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Biomedical subjects

H Ector

Publications and source records attributed to H Ector.

At least 55 records · Page 3Linked to original sources
PubMed1992

Influence of short atrioventricular delay on late diastolic transmitral flow and stroke volume.

Atrial transport function and the corresponding transmitral flow and stroke volume depend on the timing of atrial contraction. To study the influence of short atrioventricular delay (AVD) on these hemodynamic parameters, transmitral flow velocity (by pulsed wave Doppler) and aortic flow (by electromagnetic technique) were studied and compared (paired t test) during normal and short AVD at fixed rate DDD pacing (80 bpm) in AV-blocked, open-chest canine preparations (n:16). The short AVD resulted in a shorter acceleration (difference 4.1 +/- 4.9 msec, mean +/- SD, p less than 0.05), a lower peak velocity (difference: 7.1 +/- 3.2 cm/sec, p less than 0.001), a shorter (difference: 26.9 +/- 16.2 msec, p less than 0.001) and more rapid deceleration (difference: 220.7 +/- 291.7 cm/sec2, p less than 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 +/- 5.2%, p less than 0.001) during short AVD as a consequence of a reduced left ventricular filling due to the interruption of the active atrial transport by the onset of the ventricular contraction.

Animals↗
PubMed1991

Crosstalk with external bipolar DVI pacing: a case report.

An increase of the basic atrial pacing rate from a preset value of 70 beats/min up to 91 beats/min was recorded in a patient with an external bipolar dual chamber pacing system. This observation could be explained by the occurrence of crosstalk; this specific manifestation of crosstalk was the result of the use of an uncommitted DVI pacing mode.

Cardiac Pacing, Artificial↗
PubMed1990

Effect of short atrioventricular delay on cardiac output.

Short atrioventricular (AV) delay modifies late diastolic filling dynamics. The effect of this change on cardiac output (CO) was studied in closed chest, AV blocked canine preparations (N:10), during AV sequential pacing (80 bpm). CO (thermodilution technique) and transmitral flow velocity (TMFV, pulsed-wave Doppler) were measured and compared (paired t-test) on the basis of TMFV pattern, when atrial contraction (A wave) started just after early diastolic transmitral flow deceleration (PR: 219 +/- 25 ms, mean +/- SD) and when A wave occurred at the end of late diastole and shortened due to the next ventricular contraction (PR: 56 +/- 11 ms). The short AV delay resulted in 12.0 +/- 5.9% decrease of CO, reflecting the interrupted late diastolic atrial transport. Properly timed atrial contraction is necessary for optimal AV sequential pacing.

Animals↗
PubMed1989

Extracorporeal shock wave lithotripsy and cardiac arrhythmias.

Holter monitoring was performed in 400 patients undergoing extracorporeal shock wave lithotripsy (ESWL). The highest heart rate occurred before and after ESWL. During respiratory-triggered ESWL, 30% of the patients had one or more ventricular premature beats (VES), and 7% had couplets of VES. The number of ventricular and supraventricular premature contractions was significantly lower during ECG-triggered ESWL. Ventricular tachycardia occurred in seven patients during respiratory-triggered ESWL, and in one patient during nontriggered ESWL. All ventricular tachycardias were nonsustained, asymptomatic, and slow. Supraventricular tachycardia was seen in nine patients. The preference of the urologist for respiratory-triggered ESWL, conflicts with its higher incidence of ventricular arrhythmias.

Adult↗
PubMed1989

Filter characteristics of the atrial sensing circuit of a rate responsive pacemaker. To see or not to see.

The intra-atrial electrograms (P waves) from floating orthogonal atrial electrodes of acutely implanted pacemaker leads (SRT lead) were recorded and the frequency characteristics were determined. The atrial sensing properties of the rate responsive pacemaker (RS4) used in conjunction with these leads, were studied in relation to the frequency spectra of atrial electrograms. Whereas the P waves showed a bandwidth to 65 Hz, the filter had an upper cutoff frequency of 35 Hz. We conclude that unreliable atrial sensing with the RS4-SRT pacing system is primarily due to an inappropriate filter match and therefore no satisfactory rate responsiveness is achieved.

Cardiac Pacing, Artificial↗
PubMed1988

New high-frequency catheter technique for His bundle ablation in dogs.

A new method is presented for the production of complete atrioventricular heart block. It consists of a special catheter, which is inserted into the right atrium via a femoral vein and positioned in the region of the His bundle for His bundle potential recording. Production of heart block is achieved by a high frequency current pulse from an electrocautery unit.

Animals↗
PubMed1987

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.

Atrial Function↗
PubMed1987

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.

Atrial Function↗
PubMed1987

Effects of betaxolol on heart rate in patients with a recent transmural myocardial infarction.

