PubMed Health⌕ Search

Biomedical subjects

O J Ohm

Publications and source records attributed to O J Ohm.

At least 73 records · Page 4Linked to original sources
PubMed1982

Acute and chronic pulse-width thresholds in solid versus porous tip electrodes.

Sixty-one patients given programmable pacemakers at initial implantation have been followed for a mean of 18 months (3-42) with non-invasive measurements of myocardial pulse-width threshold. Fifty of the patients had CPI 0505/0522 (Microlith-P/Microthin-PI) pacemakers with either Cordis 322-462 8 mm2 ball tip (n=12), Cordis 322-620 17.5 mm2 (n=23), or CPI 4116 porous tip electrodes (stimulation area 7.5 mm2 and sensing area 50 mm2) (n=15). Eleven patients had Medtronic 5985 (Spectrax-SX) pacemakers with either Medtronic 6907-R 8 mm2 ring tip (n=7), 6907 11 mm2 (n=3) or 6917 myocardial electrodes (area 12 mm2) (n=1). At acute implant, the ball tip and porous tip electrodes had the lowest stimulation thresholds, but the differences were only statistically significant in comparison with the 17.5 mm2 electrode (p less than 0.01). Chronically there were no significant differences between the various electrodes (p greater than 0.1), but the ball tip electrode tended to give best long-term results, and the porous tip electrode the poorest. Thirty-eight of the 61 patients (62.3%) had chronic pulse-width thresholds of 0.1 ms or less at approximately equal to 5 V output, indicating that pulse-width programming is a useful way to conserve battery energy. However, at some stage of the study, six of the patients (9.8%) had a pulse-width threshold of 0.5 ms or more. Pulse width should therefore not be set too narrow in standard nonprogrammable pacemakers.

Adolescent↗
PubMed1982

Antihypertensive therapy in patients above age 60 with systolic hypertension. A progress report of the European Working Party on High Blood Pressure in the Elderly (EWPHE).

1. Although systolic blood pressure elevation is responsible for increased incidence of cardiovascular accidents in old people, the preventive benefit of lowering systolic hypertension in elderly has not been confirmed. 2. A double blind study comparing the effects of a placebo and of an active regimen (hydrochlorothiazide-triamterene with or without methyldopa) in people over 60 years with isolated systolic hypertension has been undertaken by the European Working Party on High blood pressure in the Elderly (EWPHE). 3. The actively treated group shows a lowered sitting blood pressure (-15/6 mm Hg), a mild increase of serum creatine, serum uric acid and blood glucose and a mild decrease of serum potassium after two years of treatment when compared to the spontaneous changes observed in the placebo treated group. 4. The study is continuing to evaluate if the blood pressure reduction prevents or reduces the incidence of cardiovascular accidents, although some biochemical changes were provoked by the treatment.

Aged↗
PubMed1982

New temporary pacing lead for use after cardiac operations.

A newly designed temporary pacemaker lead (Medtronic Model 6400), which has a solid defined electrode surface area of 7.5 mm2, was compared with a multifilamental stainless steel electrode in common use (Davis & Geck, DG). Thirty-nine patients had both types of electrodes inserted intramyocardially in the right ventricle. A DG electrode fastened to the pericardium served as a reference lead. In addition to the standard Medtronic 7.5 mm2 electrode (n = 11), specially made Medtronic electrodes with areas of 5 mm2 (n = 10), 10 mm2 (n = 10), or 7.5 mm2 with platinum-iridium tips (n = 8) were studied. Measurements of myocardial stimulation threshold and resistance were made in both electrodes throughout the postoperative period. The patients' electrograms were recorded on magnetic tape for computer analysis of amplitudes and slew rates. The Medtronic 7.5 mm2 electrodes showed overall better results than 5 and 10 mm2 leads. Maximum stimulation threshold on the Medtronic 7.5 mm2 electrodes was medium 3.4 mA versus 10 mA on DG electrodes (p less than 0.001). The tissue resistance on Medtronic 7.5 mm2 was almost double than on the Davis & Geck electrodes (median 311 ohms versus 164 ohms on the day of minimum resistance, p less than 0.001). There were no significant differences in electrogram amplitudes between the two electrode types studied (5.52 versus 4.68 mV, p greater than 0.1), but the slew rates were significantly higher on the Medtronic (0.56 versus 0.37 V/sec; p less than 0.01). The new lead is an important innovation in temporary pacemaker lead design compared to the commonly used multifilamental leads.

