Biomedical subjects

B E Kristensson

Publications and source records attributed to B E Kristensson.

9 recordsLinked to original sources

PubMed1990

Atrial rate-responsive pacing in sinus node disease.

Patients with sinus node disease (SND) who are unable to achieve an adequate increase in heart rate during exercise are candidates for atrial rate-responsive pacing (AAI-R). We have implanted 40 AAI-R systems in SND patients with an average follow-up of 12.5 +/- 8 (range 3-30) months. All the patients received an activity-sensing pulse generator (Activitrax, Medtronic or Sensolog, Siemens-Pacesetter) with a single atrial lead. Only patients with an intraoperative AV nodal block cycle-length above 100 beats min-1 were included. During follow-up, one patient was observed to have transient asymptomatic 2:1 AV-block during sleep. No patient developed persistent AV-block or chronic atrial fibrillation. Twelve patients with persistent chronotropic incompetence were assigned for a randomized double-blind crossover study, comparing exercise treadmill capacity in AAI-R with conventional atrial inhibited pacing (AAI). During AAI-R pacing the maximum heart rate during exercise was 120 +/- 1 beats min-1 compared with 97 +/- 21 beats min-1 during AAI pacing (P less than 0.01). The average exercise time increased from 11.2 +/- 2 min during AAI-pacing to 13.4 +/- 3 min during AAI-R pacing (P less than 0.01). AAI pacing should be considered for patients with SND and chronotropic incompetence.

Cardiac Pacing, Artificial↗

PubMed1988

Effect of controlled-release metoprolol on blood pressure and exercise heart rate in hypertension: a comparison with conventional tablets.

In a double-blind study with parallel groups a new controlled-release (CR) formulation of metoprolol, 100 mg once daily, was compared with conventional metoprolol tablets, 100 mg once daily, in 27 patients with primary hypertension. Exercise tests on a bicycle ergometer were undertaken 24 h after intake of the last dose of the drug following a four-week placebo run-in period and after four weeks of active treatment. Heart rate, measured in the supine position and during exercise at the highest comparable workload, was reduced significantly more by metoprolol CR (p less than 0.05), thus indicating a higher degree of beta 1-blockade at the end of the dose interval with metoprolol CR. There was a greater reduction in supine systolic pressure (p less than 0.05) but not in supine diastolic pressure after metoprolol CR than after conventional tablets at 24 h. There was no significant difference between the two groups with respect to reduction in systolic blood pressure during exercise. The 24-h plasma concentrations of metoprolol CR and conventional tablets correlated with the effects on heart rate, but not with blood pressure. The tolerability of metoprolol CR was comparable with that of metoprolol administered as conventional tablets. In conclusion, there was significantly greater beta 1-blockade 24 h after the intake of drug after metoprolol CR compared with conventional tablets.

Adult↗

PubMed1988

The importance of different atrioventricular intervals for exercise capacity.

In order to determine whether different atrioventricular intervals influence the maximal exercise capacity, 15 patients with second degree or complete atrioventricular block and no signs of left ventricular failure were studied. They all had atrioventricular synchronous pacemakers. Maximal exercise tests (sitting bicycle ergometry) were performed at four different atrioventricular intervals (50, 100, 150, and 200 ms) and during rate-matched asynchronous ventricular pacing. The patients thereby served as their own controls. Ventricular rate, maximal oxygen uptake and minute ventilation were measured and perceived exertion estimated every minute. Different atrioventricular intervals did not affect the maximal exercise capacity, the maximal oxygen uptake, the perceived exertion or minute ventilation. Since the results were similar during atrioventricular synchronous pacing at various atrioventricular intervals and on rate-matched asynchronous ventricular pacing, this study supports previous findings that the important factor for maximal physical performance is not a preserved atrioventricular synchronization but the ability to increase the ventricular rate.

Adaptation, Physiological↗

PubMed1987

Rate-responsive pacing by means of activity sensing versus single rate ventricular pacing: a double-blind cross-over study.

