Bart G. Denys

Sensing Characteristics of Unipolar and Bipolar Orthogonal Floating Atrial Electrodes: Morphology and Spectral Analysis

We investigated wave morphology and spectral energy distributions of signals picked up by floating atrial unipolar and bipolar orthogonal sensing electrodes. Our data show that atrial P and QRS waves from unipolar floating electrodes are comparable. On the other hand, atrial P and QRS waves from bipolar orthogonal floating electrodes are significantly different. Even at high and mid right atrial locations, QRS waves are either absent or much smaller in amplitude and lower in frequency content than P waves. We conclude that the bipolar orthogonal floating atrial electrode is superior to the unipolar one for sensing due to its P to QRS wave discriminating power, which makes complex input filters or algorithms unnecessary. Our data support the idea that physiologic pacing with a VDD or VAT pacemaker is possible using a single pass lead.

Detection of ventricular tachycardia and fibrillation using ECG processing and intramyocardial pressure gradients.

The automatic termination of malignant tachyarrhythmias and of ventricular fibrillation by an implantable device requires a reliable sensing of these episodes of abnormal ECG. Therefore, we induced tachyarrhythmias and fibrillation in eleven dogs and recorded electrograms and intramyocardial pressure. The electrograms were analyzed using the autocorrelation function and the probability density function. Intramyocardial pressure was monitored as a hemodynamic parameter. Results show that in the case of sinus rhythm, all methods are reliable, but in the case of VT and VF, electrogram processing only is insuffcient. It is concluded that combined monitoring of ECG processing and a hemodynamic parameter may increase the sensitivity of an automatic tachycardia‐fibrillation detection system.

Computer processing of echo-mechanocardiograms: Methods and results

Abstract An interactive computer program was developed for the analysis of combined M-mode echo-mechanocardiograms obtained from experiments on dogs. Computerized measurements of dimensional changes and dynamic behavior of the heart throughout a cardiac cycle can assess left ventricular function. Mechanocardiographic and dimensional data were combined to calculate wall tension and stroke work. Signal recording and acquisition, semiautomatic waveform measurements and calculations, interactive processing and production of end-result graphs, and numerical data are presented. Values for ventricular dimensions (diameter and wall thickness) from dogs were obtained. Results indicate the effectiveness of the analyzing methods.

Sensing and pacing with floating electrodes in the right atrium and right atrial appendage

Unipolar and bipolar floating atrial electrograms from 58 pacemaker patients were recorded and compared. Twenty-four floating unipolar electrodes and 29 floating bipolar electrodes were used at mid-right atrial level and five orthogonal atrial J leads within the right atrial appendage. Each signal was analyzed in the time domain: peak to peak deflection of P wave and QRS complex, duration of P wave and QRS complex and slew rate; and in the frequency domain: maximum of the energy spectrum and frequency at which a decrease of 3 dB from the maximal amplitude occurred. Atrial P (1.31 +/- 0.94 mV, mean +/- SD) and QRS (1.0 +/- 0.56 mV) waves from unipolar floating electrodes were comparable, whereas they were significantly different from bipolar floating electrodes (1.15 +/- 0.77 mV and 0.25 +/- 0.39 mV). Amplitudes of P waves from orthogonal J leads were largest (3.1 +/- 2.6 mV) and QRS complexes (0.21 +/- 0.13 mV) smallest. The P waves had the highest frequency content (17.1 +/- 19.4 Hz). It is concluded that atrial electrograms from orthogonal electrodes (bipolar or orthogonal J) offer superior sensing characteristics because of the large amplitude P wave and discriminating power between P and QRS waves (P/QRS voltage 15:1). An orthogonal J lead can thus be used for P synchronous pacing at the atrial level, whereas an orthogonal ventricular lead can be used for rate-response pacing systems.

