Algorithm for ventricular capture verification based on the mechanical evoked response.

Automatic pacemaker capture verification is important for maintaining safety and low energy consumption in pacemaker patients. A new algorithm was developed, based on impedance measurement between pacing electrode poles, which reflects the distribution of the conducting medium between the poles and changes with effective contraction. Data acquired during pacemaker implant in 17 subjects were analysed, with intracardiac impedance recorded while pacing was performed in the ventricle at varying energies, resulting in multiple-captured and non-captured beats. The impedance signals of all captured/non-captured beats were analysed using three different algorithms, based on the morphology of the impedance signal. The algorithm decision for each beat was compared with an actual capture or non-capture, as determined from the simultaneous recording of surface ECG. Two of the three algorithms (Z1 and Zn) were based on impedance values, and one (Z'n) was based on the first derivative of the impedance. Z1 was based on a single sample, whereas Z'n and Z'n were based on several samples in each beat. The total accuracy for each was Z1: 43%, Zn: 87%, Z'n: 92%. It was concluded that impedance-based capture verification is feasible, that a multiple rather than single sample approach for signal classification is both feasible and superior, and that first derivative analysis with multiple samples (Z'n) provides the best results.

Statistical analysis of the DIAMOND MI study by the multipole method.

We present a new method to describe the dynamics of the beat-to-beat RR time series. The classification of the phase-space plots obtained from RR time series is performed by a calculation of parameters which describe the features of the two-dimensional plot. We demonstrate that every parameter has its specific consequence on the evaluation of the state of the cardiac function. By applying the method to the DIAMOND MI study we demonstrate that these parameters have more prognostic power than previously suggested risk markers. The results suggest that the RR intervals constitute a highly complex time series which necessitates the use of refined mathematical-statistical methods in order to reveal pathologies in the heart rate.

The adenosine triphosphate test: a bedside diagnostic tool for identifying the mechanism of supraventricular tachycardia in patients with palpitations.

OBJECTIVES: This study assesses the value of the "ATP test" (injection of adenosine triphosphate [ATP] during sinus rhythm) for identifying patients with palpitations of unclear etiology who actually have atrioventricular (AV) nodal re-entry tachycardia (AVNRT) or AV re-entry tachycardia (AVRT). BACKGROUND: Because AVNRT and AVRT can be cured with radiofrequency ablation, documentation of spontaneous AVNRT or AVRT usually prompts referral for electrophysiologic (EP) evaluation. However, these paroxysmal arrhythmias may elude clinical diagnosis. We recently showed that administration of ATP during sinus rhythm often reveals dual AV node physiology or a concealed accessory pathway (AP) in patients with documented AVNRT or AVRT. Thus, we postulated that the ATP test could identify patients with palpitations who actually have AVNRT or AVRT and would therefore benefit from EP evaluation. METHODS: One hundred forty-six patients (54 with "palpitations without documented arrhythmias" and 92 with "documentation of arrhythmias of unclear mechanism") underwent a noninvasive ATP test. ATP was injected during sinus rhythm using 10 mg increments. The ATP test was considered positive when prospectively defined signs of dual AV node physiology or concealed AP were disclosed in the electrocardiogram. These findings were correlated with the results of EP evaluation. RESULTS: A positive ATP test predicted induction of AVNRT or AVRT with a positive predictive value of 93% (sensitivity 71%) but a negative predictive value of 37% (specificity 76%). CONCLUSIONS: A bedside ATP test identifies patients with palpitations who are likely to have AVNRT or AVRT (and who are therefore likely to benefit from EP evaluation) with a high positive predictive value.

The implantable cardioverter defibrillator.

Implantable cardioverter defibrillators (ICDs) have evolved from the treatment of last resort to the gold standard therapy for patients at high risk for ventricular tachyarrhythmias. High-risk patients include those who have survived life-threatening arrhythmias, and individuals with cardiac diseases who are at risk for such arrhythmias, but are symptomless. Use of an ICD will affect the patient's quality of life. Some drugs can substantially affect defibrillator function and efficacy, and possible drug-device interactions should be considered. Patients with ICDs may encounter cell phones, antitheft detectors, and many other sources of potential electromagnetic Interference. In addition to treating ventricular tachyarrhythmias, new defibrillators provide full featured dual chamber pacing, and could treat atrial arrhythmias, and congestive heart failure by means of biventricular pacing.

