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J K Triedman

Publications and source records attributed to J K Triedman.

At least 19 recordsLinked to original sources
PubMed1999

Value of programmed ventricular stimulation in patients with congenital heart disease.

INTRODUCTION: The role of programmed ventricular stimulation (VSTIM) for risk stratification in congenital heart disease is unclear. We analyzed the results of VSTIM in selected congenital heart disease survivors at a single center to determine whether it improved the ability to predict a serious outcome. METHODS AND RESULTS: Between July 1985 and September 1996, 140 primary VSTIM studies were performed on 130 patients (median age 18.1 years, range 0 to 51). Tetralogy of Fallot (33 %), d-transposition of the great arteries (25 %), and left ventricular outflow tract obstruction (12%) accounted for the majority of patients. Indications included spontaneous ventricular tachycardia (VT) of > or = 3 beats (72%) and/or symptoms (68%). Sustained VT was induced in 25% of the studies, and nonsustained VT in 12%. Atrial flutter or other supraventricular tachycardia was documented in 32% and bradyarrhythmias in 26%. By univariate analysis, mortality was increased in patients with positive VSTIM versus negative VSTIM (18% vs 7%, P = 0.04). Using multivariate analysis, positive VSTIM was associated with a sixfold increased risk of decreased survival and a threefold increased risk of serious arrhythmic events, allowing up to 87% sensitivity in predicting mortality. However, 7 (33%) of 21 patients with documented clinical VT had false-negative studies. CONCLUSION: VSTIM in a large, selected group of congenital heart disease patients identified a subgroup with significantly increased mortality and sudden arrhythmic events. Failure to induce VT was a favorable prognostic sign, but the frequency of false-negative studies was high. Frequent supraventricular tachycardia further complicated risk stratification. Although VSTIM appears to be a reasonable tool for evaluation of this population, a larger, multicenter trial is recommended to clarify its utility.

Adolescent↗
PubMed1998

Long-term performance of bipolar epicardial atrial pacing using an active fixation bipolar endocardial lead.

Bipolar epicardial leads are not yet widely available for atrial use. Since September 1986, we have used a bipolar active fixation endocardial lead (Cardiac Pacemakers model number's 4266, 4268, and 4269) as a bipolar epicardial atrial lead by attaching the corkscrew tip to the atrial surface and imbricating atrial tissue around the more proximal electrode. A total of 77 bipolar epicardial atrial leads have been implanted using this approach in 72 patients with congenital heart disease (ages 3 months to 38.7 years; mean 8.9 +/- 8.8 years). Indications for atrial pacing included AV block (n = 46), sinus node dysfunction (n = 17), and antitachycardial pacing (n = 9). Indications for epicardial pacing included the presence of an intracardiac right to left shunt (n = 33), concomitant cardiac surgery (n = 26), surgeon preference (n = 7), and lack of transvenous access to the atrial endocardium (n = 6). Follow-up (median 23 months; mean 28.0 +/- 23.1 months; range 1-78 months) data beyond 1 month postimplantation were available for 44 leads. Atrial sensing was > or = 2.0 mV for 26 leads (59%) with sensing possible at > or = 0.75 mV for 42 leads (95%). Threshold data were available at 5 V for 37 leads and at 2.5 V for 36 leads with mean pulse width thresholds measuring 0.21 +/- 0.33 ms and 0.34 +/- 0.34 ms, respectively. Two leads failed (high capture thresholds at 5 days [n = 1], lead fracture at 42 months [n = 1]; one of which was replaced. Four additional leads were replaced electively (marginal thresholds [n = 1], intermittent phrenic nerve stimulation [n = 1], damaged during subsequent surgery [n = 1], clinically irrelevant insulation break [n = 1]) concomitant with additional cardiac surgery. Until a commercially available lead is developed and released, improvisation with a bipolar active fixation endocardial lead as a bipolar epicardial atrial lead is a reasonable approach to providing bipolar atrial sensing and pacing in patients for whom endocardial pacing is contraindicated.

