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C T Peter

Publications and source records attributed to C T Peter.

At least 19 recordsLinked to original sources
PubMed2001

Initial experience with an active-fixation defibrillation electrode and the presence of nonphysiological sensing.

Nonphysiological sensing by a pacing and defibrillation electrode may result in inappropriate defibrillator discharges and/or inhibition of pacing. Active-fixation electrodes may be more likely to sense diaphragmatic myopotentials because of the protrusion of the screw for fixation. In addition, the movement of the fixation screw in an integrated bipolar lead system could also result in inappropriate sensing. This may be increasingly important in patients who are pacemaker dependent because the dynamic range of the autogain feature of these devices is much more narrow. Five of 15 consecutive patients who received a CPI model 0154 or 0155 active-fixation defibrillation electrode with an ICD system (CPI Ventak A V3DR model 1831 or CPI Ventak VR model 1774 defibrillator) are described. In 2 of the 15 patients, nonphysiological sensing appearing to be diaphragmatic myopotentials resulted in inappropriate defibrillator discharges. Both patients were pacemaker dependent. Changes in the sensitivity from nominal to less sensitive prevented inappropriate discharges. In one patient, discreet nonphysiological sensed events with the electrogram suggestive of ventricular activation was noted at the time of implantation. This was completely eliminated by redeployment of the active-fixation lead in the interventricular septum. In two other patients, discreet nonphysiological sensed events resulted in intermittent inhibition of ventricular pacing after implantation. These were still seen in the least sensitive autogain mode for ventricular amplitude. These were not seen on subsequent interrogation 1 month after implantation. Increased awareness of nonphysiological sensing is recommended. The CPI 0154 and 0155 leads seem to be particularly prone to this abnormality. Particular attention should be made when deploying an active-fixation screw for an integrated bipolar lead. This increased awareness is more important when a given individual is pacemaker dependent, which may warrant DFT testing in a least or less sensitive mode in these patients.

Adult↗
PubMed2001

Differential atrial stunning after electrical cardioversion: an echo tissue Doppler case study.

Left atrial stunning after cardioversion is a well-known phenomenon. It has been associated with higher risk of postcardioversion thromboemboli and increased risk of recurrence of atrial fibrillation. We present a case of differential atrial stunning after electrical cardioversion for atrial fibrillation. Diagnosis was made by pulsed wave Doppler of mitral, tricuspid, and pulmonary vein inflow and mitral and tricuspid annuli. Differential mechanical atrial stunning may be a common phenomenon after cardioversion and may suggest difference in right and left atrial transport function. Its prevalence needs to be determined by a large study. Doppler tissue imaging might be routinely used in patients after cardioversion for atrial fibrillation to detect atrial stunning.

Aged↗
PubMed2000

Vein of marshall cannulation for the analysis of electrical activity in patients with focal atrial fibrillation.

BACKGROUND: Whether or not the muscle bundle within the ligament of Marshall (LOM) can serve as the origin of focal atrial fibrillation (AF) is unknown. METHODS AND RESULTS: A total of 28 consecutive patients with paroxysmal AF underwent balloon-occlusion coronary sinus angiograms to identify the vein of Marshall (VOM). Attempts were then made to advance a 1.5-French electrophysiological catheter into the VOM via the coronary sinus orifice. In 17 of the 28 patients (10 of 17 were men aged 38+/-15 years), cannulation was successful. Double potentials were registered in 8 of these 17 patients. The first potential corresponded with local left atrial activation. The second potential was shorter and narrower than the first. The sequence of activation in the second potential in the VOM was proximal to distal. In 6 patients with direct VOM recordings, we documented that the origin of AF was in the muscle bundle within the LOM. Radiofrequency catheter ablation aimed at the insertion site of the VOM successfully terminated AF in 4 of these 6 patients. CONCLUSIONS: (1) It is possible to cannulate and to record electrical potentials from the VOM. (2) The characteristics of the double potentials within the VOM suggest that the second potential is from the muscle bundle (Marshall bundle) within the LOM. (3) The Marshall bundle may be the origin of focal AF in some patients.

Adult↗
PubMed2000

Exercise conditioning and heart rate variability: evidence of a threshold effect.