Simultaneous right atrial appendage sensing with a target tip, a solid tip and j orthogonal electrodes

To compare the sensing characteristics of a solid tip, target tip (Medtronic) and orthogonal electrodes within the right atrial appendage, atrial electrograms were simultaneously recorded from 2 pacing leads in 11 patients. No significant differences were noted between atrial electrograms derived from target tip or a solid tip electrode in contact with atrial myocardium. Mean values for P-wave amplitudes of 3.0 vs 3.1 mV and slew rates 0.4 V/s vs 0.6 V/s, and QRS amplitudes of 1.0 vs 1.2 mV and slew rates 0.4 vs 0.2 V/s were obtained. The frequency content was also similar, with spectral maxima at 8 vs 9 Hz (P wave) and 7 vs 6 Hz (QRS). In contrast, atrial electrocardiograms derived from the orthogonal electrodes were significantly different: P-wave amplitude of 6.1 mV (p less than 0.025) and slew rate of 1 V/s and QRS of 0.13 mV and slew rate of 0.04 V/s. Spectral analysis was also dissimilar with maxima at 34 Hz (P wave) and 3 Hz (QRS). Orthogonal noncontacting sensing electrodes positioned within the atrial appendage offer substantially better electrographic P-wave amplitude detection and QRS rejection than contacting tip electrodes. These leads yield a significant improvement when discriminate atrial sensing is required.

Relationship between apexcardiogram, left ventricular pressure and wall stress.

Simultaneous measurement of left ventricular dimension and wall thickness by M-mode echocardiography, of left ventricular pressure by a tip-transducer manometer, and of the calibrated apexcardiogram with a pixie beam transducer, were made during acute experiments on anaesthetized dogs. Instantaneous values for chamber dimensions and wall thickness were obtained throughout the heart cycle by digitizing the echo-mechanocardiograms. From these data myocardial stresses, derived from a thick shell theory (meridional and circumferential components) and from Laplaces law, were computed. Laplace stress if shown to be an adequate expression for average wall stress. Its value was correlated with the calibrated apexcardiogram. The present investigation suggests that to a certain extent, the apexcardiogram not only reflects pressure changes but also dimensional changes of the left ventricle.

Relaxation within the Left Ventricular Myocardial Wall

To evaluate relaxation mechanics in the wall of the left ventricle needle mounted miniature pressure transducers were inserted at the subendocardial (ENDO) and subepicardial (EPI) level of the anterior wall of the left ventricle during acute open-chest experiments in 10 mongrel dogs. Pressures were recorded during control, volume load and after verapamil administration. The relaxation time constant (tau) was determined by fitting a monoexponential with offset to the isovolumic relaxation period of the ENDO, EPI and left ventricular pressure (LVP) tracings: p = p0e-t/tau + p1. Mean tau-values for LVP, ENDO and EPI during control were (mean +/- 1 SD, ms): 38 +/- 5, 60 +/- 12, 83 +/- 5; during volume overload: 55 +/- 10, 72 +/- 20, 85 +/- 31 and after verapamil administration: 58 +/- 13, 60 +/- 17 and 73 +/- 15, respectively. Relaxation time constants of ENDO and EPI were significantly longer than those of LVP during control and volume loading but not after verapamil when only EPI was significantly different from LVP. These results demonstrate that relaxation indices obtained from LVP may not always reflect intramyocardial mechanics.

Orthogonal atrial appendage sensing.

The characteristics of electrograms derived from a solid platinum‐iridium pacing catheter tip in contact with the right atrial appendage are compared to those derived from a Target‐tip electrode. Both are then compared to electrograms from two noncontacting orthogonal electrodes positioned more proximally within the atriai appendage. Wave form morphology and spectral energy distribution were determined for the three sets of electrograms. It is concluded that orthogonal electrodes placed within the atrial appendage may offer enhanced atrial sensing required by more sophisticated pacemakers.

Ventricular Fibrillation Detection by Intramyocardial Pressure Gradients

Ventricular fibrillation recognition is a major problem before automatic implantable defibrillators (AID) will become useful on a large scale. In this work a pressure gradient measurement is proposed instead of using some kind of ECG processing. Endo- and epicardial pressures in the left ventricular wall were measured with high fidelity tip transducers. The intramyocardial wall gradient was determined by digital subtraction of these pressures.

Transfer characteristics of an ink-jet writer for cardiovascular studies

The transfer characteristic of a 16 channel ink-jet writer used in a cardiovascular laboratory is described. The test method for measuring linearity, gain and phase response is described and results given. The transfer function was calculated from the normalized experimental results and allows prediction of the behaviour of the writer for different input signals. It is shown that the ink-jet galvanometers are linear for signal input amplitudes between 0 and 2.5 V, and have a flat frequency response between DC and 640 Hz (+/- 1%).