A randomized double-blind trial was performed with betaxolol, a beta 1-selective and long-acting beta-blocker, in patients with a recent first uncomplicated acute myocardial infarction (AMI). Patients were treated between the 3rd and 14th day after the onset of AMI with either a single oral dosage of 20 mg betaxolol or placebo. The effects on heart rate, ventricular and supraventricular arrhythmias were studied by continuous 24 hours ECG recordings on the 7th and between the 9th to 12th after the onset of AMI and by a submaximal exercise test on the 12th day. Hourly mean, peak and minimal heart rate were during the whole day significantly lower in the active treatment group. In betaxolol treated patients diurnal variations in heart rate were definitely changed. No differences in the occurrence of ventricular arrhythmias were found between both groups; auricular fibrillation was more common in placebo treated patients. Heart rate and pressure rate product were significantly higher during exercise in the placebo group. During exercise ventricular arrhythmias were infrequent in both groups. The clinical tolerance of betaxolol was excellent.

Adrenergic beta-Antagonists↗
PubMed1986

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.

Electrocardiography↗
PubMed1986

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 insufficient. It is concluded that combined monitoring of ECG processing and a hemodynamic parameter may increase the sensitivity of an automatic tachycardia-fibrillation detection system.

Animals↗
PubMed1986

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 atrial 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.

Electrocardiography↗
PubMed1985

Measurement of pacing threshold.

Thresholds in constant current and constant voltage are reported for 405 CPI 4118 (Cardiac Pacemakers, Inc.) tined leads. In 98% of the cases, the constant current threshold was equal to or lower than 0.6 mA. A constant voltage threshold was equal to or lower than 0.5 V in 96% of the cases. Three external pacemakers and two pacing system analyzers were evaluated as threshold testing devices. For analyzing the waveforms of current and voltage stimuli, a calibrated isolation amplifier was used. We could not find a definite difference between the value, at which pacing is lost with reduction of the pulse generator output, and the value at which increase reestablishes pacing.

Pacemaker, Artificial↗
PubMed1985

Pacing in children.

Fourteen children had a permanent pacemaker implanted between May 1967 and July 1983. Postoperative complete heart block was the indication in nine cases, congenital complete heart block in three, and sick sinus syndrome in two. Two patients died, one suddenly and one after aortic valve replacement. A total of 48 pulse generators were implanted; five patients were given an isotopic pacemaker. Twelve patients had epicardial leads implanted initially, and two received a transvenous endocardial system. The lead system implanted initially remained without malfunction in only seven patients. In the other seven patients 20 lead malfunctions occurred. Psychological maturity and physical development seemed to be normal in all 14 children. Improvement in equipment and technique will improve the outlook for paced children in the future.

Cardiac Pacing, Artificial↗
PubMed1985

Catheter technique for electrical ablation of the atrioventricular conduction system.

Seven patients with recurrent supraventricular arrhythmias, resistant to conventional drug therapy, were treated with electrical ablation of the atrioventricular (AV) conduction system. Permanent AV block was produced in five patients. Restoration of AV conduction occurred in two patients. The procedure of electrical ablation was well tolerated, without complications.

Adult↗
PubMed1985

Intramyocardial pressure in the canine heart. An experimental study.

During 11 acute open-chest experiments with dogs, intramyocardial pressure was measured in the anterior wall of the left ventricle with a miniature pressure transducer mounted on a 1.6 mm diameter needle. Pressures were measured at the subendocardium (+/- 10 mm), midwall (+/- 7.5 mm), and subepicardium (+/- 5 mm). Simultaneous recordings of left ventricular pressure and two measures of intramyocardial pressure were made during control, acute volume overload, and after administration of verapamil. Maximal amplitude of the subendocardial pressure was higher and the maximal amplitude of the subepicardial pressure was lower than maximal left ventricular pressure for all interventions (p less than 0.001 and p less than 0.01). During volume overload left ventricular pressure increased more than intramyocardial pressure (left ventricular pressure 34%, subendocardial pressure 6%, midwall pressure 14%, and subepicardial pressure 14%). After the administration of verapamil intramyocardial pressure decreased more than left ventricular pressure (left ventricular pressure 16%, subendocardial pressure 26%, midwall pressure 13%, subepicardial pressure 32%). Positive and negative first derivatives of subendocardial pressure were higher than those of left ventricular pressure during control and after verapamil (between p less than 0.01 and p less than 0.001). Positive and negative first derivatives of subepicardial pressure were lower than those of left ventricular pressure during all interventions (p less than 0.001). The timing of the C-point (onset of mechanical contraction) and the positive first derivative of all tracings was synchronous within 8 msec in all interventions. The 0-point (crosspoint of the tangent to the diastolic plateau and the tangent to the relaxation slope; early diastole) of intramyocardial pressure came later than the 0-point of left ventricular pressure, indicating longer relaxation times in the myocardium (subendocardial pressure: control, p less than 0.001, volume, p less than 0.05, verapamil, no significance; midwall pressure: between p less than 0.05 and p less than 0.001; subepicardial pressure: between p less than 0.01 and p less than 0.001).

Animals↗
PubMed1984

Bradycardia, ventricular pauses, syncope, and sports.

16 athletic patients were examined because of syncope, Stokes-Adams attacks, or both. The life-threatening condition required pacemaker implantation in 7 patients. 8 of the 9 other subjects became symptom-free after stopping heavy physical training. 37 top-ranking athletes underwent 24 h Holter monitoring. Pauses longer than 2 s occurred in 19% and resulted from sinus arrest. The longest pause lasted 2.5 s. Second-degree atrioventricular block was noted in 13%.

Adams-Stokes Syndrome↗