Adolescent↗
PubMed1997

Five-year experience with radiofrequency catheter ablation: implications for management of arrhythmias in pediatric and young adult patients.

OBJECTIVE: A review of the results of the first 5 years of radiofrequency catheter ablation procedures performed at Children's Hospital, Boston, a large tertiary referral center for patients with congenital heart disease and arrhythmias common to the infant, child, and young adult. STUDY DESIGN: A retrospective review of 410 consecutive procedures in 346 patients who underwent at least one application of radiofrequency energy for the treatment of recurrent supraventricular or ventricular tachycardia. RESULTS: The overall final success rate for all diagnoses was 90%, with a higher success rate in patients with an accessory pathway (96%). During the 5-year study period, the success rate improved while the rates of failures and late recurrences declined. The incidence of serious complications was 1.2% (1 late death, 1 ventricular dysfunction, 1 complete heart block, 1 cardiac perforation, and 1 cerebrovascular accident). CONCLUSIONS: This report of a large series of radiofrequency catheter ablation procedures performed at an institution committed to treating congenital heart disease and pediatric arrhythmias confirms the safety and efficacy of this procedure. The pediatric cardiologist/electrophysiologist treating such patients must be aware of specific technical, anatomic, and electrophysiologic variations in the pediatric patient that are critical to the success of this therapy.

Adolescent↗
PubMed1997

Evaluation of a staged treatment protocol for rapid automatic junctional tachycardia after operation for congenital heart disease.

OBJECTIVES: This study sought to 1) develop an efficient treatment protocol for postoperative automatic junctional tachycardia (JT) using conventional drugs and techniques, and 2) identify clinical features associated with this disorder by analyzing a large study group. BACKGROUND: Postoperative JT is a transient arrhythmia that may be fatal after operation for congenital cardiac defects. Its precise cause is unknown. A variety of palliative treatments have evolved, but because of a low incidence of JT, large studies of the most efficient therapeutic sequence are lacking. METHODS: A protocol for rapid JT (>170 beats/min) was adopted in 1986, and was tested in 71 children between 1986 and 1994. Staged therapy involved 1) a reduction of catecholamines; 2) correction of fever; 3) atrial pacing to restore synchrony; 4) digoxin; 5) phenytoin or propranolol or verapamil; 6) procainamide or hypothermia; and 7) combined procainamide and hypothermia. Effective therapy was defined as a sustained reduction of JT rate <170 beats/min within 2 h. Clinical profiles of the study group were contrasted with all patients without JT from this same era to identify features associated with JT. RESULTS: Of the multiple treatment stages, only correction of fever and combined procainamide and hypothermia appeared to be efficacious. By refining the protocol to eliminate nonproductive stages, the time to JT control was significantly shortened for the last 30 patients. Treatment was ultimately successful in 70 of 71 children. Postoperative JT was strongly associated with young age, transient atrioventricular block and operations involving ventricular septal defect closure. CONCLUSIONS: A staged approach to therapy, with emphasis on combined hypothermia and procainamide in difficult cases, appears to be an effective management strategy for postoperative JT. These results may also serve as comparison data for evaluation of newer and promising JT options, such as intravenous amiodarone. Trauma to conduction tissue may play a central role in the etiology of this disorder.

Adolescent↗
PubMed1997

Efficacy of radiofrequency ablation for control of intraatrial reentrant tachycardia in patients with congenital heart disease.

