The QT-Sensitive Cybernetic Pacemaker: A New Role for an Old Parameter?

A critical review of the available data on QT interval is presented to delineate techniques useful to the development of a QT-sensitive cybernetic pacemaker. The reason for the development of this unit stems from the ability of QT prolongation to predict the onset of life-threatening ventricular arrhythmias in some clinical situations; the QT interval is physiologically related to the cardiac cycle length, therefore providing adequate information to drive both ventricuiar and atrioventricuiar sequential rate-responsive pacemakers. This unit might also monitor cardiac rhythm and detect the pathophysioiogic precursors of advanced grades of ventricular arrhythmias. A therapeutic role, both pharmacologic and electrical, may also be possible in the future. Integration of these concepts and cooperation between interested physicians, technicians and manufactors will be necessary to produce such a unit at a low cost-benefit ratio. The potential clinical application of this pacemaker deserves attention for the prophylaxis and treatment of sudden arrhythmic death.     

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.     

Impact of the Main Implantable Cardioverter-Defibrillator Trials for Primary and Secondary Prevention in Italy: A Survey of the National Activity During the Years 2001–2004

Background: Several trials demonstrated the lifesaving role of implantable cardioverter-defibrillator (ICD) in high-risk groups of patients. Aim of this review was to report the clinical characteristics of patients enrolled in the ICD Registry of the Italian Association of Arrhythmology (AIAC) in the years 2001–2004.
Methods: The Registry collects prospectively 85% of national ICD implantation activity on the basis of European ICD form (EURID).
Results: The number of implanted ICDs in Italy was 2,418 in the year 2001, 3,992 in the year 2002, 5,595 in the year 2003, and 7,190 in the year 2004. The number of ICDs per million of inhabitants was 42.1 in the year 2001 (+11.8% respect to 2000), 70.0 in the year 2002 (+65.1% respect to 2001), 98.3 in the year 2003 (+40.4% respect to 2002), and 125.0 in the year 2004 (+27.2% respect to 2003). The median age was 67 years in the years 2001–2002, 68 years in the years 2003–2004. The main indications during the study were syncope (24.2–14.9%) and cardiac arrest (28.5–17.3%), followed by palpitations and dizzy spells (15.5–17.2%, and 9.4–6.9% of patients, respectively). The use of prophylactic ICD had a fourfold increase in the examined period (5.8% in 2001, 22.9% in 2004). Ventricular tachycardia was the main arrhythmic indication in 44.4–54.6% of cases, ventricular fibrillation in 11.8–18.0%, both in 3.5–6.5%. In the years 2002, 2003, and 2004 single chamber ICDs were implanted in 45.5%, 38.8%, and 33.7% of patients, dual chamber ICDs in 35.1%, 32.3%, and 30.5%, biventricular ICDs in 19.4%, 28.9%, and 34.7%, respectively.
Conclusion: The ICD implantation rate in Italy increased significantly in the period 2001–2004, similarly to the trend in other western countries. The Registry showed an important increase of prophylactic and dual or triple chamber ICDs use.     

Permanent Overdrive Atrial Pacing in the Chronic Management of Recurrent Postoperative Atrial Reentrant Tachycardia in Patients with Complex Congenital Heart Disease

This study investigated the value of permanent atrial pacing as an adjunct to the current therapy in the chronic management of recurrent postoperative atrial reentrant tachycardia in patients with complex congenital heart disease. We studied the postpacing clinical course in 18 patients with recurrent atrial reentrant tachycardias unresponsive to conventional therapy who had an implanted atrial pacemaker. The pacemaker was programmed at a lower pacing rate 20% faster than the spontaneous mean daily rate previously determined with 24-hour Holter monitoring. Serial Holter recordings and pacemaker programming sessions were subsequently performed trying to mantain a paced atrial rhythm overdriving the spontaneous rhythm as long as possible. Twenty-four hour Holter monitoring documented a prevalent (> 80%) paced rhythm during the daily hours in all patients during the follow-up; all patients, however, required at least once a variation In programmed mode and pacing rate. Antiarrhythmic medications were discontinued after 6 months if the patient remained arrhythmia free while on pacing. Recurrences of atrial reentrant tachycardia occurred in five patients (29%) during the initial 6 months interval after the pacemaker implantation, while late recurrences occurred in only two patients (11 %). One patient died suddenly 10 months after the pacemaker implant. At the end of the follow-up, 15 patients (83%) were arrhythmia-free and only 2 of them were still on antiarrhythmic drugs. We conclude that permanent atrial overdrive pacing can be an important tool in the management of patients with atrial reentrant tachycardia following repair of congenital heart disease.     

