Lack of Influence of Atrioventricular Delay on Stroke Volume at Rest in Patients with Complete Atrioventricular Block and Dual Chamber Pacing

Dual chamber pacing (DDD) maintains atrioventricular (AV) sequence; AV delay programmability modifies the relationship between atrial and ventricular contraction. To evaluate the hemodynamic effects of such a modification, ten patients with a DDD unit for complete AV block were studied by time-motion (M-mode) and Doppler echocardiography during inhibited ventricular pacing (VVI), atrial-triggered ventricular pacing (VDD) and atrioventricular sequential pacing (DVI) at different AV delay (90, 140, 190, 240 msec). A significant improvement in stroke volume (SV) (15%-20%, P less than 0.05) was seen during DDD versus VVI pacing; no changes, however, were observed in the same patient with different AV delay or during DVI versus VDD pacing. These data suggest that programming of AV delay does not affect systolic performance at rest; longer diastolic filling times recorded during DDD pacing with "short" AV delay (90-140 msec) do not seem to be a hemodynamically relevant epi-phenomenon of PM programming.     

Clinical Experience with Orthocor II Antitachycardia Pacing System for Recurrent Tachyarrhythmia Termination

Between June 1986 and December 1988, eight patients were treated with an Orthocor II 284 A antitachycardia pacemaker (Cordis Corp., Miami, FL, USA) forsupraventricular tachycardia (SVT) and ventricular tachycardia (VT) termination. Four patients had intra-AV nodal reentrant tachycardias; 1 patient had AV reentrant tachycardia with an atrio-nodal accessory bypass tract; 2 patients had AV reentrant tachycardias with concealed Kent bundle, and 1 patient had ventricular tachycardia. All patients had been treated with three or more drugs and were considered to be drug refractory. The programmed antitachycardia mechanism used for patients with SVT were: automatic overdrive in five patients and burst scanning in two patients. In the patient with VT, a critically timed double extrastimulus with fixed coupling interval was programmed. Follow-up ranged from 2 to 30 months. The pacemaker proved to be effective in terminating tachycardias in all cases with SVT; in the patient with VT, the programmed antitachycardia mechanism was effective for a long time, but after an episode of sustained VT not interrupted by the pacemaker, the patient underwent automatic cardioverter/defibrillator (AICD) implantation. Additional antiarrhythmic therapy was required in 3 patients to control their maximum sinus rate, in 1 patient to reduce tachycardia episodes and to enable termination, and in 2 patients to prevent spontaneous atrial fibrillation. It is concluded that Orthocor II is a flexible and versatile antitachycardia pacemaker providing a safe and effective control of recurrent tachycardia in selected patients.     

Retroconduction Selective Recognition in Wide-Dipole Floating Atrial Sensing

Effective discrimination of retrogradely conducted P waves would allow distinguishing sinus tachycardia from supraventricular tachycardias due to A V or nodal reentry, and would prevent pacemaker-mediated tachycardia in AV sequential pacing. This might be especially relevant in VDD implants, where retroconduction could be induced by escape ventricular stimulation. In order to analyze the respective waveform properties, anterograde and retrograde atrial signals were recorded by a wide floating electrode dipole, on the implantation of a permanent single-pass lead for VDD pacing. Generally, bipolar recording did not allow reliable discrimination, while the signal nature could be readily diagnosed from the main features of the unipolar atrial electrograms. The unipolar waveform recorded under sinus rhythm in high right atrium, close to the superior vena cava opening (proximal EGM), started with a negative deflection in 88% of the patients. In 7% of the patients, the first deflection of the signal was positive in some cardiac cycles only, and, on the average, the amplitude of the positive phase was not higher than 5% of the signal peak-to-peak amplitude. Conversely, under retroconduction, the starting deflection attained higher positive values in 98% of the patients, being stably over 15% of the peak-to-peak amplitude in 86% of the cases. Furthermore, in 69% of the cases, the lag time between the onset of the negative deflection of proximal and distal (mid-low atrium) unipolar EGM changed unambiguously when retroconduction occurred, exceeding the range of variation observed in each patient during sinus activity. The combined evaluation of unipolar EGM shape and lag time allowed specific retroconduction recognition in 95% of the patients. We suggest that this approach may yield useful information for the discrimination of retrograde atrial signals, provided that the recording dipole is sufficiently long and the proximal electrode is properly positioned in the high right atrium.     