BACKGROUND: A protective effect of exercise in preventing sudden cardiac death is supported by studies in healthy populations as well as in patients with cardiac disease. The mechanisms involved in this protective effect are unknown. HYPOTHESIS: We hypothesized that exercise conditioning would beneficially alter autonomic nervous system tone, measured by heart rate variability. METHODS: We prospectively studied 20 cardiac patients enrolled in a Phase 2 12-week cardiac rehabilitation program following a recent cardiac event. The patients underwent 24 h Holter monitoring at program entry and 12 weeks later. Heart rate variability analysis was assessed for both time domain and spectral analysis. RESULTS: The group demonstrated a modest mean conditioning effect, indicated by an average reduction in resting heart rate from 81 +/- 16 to 75 +/- 12 beats/min (p = 0.03), and an increase in training METS from 2.1 +/- 0.4 to 3.3 +/- 1.1 (p < 0.0001). Overall, 15 of 20 (75%) patients demonstrated increased total and high-frequency power, and mean high-frequency power was significantly increased (3.9 +/- 1.4 vs. 4.4 +/- 1.0 ln, p = 0.05). When stratified according to the magnitude of exercise conditioning, patients achieving an increase of > 1.5 training METS demonstrated significant increases in SDNN, SDANN index, SDNN index, pNN50, total power, and high-frequency power (all p < 0.05) (see text for explanation of abbreviations). CONCLUSIONS: Exercise conditioning improves heart rate variability in cardiac patients, particularly in patients who achieve a threshold of > 1.5 training METS increase over a 12-week period. These study results are supportive of the concept that exercise training lowers the risk of sudden cardiac death via increased vagal tone, which likely beneficially alters ventricular fibrillatory and ischemic thresholds.

Aged↗
PubMed2000

Are implantable cardioverter- defibrillators cost-effective?

Sudden cardiac deaths account for a large number of cardiovascular deaths, and ventricular tachyarrhythmias are implicated in many of these. In survivors of sudden cardiac deaths and other selected groups of patients, implantable cardioverter-defibrillators (ICDs) have been shown to have significant survival benefits in randomized controlled trials. The incremental costs for each extra year of survival conferred by ICDs were compared to the cost of antiarrhythmic drug therapy in some of these trials. In patients with nonsustained ventricular tachycardia with low ejection fraction (< 35%) and inducible sustained ventricular tachycardia on programmed electrical stimulation (nonsuppressible by procainamide), the incremental costs of ICD therapy amounted to $27,000 per life-year saved, compared with drug therapy. These costs may be acceptable increments for adaptation of the new technology in view of the definite survival advantage conferred by ICDs. Evolving technology may further reduce these costs by development of better devices with longer battery life.

Amiodarone↗
PubMed1999

Correlation of acute and chronic defibrillation threshold with upper limit of vulnerability determined in normal sinus rhythm.

BACKGROUND: The upper limit of vulnerability (ULV) is the stimulus strength above which ventricular fibrillation cannot be induced, even when the stimulus occurs during the vulnerable period of the cardiac cycle. Determination of ULV using T-wave shocks during ventricular pacing has been shown to closely correlate with the defibrillation threshold (DFT) at ICD implantation. However, there are no data correlating ULV determined in sinus rhythm at ICD implantation, with DFT determined at implantation or during long-term follow-up. This is of clinical importance since ULV may be used to estimate DFT during ICD implantation, both during ventricular pacing or sinus rhythm. METHODS AND RESULTS: Twenty-one patients receiving a transvenous ICD system were studied prospectively. There were 16 males and 5 females, mean age 68 +/- 15 years, with mean ejection fraction 37.4 +/- 17.4%. All had structural heart disease. The ULV was defined as the lowest energy that did not induce ventricular fibrillation with shocks at 0, 20 and 40ms before the peak of the T-wave, using a step-down protocol. The initial energy tested was 15J and the lowest energy 2J. DFT was determined following a similar step-down protocol. The DFT was defined as the lowest energy that successfully defibrillated the ventricles. The linear correlation coefficient between ULV and DFT was r = 0.73 (p < 0.001). At implant, mean ULV was 9.2 +/- 5J, not statistically different from mean DFT 9.4 +/- 4J. ULV plus 5J successfully defibrillated 19 of 21 patients. During long-term follow-up of 10.1 +/- 1.8 months in eight patients, DFT was 8.8 +/- 5.8J, not significantly different than the DFT of 7.5 +/- 4.1J or ULV of 8.0 +/- 5.3 at implant. CONCLUSION: 1) When determined during normal sinus rhythm the ULV significantly correlates with DFT. 2) ULV testing might be used in lieu of standard DFT testing to confirm adequate lead placement thus minimizing or eliminating VF inductions, particularly in hemodynamically unstable patients. 3) Since ULV + 5J has a high probability of successful defibrillation in most patients, programming ICD first shock energy for VF at ULV + 5J may result in lower first shock energies compared to the standard methods of programming first shock energy at twice DFT. CONDENSED ABSTRACT: The purpose of this study was to determine if the upper limit of vulnerability (ULV) determined during normal sinus rhythm correlates with the defibrillation threshold (DFT), as has been previously shown when determined during ventricular pacing. The linear correlation coefficient between the ULV and DFT was r = 0.73 (p < 0.001). Mean ULV at implant was 9.2 +/- 5J, not statistically different from mean DFT of 0.4 +/- 4J. During long-term follow-up of 10.1 +/- 1.8 months in 8 patients, DFT was 8.75 +/- 8J, not significantly different than the DFT of 7.5 +/- 4.1J or ULV of 8.0 +/- 5.3 at implant. Shocks energies of ULV + 5J successfully defibrillated 19 of 21 patients at implant and 8 of 8 at follow-up. This study indicates that the ULV determined in normal sinus rhythm closely correlates with the DFT, and that ULV + 5J defibrillated most patients. ULV testing could be used to predict DFT and reduce or eliminate the need for DFT testing and VF induction. Programming ICD first shock energy for VF to ULV + 5J will result in lower energy than that used with standard DFT testing.