The clinical applicability of rate-responsive pacing (RRP) by means of activity sensing has been tested in 15 patients. The patients (ages 24-85) had sinus node dysfunction (2), atrial fibrillation (7), or sinus rhythm (6) combined with complete atrioventricular block. Exercise capacity was investigated on a bicycle ergometer and on a treadmill in a double-blind cross-over study design following one week each of fixed rate ventricular pacing (70 bpm) and rate-responsive pacing (60/125-150 bpm). The patients answered a questionnaire concerning subjective symptoms. A Holter ECG was recorded during 24 hours of all day activity on rate-responsive pacing. During exercise in the rate-responsive mode, heart rate increased more on the treadmill than on the bicycle. A majority of the patients (13 of 15) preferred rate-responsive pacing mainly due to less dyspnea and tiredness. Exercise capacity improved significantly both on bicycle (+7%; p less than 0.01) and on treadmill (+19%; p less than 0.01) during rate-responsive pacing. There were no complications during the follow-up period. In conclusion, the activity-sensing pacemaker is a valuable supplement to existing types of pacemakers. It should be used in patients in whom an atrial electrogram cannot be used for rate triggering.

Adult↗

PubMed1986

Holter-monitored heart rhythm during atrioventricular synchronous and fixed-rate ventricular pacing.

The purpose of this investigation was to study rate variability during normal everyday activities among physiologically paced patients. A comparison of the spontaneous occurrence of arrhythmias with ventricular inhibited pacing was also made. VDD pacemakers in 44 patients were randomly programmed to three-week long periods of VVI (70 bpm) or VDD (back-up rate 40-50 bpm, upper rate 125-150 bpm) pacing, respectively. A Holter ECG was recorded during the last 24 hours of each period. Although the total number of QRS complexes was similar in the two pacing modes (4.3 X 10(6)/24 hours), the rate span was extensively utilized during VDD pacing. During VDD pacing, only five patients of 39 with a programmed upper rate of 150 bpm reached this limit, while one of five with 125 bpm reached that rate. Occasional episodes of pacing at the back-up rate of 40 or 50 bpm were recorded in 33 patients. Episodes of asymptomatic rhythm disturbances were recorded in both pacing modes. No significant differences existed as regards ventricular tachyarrhythmias between the two modes of pacing and it did not seem that the incidence was higher than could be expected in a patient population of the present age. Since severe AV block does not permit conduction of atrial impulses during VVI pacing, no direct comparison between the two pacing modes can be made concerning atrial tachyarrhythmias. Only one episode of pacemaker-mediated SVT was found, and this was unsymptomatic.

Adolescent↗

PubMed1985

The haemodynamic importance of atrioventricular synchrony and rate increase at rest and during exercise.

To compare the added haemodynamic importance of atrioventricular synchrony to rate increase, we studied 10 patients, healthy except for atrioventricular block, treated with atrioventricular synchronous pacemakers. Haemodynamic data were obtained by brachial and pulmonary arterial catheterisation. Recordings were made at rest and during upright bicycle ergometry at two submaximal work loads (50% and 80% of maximal aerobic exercise tolerance). The investigation was first performed in the atrioventricular synchronous mode of pacing (VDD) and later repeated during fixed-rate ventricular pacing (VVI) at ventricular rates adjusted to the levels achieved during atrioventricular synchronous pacing. At rest (mean rate 74 bpm), preserved atrioventricular synchrony increased cardiac output (5.0 +/- 0.7 l min-1; mean +/- SD) compared with asynchrony (4.5 +/- 1.0; P less than 0.05), owing to a higher stroke volume (70 +/- 19 versus 64 +/- 22 ml; P less than 0.05), illustrating the importance of the atrial contribution to ventricular filling. During exercise at 50% (mean rate 122 bpm) and 80% (mean rate 146 bpm) of maximal aerobic tolerance, there were no significant differences in cardiac output (50%: VVI 10.1 +/- 2.5, VDD 10.5 +/- 1.6 NS; 80%: VVI 12.8 +/- 4.1, VDD 12.3 +/- 3.5, NS) or in stroke volume (50%: VVI 83 +/- 23, VDD 88 +/- 17, NS; 80%: VVI 89 +/- 32, VDD 85 +/- 27, NS). We conclude that the capacity for rate increase is of major importance while preserved atrioventricular synchrony seems to be much less important for the ability of the individual to increase cardiac output during exercise, at least in patients without myocardial disease.

