipolar mode, 14/15 patients (93.3%) showed inhibition during provocative tests and 12/12 patients (100%) during monitoring at a programmed sensitivity of 0.8 mV. No patients had myopotential interference at a sensitivity level of 3.5 mV. All patients have their pacemakers programmed in the bipolar mode after six months. This study confirms earlier acute data that the bipolar pacing mode is superior to the unipolar mode for permanent pacemaker therapy.

Aged↗
PubMed1983

Bipolar atrial application of a new temporary pacing lead after cardiac operations.

A new temporary pacing lead. Medtronic Model 6400, with a defined electrode surface area of 7.5 mm2, has been clinically and electrophysiologically evaluated during bipolar atrial application in 20 patients after cardiac operations. A silicon disc was used for fixation of the electrodes to the right atrium in 10 patients, and an atrial plication technique was used in the other 10. Myocardial stimulation threshold and resistance were measured throughout the postoperative period. Atrial electrograms were recorded on magnetic tape for computer analysis of amplitudes, slew rates, and signal source impedance. No significant differences (p greater than 0.1) were found in myocardial stimulation threshold between the two fixation modes. During constant-current pacing, median threshold rose from 0.65 mA to 2.3 mA. Stimulation resistance, measured during constant-voltage pacing, fell from 567 to 365 omega, with a subsequent rise to 425 omega before electrode removal. Again no difference was found between silicon disc and plication fixation of the electrodes. P-wave amplitudes were significantly higher with plication than with silicon disc fixation (2.26 versus 0.86 mV, p less than 0.01), as were slew rates (0.34 versus 0.18 V/s, p less than 0.05). Signal source impedance had a magnitude of 6 k omega. The electrodes were used successfully in 12 (60%) of the patients for diagnosis and/or treatment of arrhythmias. We find the new lead well suited for atrial application.

Aged↗
PubMed1982

Electrophysiologic effects of flecainide acetate in patients with sinus nodal dysfunction.

Flecainide acetate (R818) is a new antiarrhythmic agent for oral and intravenous use; it has predominantly class I properties and a long plasma half-life. Electrophysiologic effects were evaluated in 11 patients with sinus nodal dysfunction before administration of flecainide acetate and 15 to 60 minutes after intravenous administration of 1.5 mg/kg body weight of flecainide acetate given over 15 minutes. In 8 of 11 patients with maximal sinus nodal recovery time increased after flecainide acetate. However, the mean maximal sinus nodal recovery time was not statistically significantly increased from 1,929 +/- 184 (mean +/- standard error of the mean [SEM]) to 2,770 +/- 500 ms (p less than 0.10). The corrected sinus nodal recovery time increased from 875 +/- 181 before to 1,727 +/- 507 ms after administration of flecainide acetate (p less than 0.05). The sinus cycle length and sinoatrial conduction time were not significantly changed. Flecainide acetate induced a marked prolongation of the H-V interval (from 41 +/- 3 to 52 +/- 4 mg [p less than 0.01]) as well as a significant increase in the A-H interval, QRS duration, and QT100 interval. The effective and functional refractory periods of the atria increased by 12% (p less than 0.01) and 11% (p less than 0.01), respectively. The atrioventricular (AV) nodal functional refractory period increased significantly by 7% (p less than 0.01), whereas the 9% prolongation of the effective refractory period was not statistically significant. No side effects were observed. It is concluded that flecainide acetate prolongs atrial and ventricular conduction and refractoriness, and thus appears to be a potent antiarrhythmic agent. However, the sinus nodal function is depressed, and thus caution is advised in the use of flecainide acetate in patients with sinus nodal dysfunction.

Adult↗
PubMed1982

Electrophysiological properties of a new permanent endocardial lead for uni- and bipolar pacing.

Unipolar and bipolar electrode systems were compared for electrogram amplitudes and slew rates, signal source impedance, and myocardial stimulation threshold and resistance in 15 consecutive patients who received a new endocardial electrode (Cordis 325-161). The bipolar electrograms showed the highest amplitude in nine of the patients (60%). The unipolar and bipolar electrograms were equal in four patients (26.7%), whereas the unipolar electrograms were highest in only two patients (13.3%). The difference in mean amplitude between bipolar (11.1 mV) and unipolar (10.1 mV) electrograms was statistically significant (p 0.05). Mean slew rates were almost equal (1.7 versus 1.6 V/s; p greater than 0.1). The bipolar electrode system always gave somewhat higher signal source impedance than the unipolar system (p 0.001). The current threshold was significantly lower during bipolar pacing (0.59 mA) in constant current pacing mode, than during unipolar pacing (0.65 mA) (p less than 0.05). No significant differences were found during constant voltage pacing. Stimulation resistance was highest in the bipolar electrode system (p less than 0.001). We conclude that the bipolar electrode system is as good as, or better than, the unipolar system both for ventricular sensing and for pacing.

Aged↗
PubMed1982

Pulse width dependent increase in the pacemaker automatic interval.

From a total of 51 patients equipped with rate and pulse width adjustable pulse generators (Microlith-P 0505, Microthin-PI 0522) implanted over the last 3 years, 10 (19.6%) showed an unexpected drop in pacemaker pulse rate during pulse width programming. For one of the pulse generators used (Microthin-PI 0522), unexpected rate decrease occurred in 7/13 cases (53.8%). For all except one patient, decrease in pacemaker pulse rate corresponded with the total refractory period of the pulse generator ( 320 ms), at a certain pulse width when rate drop first occurred. In seven of the patients the pulse generator automatic interval was extended from 13 ms to 171 ms beyond the refractory period. In two patients it was necessary to replace the pulse generators. Our study strongly proves that this abnormal pacemaker functioning is a result of sensing of the polarization voltage at the pacemaker electrode/tissue interface and/or the T-wave. The polarization voltage is highly dependent on the total pacemaker electrode/tissue interface impedance. Using typical values for pulse generator output and input resistance and output capacitance, Faraday resistance, Helmholtz capacitance and tissue resistance at the electrode/tissue interface it was shown mathematically that in some cases the polarization voltage alone would be of sufficient amplitude and slew rate for pacemaker inhibition. The study demonstrates an urgent need for change in the filter characteristics by making the pulse generators less sensitive in the low frequency region and reducing the polarization voltage by reducing the output circuit capacitance.

Adult↗
PubMed1982

Clinical and electrophysiological properties of a new temporary pacemaker lead after open-heart surgery.

A new temporary pacemaker lead, Medtronic 6400, with a solid defined electrode surface area of 7.5 mm2, has been implanted in 50 patients after open-heart surgery. One electrode was inserted intramyocardially on the right ventricle, while another was placed extracardially and served as a reference lead. Forty-six of the patients were followed postoperatively with measurements of myocardial stimulation threshold and resistance. In 25 of the patients, electrograms were recorded on magnetic tape for further computer analysis of amplitudes, slew rates, and signal source impedance. During constant current pacing, myocardial stimulation threshold increased from a median of 0.4 mA one hour postoperatively to a maximum value of 2.3 mA. In two patients (4.3%) intermittent pacing failure was seen. Stimulation resistance fell from a median of 875 omega to a minimum of 487 omega, with a subsequent increase of 598 omega before electrode removal. Both mean electrogram amplitude (7.35 mV) and slew rate (0.82 V/s) had their minimum values on the sixth postoperative day. Intermittent sensing failure was observed in 2/25 patients (8%). Signal source impedance was of a magnitude not likely to contribute to sensing failure. No complications were seen from the use of this lead. The new electrode is an important improvement in temporary pacemaker lead design.

Adult↗