Aged↗
PubMed1997

Programming of implantable cardioverter-defibrillators on the basis of the upper limit of vulnerability.

BACKGROUND: A patient-specific measure of defibrillation efficacy that requires a minimum number of ventricular fibrillation (VF) episodes would be valuable for programming implantable cardioverter-defibrillators (ICDs). The upper limit of vulnerability (ULV) is the weakest shock strength at or above which VF is not induced when a stimulus is delivered during the vulnerable phase of the cardiac cycle. It correlates with the defibrillation threshold (DFT) and can be determined with a single episode of VF. The objective of this study was to test the hypothesis that ICDs programmed on the basis of the ULV convert spontaneous ICD-detected VF reliably. METHODS AND RESULTS: We studied 100 consecutive patients at ICD implantation and during follow-up of 20 +/- 7 months. At implantation, the ULV and DFT were determined, and the ICD system was tested at a shock strength equal to the ULV + 3 J. During follow-up, the strength of the first shock was programmed to the ULV + 5 J for arrhythmias detected in the VF zone (cycle length < 292 +/- 17 ms). We reviewed stored detection intervals and electrograms from spontaneous episodes of ICD-detected VF to determine the success rate for appropriate first shocks. The programmed first-shock strength was 17.5 +/- 5.2 J. During follow-up, there were 120 appropriate first shocks in 37 patients. The arrhythmia was rapid monomorphic ventricular tachycardia (VT) in 70% of episodes (31 patients), VF in 11% (13 patients), polymorphic VT in 1%, and unclassified in 17% (15 patients). The first shock was successful in 119 of 120 episodes (99%; 95% CI, 93% to 100%). One unclassified episode required two shocks. No patient had syncope associated with an ICD shock or arrhythmic death. CONCLUSIONS: ICD shocks can be programmed on the basis of the ULV, a measurement made in regular rhythm, without a direct measure of defibrillation efficacy.

Aged↗
PubMed1997

Atypical atrioventricular node reciprocating tachycardia masquerading as tachycardia using a left-sided accessory pathway.