A New Algorithm for Closed-Loop Stimulation: A Feasibility Study

PIERAGNOLI, P., et al .: A New Algorithm for Closed-Loop Stimulation: A Feasibility Study. Closed-loop stimulation (CLS) is a physiological system for adaptive rate pacing based on monitoring and processing of the intracardiac impedance. The "standard" CLS algorithm (SCLS) requires continuous ventricular pacing. A new, enhanced CLS algorithm (ECLS) provides rate modulation during sensed and paced ventricular depolarizations. The aim of this study was to validate ECLS and to compare its effectiveness with that of SCLS. Ten patients received Inos²⁺ CLS pulse generators. SCLS and ECLS were uploaded to the device and evaluated in a randomized, crossover fashion at 30 and 45 days after pacemaker implantation. At each follow-up visit, ambulatory and posture tests were performed. Heart rate (HR) during daily activity was evaluated based on 24-hour Holter recordings. During all phases of the ambulatory test, both algorithms provided physiologically appropriate rates in all patients. The proportion of sensed ventricular events was significantly higher in ECLS (93.9%) than in SCLS (0.7%). The proportion of paced ventricular events during 24 hours was substantially lower with ECLS (25.7%) than with SCLS (98.4%). Postural changes did not influence HR with either algorithm. The Holter recordings indicated prompt, safe, and effective rate modulation appropriate to patient activity. In conclusion, analysis of these clinical data demonstrated the safety and effectiveness of the ECLS algorithm. Moreover, with this algorithm the ventricle is paced only when required, which may be expected to retard battery depletion and retain the natural ventricular activation pattern whenever possible. (PACE 2003; 26[Pt. II]:229–232)     

Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate

BONGIORNI, M.G., ET AL.: Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate. One of the most important problems in rate responsive (RR) pacing is the clinical experimental evaluation of the reliability of various sensors. In particular, it is difficult to test their sensitivity and specificity during daily activity of the patients. Atrial rate, when present and normal, is the most physiological marker of metabolic requirements, but sometimes it is impossible to analyze the P wave in ventricular paced rhythm during routinely performed tests (e.g., ergometric test and 24-hour Holter monitoring). During various physical activities, we monitored atrial electrograms on an esophageal lead on the first channel of a standard Holter tape recorder; on the second channel a surface ECG lead was recorded. We selected 10 patients with high grade heart block and normal sinus node function paced in RR-VVI mode. RR pacing was obtained using various sensors (body activity, blood temperature, spike-T interval, minute ventilation). The good quality of recording allowed an easy evaluation of atrial and ventricular rates. In four cases an appropriate increase in heart rate was documented; sensitivity threshold and/or rate response slope were reprogrammed when indicated. The pacing rate of one patient did not parallel the atrial rate during walking only. In three cases, we observed a delay in the ventricular rate increase, with ventricular rate decreasing at peak exercise despite further atrial rate increase. In the last two patients, we observed inappropriate pacing response; pacing rate increased later and to a lower level than the atrial one. This new method is applied easily and appears reliable to evaluate the response of RR pacemakers to individual metabolic needs. Its applicability is, however, limited by the need for a normal sinus node function. In conclusion, transesophageal atrial rate recording is a useful tool for the clinical evaluation of RR pacemakers, and it can be proposed as a new method for testing new sensors.     

