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Biomedical subjects

J Kron

Publications and source records attributed to J Kron.

At least 37 records · Page 2Linked to original sources
PubMed1993

Serial electropharmacologic studies in patients with ischemic heart disease and sustained ventricular tachyarrhythmias: when is drug testing sufficient?

Serial testing of antiarrhythmic drugs by programmed electrical stimulation can be costly in time, expense and risk. The purpose of this study was to evaluate the results of serial electropharmacologic tests for similarities that might obviate the need for protracted drug testing. Serial electropharmacologic testing was performed in 283 patients with coronary artery disease and clinical sustained ventricular tachycardia (VT) or fibrillation (VF). Drug tests were defined as concordant if sustained VT or VF could be consistently induced, or failed to be consistently induced during all such trials in a given patient. The following drugs were included for testing: procainamide, quinidine and disopyramide (class IA); phenytoin, mexiletine and tocainide (class IB); and flecainide and encainide (class IC). All patients were serially tested with > or = 2 (mean and median, 3) antiarrhythmic agents regardless of results from drug-free testing or initial acute drug testing. Overall, the results of serial drug trials directed by programmed stimulation were concordant in more than two thirds of patients. Concordance was comparably high whether patients were serially tested with drugs within the same antiarrhythmic class, or with drugs from differing classes, and was not related to patients' clinical or electrophysiologic characteristics. Protracted serial electropharmacologic testing does not appear necessary for predicting successful or unsuccessful antiarrhythmic drug therapy in survivors of clinical VT or VF. Single drug testing can identify most patients whose arrhythmia will or will not respond to medications.

Action Potentials↗
PubMed1993

Phase image analysis of anomalous ventricular activation in pediatric patients with preexcitation syndromes or ventricular tachycardia.

This prospective study evaluated the accuracy of phase analysis of scintigraphic imaging in defining the site of earliest ventricular activation in pediatric patients with electrophysiologic disorders. Twenty patients (10.8 +/- 5.5 years) with preexcitation (n = 16) or ventricular tachycardia (VT) (n = 4) were independently evaluated by phase image analysis and endocardial catheter mapping. The earliest phase angle (contraction), which was common to three scintigraphic imaging planes during preexcited sinus rhythm or VT, was compared with the earliest retrograde atrial activation during reciprocating tachycardia or the origin of VT, as defined by catheter mapping. Phase analysis of earliest contraction was concordant with catheter mapping of electrical activation in all 13 free-wall accessory connections and in three of four patients with VT. Inconclusive definition of activation occurred only in paraseptal accessory connections or VT. In conclusion, phase analysis accurately defines anomalous ventricular activation that is due to free-wall accessory connections or VT. In patients with complex anatomy or small size, phase analysis allows noninvasive localization of the anatomic substrates of tachycardia.

Adolescent↗
PubMed1993

Sudden cardiac death and the use of implantable cardioverter-defibrillators in pediatric patients. The Pediatric Electrophysiology Society.

