V. LEONHARDT, C.VANGROENINGEN
Introduction
In the Western world, health care budgets are increasingly under pressure.
With an increasingly older population, more people require more medical care. In addition, medical standards have become higher and people are remaining active longer and thus expecting better care. At the same time, the relative number of people working is decreasing.
In the USA, the number of implantations of cardiac device has increased by 7% per year, from 294 000 in 2001 to 401 000 in 2005 (pacemaker, ICD, and CRT devices combined) and the number of follow-ups (FUs) doubled in the same period. This rise in FUs translates into an increasing burden on individual clinics and especially on specialised centres. For example, in our clinic the number of implantations rose dramatically, from only 46 in 1999 to 385 in 2004, and we have now 6500–7500 FUs per year. The ever-growing demand on medical care therefore calls for new technologies to be developed.
Increasing Follow-Up Burden
A pacemaker implantation and more specific dual chamber systems seem to be cost-effective treatments. The reimbursement of an implantation renders a profit when cost for staff and materials are deducted. However, clinicians’
reimbursement for FUs does not counter-balance the costs of an average 5 years of FU. This is a growing financial problem for the clinic.
Facharzt für Innere Medizin, Berlin, Germany
One of the reasons that FUs are a problem is that, over the years, pace- makers have become increasingly complex. In the late 1970s, pacemaker memories were small and only a few parameters were stored. With increas- ing memory size, counters were added to basically store sensed and paced events; as sensing circuits remained analog and pacing therapies remained simple, there was no extra information to store anyway. Pacemaker FUs thus consisted of simply checking the functionality of the pacemaker device.
The introduction of microprocessors (DPG-1, Vitatron Medical), in 1981, created the possibility to make intelligent decisions based on rate and rhythm information. Simultaneously, more data could be stored, and Holters and histograms were added that stored more clinically relevant data over longer periods of time. This meant that during FU this clinical data had to be analysed and interpreted in order to optimise pacemaker therapy.
Over the years, memory size has continued to increase (more counters, Holters, and histograms) and information about relevant arrhy thmic episodes can be stored as markers or, currently, as digitally stored IEGMs. All these developments have led to an increase in time and effort needed to carry out proper follow-up.
Digital vs Analogue Technology
In 2003, Vitatron introduced the world’s first fully digital pacemaker. In con- ventional pacemakers, the analogue input is digitised in an analog/digital (AD) converter to store the IEGM, but for event sensing only the analogue signal is used. In fully digital devices, the analogue input out of the heart is amplified and then digitised. All subsequent steps, filtering, event detection, IEGM storage, and signal analysis, are performed on this digital signal (Fig.
1). Digitisation allows digital signal processing (DSP) in pacemakers, a tech- nology that has been used in many types of electronic equipment available for the consumer for more than 15 years and which includes CDs, mobile telephones, and handheld cameras to mention a few. This is equipment that requires many times more energy than is available in pacemakers. A mobile phone has a battery capacity of 0.72 mA that lasts about 1 week with the typical current consumption of 4.2 Ah. A pacemaker battery has nearly dou- ble the capacity (1.36 mA), but it is of course unacceptable to change pace- makers every 2 weeks. It therefore was an impressive engineering feature to make DSP possible while maintaining an acceptable life span for the pace- maker. For a life span of 9 years, the power consumption had to be reduced to 0.03 Ah.
New Technologies Making Follow-Up Easier
The resulting digital pacemaker is able to analyse the cardiac signals based on the morphology of the signal. Morphology analysis can be used to distin- guish between PACs, retrograde, and physiologic atrial events, and to reduce the detection thresholds without fear of noise, far fields, or muscle potentials [1]. In the future, morphology will be used to reveal pathologies, for instance, ischaemia.
The increased storage capabilities have added more data that must be analysed at each FU. It could be considered that in this aspect digital pace- maker technology has brought the healthcare system from bad to worse.
Automaticities
To reduce FU duration, a number of basic pacemaker settings have been made automatic or semi-automatic. Auto-sensing and auto-capture features make cumbersome threshold testing at each FU redundant, thus freeing-up FU time.
