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Biomedical subjects

F Morady

Publications and source records attributed to F Morady.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1997

A randomized comparison of fixed power and temperature monitoring during slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia.

Temperature monitoring may be helpful for ablation of accessory pathways, however its role in ablation of atrioventricular nodal reentrant tachycardia (AVNRT) using the slow pathway approach is unclear. Therefore, the purpose of this study was to prospectively compare slow pathway ablation for AVNRT using fixed power or temperature monitoring. The study included 120 patients undergoing ablation for AVNRT. Patients were randomly assigned to receive either fixed power at 32 watts, or to temperature monitoring with a target temperature of 60 degrees C. The primary success rate was 72% in the fixed power group and 95% in the temperature monitoring group (p = 0.001). The ablation procedure duration (35 +/- 29 min vs 35 +/- 30 min; p = 0.9), fluoroscopic time (32 +/- 17 vs 35 +/- 19 min; p = 0.4), mean number of applications (10.2 +/- 8.1 vs 8.4 +/- 7.9; p = 0.2), and coagulum formation per application (0.2% vs 0.5%; p = 0.6) were statistically similar in the fixed power and temperature monitoring groups, respectively. The mean temperature (47.3 +/- 4.8 degrees C vs 48.6 +/- 3.8 degrees C; p < 0.01), and the temperature associated with junctional ectopy (48.2 +/- 3.8 degrees C vs 49.3 +/- 3.6 degrees C, p < 0.01) were less for the fixed power than the temperature monitoring group. In the temperature monitoring group, only 31% of applications achieved an electrode temperature of 60 degrees C. During follow up of 6.6 +/- 3.6 months there were two recurrences in the fixed power group and one in the temperature monitoring group (p = 1.0). In summary, power titration directed by temperature monitoring was associated with an improved primary procedural success rate. Applications of energy were associated with a temperature of approximately 50 degrees C with both techniques, suggesting that there is a low efficiency of heating in the posterior septum.

Adult↗
PubMed1997

Rise in chronic defibrillation energy requirements necessitating implantable defibrillator lead system revision.

The chronic defibrillation energy requirement (DER) is believed to remain clinically stable in patients with defibrillators. Six patients (two with an epicardial and four with a nonthoracotomy system) were identified with a rise in their chronic DER, which eliminated a 10-J safety margin, thus necessitating a defibrillator lead system revision. The mean increase in DER was 14.7 +/- 4 J and was discovered at a mean of 16.0 +/- 18 months (range 2-41) following implantation. Management included placement of a defibrillator with a biphasic waveform, placement of an additional defibrillation electrode, or both. At 2 months following revision of the defibrillation system, a 10-J DER safety margin was present in each patient. In some patients, there is a progressive increase in the chronic DER with elimination of a 10-J safety margin necessitating revision of the defibrillation system. Routine reevaluation of the chronic DER, therefore, is necessary to identify these patients.

Aged↗
PubMed1997

Accuracy of the unipolar electrogram for identification of the site of origin of ventricular activation.

INTRODUCTION: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventricular activation. The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave. However, the accuracy of this technique is unknown. METHODS AND RESULTS: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature depolarization site of origin. Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients. No R waves were detected at the ventricular premature depolarization site of origin. R waves were detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode. An R wave was not observed at distances < or = 11 mm from the site of tachycardia origin in 13 of 20 patients (65%). CONCLUSIONS: While an R wave in the unipolar electrogram can be seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.

Adult↗
PubMed1997

Idiopathic left ventricular tachycardia with left and right bundle branch block configurations.

INTRODUCTION: Idiopathic left ventricular tachycardia typically has a right bundle branch block configuration. The purpose of this case report is to demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle also may have a left bundle branch block configuration. METHODS AND RESULTS: A 27-year-old woman underwent an electrophysiologic procedure because of recurrent, verapamil-responsive, wide QRS complex tachycardia. Two types of ventricular tachycardia (cycle lengths 330 to 340 msec) were reproducibly inducible, one with a right bundle branch block configuration and left-axis deviation that had been documented clinically, and the other with a left bundle branch block configuration and axis of zero. A Purkinje potential recorded at the junction of the left ventricular mid-septum and inferior wall preceded the ventricular complex by 40 msec in both tachycardias. A single application of radiofrequency energy at this site successfully ablated both ventricular tachycardias. CONCLUSION: The findings of this case report demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle may have a left bundle branch block configuration.

Adult↗
PubMed1996

Effect of an irregular ventricular rhythm on cardiac output.

