Introduction

Pacemakers are the standard treatment for symptomatic bradyarrhythmia. Professional societies have issued guidelines for the implantation of cardiac pacemakers.^1-3 Although these guidelines have all been similar, considerable differences have been reported in the frequency of implantation of pacemakers and in the system selected.⁴ Relatively little is known about the reasons for these differences.⁵ There is some evidence that patients' sex might play a part in clinical decision making.^6-8 We used a large database to analyse whether sex can explain differences in the selection of pacemaker systems.

Subjects and methods

Doctors who perform implants transfer information available from the European pacemaker patient identification card to the German central pacemaker register on a voluntary basis. Customs' statistics and manufacturers' sales figures suggest that the register comprises 64% of all implantations in Germany. Of the 880 German hospitals in which implants are done (number estimated by a survey), 634 (72%) sent their reports to the register.⁹ Our analysis is based on complete data for the years 1992 and 1993. We excluded cases that had classification errors (for example, non-existent categories) from the total of 15 914 patients in 1992 and 15 999 patients in 1993. Table 1 gives the characteristics of the patients.

Statistical analysis
We examined the pooled data for 1992 and 1993 according to patient characteristics (age, sex, clinical symptoms, underlying disease, electrocardiographic findings), type of pacemaker (single chamber, dual chamber), and rate responsive systems. The ² test was used to analyse discrete variables and Student's t test used for continuous variables.

Results

Table 1 shows that single chamber systems were implanted in a higher proportion of women (atrial 492 (3.2%), ventricular 11 065 (71.9%)) than men (atrial 429 (2.7%), ventricular 10 499 (66.1%)). In contrast, men received more dual chamber (4892 (30.8%)) and rate responsive systems (4273 (26.9%)) than women (3770 (24.5%), 3186 (20.7%)). Sex differences were also found for various clinical variables.

In the univariate analysis, where 21 858 patients could be included (68.5% of the sample), age, sex, several clinical symptoms, underlying disease, and electrocardiographic findings were significantly associated with the pacemaker system selected for implantation (table 2). After the effects of age, clinical symptoms, underlying disease, and electrocardiographic findings had been adjusted for in a multivariate analysis (n=16 289 (51.0% of the data)), women were still more likely to receive a ventricular single chamber pacemaker and less likely to receive a dual chamber or rate responsive system than men (table 3).

Discussion

Analysis of data from over 15 000 patients suggests a sex bias in choice of a pacemaker system. Women were more likely to receive single chamber systems and less likely to receive dual chamber or rate responsive systems than men. Can these findings be explained by differences in the underlying cardiac disorders or demographic data? In our cohort a higher proportion of men presented with an atrioventricular block than women. It is generally accepted that dual chamber pacemakers achieve better haemodynamic results than single chamber systems in atrioventricular block. ^{2 10} Women, on the other hand, had a higher frequency of sinus node dysfunction. In this disorder a single chamber system often seems to be sufficient, although several authors have found that dual chamber pacemakers produce better outcomes in terms of haemodynamics, subjective symptoms, the development of atrial fibrillation, and prognosis.¹¹ Finally, cardiovascular diseases occur at a later age in women than in men.¹² In our cohort women were on average 3.8 years older than men. Doctors generally implant single chamber pacemakers in elderly patients rather than dual chamber systems.¹³

Several studies of factors influencing cardiovascular interventions showed that sex was no longer a determinant once demographic and clinical variables had been adjusted for. ^{14 15} In our study, however, even after we controlled for demographic and various clinical variables sex remained independently associated with the selection of a pacemaker system. Our results agree with two retrospective studies in the United States in which women were found to receive a dual chamber system less frequently than men. ^{16 17} The clinical importance of the suggested undertreatment of women with dual chamber and rate responsive pacemakers is not easy to evaluate. In addition to the advantages of dual chamber pacemakers in patients with atrioventricular block and sinus node dysfunction mentioned above, rate responsive systems have been shown to offer haemodynamic advantages over fixed rate systems in patients with chronotropic incompetence receiving ventricular single chamber pacing or dual chamber pacing.¹⁸ Although there is evidence that patients treated by advanced pacing have a better quality of life,¹⁹ it is not known whether this improvement is equal in men and women.

Is there sex discrimination?
What other reasons could there be for doctors deciding in favour of a single chamber pacemaker in women? Firstly, there are some "soft" indications for implanting pacemakers (class II indications in the American College of Cardiology/American Heart Association guidelines² and corresponding recommendations in many countries, including Germany) Furthermore, guidelines are not always unanimously adhered to in clinical practice. ^{5 20} Doctors are known to behave differently towards men and women as far as both diagnostic and therapeutic strategies are concerned.²¹ Doctors seeing women with "soft" indications may tend to implant single chamber pacemakers whereas they choose dual chamber for men. Some of the "hard" indications may also be being neglected in women. Women often present their symptoms differently from men.²² They are more likely to receive the same treatment as men if they present their symptoms as men do.²³ Finally, we found some published evidence that women sometimes reject sophisticated care in favour of more simple treatments. They may therefore choose not to have dual chamber systems.²⁴