BACKGROUND: During the past decade, the implantable cardioverter-defibrillator (ICD) has emerged as the primary therapeutic option for survivors of sudden cardiac death (SCD). Investigation of the clinical efficacy of these devices has primarily assessed outcome in adults with coronary artery disease. The purpose of this cooperative, international study was to evaluate the impact of ICDs on the pediatric population of SCD survivors, based on an analysis of the clinical characteristics and outcomes of young patients who underwent ICD implantation following an episode of life-threatening ventricular tachycardia or resuscitation from SCD. METHODS AND RESULTS: An initial data base, established by contacting the manufacturers of the various commercially and investigationally available devices, identified 177 patients who were less than 20 years of age at the time of initial implantation of an ICD. With this data base as a reference, detailed responses were subsequently obtained from physicians involved in the care of 125 (71%) of these patients. The patients ranged in age from 1.9 to 19.9 years (mean, 14.5 +/- 4 years) and weighted 9.7-117 kg (mean, 44.6 +/- 14 kg). Of the 125 patients, 76% were survivors of SCD, 10% had drug refractory ventricular tachycardia, and 10% had syncope with heart disease and inducible sustained ventricular tachyarrhythmias. The most common types of associated cardiovascular disease were hypertrophic and dilated cardiomyopathies (54%), primary electrical diseases (26%), and congenital heart defects (18%). Ventricular function was abnormal in 46% of the patients. During a mean follow-up of 31 +/- 23 months, at least one ICD discharge occurred in 85 of the 125 (68%) patients. Seventy-three patients (59%) received at least one appropriate ICD discharge, and 25 patients (20%) had one or more spurious or indeterminate discharges. Duration of follow-up > 24 months (p = 0.001) and inducibility of a sustained ventricular arrhythmia (p = 0.05) were correlated with appropriate ICD discharges. There were nine deaths during the study period: five sudden, two due to recurrent ventricular arrhythmias, and two related to congestive heart failure. Abnormal ventricular function (p = 0.002) and prior ICD discharge (p = 0.01) were univariate correlates of patient mortality; by multivariate logistic regression, abnormal ventricular function was the only significant correlate of death (p = 0.005). By actuarial analysis, the estimated overall post-ICD implant survival rates at 1, 2, and 5 years were 95%, 93%, and 85%, respectively. The corresponding sudden death-free survival rates were 97%, 95%, and 90%. CONCLUSIONS: Pediatric patients resuscitated from SCD appear to remain at risk for recurrence of life-threatening tachyarrhythmias. During a mean follow-up of 31 months, the ICD provided an effective therapy for such arrhythmias in the majority of patients in this study. Following ICD implant, impaired ventricular function was the primary factor correlated with mortality. The patterns of ICD discharge observed in young patients and, thus, inferred risk of recurrent life threatening arrhythmias are similar to those of adult survivors of SCD. Thus, the use of ICDs in pediatric patients, with implant selection criteria similar to adults, appears valid.

Adolescent↗
PubMed1993

Unmasking accessory pathway conduction with adenosine-induced atrioventricular nodal block after radiofrequency catheter ablation.

Radiofrequency catheter ablation is very effective in eliminating conduction over accessory pathways in patients with Wolff-Parkinson-White syndrome. However, accessory pathway conduction recurs in approximately 5 to 9 percent of patients in the weeks to months following ablation. We describe two cases in which intravenous adenosine revealed persistent accessory pathway conduction after apparently successful ablation, thus providing an indication for the delivery of further ablative therapy. Adenosine may improve the long-term efficacy of radiofrequency catheter ablation of accessory pathways by manifesting latent accessory pathway conduction.

Adenosine↗
PubMed1992

Long-term multicenter experience with a second-generation implantable pacemaker-defibrillator in patients with malignant ventricular tachyarrhythmias. The Guardian Multicenter Investigators Group.

A second-generation implantable pacemaker-cardioverter-defibrillator was evaluated in 200 patients with sustained ventricular tachycardia, ventricular fibrillation or prior cardiac arrest. The device permits demand ventricular pacing for bradyarrhythmias and for long QT interval or tachycardia suppression, uses programmable (3 to 30 J) energy shocks for conversion of ventricular tachycardia and ventricular fibrillation and is used with conventional pacing and defibrillation leads. Ventricular tachycardia/fibrillation recognition is based on the ventricular electrogram rate and requires reconfirmation before shock delivery. Two hundred patients (mean age 62 years, mean left ventricular ejection fraction 36%) were enrolled and followed up for 0 to 23 months (mean 12). Epicardial lead system implantation was performed with use of an anterolateral thoracotomy (38%), median sternotomy (26%) and subxiphoid (20%) or subcostal (16%) approach. Perioperative mortality rate was 5.5% (all nonarrhythmic deaths). Implant defibrillation threshold ranged from 3 to 30 J (mean 15), with initial programmed shock energy ranging from 3 to 30 J (mean 22). Ventricular tachycardia/fibrillation sensing threshold ranged from 0.7 to 1.8 mV (median 1) and the tachycardia detection interval from 288 to 416 ms (median 320). Reprogramming of implant variables was necessary for reliable electrographic sensing (54 patients), programmed shock therapy (61 patients) and tachycardia detection rate (63 patients). Device activation for potential shock delivery occurred in 111 patients (55.5%) with actual shock delivery after ventricular tachycardia/fibrillation reconfirmation in 66 patients (33%). During follow-up study, there was a 1% arrhythmia mortality rate, 6.5% cardiac mortality rate and 10.5% total mortality rate. This study demonstrates that the programmable implantable pacemaker-cardioverter-defibrillator is effective in preventing arrhythmic death, yet reduces patient exposure to repeated shock therapy. Reprogramming is usually necessary during follow-up for optimal function.