Increasing Cardiac Rate by Tracking the Respiratory Rate

Un stimulateur asservi qui utilise la fréquence venlilatoire comme capteur a été implunté chez 22 patients, dont 19 pour la stimulation ventriculaire et 3 pour la stimulation auriculaire. Le niveau d'exercice atteint en utilisant ce système a été toiijours supérieur à celui de la stimulation ventriculaire à fréquence fixe. En plus, aucun capteur chimique ou mécanique n'était utilisé; le capteur même est simple, durable et utilise une faible énérgie. Done, ce système s'adapte facilement à chaque patient individuel.     

A New Approach to the Prevention of Endless Loop Tachycardia in DDD and VVD Pacing

Endless loop tachycardia (ELT) is a possible complication in dual chamber pacing; it is usually prevented by programming the atrial refractory period (PVARP) longer than the retrograde ventriculoatrial (VA) conduction interval; this in some patients limits the upper rate. In 15 patients with a DDD (nine patients) or a single-pass lead VDD pacemaker (six patients) and retrograde atrial activation, telemetric recording documented a significant difference in amplitude of antegrade, and retrograde atrial potentials (VDD 1.21 ± 0.32 mV vs 0.56 ± 0.23 mV, P = 0.008; DDD 2.7 ± 1 vs 1.8 ± 1 mV, P - 0.038; Student's t-test for paired data). In 3/15 patients ELT stopped after programming of atrial sensitivity to a value. greater than the retrograde P wave amplitude; in 11/15 patients this occurred at a sensing value lower than or equal to retrograde P wave amplitude with a high pass band filter operating. One patient required PVARP lengthening. Holter monitoring showed no more ELTs. In most patients with a DDD or single-pass lead VDD pacemaker with widely programmable sensing amplitude and Hi/Low bandpass filters. individual programming of atrial channel sensitivity prevents ELT without affecting the PVARP and, consequently, upper rate limit.     

Physiological Sensitivity of Respiratory-Dependent Cardiac Pacing: Four-Year Follow-Up

Clinical and physiological data on long-term follow-up of 143 patients with respiratory-dependent pacemakers (RDP3) are reported; 121 patients received ventricular (VVI-RD) and 22 patients atrial (AAI-RD) respiratory-dependent stimulation. Functional evaluation was based on the exercise testing (130 pts) with oxygen uptake VO2, ventilation, ECG and arterial pressure monitoring and the dynamic Holter electrocardiogram (95 pts). In each patient, the stimulation rate curve selected was that which produced the best work tolerance and moved the anaerobic threshold to the right. Respiratory levels were assessed by telemetry verifying proper sensing of tidal volume variations and absence of interference and artefacts. In patients with VVIR or AAIR stimulation, exercise tolerance, oxygen uptake and anaerobic threshold increased significantly in comparison with VVI or AAI pacing respectively. The physiological sensitivity of the stimulation system (i.e., a linear relationship of the pacing rate with metabolic requirements) was excellent (up to exhaustion) in 70%, very good (up to anaerobic threshold) in 20% and erratic (no relationship between pacing rate and VE/VO2) in 10% of patients. In dynamic electrocardiographic monitoring, the automatic pacing rate was always predominant during the night and during rest periods; the pacing rate increased properly with daily activity; myopotential inhibition (none longer than 3,500 ms) was observed in 38 patients, but without subjective complaints. The incidence of the RDP3 malfunction was less than 8%; it may have stemmed from the pacing system itself, or from other clinical conditions. Oversensing of impedance system pulses has not been recorded in the last 3 years. Partial respiration undersensing results from incorrect accessory lead position, pulmonary emphysema, marked obesity or other causes. Respiratory sensing becomes erratic at the anaerobic threshold point in such patients, but functions well at submaximum exercise levels. In patients with left ventricular failure, exercise tolerance was improved by setting a lower ratio between the pacing rate and respiration, which prevented the occurrence of excessive pacing rates.     

