Relative ventricular volume measurements by intracardiac impedance.

The purpose of this study was to investigate whether changes of the right ventricular end-diastolic and end-systolic volumes can be detected by the DC-coupled electrical intracardiac impedance signal. Measurements were conducted in 13 patients with an implanted or external pacemaker, testing various measurement configurations. Volume changes were induced by incremental overpacing and by postural changes. The pulse contour systolic integral from the peripheral blood pressure was used as a marker of stroke volume changes. The results show, that DC-coupled impedance can detect volume changes of the right ventricle. The quadrupolar impedance measurement configurations offer better amplitude resolution, but the tripolar and intraventricular bipolar configurations are better hemodynamic markers.

Proposal of a method for automatic optimization of left heart atrioventricular interval applicable to DDD pacemakers.

Electrical pacing of the right heart is known to cause delays in the depolarization of left heart chambers, leading to abnormal left heart AV sequence. Interatrial conduction time, defined as the time from the right atrial pacing pulse or intrinsic P to the onset of left atrial P wave, and P wave sensing delay cause a shorter left heart AV interval during atrial pacing-ventricular sensing and atrial sense-ventricular pace. Interventricular conduction time (the time from the right ventricular pacing pulse to the onset of left ventricular depolarization), lengthens left heart AV interval during atrial sensing-ventricular pacing. These delays may add up or partly cancel out, depending on pacing mode. Thus, an algorithm for DDD pacemakers to optimize left heart AV interval by compensating for the above delays is proposed. This algorithm takes into account pacing and sensing delays to deliver a certain AV sequence to the right heart, aimed at producing a physiological left heart AV interval. The optimization of left heart AV interval is achieved by automatically changing right heart AV interval and pacing mode in accordance with known interatrial and interventricular conduction delays, and P wave sense offset.

Feasibility of measuring relative right ventricular volumes and ejection fraction with implantable rhythm control devices.

Ejection fraction (EF), the ratio between stroke volume (SV) and end-diastolic volume (EDV), is a valuable contractility indicator. Unlike SV, the Frank-Starling effect is automatically compensated in the calculation of EF. It was the aim of this study to evaluate the physiological behavior of impedance derived measurements of relative right ventricular (RV) volumes and EF, obtained with standard pacing leads. Seven patients were evaluated at the time of pacemaker implant or replacement. Since no absolute standard of comparison was available for RV volumes, the value of the measurements was assessed by observing their behavior under cardio-circulatory challenges. A 2.5-kHz carrier was fed to the ring and tip electrodes of standard bipolar pacing leads and the resulting voltage was digitized and stored. The peak-to-peak voltage (PPV) of the carrier at the time of QRS was used as EDV, and the largest PPV as end-systolic volume (ESV). Relative SV was the difference between EDV and ESV, and EF = SV/EDV x 100. Pacing was used to reduce EDV, and the effect of contractility was tested with isometric hand grip, recumbent leg exercise, or isoproterenol drip. Only minimal changes in EF were noted during incremental pacing; relative SV and EDV decreased as expected; and EF increased significantly during contractility challenges. A high correlation coefficient was observed between EDV and SV changes induced by incremental pacing at rest (r values from 0.62 to 0.98, P from < 0.01 to 0.001). The study revealed that impedance volumetry, utilizing conventional bipolar pacing leads, yields useful hemodynamic data related to EDV, ESV, and EF. Given the simplicity of the method, it is reasonable to conclude on the feasibility of using said impedance derived hemodynamic parameters in implantable rhythm control devices.

Nonphysiological left heart AV intervals as a result of DDD and AAI "physiological" pacing.