Long-Distance Follow-Up
Another development is long-distance FU. Pacemaker patients can check their pacemakers at home, and in case disturbing diagnostics are detected an alarm Fig. 1.aDesign of conventional pacemakers. The entire signal processing is done on the analog signal. Only the IEGM is digital. b Design of digital pacemakers. The signal is converted as soon as possible and all signal processing is done digitally
a
b
is sent to specialised centres or the physician in attendance. In theory, this reduces the FU burden because patients only come to the clinic for FU when required. However, in practice, it is yet not totally clear which problems require the attention of a physician, and patients are often referred to the clinic ‘just in case’, thereby increasing the FU burden. Of course, it is expected that in-home analysis will improve as the systems performing the analysis mature over time.
An example of an expert system having this potential is the Therapy Advisor – although currently it is only available for use in the clinic.
Therapy Advisor
In light of clinicians’ limited time available for FUs, it is annoying to realise that a lot of FU time is spent on interrogating and adapting pacemaker set- tings that are important for the proper functioning of the device itself and its collection of clinically relevant data. This is a problem especially with the devices of atrial fibrillation patients. FUs should be about patient manage- ment and diagnostics about their treatment.
To handle the problem of the complicated and time-consuming interpre- tation of the large amount of pacemaker data, Vitatron developed the Therapy Advisor, which is an expert system that, in the time needed to inter- rogate the collected diagnostic data from the pacemaker, analyses the data for clinically relevant information. It identifies clinical issues, guides the physician to the specific diagnostics for evaluation if desired, and provides programming recommendations. By guiding the physician through these complicated issues, he or she can focus on important clinical questions and take care of them during the limited FU time.
Evaluation of the Therapy Advisor
Currently, two studies are in progress to evaluate the performance of the Therapy Advisor and physicians’ satisfaction with its use: the C-STAR and the T-STAR registries. Both registries are international, multi-centre, prospective Post Marketing Studies aimed at gathering data related to the usefulness and appropriateness of the Therapy Advisor.
C-STAR was the first study and it focuses on the general diagnostics; the focus of T-STAR is atrial tachycardia.
C-STAR [2]
Methods
In the C-STAR registry, all patients with a class I or class II pacing indication and a Vitatron C-series pacemaker are included. Physicians follow each
patient per normal practice. Each of the patients receives the standard of medical care that is typically provided by the investigator with respect to device FU, management of co-morbidities, etc. The registry does not require specified FU visits. However, in order to have the patient’s data contribute to the study objectives, the data of at least two follow-ups within a different time frame in the first 12 months following discharge are required.
In the first inter im analysis, data use was limited to the enrolment/implant, 2-month FU, and 6-month FU, and the data passed all validation levels. Patients were only included in this interim analysis if both the CRF data and diskette data were available for a FU. This resulted in 96 patients with a 2-month FU being analysed and 33 of these with an addition- al 6-month FU.
The interim analysis focuses on the opinion of the clinician regarding the helpfulness of the Therapy Advisor in assessing the patient’s condition, mak- ing an efficient FU, and optimising pacemaker programming and drug regi- men.
Results
The most common diagnostic observations generated by the Therapy Advisor are listed in Table 1. The total number of messages was 169, with 131 messages for the 2-month FU (n = 96) and 39 messages for the 6-month FU (n = 33). Since it is possible for the Therapy Advisor to generate more than one message per patient, this resulted in a percentage for both the 2- month FU and the 6-month FU of more than 100%.
The investigators’ opinions about the helpfulness of the Therapy Advisor in assessing the patient’s condition were positive to neutral; only 11.6% were negative. Within the group of patients with both a 2- and a 6-month FU, the percentage of positive-minded investigators increased from 36.4% at the 2- month FU to 72.7% at the 6-month FU.
