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Biomedical subjects

F Morady

Publications and source records attributed to F Morady.

At least 91 records · Page 5Linked to original sources
PubMed1998

Changes in cardiac repolarization following short periods of ventricular pacing.

INTRODUCTION: "Cardiac memory" (primary T wave change) is thought to occur after 15 minutes to several hours of right ventricular (RV) pacing. The two components of the temporal change in repolarization are memory and accumulation. The purpose of this study was to examine quantitatively the effect of short periods of ventricular pacing on the human cardiac action potential, using monophasic action potential (MAP) recordings. METHODS AND RESULTS: Thirty-one patients (ages 43+/-14 years) with structurally normal hearts undergoing a clinically indicated electrophysiologic procedure were enrolled. Catheters were placed in the right atrium (RA) and RV, and a MAP catheter was positioned at the RV septum. APD90 was calculated from digitized MAP recordings. MAP morphology comparisons were performed using the root mean square (RMS) of the difference between complexes. All pacing was at 500-msec cycle length. There were four pacing protocols: (1) RA pacing was performed for approximately 15 minutes to evaluate temporal stability of the MAP recordings (5 pts); (2) to evaluate the memory phenomenon, four successive 1-minute episodes of RV pacing were interspersed with 2 minutes of RA pacing (5 pts); (3) the accumulation phenomenon was evaluated by assessing the effects of 1, 5, 10, and 15 minutes of RV pacing on the MAP during RA pacing (16 pts); and (4) 20 minutes of RV pacing was followed by 10 minutes of RA pacing to correlate visually apparent T wave changes with changes in MAP recordings (5 pts). In the control patients, no changes in APD90 or RMS analysis were noted during 14.9+/-1.4 minutes of RA pacing. In the second protocol, RMS of the difference between the baseline MAP complexes and the signal average of the first 50 beats following each of four 1-minute RV pacing trains demonstrated progressively greater differences in morphology after successive episodes of RV pacing. In protocol 3, RMS analysis identified a progressively greater difference between the baseline MAP recording and the average of the first 50 beats after 1, 5, 10, and 15 minutes of RV pacing. In protocol 4, visually apparent changes in T waves occurred in parallel with the RMS of the difference between the baseline MAP recordings and the average of the first 50 beats after 20 minutes of RV pacing. Similar changes also were demonstrated by APD90 analysis. CONCLUSION: This study is the first to demonstrate that episodes of abnormal ventricular activation as short as 1 minute in duration may exert lingering effects on the repolarization process once normal ventricular activation resumes.

Action Potentials↗
PubMed1998

Pathophysiology of atrial flutter.

Atrial flutter is a macroreentrant tachyarrhythmia most often contained within the right atrium. Typical atrial flutter is defined on an electrocardiogram by the classic "sawtooth" pattern of flutter waves with negative polarity in leads II, III, and aVF. In contrast to atrial fibrillation, which is sustained by multiple reentrant wavelets defined by anatomic and/or functional barriers, typical atrial flutter is sustained by a single reentrant circuit defined by anatomical barriers. The isthmus of atrial tissue bordered by the inferior vena cava and the tricuspid annulus forms a critical zone of slow conduction in the reentry circuit of atrial flutter. The goal of radiofrequency catheter ablation is to create a line of conduction block across this isthmus. This line of block interrupts the flutter circuit and often provides long-term freedom from recurrence.

Atrial Fibrillation↗
PubMed1997

Preoperative amiodarone as prophylaxis against atrial fibrillation after heart surgery.