Adolescent↗
PubMed1992

Supraventricular tachyarrhythmias, congenital heart disease, and sudden cardiac death.

The etiologies of sudden cardiac death following the surgical treatment of congenital heart defects remain uncertain. A young patient with prior repair of partial anomalous pulmonary venous return is presented, in whom brief episodes of a supraventricular tachyarrhythmia (rate 170/min) were documented to result in ventricular fibrillation. This unusual sequence may represent a basis for unexplained sudden cardiac death in other patients following atrial surgical procedures for the treatment of congenital heart disease.

Adolescent↗
PubMed1992

Analysis of local electrogram characteristics correlated with successful radiofrequency catheter ablation of accessory atrioventricular pathways.

UNLABELLED: Due to the limited myocardial lesions produced by radiofrequency current, the ablation of accessory pathways (AP) requires precise localization of such connections. The purpose of this study was to ascertain which characteristic(s) of the local bipolar electrogram, recorded from the ablation and adjacent electrode immediately prior to the application of radiofrequency current, correlated with precision in localization adequate to permit AP ablation. Signal analysis was performed for 326 sets of electrograms preceding the attempted ablation of 107 APs in 100 consecutive patients. For 80 antegrade APs, the following variables were evaluated: (1) the presence or absence of an AP potential; (2) the local atrial-AP interval; (3) the local atrioventricular (AV) interval; and (4) the relationship between the onset of local ventricular depolarization and onset of delta wave of the surface electrocardiogram. For the 27 concealed APs, the following characteristics were evaluated: (1) the presence or absence of an AP potential; and (2) the local VA interval during reciprocating tachycardia or ventricular pacing. RESULTS: Antegrade APs: By statistical analysis, the best correlate of successful ablation of an antegrade AP was a local AV interval less than or equal to 40 msec (positive predictive value = 94%; 95% confidence intervals [CI] = 81%-100%). Local AV intervals less than or equal to 50 msec preceded 88% of successful AP ablations, compared to only 8% of failed radiofrequency current applications. The positive predictive value of the other variables were: presence of an AP potential: 35% (95% CI = 27%-40%); local atrial-AP intervals less than or equal to 40 msec: 54% (95% CI = 43%-66%); and local ventricular depolarization preceding onset of the delta wave 43% (95% CI = 34%-52%). For concealed APs, the positive predictive value of a VA interval less than 60 msec was 71% (95% CI = 48%-88%); the positive predictive value for the presence of an AP potential was 58% (95% CI = 32%-81%). CONCLUSIONS: No single electrogram characteristic had a positive predictive value and a sensitivity greater than 90% for AP localization adequate for radiofrequency current ablation. For antegrade APs, the best correlate of adequate localization was a local AV interval less than or equal to 40 msec; as a corollary, radiofrequency current applications at sites where the local AV was greater than 60 msec, were unlikely to be effective. Objective criteria for the localization of concealed APs were less certain. Electrogram analysis, as a guide to AP localization and ablation, requires careful analysis of multiple variables, with analysis of the local AV interval a salient objective factor.