OBJECTIVES: The study was performed to document that atrioventricular node reciprocating tachycardia (AVNRT) can be associated with eccentric retrograde left-sided activation, masquerading as tachycardia using a left accessory pathway. BACKGROUND: The eccentric retrograde left-sided activation during tachycardia is thought to be diagnostic of the presence of a left free wall accessory pathway. However, it is not known whether AVNRT can occur with eccentric retrograde left-sided activation. METHODS: We studied 356 patients with AVNRT who underwent catheter ablation. Retrograde atrial activation during tachycardia and ventricular pacing were determined by intracardiac recordings, including the use of a decapolar coronary sinus catheter. RESULTS: The retrograde atrial activation was eccentric in 20 patients (6%). Eight of these patients had the earliest retrograde atrial activation recorded in the lateral coronary sinus leads, and 12 had the earliest retrograde atrial activation recorded in the posterior coronary sinus leads, with the most proximal coronary sinus electrode pair straddling the coronary sinus orifice. These tachycardias were either the fast-slow or the slow-slow form of AVNRT. The slow-fast form of AVNRT was also inducible in 17 of the 20 patients. Successful ablation of the slow pathway in the right atrial septum near the coronary sinus ostium prevented the induction and clinical recurrence of reciprocating tachycardia in all patients. CONCLUSIONS: Atypical AVNRT with eccentric retrograde left-sided activation was demonstrated in 6% of all patients with AVNRT masquerading as tachycardia using a left-sided accessory pathway. Ablation of the slow pathway at the posterior aspects of the right atrial septum resulted in a cure in these patients.

Adult↗
PubMed1997

Upper limit of vulnerability predicts chronic defibrillation threshold for transvenous implantable defibrillators.

INTRODUCTION: The upper limit of vulnerability (ULV) is the shock strength at or above which ventricular fibrillation cannot be induced when delivered in the vulnerable period. It correlates acutely with the acute defibrillation threshold (DFT) and can be determined with a single episode of fibrillation. The goal of this prospective study was to determine the relationship between the ULV and the chronic DFT. METHODS AND RESULTS: We studied 40 patients at, and 3 months after, implantation of transvenous cardioverter defibrillators. The ULV was defined as the weakest biphasic shock that failed to induce fibrillation when delivered 0, 20, and 40 msec before the peak of the T wave. patients were classified as clinically stable or unstable based on prospectively defined criteria. There were no significant differences between the group means for the acute and chronic determinations of ULV (13.5 +/- 5.3 J vs 12.4 +/- 6.8 J, P = 0.25) and DFT (10.1 +/- 5.0 J vs 9.9 +/- 5.7 J, P = 0.74). Five patients (15%) were classified as unstable. The strength of the correlation between acute ULV and acute DFT (r = 0.74, P < 0.001) was similar to that between the chronic ULV and chronic DFT (r = 0.82, P < 0.001). There was a correlation between the change in ULV from acute to chronic and the corresponding change in DFT (r = 0.67, P < 0.001). The chronic DFT was less than the acute ULV +3 J in all 35 stable patients, but it was greater in 2 of 5 unstable patients (P = 0.04). CONCLUSIONS: The strength of the correlation between the chronic ULV and the chronic DFT is comparable to that between the acute ULV and the acute DFT. Temporal changes in the ULV predict temporal changes in the DFT. In clinically stable patients, a defibrillation safety margin of 3 J above the acute ULV proved an adequate chronic safety margin.

Aged↗
PubMed1995

Optimal electrode configuration for pectoral transvenous implantable defibrillator without an active can.

A new 83 cm3 implantable cardioverter-defibrillator (ICD) designed for pectoral implantation has been implanted most frequently using right ventricular and superior vena cava (RV-->SVC) electrodes; a patch electrode (RV-->patch + SVC) has been added when necessary to decrease the defibrillation threshold (DFT). The goal of this prospective study was to compare biphasic waveform DFTs for 3 electrode configurations: RV-->patch, RV-->SVC, and RV-->patch + SVC in 25 consecutive patients. The patch was positioned in a left retro-pectoral pocket, and the SVC electrode was positioned with the tip at the junction of the SVC and innominate vein. In the first 15 patients, all 3 electrode configurations were tested in random order; in the last 10 patients, only the RV-->patch and RV-->patch + SVC configurations were tested. In the first 15 patients, the stored-energy DFT for the RV-->SVC configuration (15.2 +/- 7.7 J) was higher (p < 0.001) than the DFT for the RV-->patch configuration (11.3 +/- 6.2 J) and the RV-->patch + SVC configuration (10.0 +/- 5.8 J). For all 25 patients, the DFT was lower for the RV-->patch + SVC configuration (9.7 +/- 5.1 J) than for the RV-->patch configuration (12.4 +/- 6.6 J, p = 0.005). The pathway resistance was highest for the RV-->patch configuration (72 +/- 9 omega), lower for the RV-->SVC configuration (63 +/- 6 omega, p < 0.01), and lowest for the RV-->patch + SVC configuration (46 +/- 3 omega, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Arrhythmias after cardioverter-defibrillator implantation: comparison of epicardial and transvenous systems.