DDD and AAI pacemakers are considered physiological, since they preserve atrioventricular (AV) synchrony. Artificial pacing, however, is performed largely from right heart chambers, causing aberrant depolarization pathways. Pacing at the right atrial appendage (RAP) is known to delay left atrial contraction due to interatrial conduction time (IACT), and right ventricular (RV) apical pacing (RVP) delays left ventricular (LV) contraction due to interventricular conduction time (IVCT). These delays may render the left heart AV intervals (LAV) either too short or too long, thus affecting LV systolic function. The purpose of this study was to evaluate the actual LAV intervals during conventional, right heart AAI and DDD pacing. Resulting LAV intervals were compared to programmed AV values during all DDD pacing modalities. Ten patients with DDD and six patients with AAI pacemakers were studied. IACT was measured from the atrial spike to the onset of left P wave, as recorded by an esophageal lead. Systolic time intervals were measured using either a carotid pulse tracing or a densitogram (photoplethysmography). LV function was appraised by measuring rate-corrected LV ejection time (LVETc). IVCT was measured indirectly as the lengthening of LV preejection period (PEP) caused by RV pacing, as compared to normal depolarization pathway. Intrinsic IACT and IVCT were considered zero. Right heart AV intervals (RAV) were measured from surface ECG and LAVs were calculated according to the following equations: Sinus Rhythm: LAV = RAV; Atrial Pace + Ventricular Sense: LAV = RAV - IACT; Atrial Sense + Ventricular Pace: LAV = RAV + IVCT; Sequential AV Pace: LAV = RAV - IACT + IVCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensor for right ventricular volumes using the trailing edge voltage of a pulse generator output.

Cardiac and thoracic volume (Vol) signals are useful for diagnosis and adaptive rate pacing. Present systems need an AC or pulsed constant current carrier to measure conductivity (proportional to Vol), causing high battery drain and requiring complex detection algorithms or special leads. The aim of this study was to propose a new and simple sensor for cardiac volumes using standard pacing leads and no AC carrier signal. "Constant voltage" pulse generators (PG) deliver a square pulse to the lead via a capacitor (Cap). The signal resulting from the interaction between the PG and the tissues and blood is trapezoidal, with a leading edge voltage determined by PG output and a trailing edge voltage (TEV) dependent on electrode surface and Cap value (device constants), and patient load. The hypothesis that right ventricular (RV) and chest Vol variations could produce load-related TEV changes was tested. Four PGs were connected to bipolar (Bip) leads within containers with 5-80 cc of saline, and TEV was measured with every 5 cc Vol change. Fifteen patients with previously implanted Bip PGs were studied during VOO pacing, scanning the intrinsic cardiac cycle. TEV was noninvasively measured as a function of time from onset of QRS.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological principles of a new method for rate responsive pacing using the pre-ejection interval.

The pre-ejection interval (PEI) was measured in 30 patients during isotonic and isometric exercise, emotional stress, isoproterenol infusion, Valsalva maneuver, carotid massage, atropine injection and incremental pacing. In patients with complete AV block, the simultaneous atrial rate was used as a standard of comparison to assess the changes observed in PEI. The sensitivity, specificity, proportionality and speed of response were evaluated to determine the applicability of PEI for rate responsive pacing. PEI shortened promptly and proportionately to atrial cycle length with isotonic and isometric exercise, emotional stress, and isoproterenol (R values from 0.88 to 0.98, p less than 0.001). It was neither affected by preload changes (Valsalva) nor by parasympathetic system (carotid massage and atropine). Incremental pacing had no effect in most of the patients but some showed a slight prolongation, similarly to what is observed with atrial cycle length. It is concluded that PEI is suitable for rate control in physiologically adaptive pacemakers.

Electrocardiographic detection of left atrial enlargement. Correlation of P wave with left atrial dimension by echocardiography.

The validity of various electrocardiographic P wave measurements was tested in 48 patients by comparing them to left atrial dimensions determined by echocardiography (echo), a proved method of left atrial size estimation. Of all the measurements considered, only the width of the P wave (PW), the P terminal force in lead V1 (PV1), and the PW/PR segment ratio (PW/PR) showed statistically significant correlations with left atrial size measurements by echo, with r values of 0-746, 0-491, and 0-479, respectively. The results indicated that P widths in excess of 105 ms were present in all the patients who had left atria equal to or greater than 3-8 cm by echo and in 11 per cent of patients without atrial enlargement (false positives), and that when measurements were less than 105 ms left atrial enlargement was unlikely.