Adult↗
PubMed1990

Caffeine and ventricular arrhythmias. An electrophysiological approach.

Little information is known regarding caffeine's effect on the substrate supporting sustained ventricular arrhythmias. This prospective study evaluated the effect of coffee (275 mg of caffeine) on this substrate with programmed ventricular stimulation in 22 patients with a history of symptomatic nonsustained ventricular tachycardia, ventricular tachycardia, or ventricular fibrillation. Patients underwent electrophysiological testing before and 1 hour after coffee ingestion. Mean (+/- SEM) plasma caffeine level achieved after coffee consumption was 6.2 +/- 0.5 mg/L. Mean plasma catecholamine and potassium values were not altered significantly 1 hour following caffeine ingestion. The number of extrastimuli required to induce an arrhythmia was unchanged in 10 patients (46%), increased in six (27%), and decreased in six (27%). Rhythm severity was unchanged in 17 patients (77%), more severe in two (9%), and less severe in three (14%). In those patients with clinical ventricular arrhythmias, caffeine did not significantly alter inducibility or severity of arrhythmias, suggesting little effect on the substrate supporting ventricular arrhythmias.

Adult↗
PubMed1990

Analysis of programmed stimulation methods in the evaluation of ventricular arrhythmias in patients 20 years old and younger.

The purpose of this study was to systematically evaluate programmed ventricular stimulation in patients less than 21 years of age undergoing electrophysiologic testing. A standardized protocol was applied in 55 consecutive patients (mean age 14 years) with the following clinical presentations: sustained ventricular tachycardia (VT) (n = 17); ventricular fibrillation (VF) (n = 7); syncope with heart disease (n = 10); nonsustained VT (n = 6); and syncope with an ostensibly normal heart (n = 15). The stimulation protocol consisted of 1 and 2 ventricular extrastimuli during sinus rhythm, followed by 1 to 4 (S2, S3, S4, S5) extrastimuli during pacing at 2 ventricular sites. Of the 17 patients with sustained VT, 12 had induction of the arrhythmia (sensitivity = 71%). Overall, 18 of 55 patients had inducible sustained VT, with this response significantly enhanced by use of S4 or S5 protocols (p = 0.02). Although no syncope patients with an ostensibly normal heart had inducible sustained VT, 7 had polymorphic nonsustained VT in response to ventricular stimulation. The mean number of extra-stimuli preceding the induction of nonsustained or sustained VT or VF did not differ. The induction of VF in 5 cases during this study was preceded in each case by extrastimuli intervals less than or equal to 190 ms. Thus, data indicate that aggressive stimulation protocols appear to be required for induction of sustained VT in most young patients, nonsustained polymorphic VT as a response to aggressive programmed stimulation is of uncertain significance, and that coupling intervals less than or equal to 190 ms may correlate with the induction of VF.

Adolescent↗
PubMed1990

Day-to-day reproducibility of antiarrhythmic drug trials using programmed extrastimulus techniques for ventricular tachyarrhythmias associated with coronary artery disease.

Forty-nine patients with coronary artery disease and documented clinical sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) were studied twice in the drug-free state and twice during treatment with an identical antiarrhythmic medication at therapeutic plasma concentrations using an identical programmed electrical stimulation protocol. Tested drugs included procainamide, quinidine, disopyramide and phenytoin. During their 2 paired tests, 11 patients had nearly identical therapeutic plasma concentrations of antiarrhythmic agents (group I) and 38 patients had therapeutic plasma concentrations, but with more variation in drug levels between otherwise identical paired drug tests (group II). Overall, 71% of patients had inducible sustained VT or VF during drug testing. Induced ventricular arrhythmias were not reproducible in 45% of group I patients, despite restudy at nearly identical therapeutic plasma concentrations of an identical antiarrhythmic agent. Induced arrhythmias were also not reproducible in 16% of group II patients. This variability could not be attributed to the electrophysiologic characteristics of the patients studied. Drug trials directed by programmed stimulation should be cautiously interpreted because time-associated changes can mimic a change attributed to a beneficial or deleterious drug effect.