BACKGROUND: Intraatrial reentrant tachycardia (IART) is a common problem in patients with congenital heart disease (CHD). The progression of clinical symptoms of IART and their response to radiofrequency (RF) ablation are not yet well described. OBJECTIVES: The objective of the study was to determine the early and midterm success rates of RF ablation in effecting a reduction of clinical arrhythmic events in patients with IART and CHD. METHODS: Clinical records of patients undergoing early, successful RF ablation were analyzed retrospectively to document the occurrence and frequency of documented IART, cardioversion and arrhythmia-related hospital visits before and after ablation. RESULTS: Fifty-five catheterizations for intended RF ablation of IART were performed in 45 patients (mean [+/-SD] age 24.5 +/- 10.5 years, 40 after surgical palliation of CHD). Early success was achieved for one or more IART circuits in 33 patients (73%). Mean clinical follow-up of those patients with successful ablation is 17.4 +/- 11.3 months (total 574 patient-months). Documented IART recurrence was noted after 21 (53%) of 40 early, successful catheterizations in 17 (52%) of 33 patients, with a mean time to recurrence of 4.1 months, often with electrocardiographically novel configurations. A more prolonged and frequent history of IART was a univariate risk factor for recurrence. Seven patients underwent repeat RF ablations, and eight patients were restarted on antiarrhythmic medications after ablation. Two patients who had severe ventricular dysfunction before RF ablation died 1.5 and 11 months after RF ablation without known arrhythmia recurrence. Clinical events related to IART increased steadily in frequency for 24 months before RF ablation. Radiofrequency ablation resulted in a reduction of event frequency to levels significantly lower than those in the 12-month period before RF ablation and not significantly different from those levels observed at baseline 3 to 4 years before RF ablation. CONCLUSIONS: In patients with successful RF ablation, the frequency of subsequent events was reduced compared with the 2 preceding years. However, recurrence of IART in patients who showed clinical improvement was frequent, and often revealed the presence of new IART configurations.

Adolescent↗
PubMed1997

Spontaneous accelerated junctional rhythm: an unusual but useful observation prior to radiofrequency catheter ablation for atrioventricular node reentrant tachycardia in young patients.

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2-25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500-750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6-31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.

Adolescent↗
PubMed1997

Radiofrequency ablation of intraatrial reentrant tachycardia after surgery for congenital heart disease.

Intraatrial reentry tachycardia is a common cause of both morbidity and mortality after surgery for a variety of congenital heart defects. Despite an armamentarium of arrhythmia management tools, including drug therapy, antibradycardia, and antitachycardia pacing, and catheter ablation, management of these arrhythmias remains a challenge. This report briefly reviews the problem, assesses the current successes and failures of radiofrequency catheter ablation for treating it, and discusses a number of ongoing developments that may improve both early and late outcome.

Anti-Arrhythmia Agents↗
PubMed1997

Multipolar endocardial mapping of the right heart using a basket catheter: acute and chronic animal studies.

The development of catheter-based ablative techniques for primary atrial and ventricular arrhythmias is likely to be assisted by improved techniques for systematic endocardial activation sequence mapping. RA mapping using a multielectrode basket catheter has been shown to be feasible with minimal acute toxicity in a prior study. The objectives of the current study are to investigate: (1) the utility of the basket catheter for mapping RV activation; and (2) the evolution of acute endocardial lesions produced by basket catheter use in both the RA and RV over 4-8 weeks time. A flexible, 5-spoke basket catheter bearing 25 electrode pairs was placed in the RA (n = 9) or the RV (n = 13) in 22 juvenile sheep (22-56 kg). The catheter was deployed for 0.1-4.1 hr (RA) and 0.3-3.9 hr (RV). In 20 of these 22 animals, 32 recordings were made of filtered (30-250 Hz) bipolar electrograms and surface ECG. Electrograms were timed and used to construct activation sequences based on a schematic of catheter geometry. Hearts were examined either acutely (4 RA and 9 RV studies) or 4-8 weeks after the procedure (5 RA and 4 RV studies). One animal undergoing RA placement had an air embolism resulting in cardiac arrest immediately prior to basket placement; all other animals were stable during placement. RA electrograms of sufficient quality to determine activation time were recorded from 82% of pairs in RA maps, and RV electrograms from 89% of pairs in RV maps. Mean activation sequence duration in RV was 16 ms versus 47 ms in RA (P < 0.0001), making construction of RV maps more difficult. Acute postmortem studies of RV placement revealed a silent apical RV puncture in one animal. Superficial abrasion or ecchymosis of RV endocardium and/or tricuspid valve were noted in six animals. Postmortem exams in both RA and RV chronic studies showed healed endocardial lesions, with only superficial scarring. Rapid RV activation mapping using a basket catheter is feasible, but requires precision recording techniques. Endocardial abrasions produced in lambs both by RA and RV placement of the catheter are healed in < 4-8 weeks, with trivial residua. The multielectrode basket catheter may be applicable to the mapping of tachycardias originating in or involving the right ventricle.