Adult↗
PubMed1981

Acute hemodynamic and long-term clinical effects of prazosin in the treatment of chronic congestive heart failure.

The effect of prazosin in congestive heart failure was assessed in 10 patients (age 39--69) years) with ischemic heart disease or cardiomyopathy in functional class II-IV (NYHA). All patients were treated with digitalis and diuretics in optimal doses. Mean (+/- S.E.M.) cardiac index (CI) was 2.2 +/- 0.2 l/min/m2 before and 2.3 +/- 0.1 one hour after oral administration of 2--4 mg prazosin (given as tablets) (p less than 0.10). Mean pulmonary capillary wedge pressure (PWP) fell from 24 +/- 4 to 20 +/- 4 mmHg (p greater than 0.10). Prazosin seemed to have a more beneficial effect on patients with markedly elevated PWP or reduced CI before prazosin administration. The effect of prazosin on heart rate and systolic blood pressure was insignificant. During a follow-up period of 1--20 months (mean 7.3), 2 of 7 patients treated with prazosin (2--4 mg daily) improved their clinical condition, one patient was unchanged and 4 patients died in progressive cardiac failure. The results indicate that some patients with severe heart failure may benefit from prazosin when conventional treatment has failed.

Adult↗
PubMed1981

Spontaneous heart activity in pacemaker treated patients with high-grade atrioventricular block. A Holter monitor study.

A Holter monitor study was performed to assess the occurrence of spontaneous heart activity in 70 pacemaker treated patients (mean age 72.1 years) with high-grade atrioventricular (AV) block, who have been treated with permanent pacemakers for a mean of 60 months (range 5-161). Nineteen patients had asynchronous (VOO), and 51 QRS-inhibited (VVI) pacemakers. The patients were monitored for a mean of 23 hours (range 15.5-26). Twenty-five patients were re-studied for day-by-day variations in spontaneous heart activity. At clinical observation, thirty-eight patients had some kind of spontaneous cardiac activity, mostly ventricular ectopic beats. Three patients had short episodes of sinus rhythm of more than 70 beats/min. Patients in functional class III-IV (NYHA) or with an enlarged heart had the most spontaneous heart activity. No tachyarrhythmias precipitated by interference between intrinsic heart beats and asynchronous pacemakers were seen. Twenty patients studied twice had a relatively stable occurrence of spontaneous heart activity, while five (20%) varied considerably. On the basis of these long-term observations it is difficult to predict when interference rhythm will occur, and asynchronous pacemakers therefore cannot be recommended for the first implantation.

Adult↗
PubMed1980

Demand failures occurring during permanent pacing in patients with serious heart disease.

Demand failures during permanent cardiac pacing were studied in four patients with coronary heart disease and cardiomyopathies, by means of in vivo and in vitro analyses of the pacemaker system. A common feature of the electrogram analyses (except during a second replacement in one patient), was extremely low values of amplitudes (0.77-4.36 mV) and maximum derivatives (0.16-1.06 V/sec). In spite of low electrogram amplitudes, the myocardial threshold values were low in all patients. An attempt in one patient at unipolarizing a bipolar system made the adaptation between electrogram and pulse generator more difficult. Autopsy showed that the tip of the bipolar electrode was positioned in a fibrotic area of the myocardium. The signal available for the sensing circuit will also be reduced because of voltage division between the electrode/tissue interface impedance and the input impedance of the pulse generator. Although the pulse generators used had a high input impedance (10-50 K omega), the tissue interface impedance may have caused a further reduction in the electrogram amplitude of 10-30%. This may have contributed to demand failure. In vitro studies confirmed that test pulses with characteristics similar to those of the electrograms found in this investigation, were inadequate for pacemaker inhibition. Special care should be taken during electrogram recordings in patients with severe myocardial disease. One should consider the implantation of a high sensitivity pulse generator or the recently introduced sensitivity programmable pulse generators as first choice for this group of patients.