Implantable Cardioverter Defibrillators and Cellular Telephones: Is There Any Interference?

The aim of our study was to consider cellular telephone interference using different cellular telephones and implantable cardioverter defibrillator (ICD) models. Thirty (26 men, 4 women) patients with ICDs were considered during follow-up. The ICD models were: Telectronics (7), CPI (7), Medtronic (7), Ventritex (5), and Ela Medical (4). All patients were monitored with surface ECG; permanent telemetric endo-ECG monitoring was activated. Then, the effect of two different European telephone systems were tested: TACS system (Sony CM-R111, 2W power) and GSM system (Motorola MG1-4A11, 2 W power). For both systems, the effect during call, reception, active conversation (dialogue), and passive conversation (listening) were observed. Cellular telephones were located first in contact with the programming head, then near the leads system, and lastly, in the hands of the patient. At the end of the evaluations, memories were interrogated again to check for false arrhythmia detections. In five of these patients during arrhythmia induction at device implant (first implant or ICD replacement), we also evaluated possible interference between cellular telephones in the reception phase and the ventricular fibrillation detection phase of the ICD. All evaluated models showed significant noise in the telemetric transmission when the cellular telephone (both TACS and GSM) was located near the ICD and the programming head; noise was particularly significant during call and reception, in most cases leading to loss of telemetry. No false arrhythmia detections have been observed during tests with cellular telephones located on the ICDs. During tests performed with cellular telephones located near the leads or in the hands of patients, no telemetric noises orfalse arrhythmia detections were observed. During induced ventricularfibrillation and cellular telephones in reception mode near the device, the arrhythmia recognition was always correct and not delayed. In conclusion, present ICD models seem to be well protected from electromagnetic interference caused by European cellular telephones (TACS and GSM), without under-/oversensing of ventricular arrhythmias. However, cellular telephones disturb telemetry when located near the programming head. ICD patients should not be advised against the use of cellular telephones, but it has to be avoided during ICD interrogation and programming.     

Clinical Characteristics,Mortality, Cardiac Hospitalization,and Ventricular Arrhythmias in Patients Undergoing CRT‐D Implantation: Results of the ACTION‐HF Study

CRT Patient Characteristics and Outcomes . Introduction: The characteristics and outcomes of patients who undergo cardiac resynchronization therapy (CRT) device implantation in current clinical practice may differ from those of reference trial populations. Study objectives were to assess 2‐year outcomes in a population implanted with a CRT plus defibrillator device in accordance with the standard of care and to evaluate any independent association between clinical variables and outcome. Methods and Results: A total of 406 patients enrolled at 35 centers in Italy were followed up prospectively for 2 years. All patient management decisions were left to the treating physician's discretion, in accordance with clinical practice. ACTION‐HF patients had a better baseline clinical status than patients enrolled in the COMPANION study: shorter HF history (1 vs 3.5 years, P < 0.01), less advanced NYHA functional class (III–IV: 73% vs 100%, P < 0.01), higher LVEF (26% vs 21%, P < 0.01), higher SBP (122 vs 112 mmHg, P < 0.01), and less diabetes (27% vs 41%, P < 0.01). This status was reflected in lower mortality (11.5% vs 26%) and a lower incidence of appropriate ICD shocks (12.1% vs 19.3%). AF history was an independent predictor of the combination of all‐cause mortality and cardiac‐cause hospitalization (HR: 3.31; P < 0.001). Recurrent or new atrial arrhythmias were independently associated with the development of ventricular arrhythmias (HR: 3.4; P < 0.001). Conclusions : This population appears clinically less compromised and had a lower incidence of adverse clinical outcomes than those of reference trials. However, we recorded a substantial burden of atrial arrhythmias, which was independently associated with a higher incidence of ventricular arrhythmias. (J Cardiovasc Electrophysiol, Vol. 24, pp. 173‐181, February 2013)