Animals↗
PubMed1997

Predictors of permanence of successful radiofrequency lesions created with controlled catheter tip temperature.

Transient interruption of accessory pathway (AP) conduction is often encountered during creation of RF lesions, with return of conduction after seconds to weeks. Maximum catheter tip temperature (Tmax) has not been shown to be a good predictor of successful RF ablation. However, other indices related to catheter tip temperature (T) may predict permanent AP interruption. Ninety-one successful RF applications in 58 patients (mean age 11.9 +/- 5.5 years, 38 WPW syndrome, 18 concealed AP, 2 both) were reviewed retrospectively. Forty-two RF applications were transiently successful, with a median time of AP conduction recurrence of 120 seconds (sec; range, 1 sec to > 1 day). This group was compared with 49 permanently successful RF applications. T was measured and controlled using the Medtronic Atakr system (San Jose, CA, USA). RF lesion duration, power output, Tmax and time to Tmax (tmax) were not significantly different between the two groups. By univariate analysis, each of the following indices was able to discriminate between the transient and permanent lesions, and highly correlated with one another, T at the moment of AP interruption (Tsucc; transient 55.0 +/- 7.9 degrees C vs permanent 49.8 +/- 7.7 degrees C, P = 0.0025), time to success (tsucc; transient 4.0 +/- 3.0 sec vs permanent 1.8 +/- 1.3 sec, P = 0.0001), ratio of Tsucc/Tmax (transient 0.76 +/- 0.23 vs permanent 0.57 +/- 0.27, P = 0.0007) and ratio of tsucc/tmax (transient 0.91 +/- 0.69 vs permanent 0.41 +/- 0.41, P = 0.0001). By logistic regression analysis, no single variable or combination of variables was superior to tsucc for prediction of outcome, with a breakpoint of 2.3 seconds having a sensitivity of 74% and a specificity of 65%. During temperature controlled RF application, indices of time and temperature were well-correlated with permanent elimination of AP conduction. Time to interruption of AP conduction < 2.3 seconds after the onset of RF application was predictive of the permanence of successful RF applications. Known relations between RF lesion volume and catheter tip temperature suggest that early conduction block may be an indicator of anatomical proximity of the catheter tip and the AP. These data suggest that, in conjunction with electrogram criteria, selection criteria for optimal sites for RF, application may continue to be refined after the onset of RF application, and support the practice of terminating RF application if AP conduction is not rapidly interrupted.

Adolescent↗
PubMed1997

Intra-atrial reentrant tachycardia after palliation of congenital heart disease: characterization of multiple macroreentrant circuits using fluoroscopically based three-dimensional endocardial mapping.

INTRODUCTION: The anatomic substrate of intra-atrial reentrant tachycardia (IART) following congenital heart surgery is poorly understood, but is presumed to be different than common atrial flutter. METHODS AND RESULTS: To study the mechanisms of IART, we used a new technique for high-density endocardial mapping using recordings from a multipolar basket recording catheter (25 bipolar pairs). For each recording, biplane fluorographic reference points were digitized to obtain the spatial locations of electrode pairs, and activation times were calculated using temporal reference points from the surface ECG. Using custom software, data were combined to create three-dimensional atrial activation sequence maps, which were displayed as animated sequences. Using this technique, recordings were made in induced and/or spontaneous IART in 8 patients following congenital heart surgery (5 Fontan, 2 tetralogy of Fallot repair, 1 ventricular septal defect repair), and in 3 patients with normal intracardiac anatomy (1 with type I atrial flutter). Ten discrete IART activation sequences were recorded; 2 patients had 2 sequences each. IART maps were constructed using a median of 108 electrode positions (range 27 to 197) from a median of 6 recordings/sequence (range 3 to 11). Sinus or paced atrial rhythms were also recorded, and maps were created in a similar fashion. Visual analysis of activation sequences of sinus and paced rhythm were anatomically concordant with known mechanisms of atrial activation. IART sequences revealed diverse mechanisms; only 1 IART circuit was similar to that associated with common atrial flutter. Activation wavefront emergence from presumed zones of slow conduction, lines of conduction block, and apparent bystander activation were observed. CONCLUSIONS: High-density atrial activation sequence maps demonstrate that IART following congenital heart surgery utilizes diverse circuits and is distinct from common atrial flutter. The technique used to create these three-dimensional activation sequences may improve understanding of these complex atrial arrhythmias and assist in the development of ablative therapies.