Adult↗
PubMed1980

Temporary pacemaker treatment in open heart surgery: pre- to postoperative changes in the electrogram characteristics.

Thirty-three patients undergoing cardiac surgery in general hypothermia were investigated during temporary pacemaker treatment for changes in right ventricular electrogram amplitudes (AMAX, UMAX) and maximum derivatives (DMAX, SMAX) from pre-to postoperative phase (AMAX = amplitude of the part of the electrogram with highest mean maximum derivative (SMAX), DMAX = maximum derivative, UMAX = maximum amplitude deflection). Standard commercially available electrodes were used in 28 of the patients. A paired comparison (n = 29) showed a fall in AMAX from 8.64 +/- 0.91 mV (mean +/- SEM) preoperatively to 4.94 +/- 0.43 mV (p < 0.001) between the 4th and 6th postoperative day; UMAX dropped from 11.09 +/- 0.95 mV preoperatively to 5.44 +/- 0.42 mV (p < 0.000001) from the fourth to the sixth postoperative day. In the same period DMAX fell from 1.57 +/- 0.13 V/s to 0.67 +/- 0.05 V/s (p < 0.000001), and SMAX from 0.76 +/- 0.06 V/s to 0.32 +/- 0.02 V/s (p < 0.000001). The most marked fall in amplitudes and maximum derivatives occurred during the first 24 hours. A slight, but nonsignificant increase occurred in amplitudes and maximum derivatives from the 4th to 6th postoperative day until the electrodes were removed the 10th to 19th postoperative day. Amplitudes and maximum derivatives were of the same value in patients with aortic valve compared with coronary heart diseases in spite of a more deteriorated myocardial function in the former group. The changes in amplitudes and maximum derivatives followed the same pattern in the two groups from the pre- to postoperative phase. This indicates that the additional local hyperthermia applied to the patients undergoing valve surgery was of no importance in the electrogram changes. Despite the fact that the electrogram maximum derivative and maximum amplitude needed to inhibit a temporary pulse generator are of a low magnitude, the values found were so small that they might provoke demand failure. This actually occurred in four patients.

Adult↗
PubMed1980

Inhibition/filter characteristics and input impedances of QRS-inhibited demand pacemakers determined by in vitro studies.

There is still no standardized test procedure established for demand pacemakers. Much work has been done to reduce demand failures, but more knowledge is needed to arrive at better results. This study was initiated by in vivo observations of pacemaker malfunctions and unwanted pacemaker effects, the objective being to arrive at a better match between spontaneous cardiac activity and the pacemaker system. The study describes inhibition characteristics and input impedances in some modern temporary as well as permanent QRS-inhibited pulse generators, based on in vitro experiments with various signal waveforms. The different pulse generators tested showed a wide variety of inhibition characteristics. The interrelationship between signal amplitude and maximum derivative required to obtain pacemaker inhibition is pointed out. A better approach to describe the inhibition characteristics of demand pacemakers seems to be the introduction of the time integral (voltseconds) instead of the maximum derivative of a signal (Fig. 3). It is shown that this method nearly removed the discrepancies in inhibition characteristics between different pulse waveforms used. The input impedances were also widely dispersed and were in some instances of a magnitude so low that it would lead to marked reduction of the electrogram amplitude in case the electrode/tissue interface impedance was high. The characteristics of temporary pulse generators were in several respects different from those of the permanent ones. The results obtained with a temporary unit during a test procedure are therefore not the same as for a permanent pacemaker system.

Electric Conductivity↗
PubMed1980

Myopotential inhibition of unipolar QRS-inhibited (VVI) pacemakers, assessed by ambulatory Holter monitoring of the electrocardiogram.

