A New NOninvasive method for evaluation of heart pathophysiology after  transplantation

E. J. Tkacz¹, P. Kostka¹, D. Komorowski¹,T. Pałko², Z. Religa^1,3, P. Kołsut^3
1Institute of Heart Prostheses, Foundation of Cardiac Surgery Development, Zabrze, Poland,
²Institute of Precision & Biomedical Engineering, Warsaw University of Technology, Warsaw, Poland
³National Institute of Cardiology, Warsaw Poland

Abstract: A novel method has been suggested, which allow to evaluate the state of transplanted heart from both hemodynamic and control parameters point of view. Hemodynamic parameters such as stroke volume (SV) and cardiac output (CO) and systolic time interval (STI) are all evaluated using noninvasive impedance techniques based on application of Kubicek equations. On the other hand the control of the heart rhythm modulation strictly connected with the vegetative reinervation process in case of transplanted heart is evaluated by means of application of heart rate variability (HRV) analysis.  Also a novel technique for HRV analysis has been elaborated as well and then applied for patients examinations. Apart of classical, well known, impedance reography an impedance spectrometry has been applied. The later technique however need some further investigations.

INTRODUCTION

It is more than 30 years when first heart transplantation has been performed in South Africa by Christiaan Barnard. However many years had to pass up to the moment when in Norwegian fjord a special fungus from which a hormone like cyclosporinum has been extracted. This fact has to be considered as a new light in transplantology and following that a heart transplantation has started to be a saving life medical technique more and more popular in the whole world. Currently heart transplantation itself is not considered to be a very sophisticated, requiring special abilities cardiac surgery. It has become more less routine treatment providing that suitable donor is available at the right time. The main point is keep the patient after heart transplantation alive i.e. to follow with him a procedure guarantying complete recovery with no additional pharmacology application in the foreseeable future. This is actually the main reason why a method both invasive or noninvasive evaluation of heart pathophysiology is necessary.

METHODS

The suggested method combines two different techniques, which can be classified into biomedical engineering area, more precisely into processing of biomedical signals. These techniques are the following: impedance reography applying well known Kubicek method for hemodynamic parameters evaluation such as stroke volume (SV), cardiac output (CO) and systolic time intervals (STI), and heart rate variability (HRV) analysis using modern “on-line” Kaiser window [1] for signal extraction. The HRV analysis allows for observation of the vegetative reinervation process. It is well know that during the HTx operation there is no time for precise connection of vegetative nerves around sinus node. Technically this is impossible to perform due to the two long operation time. However the living tissue recover and according to published reports the process of vegetative reinervation can be observed. All of these parameters are evaluated totally noninvasive with a minimum stress given to the patients. Patients after heart transplantation (HTx) are examined three times: two week after transplantation, six weeks and the last examination is twelve weeks after HTx. This is in correspondence with normal rehabilitation post HTx procedure as well as with necessity of biopsy. Due to lack of control media for heart rhythm modulation the spectral analysis of recorded HRV signal shows that calculated power spectrum is flat. This is obvious as no signal variability is observed. If however during this twelve weeks with three examinations in the middle one can observe the start of power spectrum small ripples than it means that the process of reinervation has started. This is of course a positive symptom of the whole HTx rehabilitation procedure.

RESULTS

During 18 months of examination the 15 patients have  undertaken examinations i.e. signals such as impedance reography and heart rate variability have been collected in the defined above moments of time after HTx. Two patients have died due to complications in the third and fifth week after HTx.

Figure 1. Average variability range versus time in weeks after HTx

Figure 1 illustrates the average variability range growth. This is very important prognostic factor proving that in case of 13 examined patients the rehabilitation procedure has been performed correctly. There are no clinical standards in such examinations, however many researchers consider 50 ms RR variability range as a certain limit allowing to conclude that vegetative reinervation has started.

Figure 2. Average Stroke Volume (SV) in [ml]

Figure 2 illustrates the tendency of SV change within the investigated twelve weeks. The beginning growth can be observed together with tendency to stabilization. It means again that rehabilitation process after heart transplantations is correct.

DISCUSSION

It is clear that with the help of such noninvasive examination applying state-of-the-art measurements and signal processing techniques one can expect significant results allowing to differentiate clearly patients whose post HTx rehabilitation is correct from those who may need some special cardiologist intervention. Unfortunately unambiguous statement of threshold when immunoblockers can be removed  and particular patient is free from transplant rejection is impossible and needs much more examination.

 Acknowledgments:  Work supported by State Committee for Scientific Research grant number T11E 019 25

REFERENCES

[1]           S.R. Seydnejad, R. I. Kitney, “Real – Time Heart Rate Variability Extraction Using the Kaiser Window” IEEE Transaction on Biomedical Engineering, Vol. 44, No 10, October 1997, pp. 990-1005.

[2]           M. Schafer, W. Gross, J. Ackermann, M. Mory, M. M. Gebhard, “Minitoring of Physiological Process in Ischemic Heart Muscle by Using a New Tissue Model for Description of the Passive Electrical Impedance Spectra”, International Conference on Bioimpedance, Oslo, Norway June 2001, Conference Proceedings pp. 55-58.

[3]           E.J. Tkacz, P. Kostka, “An Application of Wavelet Neural Network (WNN) for Coronary Artery Disease Patients Classification”, World Congress of Medical Physics and Biomedical Engineering, Chicago, July, 2000, Conference Proceedings on CD.