Adolescent↗
PubMed1997

High-rate atrial pacing as an innovative bridging therapy in a neonate with congenital long QT syndrome.

INTRODUCTION: The neonatal presentation of the long QT syndrome is rare, although it is frequently accompanied by life-threatening arrhythmias. Infants may not survive childhood despite traditional management with beta-adrenergic blockade and pacing. METHODS AND RESULTS: This case describes a newborn with a long QT interval, T wave alternans, intermittent 2:1 AV block, ventricular arrhythmias, and a family history of sudden death. After failing medical therapy, conventional VVI and DDD pacing were unsuccessful due to prolonged ventricular refractoriness and proarrhythmia. At 2 months of life, the child was treated with high-rate (180 ppm) atrial pacing to produce intentional 2:1 AV block. Following an episode of possible syncope at 16 months of age, an automatic implantable cardioverter defibrillator (ICD) was added. Finally, as recently reported, acutely induced hyperkalemia led to both a marked decrease in QTc and functional improvement in repolarization (consistent 1:1 AV conduction at rates to 180 beats/min). Spironolactone and dietary potassium were added and have produced the same effects chronically. CONCLUSIONS: High-rate atrial pacing with 2:1 AV block is presented as a novel and "bridging" therapy for neonatal long QT syndrome and 2:1 AV block with ventricular arrhythmias. Definitive therapy with ICD implantation was then possible when patient size was substantially increased. The electrophysiologic response to intentional elevation of the serum potassium suggests a genetic defect in an inward potassium channel and demonstrates a possible therapy of long QT syndrome in some future patients.

Arrhythmias, Cardiac↗
PubMed1996

Low-temperature mapping predicts site of successful ablation while minimizing myocardial damage.

BACKGROUND: Temperatures near 50 degrees C can cause reversible loss of excitability in myocardial cells. METHODS AND RESULTS: Low-temperature, short-duration applications of radiofrequency energy were used to determine the adequacy of electrophysiological mapping of accessory pathway (AP) locations in 15 patients at 27 target sites using a closed-loop, temperature-controlled generator set to 50 degrees C. Energy was delivered until evidence of conduction block, or for a maximum of 10 seconds. If AP block occurred, a full 70 degrees C set point radiofrequency application was delivered to the same site. In the absence of AP block, tests with higher temperature settings (60 degrees C and 70 degrees C) were delivered to determine if inadequate temperature or catheter position led to failure of the initial 50 degrees C test. At 15 successful target sites where permanent AP block was achieved, the 50 degrees C test resulted in AP block in 14 (93%). Conduction returned in 13 of 14 APs after radiofrequency power was turned off. The time to block for the 70 degrees C applications was significantly shorter than for the 50 degrees C tests, and the peak temperature achieved was significantly higher. At unsuccessful sites where permanent AP block was not achieved, no block was induced with 11 of 12 tests at 50 degrees C, 6 of 6 tests at 60 degrees C, and 1 of 2 tests at 70 degrees C, suggesting that failure was due to incorrect catheter position. The sensitivity and positive predictive values of a 50 degrees C test identifying a successful site were > 90%. CONCLUSIONS: Low-temperature radiofrequency applications that cause transient AP block predict permanent success when a higher-temperature application is delivered at the same site. The time to achieve conduction block is a function of the temperature set point, and low-temperature tests produce reversible conduction block, suggesting minimal permanent injury.