Seventy-four patients with unipolar QRS-inhibited pacemakers (VVI) were Holter monitored to assess the occurrence of pacemaker inhibition caused by skeletal muscle potentials during daily activities. Fifty patients had high-grade atrioventricular block and 24 had sinoatrial disease. Chest wall stimulation prior to monitoring revealed asystole of > 4 seconds duration in 22 patients, and ventricular rates between 25 and 56 beats per minute in 52 patients. Fifty-one patients (69%) had one or more episodes of pacemaker inhibition from myopotentials. Inhibition occurred in all types of pacemakers studies, but was most frequent and of longest duration in patients with Siemens-Elema 207/70 (13/14 patients), Cordis Omni-Stanicor (6/7 patients), CPI Microlith (5/6 patients), and Medtronic 5945 (8/10 patients). This was not unexpected considering the filter characteristics of the pacemakers. Nine patients (12%) presented symptoms which might be ascribed to pacemaker inhibition. The longest asystole observed was 3.2 s. Seven patients had pacemakers spikes falling on or near T-waves of spontaneous heart beats because their pacemakers had been rendered refractory by myopotentials. No serious arrhythmias were seen during episodes of pacemaker inhibition or interference. More emphasis should be put on the improvement of filter characteristics of unipolar VVI-pacemakers. Pacemaker patients with symptoms of myopotential inhibition should be equipped with either a bipolar or ventricular triggered (VVT) pacemaker or with a sensitivity and/or pacing mode programmable pacemaker.

Action Potentials↗
PubMed1979

Sick sinus syndrome treated with permanent pacemaker in 109 patients. A follow-up study.

During the last decade implantation of permanent pacemakers has become the treatment of choice for patients suffering from the sick sinus syndrome (SSS). We have followed up 112 SSS patients treated with permanent pacemakers in Haukeland Hospital in the period 1966--76. The pacemakers were later removed from three of the patients. In the remaining 109 patients the SSS was characterized by tachy-bradyarrhythmias (TBA) in 44 and bradyarrhythmias (BA) in 65. Before implantation, 68 patients had syncopes and 27 severe dizziness. After implantation, symptomatic improvement was apparent in 104 patients; only three still had syncopes. During the follow-up period (mean 34.4 months), 29 patients died (yearly mortality 9.3%). There was no significant difference in total mortality between patients with TBA and with BA. Concomitant disturbances in atrioventricular (AV) conduction occurred in 35.8% of the patients. Among 79 of 80 patients still alive, five had developed total AV block, 19 had stable atrial fibrillation, 12 of these were possibly pacemaker-independent (ventricular rate greater than 60/min). Systemic embolization was observed in 16 patients, more frequently in the TBA (12/44) than in the BA group (4/65) (p less than 0.001). It is concluded that permanent pacemakers have an excellent symptomatic effect in patients with SSS. The prognosis is mainly determined by the presence or absence of coronary heart disease and/or heart failure.

Adolescent↗
PubMed1979

Temporary pacemaker treatment in open heart surgery: variation in myocardial threshold, tissue and interface impedances in man.

Myocardial threshold and impedance of adequately insulated multicore metal electrodes (lengths l1 and l2) were investigated in 28 patients undergoing open heart surgery. Increase in current threshold from the pre-to postoperative period was: 607 +/- 102% (mean +/- SEM) with a constant-current pulse generator and 885 +/- 129% with a constant-voltage pulse generator. Tissue impedance (RT - initial impendance) calculated as voltage/current ratio 90 mus into the pulse changed from 564 +/- 34 omega before surgery to a minimum of 134 +/- 7 omega. Thereafter, there was a gradual increase in RT to 162 +/- 9 omega the day of electrode removal. In 25 of 28 patients the minimum values were reached the third to eighth postoperative day. Electrode/tissue interface impedances--Faraday resistance (RF) and Helmholtz capacity (CH)--were calculated from regression analysis of loaded and unloaded electrograms using the method of least squares. The RF showed a fall from 14.7 +/- 1.4 K omega to 5.2 +/- 0.3 K omega, and the CH (20-40 Hz) rose from 6.0 +/- 0.9 mu F to 15.5 +/- 0.8 muF preoperatively to the day of minimum tissue impedance. There were no further changes until the day of electrode removal. A significant positive correlation was found between CH (p < 0.002), current threshold (p < 0.005) and equivalent electrode length [lequ = l1 X l2/(l1 + l2)]. The electrode signal source impedance calculated from RT, RF and CH was of a magnitude not likely to contribute to demand failures. The low postoperative electrode impendance resulted in excessive load on the constant-voltage generator (condenser discharge type), rendering stimulation of the heart with reasonable current values impossible.

