Andreas Liebrich

Proarrhythmic Effect of Pacemaker Stimulation in Patients With Implanted Cardioverter-Defibrillators

Background—We sought to determine the potential of right ventricular VVI backup pacing to induce ventricular tachyarrhythmias in patients with implanted cardioverter-defibrillators. Methods and Results—All consecutive patients presenting exclusively with pacemaker-induced tachycardias (PITs) were included in a prospective study using a crossover protocol. Patients were randomized to either group 1 (augmentation of the baseline frequency of the pacemaker to 60 bpm) or group 2 (pacemaker turned off) and were followed up for 1 year and then crossed over to the other programming, looking for reoccurrence of PIT. Of 150 consecutive patients, 39 (26%) had PIT, 13 of them exclusively (8.6%). Forty of 1063 analyzed tachyarrhythmias of all the patients were PIT (3%). Before inclusion in the study, the patients had 2.7±0.9 PITs in 11±6.5 months with their pacemakers programmed empirically at 42.3 bpm. During the study phase, no PIT occurred while the pacemaker was turned off, whereas programming to 60 bpm led to the recurrence of PIT in 5 of 6 patients (1.4±0.6 per patient). At the end of the study, 9 patients underwent a prolonged follow-up with their pacemakers turned off, resulting in spontaneous episodes of ventricular tachycardia/fibrillation in 5 patients, but PITs were no longer observed. Conclusions—This crossover protocol proves the potential proarrhythmic effect of pacemaker stimulation in implantable cardioverter-defibrillator patients. Resulting PITs led to clinical symptoms and antitachycardia therapy by the implantable cardioverter-defibrillator. Thus, in patients presenting with PIT but without a pacemaker indication, the pacemaker feature should be turned off, or, alternatively, the longest possible escape interval should be programmed.

Cardiac output in single-lead VDD pacing versus rate-matched VVIR pacing

The importance of atrioventricular synchronous pacing compared with single-chamber rate-responsive pacing is still under discussion, especially for low-intensity workload representing daily life activities. We evaluated hemodynamics in single-lead VDD pacing versus VVIR pacing in 11 patients (8 men and 3 women, aged 58.6 +/- 13.8 years) with normal left ventricular function and a previously implanted single-lead VDDR pacemaker. A low-intensity steady-state treadmill test at 1 to 2.5 mph with a gradient of 2% to 4% was performed. Cardiac output was determined using a standard carbon dioxide rebreathing technique. Initially, the VDD mode was programmed, and after 5 minutes of exercise, cardiac output was measured in steady-state conditions. The pacemaker was then reprogrammed to the VVI mode at a rate 5 to 10 beats above the maximal atrial tracking rate to simulate rate-matched VVIR pacing (VVIRm). After 5 additional minutes of steady-state exercise, cardiac output was measured again. The maximal atrial rate in the VDD mode was 119 +/- 19 beats/min versus a programmed rate of 129 +/- 18 beats/min in the VVIRm mode. VDD pacing resulted in a significantly higher cardiac output than VVIRm pacing (10.6 +/- 1.9 vs 9.2 +/- 1.4 L/min; p < 0.002), with a mean difference of 1.6 +/- 1.2 L/min between the 2 modes. In the VDD mode, stroke volume (90.7 +/- 20.1 vs 71.6 +/- 13.0 ml; p < 0.001) and maximal oxygen uptake (1,183 +/- 264 vs 1,076 +/- 289 ml/min, p < 0.01) were also higher than in VVIRm.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and efficacy of implantable defibrillator therapy with programmed shock energy at twice the augmented step-down defibrillation threshold: results of the prospective, randomized, multicenter low-energy endotak trial ☆

