A novel and simple technique to allow detection of the position of the R-waves from intraventricular pressure waveforms: Application to the conductance catheter method

A simple and novel technique that utilizes the zero-crossing points of the first time derivative of intra-ventricular pressure (dP/dt) to mark systole , is proposed. Discrete differentiation of the sampled pressure waveform is calculated using a difference equation. Filtration of high-frequency noise in dP/dt is achieved using a low-pass Butterworth filter of order 4 and a cutoff frequency of 10 Hz. The filter is realized digitally using infinite impulse response filter stages. Double filtering of discrete dP/dt is used to eliminate time shifts. The methods are evaluated on data obtained from s ix large, white, anaesthetised and open chest pigs, instrumented with a con ductance catheter. The zero-crossing points of the filtered dP/dt compare v er, well with the R-waves of the electrocardiogram (ECG) as markers of syst ole. The mean error is 1.3% of the duration of the heart-cycle. Significant ly, our results provide a solution to a problem often encountered with mult iuse pressure-volume catheters when an ECG signal cannot he obtained. In th is situation, the zero-crossing points of dP/dt, rather than the K-waves of the EGG. can be used as a marker of systole, thus enabling the constructio n of end-systolic pressure-volume relations to assess cardiac contractility .