Aged↗

PubMed1985

Physiological versus single-rate ventricular pacing: a double-blind cross-over study.

Previous comparisons of physiological and single-rate ventricular pacing are mostly based on open studies. The present investigation was designed to control possible biases of such a study design with the aim to investigate effects of the two pacing modes on maximal and submaximal exercise tolerance and the subjective feeling of well-being of the patients. Forty-four patients treated with atrioventricular synchronous pacemakers for more than 12 months participated in the study. Their pacemakers were randomly programmed to one 3-week long period of ventricular inhibited and a similar period of atrioventricular synchronous ventricular inhibited pacing. Thereafter, they went through echocardiography, symptom-limited maximal exercise test and answered a questionnaire on subjective symptoms. The study was blind since neither the patients nor the physician conducting the exercise tests were informed of pacing mode. The mean maximal exercise tolerance increased 14% (p less than 0.01) on atrioventricular synchronous pacing. Arterial lactate, respiratory rates and perceived exertion ratings during submaximal levels of exercise were higher on ventricular inhibited pacing, as well as symptoms scored during the two 3-week periods. A majority of patients improved their functional class during atrioventricular synchronous pacing and preferred the physiological pacing mode.

Adolescent↗

PubMed1984

Clinical problems in atrial synchronous ventricular inhibited pacing: a long-term follow-up of 54 patients.

Fifty-four VDD-paced patients were followed for more than 12 months; they were studied retrospectively in order to assess possible clinical problems and their management. The patients were between 19 and 84 years of age (mean, 66 +/- 11). Twenty-four of the 54 received a VDD pacemaker as a primary implant and 30 had had VVI pacemakers which were changed to VDD mainly because of limited exercise tolerance or symptoms of AV asynchrony. The follow-up time was between 12 and 69 months (mean, 39 +/- 17). Pacemaker and lead problems were neither frequent nor serious. Six patients had spontaneous paroxysmal supraventricular tachyarrhythmias, four had pacemaker-mediated supraventricular tachycardias and six had ventricular tachyarrhythmias. Treatment of tachyarrhythmias included drugs, DC conversion, reprogramming, or combinations of these measures. Frequency of hospitalization was not greater than expected. In conclusion, VDD pacing appears safe and reliable, with problems mainly associated with the underlying cardiac disease rather than to the pacing mode itself.

Adult↗

PubMed1983

Atrial synchronous ventricular pacing in ischaemic heart disease.

Atrial synchronous pacing has been considered contraindicated in patients with a high degree of atrioventricular block and concomitant ischaemic heart disease. The rationale for this view was a fear of provoking angina pectoris by a rate-dependent increase in myocardial oxygen consumption. As possible problems with atrial synchronous pacing in patients with ischaemic heart disease have not been extensively studied we have examined whether these patients could benefit from this more physiological method of pacing. Thirteen patients with ischaemic heart disease and a high degree of atrioventricular block were supplied with pacemakers, programmable both in reference to the pacing mode (ventricular inhibited (VVI) or atrial synchronous ventricular inhibited (VDD)) and for maximal synchronous rate. The patients were examined with the pacemaker programmed in the VVI and VDD modes. Maximal exercise capacity was determined by means of bicycle ergometry. There was a statistically significant increase in exercise capacity when comparing VVI (67 + 24) with VDD (79 + 25, P less than 0.001) pacing with suitable programming of maximal synchronous rate. No patient experienced increased anginal pain on VDD pacing and all preferred VDD compared to VVI pacing. In conclusion, VDD pacing should not be considered contraindicated in patients with ischaemic heart disease and a high degree of atrioventricular block, and may, on the contrary, contribute to further clinical improvement.

Aged↗