Hans Lagergren

Valsalva-Induced Variations in the Intracardiac Signal

Variations in the intracardiac signal may substantially effect the sensing function of cardiac pacemakers. As the Valsalva maneuver causes a change in heart volume, its effect on the intracardiac signal was studied in seven patients with an adequate escape rhythm who had permanent ventricular pacemakers. During generator replacement, they were asked to perform a standardized Valsalva maneuver. An increase from the baseline amplitude ranging from 5% to 70% was noted during forced expiration against the closed glottis. There was a decrease from the baseline ranging from 15% to 50% after terminafion of this maneuver. Similar changes were noted for the rate of voltage change (slew rate). The magnitude of these alterations was most pronounced in patients with comparatively low intracardiac amplitudes. Because marked changes in the intracardiac signal can result from the Valsalva maneuver, it might be an important source of undersensing among patients with permanent pacemakers.

Ten-year Follow-up on 1,000 Patients with Transvenous Electrodes

One thousand patients given a transvenous electrode EMT 588 until mid‐January, 1974, were followed up for a minimum of 10 year. Two hundred ninety‐six patients survived this time or longer. Fully 30% of them were above the age of 70 when first paced. During the observation period, 34% of the survivors had electrode complications requiring electrode replacement. These occurred in almost 14% during the first year of treatment. Electrode failures during the first year were due mainly to dislocations and rises in the stimulation threshold, while later failures were caused chiefly by damage to the lead, which was caused, in part, by repeated pulse generator replacements and infections. Half of the patients who survived for more than 15 years have the original electrode, the oldest one now exceeding 22 years.

EFFECT OF LOW-DOSE HEPARIN PROPHYLAXIS ON ARTERIAL OXYGEN TENSION AFTER HIGH LAPAROTOMY

The effect of low doses of heparin (5000 units of sodium heparin every 12 hours for 5 days) on arterial oxygenation was studied in 24 patients in the postoperative period after upper abdominal surgery. Another 24 patients served as a control group. The arterial oxygen tension was the same in both groups preoperatively and was equally significantly reduced during the 1st postoperative day. During the 2nd day, oxygen tension rose in the heparin-treated group to values which no longer differed significantly from the peroperative level. In the control group the significant reduction persisted until the 4th postoperative day. The arterial carbon-dioxide tension did not differ between the groups, neither did it vary significantly between days. There were no clinical signs of large pulmonary embolism during the postoperative period, chest X-ray was normal in all patients examined and a photoscan was normal in 23 of 24 subjects studied. Low-dose heparin treatment may apparently shorten the period of postoperative hypoxaemia, probably by counteracting both large pulmonary emboli and microthromboembolism.

Influence of Output Capacitor, Electrode and Pulse Width on Power Consumption in Cardiac Pacing‡

Three different types of unipolar endocardial electrodes—47 in all—were compared in regard to power consumption at stimulation threshold with six different output capacitors and seven pulse widths.

25 years of implanted intracardiac pacers.

In 1962, a simplified method of transvenously inserting an intracardiac electrode and implanting the whole pacemaker system under local anaesthesia was reported from the Karolinska Hospital in Stockholm. This simplified method has been universally adopted and pacemakers are now probably implanted too freely in many places. In the Stockholm area pacemakers are implanted half as frequently as in the rest of Sweden and as often as in the United Kingdom.

Phagocytic and catabolic function of the reticuloendothelial system in dogs subjected to defibrinogenation.

Abstract There is evidence that the reticuloendothelial system (RES) serves as an important protective mechanism in disseminated intravascular coagulation. The influence of defibrinogenation on the RES is studied in this investigation. For this purpose dogs were defibrinogenated with Defibrase R — a thrombin-like enzyme from the venom of Bothrops atrox. The phagocytic and catabolic functions of the RES were tested by the use of a test substance of heat-aggregated human serum albumin labelled with 125 I. Defibrase R was given in three groups of dogs at the time when the RES function was tested, 1 hour and 2 hours before the test. A significant delay of both the phagocytic and the catabolic activity was seen with increasing time between defibrinogenation and the RES-test, indicating a block of the RES with fibrin/fibrinogen degradation products. The reasons for this are discussed.