BACKGROUND: Atrial fibrillation occurs commonly after open-heart surgery and may delay hospital discharge. The purpose of this study was to assess the use of preoperative amiodarone as prophylaxis against atrial fibrillation after cardiac surgery. METHODS: In this double-blind, randomized study, 124 patients were given either oral amiodarone (64 patients) or placebo (60 patients) for a minimum of seven days before elective cardiac surgery. Therapy consisted of 600 mg of amiodarone per day for seven days, then 200 mg per day until the day of discharge from the hospital. The mean (+/-SD) preoperative total dose of amiodarone was 4.8+/-0.96 g over a period of 13+/-7 days. RESULTS: Postoperative atrial fibrillation occurred in 16 of the 64 patients in the amiodarone group (25 percent) and 32 of the 60 patients in the placebo group (53 percent) (P=0.003). Patients in the amiodarone group were hospitalized for significantly fewer days than were patients in the placebo group (6.5+/-2.6 vs. 7.9+/-4.3 days, P=0.04). Nonfatal postoperative complications occurred in eight amiodarone-treated patients (12 percent) and in six patients receiving placebo (10 percent, P=0.78). Fatal postoperative complications occurred in three patients who received amiodarone (5 percent) and in two who received placebo (3 percent, P= 1.00). Total hospitalization costs were significantly less for the amiodarone group than for the placebo group ($18,375+/-$13,863 vs. $26,491+/-$23,837, P=0.03). CONCLUSIONS: Preoperative oral amiodarone in patients undergoing complex cardiac surgery is well tolerated and significantly reduces the incidence of postoperative atrial fibrillation and the duration and cost of hospitalization.

Aged↗
PubMed1997

Long-term follow-up after radiofrequency ablation of paroxysmal supraventricular tachycardia in patients with tachycardia-induced atrial fibrillation.

Four of 12 patients (33%) with paroxysmal supraventricular tachycardia (PSVT) and tachycardia-induced atrial fibrillation (AF) had recurrences of paroxysmal AF after successful catheter ablation of the PSVT. This study demonstrates that AF often remains a problem after radiofrequency catheter ablation of PSVT in patients with tachycardia-induced AF, and it may not be possible to predict in which patients this will be the case.

Atrial Fibrillation↗
PubMed1997

Adenosine-induced atrial arrhythmia: a prospective analysis.

BACKGROUND: Adenosine is considered safe and effective for paroxysmal supraventricular tachycardia (PSVT), but anecdotal experience suggests that adenosine can precipitate atrial arrhythmias. OBJECTIVES: To determine the frequency and mechanisms of adenosine-induced atrial arrhythmias. SETTING: Clinical electrophysiology laboratory at a university medical center. DESIGN: Prospective observational study. PATIENTS: 200 consecutive patients with PSVT undergoing an electrophysiology procedure. INTERVENTION: During PSVT, 12 mg of adenosine was administered centrally through the femoral vein. MEASUREMENTS: Frequency of adenosine-induced atrial fibrillation. RESULTS: Paroxysmal supraventricular tachycardia terminated after adenosine administration in 198 patients (99% [95% CI, 96% to 100%]). Adenosine led to atrial fibrillation (n = 22) or atrial fibrillation and atrial flutter (n = 2) in 24 patients (12% [CI, 7.5% to 16.5%]). An atrial premature complex occurred in all 24 patients who developed atrial fibrillation, atrial flutter, or both and in 102 of the 176 patients (58%) who did not (P < 0.001). The mean (+/-SD) time from the preceding atrial complex to the atrial premature complex was shorter when an atrial arrhythmia occurred, and the mean ratio of this interval to the preceding atrial cycle length was also lower when atrial fibrillation developed (0.37 +/- 0.16 compared with 0.49 +/- 0.16; P = 0.002). CONCLUSIONS: The incidence of atrial fibrillation induced by 12 mg of adenosine administered through the femoral vein was 12%. Fibrillation seems to be associated with a "long-short" atrial sequence. If the mechanism of PSVT is unknown and the Wolff-Parkinson-White syndrome is possible, administration of adenosine should be limited to medical facilities that have emergency resuscitation equipment.

Adenosine↗
PubMed1997

A prospective evaluation of catheter ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an implantable cardioverter-defibrillator.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies. METHODS AND RESULTS: Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69+/-6 years, and 17 were men. The mean ejection fraction was 0.22+/-0.08, and all patients had coronary artery disease. During the 36+/-51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34+/-55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25+/-88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4+/-0.6 (range, 1 to 3) ablation procedures and required 12.5+/-9.2 applications of energy. During 11.8+/-10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60+/-80 before successful ablation to 0.1+/-0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9). CONCLUSIONS: Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.

Aged↗
PubMed1997

Cost comparison of radiofrequency modification and ablation of the atrioventricular junction in patients with chronic atrial fibrillation.