Surgery for implantable cardioverter-defibrillators can cause postoperative exacerbation of ventricular and atrial arrhythmias. It is not known whether the techniques of electrode implantation (epicardial vs transvenous) influence the incidence of arrhythmia exacerbation. We reviewed the postoperative course of 229 consecutive patients who received either epicardial (n = 119) or transvenous (n = 110) implantations from 1984 to 1994. Exacerbation of ventricular tachycardia (VT) was defined as an increase in the number of sustained VTs during the postoperative versus the preoperative 2 weeks. Of the entire cohort, 18 patients (8%) developed exacerbation of VT after operation, which was more frequent in patients with epicardial than with transvenous implantations (12% vs 4%, p < 0.03, odds ratio 3.5, 95% confidence interval 1.0 to 13.2). New-onset atrial fibrillation occurred in 15% of patients with epicardial versus 1% of those with transvenous implantations (p = 0.00005, odds ratio 19.4, 95% confidence interval 2.7 to 86.7). These differences persisted after excluding patients with concurrent cardiac surgery. Preoperative occurrence of arrhythmias was the strongest independent predictor for postoperative occurrence (p < 0.01 for VT, p < 0.0001 for atrial fibrillation). Epicardial implantation (p = 0.03) and a history of myocardial infarction (p = 0.04) were independent predictors for postoperative VT exacerbation, whereas epicardial implantation (p < 0.05) and concurrent coronary bypass surgery (p = 0.0001) were independent predictors for postoperative new atrial fibrillation. Perioperative discontinuation of antiarrhythmic drugs did not influence postoperative VT exacerbation. Epicardial implantation was associated with longer length of hospital stay than transvenous implantation (p = 0.0005), independent of age, left ventricular ejection fraction, and concurrent cardiac surgery.

Aged↗
PubMed1994

Survival and incidence of appropriate shocks in implantable cardioverter defibrillator recipients who have no detectable structural heart disease. CEDARS Investigators.

Prognosis of patients with episodes of hypotensive ventricular tachycardia (VT) or ventricular fibrillation (VF) in the absence of structural heart disease is poorly defined. To solve this problem, this study analyzed a subgroup of 25 such patients chosen from 468 consecutive patients who had an initial implantable cardioverter defibrillator (ICD) inserted between May 1984 and May 1990 in 9 medical centers and were followed up for at least 1 year. The patient group consisted of 17 men and 8 women, aged 8 to 75 years. Cardiac arrest occurred in 20 patients, 3 patients had recurrent VT, and 2 patients had both. Left ventricular ejection fraction ranged from 50% to 70%. During electrophysiologic study, a specific response was seen in 13 patients, defined as monomorphic VT (5 patients), or VF in those who had a history of VF (8 patients). In 8 patients, only a nonspecific response was seen. No arrhythmia could be induced in 4 patients. Of the 13 patients with a specific response, antiarrhythmic drug was tested in 9; in 3 of them the arrhythmia was suppressed. Within the first year, 6 of the 25 patients (24%) received appropriate shock. In the remaining 436 patients who had organic heart disease, 155 (36%) received appropriate ICD shock (p = NS). Therefore, ICD implantation appears to be warranted in patients with a history of life-threatening arrhythmias, not only in the presence but also in the absence of demonstrable structural heart disease.

Adolescent↗
PubMed1994

Effects of voltage and respiration on impedance in nonthoracotomy defibrillation pathways.

The effects of applied voltage and phase of respiration on impedance of pathways used by implantable cardioverter-defibrillators were investigated. Patients were studied at implantation of cardioverter-defibrillators using epicardial (n = 12) or transvenous and subcutaneous (SQ) (n = 30) electrodes. Transvenous-SQ pathways were right ventricular cathode to SQ anode and coronary sinus cathode to SQ anode. Transvenous-transvenous pathways were right ventricle to coronary sinus and right ventricle to superior vena cava. Patients with nonthoracotomy electrode systems were studied at end-expiration and end-inspiration. Five shocks of 65 to 745 V (0.2 to 34 J) were given in random order in sinus rhythm. Over this range, end-expiratory impedance decreased monotonically for all pathways. This effect was greatest for transvenous-SQ pathways (13 +/- 3% to 17 +/- 4%, p < 0.001), intermediate for transvenous-transvenous pathways (5 +/- 4% to 8 +/- 5%, p < 0.001), and least for epicardial pathways (3 +/- 3%, p = 0.006). Paired data in inspiration and expiration showed that inspiration increased impedance in transvenous-SQ pathways (p < 0.001) but not in transvenous-transvenous pathways. Further, the effects of respiration and voltage on impedance in transvenous-SQ pathways were interactive (p < 0.001): Inspiration increased voltage-dependence of impedance. The magnitude of the inverse relationship between voltage and impedance depends on type of defibrillation pathway. The effect of respiration on impedance suggests that voltage-dependence of impedance is greatest in the lungs. These findings have potential relevance for intraoperative testing of cardioverter-defibrillators and selection of pathways for low-energy cardioversion.

