PACEMAKER ACTROS MEMORY DATA vs HOLTER MONITORING IN DETECTION OF PACING AND SENSING EPISODES.

J.K.Wranicz, I.Cygankiewicz, M.Chudzik
Institute of Cardiology, Medical University of Lodz
Ul.Sterlinga 1/3; 91-425 Łodz, POLAND

Abstract: The aim of the study was to compare the accuracy of an implanted Biotronik Actros S (VVI) pacemaker memory data (HP) with standard Holter monitoring (HM) in estimation of pacing and sensing episodes.

77 patients ( 51 males , 26 females ) aged 34-86 yrs (av.69 yrs), implanted with Biotronik ACTROS S pacemaker were studied. In all the patients 24 hour Holter ECG (HM) using Oxford Medilog System with simultaneously restarting pacemaker’s statistics functions: event counter and activity report were performed. Correlation between following events: ventricular sense (Vs), ventricular pace (Vp), mean heart rate (HR mean) and maximum heart rate attained (HR max) was estimated.

Values of Vs and Vp retrieval from the pacemaker memory significantly correlated with data from Oxford Holter monitoring (Vs 13,2 vs 13,4%; Vp 86,7 vs 86,6%, p<0,001). HP has also revealed high accuracy in estimation of mean HR ( 81,3 vs 81,4%, p<0,001). There was a difference in evaluating of max HR that may depend on different algorithms in pacemakers memory and Holter monitoring.

INTRODUCTION

Conventional Holter monitoring may be helpful in some cases but it still reflexes only a period of 24 – or 48 hours, potentially missing rare but important events [1]. Statistical information retrievable from implanted pacemakers (PM) became available with first VVI PM in late 1970s [2].The development of computer technology provides possibility of storing much more amount of information in implanted devices [3]. Diagnostic pacemaker functions can also be used to identify events and reliable in evaluation of pacemaker performance during long follow up. In addition modern devices are becoming more and more automated and are now able to adjust their programming settings to sensed or measured parameters [4].

The aim of a study was to evaluate the accuracy of an implanted Biotronik Actros S (VVI) pacemaker retrieval memory data (HP) in estimation of pacing and sensing episodes as well as mean and maximal heart rate, compared to standard Holter surface ECG- monitoring (HM) data.

METHODS

The study population consisted of a group of 77 pts (51 males and 26 females, aged 34-86 yrs, av. 69 yrs) implanted with Biotronik Actros S pacemaker set in the mode VVI 80 bpm with unipolar pacing and bipolar sensing (bipolar leads Biotronik TIR 60-BP and PX 60-BP).

Chronic atrial fibrillation with pauses over 3 sec during day- time with Morgani-Adams-Stokes attacks was the indication for pacemaker implantation in all the patients.

At routine follow up appointment patients were fitted with 24-hour Holter recorder. Continuous ambulatory ECG monitoring with simoultaneously restarted internal pacemaker memory data statistic functions was started. Holter monitoring was performed using MR 45 3 recorders and the registrations were analysed by means of Oxford Medilog Excel 2 System. The following pacemaker memory data (event counter and activity report) were printed for analysis: ventricular sense event ( Vs), ventricular pace event ( Vp), mean heart rate ( HR mean),maximal heart rate (HR max). Continuous data (Vs, Vp, HR mean, HR max) from Holter recordings and pacemaker telemetry were presented as mean value ± SD. The results were compared by means of r- Spearman correlation test .

RESULTS

There was a statistically significant high correlation between Holter monitoring and pacemaker memory data recordings between the percentage of ventricular sense and pace events over the 24 hour period. Very high correlation (r=0,98) between standard and pacemaker Holter monitoring in assessment of the mean heart rate was also found.. The maximal heart rate retrieval from PM Holter significantly differed from standard ECG recording (p=0,67). Summarized data are shown in Table I.

TABLE I

	Vs(%)	Vp(%)	HRmean	HR max
HP	13,2±10	86,7±11	81,3±2,8	168±35
HM	13,4±10	86,6±11	81,7±2,6	135±22
R	0,98	0,97	0,95	0,1
P	<0,01	<0,01	<0,01	ns

HP – pacemaker memory data
HM- Holter surface monitoring
Vs- ventricular sense events
Vp- ventricular pace events
HR mean – mean heart rate
HR max – maximal heart rate

DISCUSSION

Although VVI Actros S pacemaker with memory data is not able to record complete continuous electrogram data, it provides very accuracy analysis of sense and pace episodes.

Our initial experience has shown that, over a 24 hour period, the pacemaker internal data offer accurate diagnoses of Vs, Vp events and mean HR when compared with surface ECG.

Mean heart rate printed from activity report and standard Holter monitoring was very highly correlated. The only parameter which differed in two types of 24 –hour monitoring was maximal heart rate.

Pacemaker algorithm for max HR estimates the shortest, only one R-R interval. In Oxford Medical System max HR is not assessed from the shortest R-R but from three continuous R–R intervals. It may constitute the possible explanation of differences in max. HR from PH and HM (maximal heart rate in Holter monitoring is lover than in PH).

The idea of continuous monitoring of cardiac rhythm by an implantable pacemaker or similar device is not new. In the early 1970s, investigators involved in cardiac pacing pointed out the need for memory functions for the diagnosis of cardiac events [2]. The concept of using pacemakers for diagnostic purpose has really become possible only with the latest generations PM. These devices are equipped with microprocessors and extended random access memory (RAM) [3,5,6]. According to memory capacity cardiac events can be stored in different ways. Pacemaker statistic functions have been available for more than 15 years. Nowadays all pacemakers provide statistic functions. However, there is a paucity of studies concerning the accuracy of an implanted Holter system. A recently published comparison of pacemaker memory data and surface ECGs found a very high correlation (r>0,9) [7].

The value of the event counter has some important limitations. Event counter can reflect only what the pacemaker has done; they do not take into account the possible clinical situation. According to Nowak [3] the counter is not able to distinguish whether a sensed event is due to properly sensed cardiac event or due to oversensing of far field signals, crosstalk, myopotencials, or electromagnetic interference [8]. First two situations are related with dual chambers pacemaker and obviously are not connected with our study.

Myopotencials and electromagnetic interference are able to occur in pts with VVI PM. However our all patients were implanted with bipolar endocardial leads and according to our studies the risk of such disturbances is very low (19, 20).

We should also take account that PM Holter is not able distinguished between effective pacing and failure to capture. Previous studies showed that in patients implanted with new leads the percentage of pacing disturbances is also very low (<1%) [9].

This preliminary studies does not suggest that the interpretation of the internal data will replace the 24-hour surface ECG in patients with pacemakers but the value of the internal data over longer periods of follow up is worth further investigation and may be useful in clinical practice in some patients.

Conclusions

Values of Vs and Vp retrieval from the pacemaker memory significantly correlated with data from Oxford Holter monitoring.

Difference in HR max may depend on different algorithms in pacemakers memory and Holter monitoring .

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