Whether the safety and efficacy of implantable cardioverter defibrillator (ICD) therapy can be assured with lower output devices is an important question. The purpose of this study was to evaluate whether programming the device output at twice the augmented defibrillation threshold was as safe and effective as using the maximum energy. Patients indicated for ICD therapy, but without slow monomorphic ventricular tachycardia (MVT), who achieved an augmented defibrillation threshold (DFT plus) < or = 15 joules (J) with a single endocardial lead system and a biphasic defibrillator were included in the study. Prior to ICD implantation, patients were randomized into 2 groups. The shock energies in test group patient were set as follows: first shock at twice DFT plus, the second to fifth shocks at maximum output (34 J). In control group patients, all shocks were programmed at 34 J. The study population consisted of 166 consecutive patients (mean age 57.4 +/- 12.1 years, mean left ventricular ejection fraction 36.8 +/- 13.8%). Mean DFT plus was 9.6 +/- 3.2 J in test group patients and 10.1 +/- 3.5 J in control group patients (p = 0.36). During a mean follow-up of 24.2 +/- 9.6 months, 736 arrhythmia episodes were analyzed. The first shock efficacy was 98.3% in the test group patients versus 97.4% in the control group (p = 0.45). Total mortality was 6%, equally distributed in both study groups. The results of this study prove that the method of doubling the defibrillation energy at the DFT plus level provides an adequate safety margin in defibrillator therapy.

IS THERE A RISK FOR INTERACTION BETWEEN MOBILE PHONES AND SINGLE LEAD VDD PACEMAKERS

Mobile phones may cause pacemaker interference. Patients with a single lead VDD pacemaker might be at special risk, since the atrial sensitivity is often programmed to low (high sensitivity) threshold values and the majority of patients are pacemaker dependent due to the underlying high degree AV block. We evaluated 31 patients with three types of single lead VDD pacemakers: 12 Unity, 292–07 (Intermedics, Inc.); 10 Thera VDD, 8948 or 8968i (Medtronic, Inc.); and 9 Saphir 600 (Vitatron, Inc.) for interference from a cellular mobile phone with a power of 2 W (D‐net). For this purpose, atrial and ventricular sensitivity settings were programmed to their most sensitive values (A: 0.1–0.25 mV; V: 1.0 mV) and ventricular sensing was programmed to unipolar. With the ECG continuously monitored, the phones extendable antenna was brought in direct contact with the patients skin at the right sternal border, with the tip of the antenna in skin contact just below the clavicle, within 5 cm of the pacemaker connector. Then multiple phases of phone calls were performed, and the effects on the pacemakers recorded. In our group of patients with three different types of single lead VDD pacemakers, no interference could be detected using a 2‐W mobile phone in the digital D‐net. The programmed values remained unchanged after the interference test. Therefore, the risk of interference seems to be low for the VDD pacemakers tested, although our study design does not allow to entirely exclude the possibility of interference from a mobile phone.

Safety of Antitachycardia Pacing in Patients with Implantable Cardioverter Defibrillators and Severely Depressed Left Ventricular Function

The purpose of this study was to investigate the efficacy and safety of antitachycardia pacing (ATP) in third‐generation implantable Cardioverter defibrillators (ICDs) for terminating spontaneously occurring ventricular tachycardias (VTs) in patients with severely depressed left ventricular (LV) function. Ninety‐one patients with active ATP were followed for 16 ± 13 months. During this period, 775 VT episodes occurring in 36 patients were treated by ATP. The patients were divided into two groups according to their LV ejection fraction (LVEF): group A with LVEF ± 30% (n = 20), and group B with LVEF ± 30% (n = 16). There were no differences between both groups in age, gender, underlying heart disease, indication for ICD therapy, or drug therapy. The VT rates were comparable (group A: 183 ± 16 beats/min; group B: 180 ± 21 beats/min; P = NS). Eighty‐three percent of all episodes (n = 332) in group A and 93% of the VTs (n = 443) in group B were ATP terminated (P ± 0.01). Ten percent of VTs in group A were accelerated by ATP into the ventricular fibrillation zone versus 2% in group B (P ± 0.01). The individual termination rate and acceleration rate per patient were comparable in both groups. All VT episodes unresponsive to ATP were converted by backup shocks. The efficacy of first‐shock therapy was similar in both groups (group A: 89%; group B: 97%; P = NS). The proportion of patients who needed at least one backup shock for unsuccessful ATP was comparable in both groups (group A: 65%; group B: 56%; P= NS). We conclude that ATP is effective and safe in patients with recurrent VTs and severely depressed LV function, and it can be safely programmed in this group of patients to minimize the use of shock therapy.