BACKGROUND: Because it is not clear which technique is less expensive, the purpose of this study was to compare the cost of radiofrequency modification and ablation of the atrioventricular (AV) node in drug-refractory patients with atrial fibrillation and an uncontrolled ventricular rate. METHODS AND RESULTS: The initial nominal charges for a successful procedure were compared in 10 patients with chronic atrial fibrillation who underwent modification of the AV node ($13 109+/-2002) and 14 similar patients who underwent ablation and pacemaker implantation ($28 302+/-2023, P<.001). On the basis of the long-term follow-up of patients who underwent each procedure, it was assumed that 31% of patients selected for the modification procedure would require a permanent pacemaker for inadvertent AV block or because of AV nodal ablation after a failed modification procedure and that the recurrence rate after AV node ablation would be 2%. The annual charges during follow-up were predicted and adjusted for recurrences and the need for additional procedures. The adjusted total charges at 1 year of follow-up were significantly lower for the modification procedure ($19 389+/-2002) than for the ablation procedure ($28 485+/-2023, P<.001). After 10 years of follow-up, the cumulative, adjusted charges for modification were $20 016 (42%) less than for ablation. CONCLUSIONS: The initial charges generated by AV node modification are significantly lower than for AV node ablation in patients with chronic atrial fibrillation. Even when adjusted for higher failure and recurrence rates, the modification procedure retains a major cost advantage over ablation during long-term follow-up.

Aged↗
PubMed1997

Effect of verapamil and procainamide on atrial fibrillation-induced electrical remodeling in humans.

BACKGROUND: Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling. METHODS AND RESULTS: In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil). CONCLUSIONS: Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

Adult↗
PubMed1997

Probability of successful defibrillation at multiples of the defibrillation energy requirement in patients with an implantable defibrillator.

BACKGROUND: The probability of successful defibrillation has been determined in normal animals but not in patients undergoing defibrillator implantation. Therefore, the purpose of this prospective study was to determine the probability of successful defibrillation in humans on the basis of a step-down defibrillation energy requirement. METHODS AND RESULTS: Fifty-three consecutive patients underwent five separate inductions of ventricular fibrillation after the defibrillation energy requirement was determined with the use of small decrements and a step-down protocol (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, and 0.8 J). The first shock energy for defibrillation was either 1.0, 1.3, 1.5, 1.7, or 2.0 times the defibrillation energy requirement, and the likelihoods of successful defibrillation were 70+/-27%, 84+/-12%, 86+/-25%, 80+/-29%, and 88+/-32%, respectively (P=.03). The frequencies of uniformly successful defibrillation (5 of 5 defibrillation attempts) were 30%, 27%, 60%, 64%, and 73%, respectively (P=.01). Seven patients in whom the defibrillation energy requirement was <4 J had an overall rate of successful defibrillation of 54+/-20% compared with 86+/-20% in the remaining 47 patients (P=.002). The likelihood of successful defibrillation at twice the defibrillation energy requirement was 98% in the 46 patients with a defibrillation energy requirement of >4 J and 67% in the 7 patients with a defibrillation energy requirement of <4 J (P=.17). An absolute safety margin of 7 J was associated with a 96% probability of successful defibrillation. CONCLUSIONS: The probability of successful defibrillation is 70% at the defibrillation energy requirement. The probability plateaus at 88%, at twice the defibrillation energy requirement. A 96% probability of successful defibrillation is achieved at an absolute safety margin of 7 J, and a 98% success rate is achieved at energies that are twice the defibrillation energy requirement if the defibrillation energy requirement is >4 J. If the defibrillation energy requirement is <4 J, larger multiples of the defibrillation energy requirement are needed to achieve a high probability of successful defibrillation.

Arrhythmias, Cardiac↗
PubMed1997

Failure of single- and multisite high-frequency atrial pacing to terminate atrial fibrillation.

This study determined the efficacy of single- and multisite atrial pacing for terminating episodes of atrial fibrillation induced in patients in the electrophysiology laboratory. One- to 5-second bursts of atrial pacing at a cycle length of 20 ms were not effective in terminating atrial fibrillation, when delivered either in the high right atrium or when delivered simultaneously at the high right atrium, midseptum, and coronary sinus.