Aged↗
PubMed1994

Underdetection of ventricular tachycardia by algorithms to enhance specificity in a tiered-therapy cardioverter-defibrillator.

OBJECTIVES: The goal of this study was to determine the incidence and clinical significance of underdetection in 125 patients treated with a tiered-therapy cardioverter-defibrillator, the Medtronic PCD. BACKGROUND: Underdetection, distinct from undersensing, is a unique, potential complication of new algorithms that enhance specificity in tiered-therapy cardioverter-defibrillators. These algorithms may delay or prevent recognition of ventricular tachycardia even though electrograms are sensed accurately and RR intervals meet the programmed interval criterion. METHODS: Underdetection was defined as delay in detection > 5 s at electrophysiologic study or symptomatic delay or detection failure at follow-up of 15 +/- 8 months. RESULTS: We identified six specific mechanisms of underdetection caused by algorithms to discriminate sustained ventricular tachycardia from sinus tachycardia, atrial fibrillation, ventricular fibrillation and nonsustained ventricular tachycardia. Underdetection caused detection delays in 13 (1.9%) of 677 induced ventricular tachyarrhythmia episodes in 12 patients (9.6%). During follow-up, underdetection occurred in 7 (9.9%) of 71 patients in whom ventricular tachycardia therapies were programmed. Failure to detect ventricular tachycardia occurred in 6 (0.6%) of 988 spontaneous ventricular tachycardia episodes in four patients (5.6%); 2 episodes required external cardioversion. After defibrillator reprogramming, underdetection did not occur. CONCLUSIONS: Algorithms to enhance specificity cause underdetection of ventricular tachycardia in a significant minority of patients with tiered-therapy cardioverter-defibrillators. Optimal programming can minimize underdetection.

Algorithms↗
PubMed1994

Discrimination of ventricular tachycardia from sinus tachycardia and atrial fibrillation in a tiered-therapy cardioverter-defibrillator.

OBJECTIVES: This study was conducted to evaluate criteria for discrimination of ventricular tachycardia from atrial fibrillation and sinus tachycardia in a tiered-therapy cardioverter-defibrillator (Medtronic PCD). BACKGROUND: Interval stability algorithms discriminate ventricular tachycardia from atrial fibrillation. Onset algorithms discriminate ventricular tachycardia from sinus tachycardia. Neither has been validated clinically. METHODS: The stability criterion requires that a ventricular tachycardia interval not vary from any of the three previous intervals by more than the programmable stability value. The onset criterion detects initiation of ventricular tachycardia only if the ratio of an interval to the mean of four previous intervals is less than a programmed onset ratio and either the second or third preceding interval exceeds the ventricular tachycardia detection interval. We evaluated these criteria in 100 patients at electrophysiologic study and exercise testing (65 patients) and during a mean (+/- SD) follow-up of 16.2 +/- 7.9 months. The PCDs were programmed to tiered therapy in 54 patients. In the remaining 46 patients, the PCD's memory for detected ventricular tachycardia was used to study the specificity of the chosen onset criterion for rejecting sinus tachycardia. We used stored intervals preceding appropriate (n = 99) and inappropriate (n = 54) detections to test a new onset criterion that was less sensitive to a single index interval. RESULTS: Programmed stability of 40 ms decreased detection of induced atrial fibrillation by 95% (20 patients), paroxysmal atrial fibrillation by 95% (6 patients) and chronic atrial fibrillation by 99% (9 patients); all episodes of spontaneous (n = 877) and induced (n = 339) ventricular tachycardia were detected. A programmed onset ratio of 87% rejected sinus acceleration (98%) but caused underdetection of 0.5% of ventricular tachycardias. The onset criterion permitted inappropriate detection of premature ventricular complexes during sinus tachycardia, but the new criterion reduced these inappropriate detections by 98%. CONCLUSIONS: The PCD's onset and stability criteria reduced inappropriate detection of atrial fibrillation and sinus acceleration while detecting 99.5% of ventricular tachycardias.