Ventilation and heart rate response during exercise in normals: relevance for rate variable pacing.

The observation of a close relationship of heart rate to oxygen uptake (HH‐VO2) and heart rate to minute ventilation (HR‐VE)has been shown to be of particular value in rate variable pacing. However, the impact of anaerobic threshold (AT)for the HH‐VO2 and HH‐VE slope has been studied Jess. Twenty‐three male and 16 female subjects, mean age 52 ± 7 years, were selected in whom complete heart catherization and extensive noninvasive sludies excluded major cardiopulmonary disease. Semisupine bicycle exercise testing with analysis of respiratory gas exchange was performed using a ramping work rate protocol with work increments of 20 watts/min. At the respiratory AT, determined by the V slope method, oxygen uptake (VO2‐AT)was 15.2 ± 3.0 mL/kg in males versus 13.8 ± 2.3 mL/kg in females and heart rate (HR‐AT)was 109 ± 18 beats/min versus 119 ± 20 beats/min, respectively. Heart rate was highly correlated (r ±0.9)to VO2 and minute ventilation (VE). A linear regression for HR‐VO2, however, was found only in 16/39 and for HR‐VE in 11/39 subjects. Assuming the AT as the breakpoint of two linear curves, it could be demonstrated that compared to low exercise HR appeared to increase at maximal exercise more in relation to VO2 but less in relation to VE; in men the individual slopes for HR‐VO2 were 2.6 ± 0.7 below but 3.2 ± 1.0 above AT (P < 0.05) and the slopes for HH‐VE were 1.6 ± 0.5 below but 1.0 ± 0,4 above AT (P < 0.05). Similarly, in women the individual slopes for HR‐VO2 were 3.7 ± 1.4 below but 4.3 ± 1.4 above AT (P < 0.05)and the slopes for HR‐VE were 2.1 ± 0.9 below but 1.3 ± 0.4 above AT (P < 0.05). The differences between male and female subjects were significant. The nonlinear behavior of the HB‐VO2 and HR‐VE relation from rest to maximal exercise should have a particular impact in respiratory controlied pacing systems.

How can we identify the best implantation site for an ECG event recorder

ZELLERHOFF, C., et al.: How Can We Identify the Best Implantation Site for an ECG Event Recorder? The aim of this study was to show how to find the preferable implantation site for an ECG event recorder (ECG‐ER). We compared the quality of bipolar ECG recordings (4‐cm electrode distance, vertical position) in 65 patients at the following sites: left and right subclavicular, left and right anterior axillary line (4th‐5th interspace), left and right of the sternum (4th‐5th interspace), heart apex, and subxyphoidal. The results were compared to the standard ECG lead II. In 30 patients, an additional comparison between vertical and horizontal ECG registrations was done using the same sites. ECG signals in five patients were compared positioning the electrodes towards the skin with turning them towards the muscle during ECG‐ER implantation. The best ECG quality (defined as highest QRS amplitude, best visible P wave and/or pacemaker spike, best measurable QRS duration, and QT interval) and best agreement with the standard lead II was found in 68% on the left of the sternum, significantly less often (P < 0.001) on the right of the sternum (14.1%), left subclavicular (6.9%), apical (5.5%) and subxyphoidal (4.2%). A significantly higher QRS amplitude was measured and the P wave was more often visible in the vertical electrode position than in the horizontal position. In all five ECG‐ER patients, there was a good agreement between the bipolar surface ECG at the implantation site and ECG‐ER stored signals. A significant noise signal occurred in all five patients when the ECG‐ER was implanted with electrodes towards the muscle. A P wave was visible in only three of those patients, but there was an insignificantly higher QRS amplitude than in ECG‐ERs implanted with electrodes towards the skin. From these results, it can be concluded that the best implantation site for an ECG‐ER is right or left of the sternum, positioning the electrodes vertically and towards the skin.