Atrial Fibrillation↗
PubMed1997

Comparison of effective and ineffective target sites that demonstrate concealed entrainment in patients with coronary artery disease undergoing radiofrequency ablation of ventricular tachycardia.

BACKGROUND: Concealed entrainment has been useful in guiding catheter ablation of monomorphic ventricular tachycardia in patients with coronary artery disease. However, not all sites with concealed entrainment result in successful ablation of the targeted ventricular tachycardia. The purpose of this prospective study was to identify factors at sites that demonstrate concealed entrainment that differentiate effective from ineffective target sites. METHODS AND RESULTS: In 14 consecutive patients with hemodynamically stable monomorphic ventricular tachycardia and coronary artery disease, radiofrequency ablation of 26 ventricular tachycardias was performed. Ablation was attempted at 46 sites that demonstrated concealed entrainment. Twenty-five of the targeted ventricular tachycardias (96%) were successfully ablated. The positive predictive value of concealed entrainment for successful ablation was 54%; it increased to 72% in the presence of a stimulus-QRS interval/ventricular tachycardia cycle length ratio of < or = 70%, to 82% in the presence of a match of the stimulus-QRS and electrogram-QRS interval, and to 89% in the presence of isolated mid diastolic potentials that could not be dissociated from ventricular tachycardia during entrainment. CONCLUSIONS: The positive predictive value of concealed entrainment for identification of successful ablation sites in patients with sustained ventricular tachycardia and coronary artery disease can be significantly enhanced by the presence of associated mapping criteria, particularly an isolated mid diastolic potential that cannot be dissociated from the tachycardia.

Adult↗
PubMed1997

Relation between amiodarone and desethylamiodarone plasma concentrations and ventricular defibrillation energy requirements.

The main finding of this prospective, controlled study is that amiodarone and desethylamiodarone plasma concentrations < 1 mg/L are associated with a 23% increase in the acute defibrillation energy requirement and with a 31% increase in the requirement for a subcutaneous patch or array. The defibrillation energy requirement does not correlate with the plasma concentrations of amiodarone, desethylamiodarone, amiodarone plus desethylamiodarone, or with the duration or daily dosage of amiodarone therapy.

Aged↗
PubMed1997

Effect of electrophysiologic properties and location of manifest accessory pathways on local electrogram intervals at effective radiofrequency ablation sites.

The purpose of this study was to determine if the electrophysiologic properties and the anatomic location of manifest accessory pathways affect the local electrogram intervals recorded at sites of successful radiofrequency ablation. Accessory pathways in 149 consecutive patients were categorized according to their anatomic location on the basis of the site of successful ablation. Three anatomic groups comprised 90 left free wall, 28 right free wall, and 31 posteroseptal pathways. The accessory pathways were also categorized according to their electrophysiologic properties on the basis of a hierarchical classification of the accessory pathway block cycle length. Four electrophysiologic groups (A, B, C, and D) comprised 54, 51, 28, and 16 accessory pathways, with mean accessory pathway block cycle lengths of 254 +/- 9, 288 +/- 10, 347 +/- 19, and 458 +/- 56 msec, respectively. The local atrial to ventricular (A-V) and atrial to accessory (A-K) pathway electrogram intervals recorded in sinus rhythm at the successful ablation site were significantly affected by the electrophysiologic group and were longest in group D compared with groups A, B, and C (A-V interval F(3,145) = 13.6, p < 0.001; A-K interval F(3,88) = 12.6, p < 0.001). The local A-V interval was also affected by the anatomic group and was longer in posteroseptal compared with free wall accessory pathways (F(2,146) = 15.0, p < 0.001). In contrast, the timing of the local ventricular activation to the delta wave onset (delta-V) was not significantly affected by the electrophysiologic group or the anatomic location of the accessory pathway. Thus the local A-V interval at the successful ablation site may vary because it is affected by the electrophysiologic properties and location of the accessory pathway, whereas the delta-V interval remains unaffected. These effects should be taken into account when selecting ablation sites in patients with manifest accessory pathways.

Adult↗
PubMed1997

Catheter ablation of accessory pathways.