Table 1.The five most common Therapy Advisor (TA) messages
Frequency of follow-up
Message All FUs 2-months 6-months
(n = 129) (n = 96) (n = 33)
TA has nothing significant to report 68 48 (50%) 20 (61%)
Fast V rhythm detected 31 25 (26%) 6 (18%)
High sensed atrial rates 21 18 (19%) 3 (9%)
Retrograde conduction detected 14 8 (8%) 6 (18%)
P-wave sensing problem suspected 12 10 (10%) 2 (6%)
With regard to whether the Therapy Advisor helps to optimise program- ming, the pacemaker investigators were mostly neutral (48.1%). Between the 2- and 6-month FU, the negative responses decreased, from 18.2% to 3.0% in favour of positive responses, which increased from 18.2 to 42.4%.
About optimising the drug regimen, most investigators were neutral (56.6%). Negative scores decreased from 27.3% to 18.2% when 2- and 6- month FUs are compared.
Finally, regarding FU efficiency, physicians were again positive to neutral (50% and 31%, respectively.) The number of positive answers increased from 36% at the 2-month FU to 67% at the 6-month FU.
In a large number of cases (50–60%), the Therapy Advisor had nothing significant to report, and the opinion of physicians about the Therapy Advisor in assessing the patient and FU efficiency in these cases was also analysed. For patient assessment, more than 30% of physicians were negative after the 2-month FU, with not a single one positive. At 6 months, there were no negative opinions and almost 80% were positive. The same holds for FU efficiency: the almost 25% negative answers at 2 months disappeared at the 6-month FU whereas the positive answers increased from 25% to almost 60%
(Fig. 2).
Fig. 2.Physicians satisfaction: compared at 2- and 6-months FU physicians are clearly more satisfied about the helpfulness of the Therapy Advisor in assessing the patient and improving FU efficiency
Discussion
The majority of investigators rated the contribution of the Therapy Advisor in assessing the patient and making the FU more efficient neutral to positive.
Over time, trust in the Therapy Advisor increased, as indicated by the increase in investigator satisfaction between the 2- and 6-month FU. This increase was particularly observed for assessment of the patient’s condition and making the FU more efficient. Increased trust is also indicated by the higher satisfaction with the message ‘Nothing significant to report’ during the 6-month FU than at the 2-month FU. Apparently, the investigators did not trust the message in the beginning and felt that it was necessary to col- lect all diagnostic information. After doing this a couple of times, the physi- cians learned that the message was useful and reliable.
This, it appears that, as investigators use Therapy Advisor over time, they become acquainted with its features and increasingly appreciate its useful- ness.
Conclusions
Pacemaker follow-ups are a burden for health budgets in general and for the clinic in particular. A reason for this is that during the last several years pacemakers have become increasingly complicated and able to store greater amounts of data. Programming the pacemaker properly and analysing the collected data for clinically relevant details have likewise become more com- plicated. Consequently, a new field of relevant diagnostics was needed to cope with the increased demands of digital pacemakers on clinicians’ time during patient FU.
New technologies can bring solutions. In the case of pacemakers, auto- maticities are taking increasing care of checking and re-programming basic functions, such as sensing and pacing thresholds. Long-distance FU have made it possible to spare patients coming to the clinic on schedule ‘just in case,’ so that they now are able to come only when required. This is a promis- ing technique although it still requires adjustment. The Therapy Advisor is a next step. It analyses all the data collected by the pacemaker, directing the physician to the clinically relevant issues. Again, this is a field under develop- ment but the interim results of the C-STAR registry show a high degree of satisfaction among physicians and a growing acceptance and trust in this new technology. New technologies such as the Therapy Advisor thus allow the physician to forget the technique behind the pacemaker and focus on the clinical aspects of the pacemaker patient.
References
1. van Hemel NA, Wohlgemuth P, Egbers JG et al (2004) Form analysis using digital signal processing reliably discriminates far-field R waves from P waves. PACE 27:1615-1624
2. Schuchert A (2004) C-STARegistry. In: Proceedings of the 11thinternational sym- posium on progress in clinical pacing. Centro Scientifico Editore Rome p 5 3. Love CJ (2004) The digital pacemaker. PACE 27:707–708