A Simple Method for Preoperative Assessment of the Best Fitting Electrode Length in Single Lead VDD Pacing

For single lead VDD pacing, electrodes with various distances between the lead tip and the floating atrial dipole (AV distance) are available. Using different AV distances allows positioning of the atrial dipole in the mid‐ to high right atrium, regardless of the size of the right heart. In this position, reliable atrial sensing and rejection of ventricular far‐field potentials can be expected. A simple test for the preoperative assessment of the best fitting AV distance in the individual patient was tested. We studied 24 consecutive patients prior to implantation of AVDD pacemaker. With the patient in supine position, a test electrode with an AV distance of 13 cm was taped onto the thorax. Under fluoroscopic control, it was moved until its course and projection onto the heart was equal to that of a ventricular lead. If fluoroscopy then showed a projection of the atrial dipole onto the mid‐ to high right atrium, a lead with a similar AV distance of 13 or 13.5 cm was used for implantation. If the atrial dipole projected itself too high or too low, a shorter or longer lead had to be implanted. The maximum time for the test was 2 minutes, and the maximum fluoroscopy time was 15 seconds. According to the test, a lead with an AV distance of 13 or 13.5 cm was implanted in 18 of 24 patients, and a lead with an AV distance of 15.5 or 16 cm was implanted in 6 of 24 patients. The atrial dipole could easily be positioned in the mid‐ to high right atrium in all patients, demonstrating a correct preoperative assessment of the best fitting AV distance. Intraoperatively, a P wave amplitude of 3.5 ± 3.0 mV was measured. The described test allows a fast and reliable assessment of the best fitting electrode length in single lead VDD pacing.

Verborgene intrakardiale Leitungsstörungen und deren spontaner Verlauf bei Patienten mit progressiver Muskeldystrophie