Adolescent↗
PubMed1979

The interdependence between electrogram, total electrode impedance and pacemaker input impedance necessary to obtain adequate functioning of demand pacemakers.

Electrogram maximum derivatives (DMAX, SMAX) and electrogram amplitudes (AMAX, UMAX) (Figure 2), were studied in 71 cases during permanent pacemaker treatment. During the acute phase, (at first implantation), 29 patients were studied, and during the chronic phase, (at pulse generator replacement), 42 patients were studied. Of these patients, 27 (acute phase) and 36 (chronic phase) were studied for tissue impedance (RT) and interface impedance (Faraday resistance RF and Helmholtz capacity CH). DMAX and SMAX changed from 3.47 +/- 0.33 V/s (mean +/- SEM) to 2.46 +/- 0.23 V/s and 1.93 +/- 0.20 V/s to 1.32 +/- 0.12 V/s; p < 0.02; p < 0.01. AMAX and UMAX remained nearly unchanged from acute to chronic phase. A paired comparison in 13 patients showed almost identical results. Electrograms recorded in patients with bundle branch block showed no statistical difference in DMAX, SMAX, AMAX, and UMAX compared with electrograms recorded in patients with QRS-complexes of normal duration. No correlation was found between rise in myocardial threshold and fall in DMAX and SMAX from acute to chronic phase; p > 0.8, p > 0.5. Patients with coronary heart disease were found to have significantly higher AMAX than patients classified as having rhythm disturbances of primary cause; p < 0.01. Extremely low values of amplitudes and maximum derivatives were found in some patients with myocardial infarctions and cardiomyopathies. No difference existed in DMAX, SMAX, AMAX, and UMAX recorded from electrodes with a 8 mm2 area compared with a 12 mm2 area (p > 0.5). RT was statistically significantly higher on the smaller compared with the larger surface electrodes (p > 0.005). There was a slight but not statistically significant fall in RT from acute to chronic phase (p > 0.2). RF ranged from 2.0-94.6 kohms. There was no statistically significant differences between the 8 mm2 compared with the 12 mm2 electrodes (p > 0.2). CH varied between 0.7 and 37.0 microfarads, with significantly lower values for the smallest electrodes (p < 0.05). In patients with electrograms of borderline amplitudes and maximum derivatives for being sensed, the low CH found with the small tip electrodes, will gave a higher risk of demand failure if the input impedance in the sensing circuit of a demand pacemaker is too low.

Adult↗
PubMed1978

Patients with high-grade atrioventricular block treated and not treated with a pacemaker.

One-hundred and eighty-one patients with chronic and with intermittent high-grade atrioventricular block (AVB) were studied retrospectively. Seventy-one were treated with fixed-rate, 51 with demand-type pacemaker, 59 were treated conservatively. Observation time was three years minimum and 14.5 years maximum. The mean age was about seven years higher, and 8.7% more patients had chronic AVB in the conservatively treated than in the pacemaker-treated group. About 12% more patients had Adams-Stokes attacks in the pacemaker group than in the conservatively treated group. There were 7% more patients with coronary heart disease (CHD) in the pacemaker group, and 10% more with aortic valve disease among the conservatively treated. Totally 4.4% of the patients had a calcification of the mitral annulus fibrosus. The two groups were comparable as regards functional class (NYHA) and heart size. Survival showed 31% more sudden deaths in the conservatively treated than in the pacemaker group. Sudden deaths were not more frequent among the patients with CHD than in those without. Long-term survival showed the more favourable result for the patients with than without pacemaker treatment. There were eight (11.3%) unexplained sudden deaths among the patients treated with fixed-rate pacemaker, only three (5.9%) among those treated with a demand unit. The fixed-rate and the demand units showed a mean longevity of 37.2 and 34.6 months, respectively.

Age Factors↗