Cardiac pacing. A review.

Pacing is a field of rapid clinical progress and technologic advances. Clinical progress in the 1990s included the refinement of indications for pacing as well as the use of pacemakers for new, nonbradycardiac indications, such as the treatment of cardiomyopathies and CHF and the prevention of atrial fibrillation. Important published data and studies in progress are shedding new light on issues of pacing mode selection, and they may influence future practice significantly. Important technologic advances include development of new rate-adaptive sensors and sensor combinations and the evolution of pacemakers into sophisticated diagnostic devices with the capability to store data and ECGs. Automatic algorithms monitor the patient for appropriate capture, sensing, battery status, and lead impedance, providing better patient safety and pacemaker longevity.

Randomized comparison of J-shaped and straight atrial screw-in pacing leads.

OBJECTIVE: To study the importance of a J shape in atrial pacing leads. PATIENTS AND METHODS: We compared in a randomized controlled study acute and chronic results with 2 steroid-eluting, polyurethane, screw-in atrial lead models that differ only in shape. A total of 208 patients were randomized to have implantation of either a straight atrial lead (n = 105) or a J-shaped atrial lead (n = 103). Patients were followed up for 1 year. RESULTS: On implantation, there were no significant differences between leads in rates of failure to implant, implant measurements, number of attempts to achieve an acceptable position, and fluoroscopy times. Before discharge and at 3-month and 1-year follow-up, electrical measurements showed no statistical differences between leads. During the first year after implantation, there were 2.9% early dislodgments (< 1 week after implantation) and 2.9% late dislodgments in the straight lead group (5.9% rate of all dislodgments) vs no dislodgments in the J-shaped lead group (P = .01). There was a trend toward higher rates of exit block and lead malfunction in the J-shaped lead group. Rates of pericardial complications, subclavian/axillary thrombosis, and chronic atrial fibrillation were the same in both groups. CONCLUSIONS: Both leads appear to have an equally favorable performance profile for 1 year of follow-up. The J-shaped lead seems to be more stable and have fewer dislodgments, although it may have a somewhat higher malfunction rate.

Effect of implantable cardioverter-defibrillator shocks on QT dispersion.

Following transvenous implantable cardioverter defibrillator shocks, a significant increase in QT dispersion was observed. We suggest shock-induced increased dispersion of myocardial repolarization as one of the mechanisms of shock-induced proarrhythmia.

Rate smoothing with cardiac pacing for preventing torsade de pointes.

Cardiac pacing remains one of the most effective means for preventing torsade de pointes in patients with long QT syndrome (LQTS). However, fatal arrhythmias may occur despite combined therapy with beta blockers and pacing, and it is possible that failure of cardiac pacing for preventing arrhythmias in the long run is related (at least in part) to suboptimal pacemaker programming. Preventing sudden pauses may be especially important for preventing arrhythmias in the LQTS because such pauses are highly proarrhythmic in this patient population. Unfortunately, properly functioning pacemakers cannot be expected to prevent postextrasystolic pauses. The use of a pause-prevention pacing algorithm-rate smoothing-for preventing pause-dependent torsade de pointes is described in 12 patients with cardiac arrest or syncope due to congenital LQTS who were followed for 21 +/- 11 months.

Adenosine-5'-triphosphate test for the noninvasive diagnosis of concealed accessory pathway.

OBJECTIVES: This study assessed the use of adenosine triphosphate (ATP) in the noninvasive diagnosis of concealed accessory pathway (AP) and dual atrioventricular (AV) node physiology in patients with inducible AV reentrant tachycardia (AVRT). BACKGROUND: Administration of ATP during sinus rhythm identifies dual AV node physiology in 76% of patients with inducible sustained slow/fast AV nodal reentry tachycardia (AVNRT). METHODS: Incremental doses of ATP were intravenously administered during sinus rhythm to 34 patients with inducible sustained AVRT involving a concealed AP and to 27 control patients without AP or dual AV node physiology. One study group patient could not complete the study and was excluded from analysis. RESULTS: The AV reentrant echo beats (AVRE), or AVRT, suggestive of the presence of concealed AP, were observed after ATP administration in 24 (73%) study patients and in none of the control group. Electrocardiographic signs suggestive of dual AV node physiology were observed after ATP administration in 7 (21%) study patients and in none of the control group. Most instances of AVRE/AVRT were preceded by a slight increase (<50 ms) in PR interval. In 8 of 9 patients tested, neither AVRE nor AVRT was no longer observed following ATP administration after successful radiofrequency ablation of the AP. In the remaining patient, a different AVRE due to the presence of an additional AP was observed. CONCLUSIONS: Administration of ATP during sinus rhythm may be a useful bedside test for identifying patients with concealed AP who are prone to AVRT and those with associated dual AV node pathways.