Adolescent↗
PubMed1996

Pediatric use of intravenous amiodarone: efficacy and safety in critically ill patients from a multicenter protocol.

OBJECTIVE: The purpose of this study was to analyze the efficacy and safety of intravenous amiodarone in young patients with critical, drug-resistant arrhythmias. BACKGROUND: Intravenous amiodarone has been investigated in adults since the early 1980s. Experience with the drug in young patients is limited. A larger pediatric study group was necessary to provide responsible guidelines for the drug's use before its market release. METHODS: Eight centers obtained institutional approval of a standardized protocol. Other centers were approved on a compassionate use basis after contacting the primary investigator (J.C.P). RESULTS: Forty patients were enrolled. Standard management in all failed. Many patients had early postoperative tachyarrhythmias (25 of 40), with early successful treatment in 21 (84%) of 25. Twelve patients had ventricular tachyarrhythmias: seven had successful therapy, and six died, none related to the drug. Eleven patients had atrial tachyarrhythmias: 10 of 11 had immediate success, but 3 later died. Fourteen patients had junctional ectopic tachycardia, which was treated with success (sinus rhythm or slowing, allowing pacing) in 13 of 14, with no deaths. Three other patients had supraventricular tachycardias, with success in two and no deaths. The average loading dose was 6.3 mg/kg body weight, and 50% of patients required a continuous infusion. Four patients had mild hypotension during the amiodarone bolus. One postoperative patient experienced bradycardia requiring temporary pacing. There were no proarrhythmic effects. Deaths (9 [23%] of 40) were not attributed to amiodarone. CONCLUSIONS: Intravenous amiodarone is safe and effective in most young patients with critical tachyarrhythmia. Intravenous amiodarone can be lifesaving, particularly for postoperative junctional ectopic tachycardia, when standard therapy is ineffective.

Amiodarone↗
PubMed1996

High-density endocardial activation mapping of the right atrium in three dimensions by composition of multielectrode catheter recordings.

The use of radiofrequency ablation for treatment of complex arrhythmia substrates has prompted interest in transcatheter endocardial activation mapping. Technical constraints on catheter fabrication and the intention to use such maps to guide ablation both demand innovative approaches to mapping. A fluoroscopically based endocardial mapping technique is proposed to improve the ability of electrophysiologists to interpret large amounts of data acquired using multielectrode catheter arrays, improving their ability to visualize the data and act on its content. This technique addresses previous limitations imposed by the number of electrodes that can be deployed and by the difficulty in determining their relative spatial locations. It is based on the composition of multiple activation sequence mappings made in a single rhythm, with the spatial locations of recording electrode pairs determined in orthogonal fluoroscopic views referenced to stable intrathoracic markers. Rather than imposing a geometry determined primarily by the measurement apparatus, the spatial locations of only those electrodes in proximity to the endocardial surface, as determined by their ability to record bipolar electrograms, are measured. In this manner, the geometry of the endocardium may be approximated by measurements made of electrode position. Using this approach, the number of endocardial sites that can be sampled in a stable rhythm is theoretically unlimited, resulting in the realization of high-resolution activation maps. Spatiotemporal data may be used to create three-dimensional activation sequence maps, displayed as animated sequences. This technique was used in anatomically normal and diseased human right atria to create activation maps of sinus and paced rhythms, classic atrial flutter, and postoperative intraatrial reentrant tachycardia, using a median of 108 electrode positions (range, 27-197) in 25 maps. The activation sequences represented by these maps were diverse, but qualitatively concordant with known mechanisms of atrial activation. High-density catheter-based activation mapping of the right atrium is feasible and may improve understanding of complex arrhythmias and assist in the development of ablative techniques. Further research is needed on the spatial correlation between cardiac anatomy and fluorography, suppression of spatial artifact, and optimal mapping densities.

Body Surface Potential Mapping↗
PubMed1996

Baroreflex gain: characterization using autoregressive moving average analysis.