Anti-Arrhythmia Agents↗
PubMed1990

Circadian variation in ventricular electrical instability associated with coronary artery disease.

Although sudden cardiac deaths and ischemic cardiac events clearly occur in a circadian pattern, such a pattern has not been shown for primary arrhythmic events. Because primary arrhythmic events are thought to play an important role in sudden cardiac death, a large series of ventricular stimulation studies was analyzed to determine whether circadian variation in ventricular electrical instability exists. If such a circadian variation could be shown, it could have implications for the conduct and interpretation of electrophysiologic testing and the etiology of circadian variation in sudden cardiac death. Results of 2 drug-free ventricular stimulation studies performed 4 to 28 hours apart in each of 162 patients with coronary artery disease were analyzed. Rate and duration of induced arrhythmia, number of extrastimuli required to induce arrhythmia and changes in these factors between the 2 tests in each patient were analyzed. Comparisons were made by half-day, by hour and in a temporally continuous manner to eliminate errors associated with any single method. No significant circadian variation was found in any electrophysiologic measure of ventricular electrical instability despite adequate statistical power. These findings show that the time of day during which ventricular stimulation tests are performed does not affect test results, and therefore does not need to be controlled during electrophysiologic studies. If these findings are parallel to those in ambulatory patients with coronary artery disease, then circadian changes in ventricular electrical instability may not play as important a role in the circadian pattern of sudden cardiac death as had been previously thought.

Cardiac Pacing, Artificial↗
PubMed1990

Spontaneous sustained ventricular tachyarrhythmias during treatment with type IA antiarrhythmic agents.

Twenty-six patients who developed their first clinical episode of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) while taking type IA antiarrhythmic agents for more benign rhythm disturbances were rechallenged with the identical drug during electrophysiologic testing. Patients with these new drug-associated spontaneous ventricular arrhythmias often manifested a preexisting substrate for such arrhythmias: sustained VT or VF was induced in 65% of patients at baseline, and in 58% of patients when tested with their previously taken antiarrhythmic drug. Among those without inducible sustained ventricular arrhythmias in the drug-free state, 78% remained free of inducible sustained arrhythmias when tested with the same drug they had been taking at the time of the clinical arrhythmia. Even patients without a definable electrophysiologic substrate for sustained VT or VF remained at risk for arrhythmia recurrence if treated with alternative antiarrhythmic medications: 40% of such patients who continued to receive an antiarrhythmic agent different from that being administered when their clinical VT or VF occurred had recurrent spontaneous ventricular tachyarrhythmias during follow-up. Thus, patients with drug-associated clinical sustained ventricular tachycardias form a heterogenous group that should be evaluated individually and not empirically managed for a "proarrhythmic effect" simply by antiarrhythmic drug withdrawal or drug substitution.

Anti-Arrhythmia Agents↗
PubMed1990

Bradycardia-mediated tachyarrhythmias in congenital heart disease and responses to chronic pacing at physiologic rates.

The coexistence of bradycardia and a tachyarrhythmia may preclude effective pharmacologic treatment of 1 arrhythmia without paradoxic aggravation of the other. This study evaluated the potential relation between the 2 types of arrhythmias and the effect of conventional modes and rates of pacing for bradycardia on the frequency of the associated tachyarrhythmias. Twenty-one young patients, aged 2 to 19 (mean 11) years with congenital heart disease and a tachyarrhythmia occurring in the setting of chronic bradycardia were studied. The effects of pacing were evaluated by comparison of the number of episodes of clinical tachycardia during the 12-month intervals before and after pacemaker implantation. During these intervals, antiarrhythmic drug therapy was not altered. Patients were analyzed as independent groups, based on the type of tachyarrhythmia: supraventricular (n = 5), atrial flutter (n = 9) and ventricular (n = 7). The modes of chronic pacing were AAI (n = 4), DDD (n = 6) and VVI (n = 11). The prevention of bradycardia by pacing was associated with a significant decrease in the frequency of supraventricular (p = 0.008) and ventricular (p = 0.02) tachyarrhythmias. However, the frequency of atrial flutter was not altered. Prevention of tachycardia was more frequently associated with the AAI and DDD modes of pacing compared to VVI (p = 0.08). Pacing represents an effective therapy for certain tachyarrhythmias associated with chronic bradycardia, although critical modes may be required.