Multiple adverse events with a dual chamber pacemaker.

The aim of the study was to evaluate our experience with Physiocor 400T, a dual chamber unipolar pacemaker manufactured by Sorin Biomedica. Between March 1993 and December 1994, 63 units of that model were implanted at our center. Patients were followed for 46 +/- 16 months. By the end of follow-up, 15 patients had died, 1 patient was lost to follow-up, and two units had been replaced for unrelated reasons. During follow-up the following phenomena had been observed: (1) Spontaneous backup reversion (VOO, 80 ppm) in 6 (9.5%) of 63 patients. In three patients this phenomenon was accompanied by concomitant ineffective pacing artifacts at 130 beats/min with very low pulse widths. (2) Unexpected battery depletion (EOL) occurred in 3 (5%) of 63 patients; two of the three occurred within weeks of routine evaluation that confirmed normal battery status. (3) Early elective replacement time (ERT) unpreceded by a gradual drop in magnet rate in 2 (3.2%) of 63 patients. (4) Total loss of telemetry without change in pacing mode in 1 (1.6%) of 63 patients. The estimated event-free 5-year survival of this model was 46%. In conclusion, 12 (19%) of 63 patients had adverse events with Physiocor 400T pacemakers. The potential risk of asynchronous pacing for prolonged periods and the risk of unexpected EOL warrants consideration of elective replacement of all remaining units.

Defibrillator challenges for the new millennium: the marriage of device and patient-making and maintaining a good match.

Although it has become clear that implantable cardioverter defibrillators (ICDs) are effective, important challenges remain for the physician. Due to the limitations of available risk stratification tools, patient selection for primary sudden death prevention remains controversial in many populations. Additionally, the proliferation of device choices has led to challenges in matching the appropriate device to the individual patient: device size is balanced against longevity; the advantages of dual chamber systems is weighed against their increased complexity; physician and patient preferences in device implant site are constrained by site-dependent effects on defibrillation effectiveness and lead failure rates; and special consideration must be given to the patient with a preexisting pacemaker. After ICD placement, determination of appropriate follow-up frequency and methodology to assess device function must be considered. This article will review patient selection, device implant site selection, device-device interactions, single versus dual chamber ICD selection, and follow-up.

Simplified "ATP test" for noninvasive diagnosis of dual AV nodal physiology and assessment of results of slow pathway ablation in patients with AV nodal reentrant tachycardia.

INTRODUCTION: We recently reported that administration of adenosine triphosphate (ATP) during sinus rhythm identifies dual AV nodal physiology (DAVNP) in 76% of patients with inducible sustained AV nodal reentrant tachycardia (AVNRT) at electrophysiologic (EP) study. In that report, however, the ATP test was considered positive for DAVNP only when the results were reproducible at a given dose of ATP. The aim of the present study was to assess the value of a simplified ATP test for noninvasive diagnosis of DAVNP and abolition or modification of the slow pathway (SP) after radiofrequency ablation (RFA) in patients with inducible sustained AVNRT. METHODS AND RESULTS: The value of a single dose of ATP was studied in 105 patients with inducible sustained AVNRT and in 31 control patients before placement of EP catheters in the cardiac chambers. ATP (10 to 60 mg, in 10-mg increments) was injected during sinus rhythm until ECG signs of DAVNP (> or = 50 msec increase or decrease in PR interval in two consecutive beats, or occurrence of > or = 1 AV nodal echo beat) or > or = second-degree AV block was observed. DAVNP was observed in only 1 (3.2%) control patient. The test could be completed in 96 study patients. DAVNP was found by ATP test in 72 (75%) patients, whereas it was diagnosed by EP criteria in 82 (85%) patients. DAVNP by ATP test disappeared in 27 (96%) of 28 patients who underwent SP abolition and in 18 (60%) of 30 patients who underwent SP modification. In the 12 patients with persistent DAVNP determined by ATP test after SP modification, the number of beats conducted over the SP was significantly reduced (from 6.3+/-3.3 to 2.5+/-2.2 beats; P = 0.002). CONCLUSION: A single administration of ATP during sinus rhythm (at a given dose) enables noninvasive diagnosis of DAVNP in a high percentage of patients with inducible AVNRT and reliably confirms the results of RFA of the SP.