In patients with progressive muscular dystrophy (PMD) invasive electrophysiologic studies can detect hidden intracardiac conduction disturbances. The aim of this study was a long-term follow-up of these patients.    Twelve consecutive patients (9m, 3f, age 28±4 yrs) without cardiac symptoms and with normal echocardiographic findings were included in the study. They suffered from different stages of PMD type Erb (n=4), Becker-Kiener (n=4), Duchenne (n=2) and Landouzy-Déjerine (n=2). At the beginning of the study all patients underwent an invasive electrophysiologic study (EPS). The follow-up of 5.5 yrs included regular clinical visits, ECGs, and Holter recordings (every 3 months) as well as an echocardiography every 6 months. In 4 patients the EPS revealed a hidden interatrial conduction disturbance (AHRS-ACS 120±18ms), and in 10 pts an infrahisian conduction disturbance was found (HV max. 156±4ms). Conduction defects were seen independently from the type of PMD and the stage of the disease. During the follow-up the initially hidden interatrial conduction disturbance became evident in the surface ECG in 2 of 4 pts. One of them developed paroxysmal atrial fibrillation.    Five of 10 pts with an initially hidden infrahisian conduction disturbance developed an AV block grade I–III and in one case additionally a bundle branch block. Four of these pts – whose PMD showed progression or who developed congestive cardiomyopathy – needed pacemaker implantation because of a first-degree AV block + bifascicular bundle branch block (n=1), a Mobitz II second-degree AV block (n=1) or a third-degree AV block (n=2).    None of the pts with normal findings at the EPS showed abnormal p-waves, an AV block, or an intraventricular conduction disturbance during the follow-up.    We conclude that intracardiac conduction disturbances, especially infrahisian defects including high-degree AV blocks, are a common finding in pts with PMD. Therefore a regular cardiological screening including an ECG and a Holter recording is reasonable in these patients. Ziel dieser prospektiven Studie war die Beobachtung des spontanen Verlaufs invasiv dokumentierter verborgener intrakardialer Leitungsstörungen bei Patienten mit progressiver Muskeldystrophie (PMD).    12 konsekutive kardial asymptomatische und echokardiographisch unauffällige Patienten (9 Männer, 3 Frauen, Alter 28±4 J) mit PMD Typ Erb (n=4), Becker-Kiener (n=4), Duchenne (n=2) und Landouzy-Déjerine (n=2) mit unterschiedlichem Schweregrad der Muskelerkrankung wurden am Anfang der Studie invasiv elektrophysiologisch untersucht und im Langzeitverlauf über 5,5 Jahre klinisch und mittels EKG, Langzeit-EKG (alle 3 Monate) und Echokardiographie (alle 6 Monate) kontrolliert. Bei 4 Patienten (33%) wurde elektrophysiologisch eine verborgene interatriale Leitungsstörung (AHRA-ACS von 120±18ms) und bei 10 Patienten (83%) eine infrahissäre Leitungsstörung (HV maximal 156±54ms) gesichert. Intrakardiale Leitungsstörungen waren bei jeder PMD-Form und jedem PMD-Schweregrad nachzuweisen. Im Follow-up entwickelte sich bei 2 von 4 Patienten aus einer zunächst verborgenen eine im EKG manifeste interatriale Leitungsstörung, wobei bei 1 Patienten auch ein paroxysmales Vorhofflimmern auftrat. Bei 5 von 10 Patienten mit initial verborgener infrahissärer Leitungsstörung war im Langzeitverlauf ein AV-Block I-III Grades und außerdem ein Schenkelblock zu beobachten. 4 von diesen 5 Patienten, die auch entweder eine dilatative Kardiomyopathie oder eine Progredienz der Muskelerkrankung aufwiesen, wurde wegen eines AVB I° und bifaszikulären Blocks (n=1), AVB II° Typ Mobitz (n=1) oder AVB III° (n=2) ein Schrittmacher implantiert.    Bei keinem der Patienten mit normalem elektrophysiologischem Befund konnte im Follow-up eine verbreiterte P-Welle, ein AV-Block oder eine intraventrikuläre Leitungsstörung dokumentiert werden.    Somit sind intrakardiale, vor allem infrahissäre Leitungsstörungen bis hin zum höhergradigen AV-Block, bei Patienten mit progressiver Muskeldystrophie ein häufiger Befund. Diese Patienten sollten daher mittels regelmäßiger EKG- und Langzeit-EKG-Kontrollen auch von Kardiologen beobachtet werden.

How Reliable is Atrial Sensing in Single-Lead VDD Pacing: Comparison of Three Systems

This study evaluated the reliability of atrial sensing, expressed as AV synchronous stimulation, in three VDD systems with the atrial sensitivity (AS) programmed to a conventional value with a 2:1 safety margin compared to most‐sensitive values. We studied 34 sex‐ and age‐matched patients with 3 VDD systems: 14 with Unity 292–07, 10 with Saphir 600, and 10 with Thera VDD (5 model 8948 and 5 model 8968i). Two 24‐hour Hollers were performed on consecutive days. The AS was programmed in a randomized order to its most‐sensitive value or to a 2:1 safety margin. All other parameters were programmed identically. The patients underwent a myopotential oversensing test and a daily life activity protocol. A beat‐to‐beat analysis of the Holters was performed to determine AV synchrony. For the entire group AV synchrony with conventional AS was 98.63%± 2.57%, compared to 99.80%± 0.43% with most‐sensitive values (p = 0.002). There was no difference between the three systems with conventional AS. With the most‐sensitive AS, AV synchrony was: Unity 99.99%± 0.03%, Saphir 99.42%± 0.60% (P = 0.002), Thera 99.81 %± 0.35% (ns). In the Saphir system with an atrial blanking period of 150 ms, ventricular far‐field sensing could be demonstrated in 5 of 10 patients. This reduced the percentage of AV synchrony due to an unwanted mode‐switch to a nontracking mode. Myopotential oversensing was not detected in any patient. Conclusion: The VDD systems tested under identical conditions showed reliable P wave sensing at the most‐sensitive atrial sensing setting without myopotential oversensing. Ventricular far‐field sensing reduced AV synchrony and must be avoided by appropriate refractory periods.