To study heart rate baroreflex gain, autoregressive moving average (ARMA) analysis, a multivariate method that allows evaluation of the dynamic ("beat-to-beat") interactions between changes in biological signals, was used to evaluate the relationships between R-R interval and arterial blood pressure (BP) during random-interval breathing. Parameters obtained by ARMA analysis of spontaneous fluctuations in BP and R-R interval in 17 volunteers were used to model the response of R-R interval to a transient 1-mmHg increase in BP; the resulting impulse-response and step-response curves were compared with baroreflex gain measured using bolus injections of phenylephrine (PE) and sodium nitroprusside (SNP). Impulse-response curves for the systolic BP-R-R relationship showed an early (0-1 s) sharp maximum of 5.5 +/- 4.2 ms/mmHg, which was smaller in magnitude but linearly correlated with baroreflex gain derived from SNP (14.5 +/- 9.7 ms/mmHg; r = 0.80, P < 0.002) and PE (31.6 +/- 26.7 ms/mmHg; r = 0.53, P < 0.05) injections. A similar relationship was also found between the one-beat ARMA step response and SNP injection (r = 0.70, P = 0.01). The integrated step response of the BP-R-R relationship over 6 s was 6.4 +/- 4.1 ms/mmHg, with no correlation to baroreflex gain determined by SNP (r = 0.33, P = 0.20) or PE (r = -0.15, P = 0.57). In conclusion, quantification of baroreflex gain consistent with other techniques may be achieved by ARMA analysis without perturbing mean BP. Correlation of baroreflex gain obtained by bolus injection to early measures of baroreflex gain obtained from the ARMA maximum impulse and early step responses, but not the late step response, suggests that the ARMA method may provide additional information regarding the frequency dependent effects of BP on R-R-interval.

Adolescent↗
PubMed1995

Use of adenosine-sensitive nondecremental accessory pathways in assessing the results of radiofrequency catheter ablation.

Adenosine can cause conduction block in about 20% of nondecremental accessory pathways. Along with atrial activation mapping, adenosine may help differentiate retrograde AV node conduction versus residual accessory pathway conduction after radiofrequency catheter ablation; however, it is important to test the accessory pathway response to adenosine before ablation, particularly with a concealed accessory pathway.

Adenosine↗
PubMed1995

Radiofrequency ablation of intra-atrial reentrant tachycardia after surgical palliation of congenital heart disease.

BACKGROUND: Intra-atrial reentrant tachycardia (IART), also called atrial flutter, is a common and potentially lethal complication of surgical correction of congenital heart disease. Medical management of IART is often problematic, which prompts an investigation of the utility of radiofrequency (RF) ablation for management of these arrhythmias. METHODS AND RESULTS: Ten consecutive patients referred for treatment of recurrent IART after surgery for congenital heart disease were studied. Median age was 18.4 years, and median duration of arrhythmia was 6.4 years; a median of three antiarrhythmic drugs had been tried. Surgical procedures used were Fontan (6), Mustard/Senning (2), and biventricular repair (2). Intracardiac electrophysiological study demonstrated 30 distinct IART circuits, defined by activation sequence and cycle length. Mean IART cycle length was 323 +/- 114 ms. Cycle length was significantly longer in IART circuits that were successfully ablated compared with those that were not (381 versus 248 ms, P < .001). RF ablation was attempted in 22 of these circuits. Ablation sites were targeted to presumed exit points from zones of slow conduction by electrophysiological criteria. Sites chosen in this manner clustered in four distinct areas of the right atrium. Of 22 IART circuit ablations attempted, 17 (77%) resulted in acute termination of the tachycardia. In 8 of 10 patients in whom at least one IART circuit was successfully ablated, 4 are free of clinical tachycardia and 3 are improved over short-term follow-up. No complications were encountered. CONCLUSIONS: Multiple IART circuits may be present in patients after surgery for congenital heart defects. Activation sequences observed were diverse and different from those observed in atrial flutter in patients with normal anatomy. Interruption of IART circuits by RF ablation is feasible using mapping techniques aimed at identifying an exit point from a zone of slow conduction. Short-term follow-up suggests that RF ablation may be a useful adjunct in management of IART in these difficult patients.

Adolescent↗