Are routine arrhythmia inductions necessary in patients with pectoral implantable cardioverter defibrillators?

INTRODUCTION: The value of ventricular arrhythmia inductions as part of routine implantable cardioverter defibrillator (ICD) follow-up in new-generation pectoral ICDs is unknown. METHODS AND RESULTS: We performed a retrospective analysis of a prospectively collected database analyzing data from 153 patients with pectoral ICDs who had routine arrhythmia inductions at predismissal, and 3 months and 1 year after implantation. Routine predismissal ventricular fibrillation (VF) induction yielded important findings in 8.8% of patients, all in patients with implantation defibrillation threshold (DFT) > or = 15 J or with concomitant pacemaker systems. At 3 months and 1 year, routine VF induction yielded important findings in 5.9% and 3.8% of tested patients, respectively, all in patients who had high DFT on prior testing. Ventricular tachycardia (VT) induction at predismissal, and 3 months and 1 year after implantation resulted in programming change in 37.4%, 28.1%, and 13.8% of tested patients, almost all in patients with inducible VT on baseline electrophysiologic study and clinical episodes since implantation. CONCLUSION: Although helpful in identifying potentially important ICD malfunctions, routine arrhythmia inductions during the first year after ICD implantation may not be necessary in all cases. VF inductions have a low yield in patients with previously low DFTs who lack concomitant pacemakers. VT inductions have a low yield in patients without baseline inducible VT and in the absence of clinical events. Definite recommendations regarding patient selection must await larger prospective studies as well as consensus in the medical community about what comprises an acceptable risk justifying avoidance of the costs and inconveniences of routine arrhythmia inductions.

Defibrillation thresholds are increased by right-sided implantation of totally transvenous implantable cardioverter defibrillators.

Whether an ICD is placed via a left- or right-sided approach depends on venous access, the presence of a preexisting pacemaker, and other factors. Since the DFT is affected by lead position, which in turn is determined in part by the side of access, right-sided venous access could adversely affect DFTs. Furthermore, right-sided active can placement directs electric current toward the right hemithorax, which could further increase DFTs. This study sought to determine whether DFTs were increased by right-sided vascular access, and whether active can technology was beneficial or detrimental with right-sided ICD placement. Stepdown to failure DFTs were found in 290 patients receiving transvenous systems at the time of initial ICD implantation. Of these, 271 (93%) received left-sided systems and 19 (7%) received right-sided systems. The mean DFT in systems placed via left-sided vascular access was 11.3 +/- 5.3 J versus 17.0 +/- 4.9 J for right-sided implantation (P < 0.0001); right-sided DFTs were elevated for both active can and cold can systems. Right-sided active can devices had a lower DFT than right-sided cold can systems (15 +/- 4.1 J vs 19 +/- 4.8 J, P = 0.05). The right-sided implantation of implantable defibrillators results in significantly higher DFTs than the left-sided approach. This may be due to the less favorable distribution of the defibrillating field relative to the myocardium with the devices on the right. When right-sided implantation is clinically mandated, active can devices result in lower thresholds and should be used.

Clinical surveillance of a tined, bipolar, J-shaped, steroid-eluting, silicone-insulated atrial pacing lead.

