Symptomatic, Inspiration-Induced Atrioventricular Block: Treated with Pacemaker Implant.

Background: The respiratory sinus arrhythmia is the most common cardiac arrhythmia. It consists of phasic variations of sinus cycle length produced by an autonomic reflex, and is characterized by increased heart rate during inspiration and decline in expiration. This phenomenon is due to a reduction of the parasympathetic tone during inspiration, causing a rise in the heart rate, while during expiration the opposite phenomenon occurs.

The systolic index: a noninvasive approach for the assessment of cardiac function: implications for patients with DDD and CRT devices.

Background: Our objective was to evaluate the systolic index (SI), the ratio between rate-corrected left ventricular ejection time (LVETc), and a preejection period surrogate (PEPsu), to assess cardiac function in patients with DDD and cardiac resynchronization therapy (CRT) pacemakers.

Methods: LVETc and PEPsu were automatically measured from electrocardiogram and finger photoplethismography. Atrioventricular (AV) and mode switch (CRT to DDD) were used as hemodynamic challenges.

Role of nitric oxide in young patients with vasovagal syncope.

Aims: Nitric oxide (NO) formed in the vascular endothelium produces, among other effects, a strong vasodilation. In order to evaluate the possible role of NO in hypotension induced by head-up tilt test (HUT), we measured plasma levels of its metabolites, nitrites and nitrates (NOx), during the test.

Methods And Results: Twelve patients with vasovagal syncope and positive HUT [HUT(+)] (mean age: 23+/-5 years) and 13 healthy volunteers with negative HUT (controls) (mean age: 24+/-5 years) were included.

Prediction of interatrial and interventricular electromechanical delays from P/QRS measurements: value for pacemaker timing optimization.

Unlabelled: Cardiac pacing creates spurious delays between and within the cardiac chambers. These are: 1. Left atrial (LA) transport delay (ATD) either sensed (s) or paced (p), (time from right atrial P-wave to the end of LA transport (mitral Doppler A-wave)).

Automatic beat-to-beat left heart AV normalization: is it possible?

Programming the right heart AV interval to a normal value may cause a nonphysiological left heart AV due to interatrial and interventricular conduction delays, thus affecting cardiac performance. Since AV normalization at rest and exercise may be invalidated by pacing or sensing (mode) changes, the aim of this study was to (1) study the feasibility of a mode independent pacemaker (PM) algorithm for automatic beat-to-beat left AV normalization, (2) establish normal values for the time between mitral flow A wave (Af) and ventricular activation (Va), the AfVa interval, the mechanical surrogate of left AV, and (C) determine the range of values of the interatrial electromechanical delays (IAEMDs) and the effect of RA pacing. To pace with the proper right AV, the previously reported RV-paced interventricular electromechanical delay and the interatrial electromechanical delay, either P-sensed (IAEMDs) or atrial-paced (IAEMDp) are required inputs.

Insulin sensitivity in young women with vasovagal syncope.

Background: Insulin, in addition to its known metabolic effects, has sympatho-excitatory and vasodilatory actions on muscular blood vessels. The goal of this study was to evaluate insulin sensitivity in young women with vasovagal syncope and positive tilt test results (HUT+) and to compare it with that in patients with negative tilt test results (HUT-) and in control subjects without a history of syncope.

Methods: Different indices of insulin sensitivity were obtained by an oral glucose tolerance test (OGTT) in 13 young women with syncope and HUT+ (age 26.

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.

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.

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.

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.

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).

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.

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.