Early Conduction Disorders Following Percutaneous Aortic Valve Replacement

Background: Percutaneous aortic valve replacement (PAVR) may be an alternative therapy for patients with severe aortic stenosis who are denied valve surgery because of age and comorbidity. Data are few regarding the incidence of early conduction disorders (CD) after PAVR. We examined the incidence and characteristics of CD in the immediate postoperative period after PAVR, and the need for permanent pacemaker (PPM) implantation.
Methods and Results: Between June 2007 and June 2008 30 patients (mean age = 82.1 ± 8.5 years) underwent PAVR in our institution. The incidence of new, postoperative CD, diagnosed by 12-lead or 24-hour Holter electrocardiogram, was 68.0%. Left bundle branch block was the most common conduction abnormality, with an incidence of 45.8%. The incidence of complete atrioventricular block requiring PPM implantation was 20%.
Conclusions: We observed a higher incidence of early conduction disorders and need for PPM implantation after PAVR than generally reported after surgery. Whether this observation is clinically important requires larger prospective studies and follow up.     

Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between Echo and Peak Endocardial Acceleration Measurements

PADELETTI, et al. : Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between ECHC and Peak Endocardial Acceleration. Interatrial septum pacing (IASP) reduces interatrial conduction time and consequently may interfere with atrioventricular delay (AVD) optimization. We studied 14 patients with an implanted BEST Living system device able to measure peak endocardial acceleration (PEA) signal. The aims of our study were to compare the (1) optimal AVD (OAVD) in right atrial appendage pacing (RAAP) and IASP, and (2) OAVD derived by the PEA signal versus OAVD derived by Echo/Doppler evaluation of the left ventricular filling time (LVFT) and cardiac output (CO). Measurements were performed in DDD VDD modes Eight patients (group A) had RAAP and six patients (group B) had IASP. In group A, OAVD measured by LVFT, CO, and PEA was 185 ± 23 ms , 177 ± 19 ms , and 192 ± 23 ms in DDD and 147 ± 19 ms , 135 ± 27 ms , and 146 ± 20 ms in VDD, respectively. OAVD measured by LVFT, CO, and PEA was significantly longer in DDD mode than in VDD (P < 0.01, P < 0.01, P < 0.001 ). In group B, OAVD measured by LVFT, CO, and PEA was 116 ± 19 ms , 113 ± 10 ms , and 130 ± 30ms in DDD and 106 ± 16 ms , 96 ± 15 ms , and 108 ± 26 ms in VDD, respectively. No statistical differences were observed between DDD and VDD. Significant correlations between OAVDs PEA derived and OAVDs LVFT and CO derived were observed (r = 0.71, r = 0.69, respectively ). When new techniques of atrial stimulation, as IASP, are used an OAVD shorter and similar in VDD and DDD has to be considered. The BEST Living system could provide a valid method to ensure, in every moment, the exact required OAVD to maximize atrial contribution to CO.     

Update on Dedicated Bifurcation Stents

Coronary bifurcation lesions represent an area of ongoing challenge in interventional cardiology. Contemporary studies using drug-eluting stents report a reduction in main vessel (MV) restenosis; however, residual stenosis and restenosis at side-branch ostium remain an issue. Multiple two-stent bifurcation strategies exist, including T-stenting, V-stenting, simultaneous kissing stenting, culotte stenting, and crush stenting technique. Each strategy has its own advantages and disadvantages, but on the basis of results of numerous randomized trials, the provisional approach of implanting one stent on the main branch has became the default approach to most bifurcation lesions. Dedicated bifurcation stents have been designed to specifically address some of the shortcomings of the conventional percutaneous approach to bifurcation intervention. The majority of the devices are aimed at facilitating the provisional approach. Dedicated bifurcation stents should enable all operators to treat the side-branch ostium simultaneously with the main branch, preserving a safe, permanent access to side branch during the procedure. In the future, the use of these new devices will probably enhance the interaction between adequate mechanical scaffolding and accurate delivery of the appropriate dosage of any new antirestenosis drugs. There are currently 11 devices available that either have completed or are undergoing first-in-man trials. The development of further drug-eluting platforms and larger controlled studies should demonstrate their clinical applicability, efficacy, and safety before they are widely incorporated into daily practice.