Since 1990, 558 Medtronic 5524 bipolar, silicone-insulated, J-shaped, tined, steroid-eluting atrial leads have been implanted at the Mayo Clinic (Rochester, MN, USA) and the Midelfort Clinic (Eau Claire, WI, USA). Implantation data were favorable, with pacing thresholds at implantation (median threshold, 0.6 V) better than most published data on other atrial leads. The rate of acute lead-related complications (dislodgment and diaphragmatic pacing) necessitating reoperation or electrical abandonment of the atrial lead was 0.9%. This rate is lower than that in most published series of atrial leads. Over a median follow-up time of 17.5 months (up to 69 months), there were no chronic lead-related complications and no definite or suspected failures of lead material. This rate is much lower than that with other atrial leads studied previously. We conclude that the Medtronic 5524 atrial lead combines the reliability of silicone insulation with a lack of chronic complications and high thresholds due to its steroid elution and with stability in the atrium due to its J shape despite a passive fixation mechanism. There is no evidence of lead material failure during up to 6 years of follow-up.

Clinical surveillance of a tined, bipolar, steroid-eluting, silicone-insulated ventricular pacing lead.

Since 1990, 1,068 Medtronic 5024 bipolar, silicone-insulated, tined, steroid-eluting ventricular leads have been implanted at the Mayo Clinic (Rochester, MN) and Midelfort Clinic (Eau Claire, WI). Implantation data were favorable: median pacing thresholds of 0.5 V at 0.5 ms, median R wave of 13.4 mV, and median impedance of 593 omega. Of the 2.1% acute lead-related complications (dislodgment, microdislocation, diaphragmatic pacing, and undersensing), 1.2% necessitated reoperation. This rate is lower than that in most published series of other leads. During a median follow-up of 23 months (up to 76 months), 12 (1.1%) chronic lead-related complications (high thresholds, loss of capture, and undersensing) and no instances of definite or suspected lead material failure occurred. This rate is much lower than that in studies of other leads. Thus, the 5024 lead combines the reliability of silicone insulation with a low rate of chronic complications that is probably the result of its steroid elution. No evidence of failure of lead material has appeared up to 6 years after implantation.

Atypical AV nodal reentry with bystander accessory pathway: an unusual mechanism of preexcited tachycardia.

We present an unusual mechanism of preexcited tachycardia--atypical AV nodal reentry with bystander AP. It can be differentiated from other preexcited tachycardias by its variable degree of preexcitation (either spontaneous or in response to atrial pacing), higher degree of preexcitation with pacing near the origin of the AP than during tachycardia, inability to preexcite the tachycardia by either late atrial or ventricular premature beats, the presence of nonpreexcited atypical AV nodal reentry tachycardia following successful AP ablation, and by exclusion of atrial tachycardia.

A stepwise testing protocol for modern implantable cardioverter-defibrillator systems to prevent pacemaker-implantable cardioverter-defibrillator interactions.

Current use of newer implantable cardioverter-defibrillators (ICDs) has changed the spectrum of pacemaker-ICD interactions and provided new tools for testing and understanding those interactions. Testing for pacemaker-ICD interactions was performed in 31 procedures involving 22 patients. The protocol included: (1) evaluation of pacemaker stimulus artifact amplitude and its ratio to that of the evoked ventricular electrogram, (2) testing for inhibition of ventricular fibrillation (VF) detection by the ICD during asynchronous pacing at maximum output, (3) evaluation by pacemaker event marker recordings of pacemaker sensing behavior while programmed to nonasynchronous mode during ventricular tachycardia (VT) or VF, and (4) evaluation of postshock interactions. Inhibition of detection of VT/VF was found in 6 of 22 patients (27.2%). Large stimulus artifact amplitude (>2 mV) or stimulus artifact:evoked QRS ratio > 1/3 had a positive predictive accuracy of 18% and 14.4%, respectively, and a negative predictive accuracy of 100% and 92.3%, respectively, for clinically significant interaction. Asynchronous pacing occurred in 16 of 31 procedures (51.6%), and was due to underdetection by the pacemaker in 4 of 16 (25%) and noise reversion in 12 of 16 (75%). Postshock phenomena occurred in 6 cases, 3 of which were clinically significant. Overall, 11 of 22 patients (50%) had clinically significant interactions discovered by this protocol, which led to system revisions in 6 and to pacemaker output reprogramming in 5. Thus, pacemaker-ICD interactions are frequently detected using a thorough and systematic protocol. Most cases can be managed by system revision or pacemaker reprogramming.