Atrial Flutter↗
PubMed1990

Comparison of ventricular arrhythmia induction with use of an indwelling electrode catheter and a newly inserted catheter.

Two methods of serial electrophysiologic testing are in widespread use. Most commonly, the electrode catheter is removed after each study and a new catheter reinserted through the femoral vein for every subsequent test. An alternative method employs an electrode catheter that remains in place during several days of serial testing. Little is known about differences between these two methods with respect to the likelihood of induction of arrhythmia or the frequency of complications. To determine whether inducibility of sustained arrhythmia is altered or if the frequency of complications is unacceptably high with use of an indwelling catheter, a prospective randomized study was conducted in 78 patients. Each patient underwent baseline testing, several days of electropharmacologic testing with an indwelling catheter, a 24 h drug elimination period and placement of a new electrode catheter. Ventricular stimulation studies were then performed in each patient with both the indwelling and new electrode catheters. No differences were found between the indwelling and new catheter tests with respect to induction of arrhythmia, number of extrastimuli required to induce arrhythmia, rate of arrhythmia or requirement for cardioversion. Ventricular pacing thresholds were higher and effective refractory periods were slightly longer when measured with the indwelling catheter. Complications related to the 156 catheter insertions included two that may have been related to the indwelling catheter (one episode of staphylococcal sepsis and one presumed pulmonary embolism) and four that were related to invasive procedures (pneumothorax in all). There were no long-term adverse sequelae of these complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1990

The automatic implantable cardioverter-defibrillator in young patients.

An international survey identified 40 patients less than 20 years old who underwent surgical implantation of an automatic implantable cardioverter-defibrillator (AICD). There was a history of aborted sudden cardiac death or sustained ventricular tachycardia in 92.5% of these patients. Twenty-two patients (55%) had structural heart disease; dilated and hypertrophic cardiomyopathy were the most common diagnoses. Eighteen patients (45%) had primary electrical abnormalities including seven with the congenital long QT syndrome. There were no perioperative deaths associated with device implantation. Concomitant drug therapy was administered to 75% of the patients. Defibrillator discharge occurred in 70% of the patients, with 17 patients (42.5%) receiving at least one appropriate shock. There were two sudden and two nonsudden deaths at 28.2 months' median follow-up. Sudden death-free survival rates by life table analysis at 12 and 33 months were 0.94 and 0.88, respectively. Total survival rates at 12 and 33 months were 0.94 and 0.82, respectively. The AICD represents an effective treatment approach for young patients with life-threatening ventricular tachyarrhythmias.

Adolescent↗
PubMed1990

Cryoablation of medically refractory nodoventricular tachycardia.

Paroxysmal wide QRS tachycardia, based on a nodoventricular accessory connection, is an uncommon arrhythmia. In this report, the endocardial and epicardial mapping and cryoablation of a nodoventricular fiber, documented to participate in medically refractory tachycardia in an 11-year-old boy, are described. Epicardial cryothermia, applied at the earliest site of right ventricular activation, resulted in the abrupt termination of tachycardia. Endocardial cryothermia was subsequently applied in the perinodal region, the presumed site of origin of the nodoventricular fiber. No tachyarrhythmias were inducible postoperatively, and no antiarrhythmic treatment has been required during 18 months of follow-up. Based on precise anatomic localization of the nodoventricular connection, a definitive cure of associated tachyarrhythmias may be possible utilizing cryothermia, without the requirement for extensive intraoperative dissection.

Bundle of His↗