Aged↗
PubMed1994

Upper limit of vulnerability reliably predicts the defibrillation threshold in humans.

BACKGROUND: The upper limit of vulnerability is the stimulus strength above which electrical stimulation cannot induce ventricular fibrillation even when the stimulus occurs during the vulnerable period of the cardiac cycle. The purpose of this study was to test the hypothesis that the upper limit of vulnerability can accurately predict the defibrillation threshold in patients undergoing implantable cardioverter-defibrillator (ICD) implantation using nonthoracotomy lead systems. METHODS AND RESULTS: We studied 77 patients at the time of ICD implantation. Multiple endocardial-endocardial and endocardial-subcutaneous shock pathways were used. Two different protocols were used to test the upper limit of vulnerability. In protocol 1 (n = 17), the upper limit of vulnerability was tested with two shocks on the peak or the up-slope of the T wave of paced rhythm. The shocks were given randomly either at the peak and 20 milliseconds before the peak of T wave (n = 7) or at 20 and 40 milliseconds before the peak of T wave (n = 10). In protocol 2 (n = 60), the upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 milliseconds before the peak of the T wave. The weakest shock that failed to induce ventricular fibrillation by a 5-J step-down or step-up method was defined as the upper limit of vulnerability. The defibrillation threshold was also determined by a 5-J step-down or step-up method. In protocol 1, the upper limit of vulnerability (9 +/- 6 J) was significantly lower than the defibrillation threshold (13 +/- 7 J) with a correlation coefficient of .87 and P < .001. In protocol 2, the upper limit of vulnerability (13 +/- 6 J) was not significantly different from the defibrillation threshold (13 +/- 6 J) with a correlation coefficient of .85 and P < .001. In 45 of the 60 patients, the upper limit of vulnerability was < or = 15 J; all had a defibrillation threshold of < or = 20 J. In 51 of the 60 patients, the upper limit of vulnerability was within 5 J of the defibrillation threshold. The upper limit of vulnerability overestimated the defibrillation threshold by > 10 J in 8 patients and underestimated the defibrillation threshold by > 10 J in only 1 patient. The overestimation and underestimation occurred only in patients with the upper limit of vulnerability > 15 J. CONCLUSIONS: When tested with three shocks on and before the peak of the T wave, the upper limit of vulnerability accurately predicted the defibrillation threshold in patients undergoing ICD implantation using nonthoracotomy lead systems. This method required either one or no episodes of ventricular fibrillation in most patients.

Aged↗
PubMed1991

Age-related changes in the clinical and electrophysiologic characteristics of patients with Wolff-Parkinson-White syndrome: comparative study between young and elderly patients.

The natural history of patients with Wolff-Parkinson-White (WPW) syndrome remains an intriguing question with respect to clinical decision-making, since serial electrophysiologic data spread over several decades in the same patient are not available in the literature. To study the age-related changes in WPW syndrome, we compared two separate groups of patients referred to this Medical Center for electrophysiologic studies because of a clinical presentation with significant arrhythmias. An elderly group of 42 patients aged 50 years or more were compared with a younger group of 51 patients aged 15 to 30 years. The groups were comparable in terms of clinical presentation, including the number of patients who had reported syncopal episodes and those requiring cardioversion of their tachyarrhythmias. Baseline electrophysiologic variables such as sinus rate; sinoatrial conduction time; corrected sinus node recovery time; AH interval; and effective refractory periods of the right atrium, atrioventricular (AV) node, and right ventricular muscle, were significantly greater in the elderly group. Similarly, the anterograde effective refractory period of the bypass tract, the shortest atrial pacing cycle length with 1:1 anterograde conduction via the bypass tract, retrograde effective refractory period of the bypass tract, the shortest ventricular pacing cycle length with 1:1 retrograde conduction via the bypass tract, the shortest consecutive preexcited R-R interval during atrial fibrillation, and the cycle length of orthodromic atrial ventricular reciprocating tachycardia were significantly greater in the elderly group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