Choosing the Stimulation Rate in Patients with Intermittent Bradycardia and a Single Lead Pacemaker

In order to assess the prevalence of intermittent bradycardia in a pacemaker population, we retrospectively evaluated the occurrence of intrinsic heart activity in 229 patients with ventricular pacing. Spontaneous heart activity was recorded in 60% of the patients. However, the stimulation rate had been decreased in onJy 40% of the patients in order to allow for longer periods of intrinsic heart activity. In the second part of the study we prospectively assessed differences in pacemaker utilization in 19 patients with intermittent bradycardia and single lead pacemakers. All patients were observed over four periods of 14 days, with the following pacing modes: 70 heats/min, 50 beats/min, hysteresis sensing 50 beats/min, and pacing 70 heats/min; and search hysteresis sensing 50 beats/min and pacing 70 beats/min. Search hysteresis pacing is a new feature that theoretically allows for a shorter time of pacing than that of hysteresis pacing. A reduction in the stimulation rate from 70 beats/min to 50 beats/ min resulted in a 60% reduction in pacemaker utilization (P < 0.05). Search hysteresis decreased pacemaker utilization by 33% (P < 0.05) There was no statistical difference between conventional hysteresis and fixed rate pacing at 70 beats/min. Most patients found fixed rate pacing preferable to hysteresis pacing. In order to minimize battery consumption and to avoid unfavorable hemodynamics in patients with ventricular pacing, the stimulation mode and rate should be optimized in patients with intermittent bradycardia to allow for longer periods of intrinsic heart activity.

Paroxysmal Complete Heart Block due to Bradycardia‐dependent, “Phase 4” Fascicular Block in a Patient with Sinus Node Dysfunction and Bifascicular Block

A 34‐year Old man with ankylosing spondylitis was admitted to the hospital because of syncopal attacks and heart block. Standard ECG, telemetry and an invasive electrophysiologic examination demonstrated right bundle branch block with left anterior fascicular block, sinus node dysfunction with spontaneous slowing of the sinus rate and, as a result, complete infrahisian atrioventricular block in the remaining fascicle at sinus rates below 57 beats per minute. Infrequent supraventricular extrasystoles and abruptly terminated atrial pacing led to the same result. Atrioventricular conduction resumed after three‐to‐four blocked atrial impulses with successively increasing rate. Pacemaker treatment provided complete symptomatic relief.

A comparison between conventional and basket transvenous electrodes.

Three transvenous electrodes, two of a conventional type and one in the shape of a wire basket, were compared. In order to make a valid comparison, the electrodes ivere all attached to the same kind of lead. The conventional large and small surface electrodes showed no difference in early complication rate. The wire basket electrode, however, had significantly fewer early complications than the others. This was true whether the patients underwent a two‐ or a one‐step procedure, and whether the surgery was done by experienced or inexperienced pacemaker surgeons. When inserted by experienced surgeons in a one‐step procedure, the wire basket electrodes had an early complication rate of only 1.2%. Since this unrefined electrode that allows tissue ingrowth for improved anchoring has shown such good results, it is likely that other electrodes that have heen perfected, of a hollow or porous design, will also he advantageous to the patients and show good results.

Centrifugal Geometric Scanning — an Alternative Concept in Pacemaker Treatment of Tachycardias

Short term efficacy and safety of a new scanning concept for termination of AV reciprocating tachycardias were assessed in five patients, two with dual AV nodal pathways and three with an accessory A V connection. The concept includes geometric partioning of the scanning interval concentrating the attempts to its early part, a centrifugal search outwardly from a memorized extra stimulus delay and alternation of the number of extrastimuli. After initial definition of the termination characteristics in each patient the system was found efficient during a 48-hours recorded period. No adverse effects were observed.