Radiofrequency catheter ablation is a highly effective, curative treatment for arrhythmias related to accessory atrioventricular connections. Compared with medical therapy, ablation is more definitive, is more cost-effective, and is associated with a lower risk of proarrhythmia. This article updates the reader on the current indications, techniques, and innovations related to ablation of accessory pathways using radiofrequency energy.

Cardiac Catheterization↗
PubMed1997

Long-term follow-up after radiofrequency modification of the atrioventricular node in patients with atrial fibrillation.

OBJECTIVES: The purpose of this study was to describe the long-term follow-up results in 62 patients with atrial fibrillation and an uncontrolled ventricular rate, who underwent radiofrequency modification of the atrioventricular (AV) node. BACKGROUND: Previous studies in small numbers of patients have suggested that radiofrequency modification may be effective in controlling the ventricular rate in patients with atrial fibrillation, but long-term follow-up data have been lacking. METHODS: The subjects of this study were 62 consecutive patients (mean age +/- SD 65 +/- 14 years; 43 with structural heart disease) who underwent an attempt at radiofrequency modification of the AV node because of symptomatic, drug-refractory atrial fibrillation with an uncontrolled ventricular rate. The atrial fibrillation was chronic in 46 patients and paroxysmal in 16. Radiofrequency energy was applied to the posteroseptal or mid-septal right atrium to lower the ventricular rate in atrial fibrillation to 120 to 130 beats/min during an infusion of 4 micrograms/min of isoproterenol. RESULTS: Short-term control of the ventricular rate was successfully achieved without the induction of pathologic AV block in 50 (81%) of 62 patients. Inadvertent high degree AV block occurred in 10 (16%) of 62 patients, with the AV block occurring at the time of the procedure in 6 patients and 36 to 72 h after the procedure in 4. During 19 +/- 8 months of follow-up (range 4 to 33), 5 (10%) of 50 patients had a symptomatic recurrence of an uncontrolled rate during atrial fibrillation. Overall, adequate rate control at rest and during exertion, without pathologic AV block, was achieved long term in 45 (73%) of 62 patients. Among 37 patients with a successful outcome, left ventricular ejection fraction increased from (mean +/- SD) 0.44 +/- 0.14 to 0.51 +/- 0.10 one year later (p < 0.001). Complications other than AV block included polymorphic ventricular tachycardia 10 to 24 h after the procedure in two patients who had a predisposing factor for ventricular tachycardia and sudden death 1 to 5 months after the procedure in two patients with idiopathic dilated cardiomyopathy, one of whom had a pacemaker for AV block. CONCLUSIONS: In approximately 70% of properly selected patients with atrial fibrillation and an uncontrolled ventricular rate, radiofrequency modification of the AV node results in excellent long-term control of the ventricular rate at rest and during exertion.

Aged↗
PubMed1997

Response to pacing at sites of isolated diastolic potentials during ventricular tachycardia in patients with previous myocardial infarction.

OBJECTIVES: The goal of this study was to determine whether isolated diastolic potentials (IDPs) recorded during ventricular tachycardia (VT) are generated in zones of slow conduction and whether the arcs of block that bound these zones of slow conduction are functional or anatomic in nature. BACKGROUND: No previous studies have systematically investigated the response to pacing during VT and sinus rhythm at sites where IDPs are recorded. METHODS: The study included 11 patients with a previous infarction who underwent radiofrequency catheter ablation of 15 hemodynamically stable, sustained VTs and in whom an IDP that could not be dissociated from the VT was detected during mapping. RESULTS: Pacing during VT at the site where the IDP was recorded resulted in concealed entrainment in each of the 15 VTs. In 10 of the 15 VTs, an IDP was present during sinus rhythm at the same site at which a diastolic potential was recorded during VT. In nine VTs, the isolated potential occurred early in diastole; in these cases, the QRS configuration during pacing in the setting of sinus rhythm was different from that during VT. In six VTs, the isolated potential occurred later in diastole, and in these cases, the QRS configuration during pacing in the setting of sinus rhythm was the same as that during VT. CONCLUSIONS: Isolated diastolic potentials may often be generated in an area of slow conduction bounded by arcs of block that are anatomically determined and present during sinus rhythm.

Cardiac Pacing, Artificial↗