Impairment of cardiac function in atrial fibrillation has been attributed to loss of atrial contraction and to a rapid ventricular rate. The results of this study suggest that irregularity of the ventricular rhythm, independent of the ventricular rate, may also contribute to impairment of cardiac function during atrial fibrillation.

Atrial Fibrillation↗
PubMed1996

Effect of coupling interval and pacing cycle length on morphology of paced ventricular complexes. Implications for pace mapping.

BACKGROUND: Ventricular pace mapping is performed by comparing the QRS morphology of ventricular paced complexes to that of a template arrhythmia, either a premature ventricular depolarization or a QRS complex during ventricular tachycardia. The objective of this study was to evaluate the effect of coupling interval and pacing cycle length on QRS morphology. METHODS AND RESULTS: The study population consisted of 20 patients (mean age, 38 +/- 16 years) undergoing a clinically indicated electrophysiology procedure. In the first 10 patients, the effect of coupling interval on the morphology of single paced ventricular complexes was evaluated visually and by signal processing techniques. Visually apparent differences in QRS morphology occurred in a mean of 4/12 electrocardiographic leads with a change in coupling interval of > or = 100 ms. In the next 10 patients, the QRS complex morphology during ventricular overdrive pacing at cycle lengths of 600 and 300 ms was found to differ significantly in a mean of 4/12 leads. The QRS morphology during overdrive pacing differed significantly from that of a single paced complex whenever the pacing cycle length differed from the coupling interval of the single paced complex by > 80 ms. CONCLUSIONS: The morphology of single paced QRS complexes may vary, depending on coupling interval, and the QRS morphology during overdrive pacing is affected by the pacing cycle length. During ventricular pace mapping, the coupling interval or cycle length of the template arrhythmia should be matched during pacing. If not, rate-dependent changes in QRS morphology that are independent of the pacing site may confound the results of pace mapping.

Adult↗
PubMed1996

Effect of atrial fibrillation on atrial refractoriness in humans.

BACKGROUND: The acute effect of atrial fibrillation (AF) on the atrial effective refractory period (ERP) in humans is unknown. METHODS AND RESULTS: In 20 patients without structural heart disease, the atrial ERP was measured before and after pacing-induced AF at drive cycle lengths of 350 and 500 ms. Immediately after spontaneous AF conversion, the post-AF ERP was measured. The pre-AF ERPs at 350 and 500 ms were 206 +/- 23 and 216 +/- 17 ms, respectively. The time to spontaneous conversion of AF was 7.3 +/- 1.9 minutes. The first post-AF ERPs at drive cycle lengths of 350 and 500 ms were 175 +/- 30 ms (P < .0001 versus pre-AF) and 191 +/- 30 ms (P < .0001 versus pre-AF), respectively. The post-AF ERP returned to the pre-AF ERP value after a mean of 8.4 +/- 0.3 minutes. In 15 patients, during the determination of the post-AF ERP, secondary episodes of AF lasting 1 +/- 1.5 minutes were reinduced 6 +/- 3 times per patient. There was a significant inverse logarithmic relationship between the time to reinduction of AF and the duration of secondary episodes of AF (P < .0001, r = 5). CONCLUSIONS: In humans, several minutes of induced AF is sufficient to shorten the ERP for up to approximately 8 minutes. The temporal recovery of the ERP is reflected in progressively shorter episodes of reinduced AF. These data imply that AF transiently shortens the atrial wavelength and suggest a mechanism by which AF may perpetuate itself.

Adult↗
PubMed1996

Spatial resolution of atrial pace mapping as determined by unipolar atrial pacing at adjacent sites.

BACKGROUND: The purpose of this study was to examine the spatial resolution of unipolar atrial pace mapping by pacing at adjacent sites within the coronary sinus and the right atrium. METHODS AND RESULTS: Unipolar pacing from each pole of a quadripolar catheter was performed in the coronary sinus (n = 29) and in the right atrium (n = 10). Pacing from the distal electrode was used to simulate the site of origin of an atrial tachycardia. These P waves were compared with the P waves generated by unipolar pacing from each of the three proximal electrodes. The P waves were analyzed for changes in amplitude, duration, and configuration. Pacing within the coronary sinus resulted in significant changes in amplitude and duration at distances of 17 and 21 mm from the distal pole, respectively. Similarly, pacing in the right atrium resulted in significant changes in amplitude and duration at distances of 17 and 32 mm from the distal pole, respectively. No significant changes in configuration were noted in the coronary sinus in any lead at packing sites < or = 32 mm from the distal pole. Configurational changes were noted in the right atrium at pacing sites 17 mm from the distal pole. CONCLUSIONS: The spatial resolution of unipolar atrial pace mapping is approximately 17 mm. These findings indicate that mapping techniques that depend on the accurate discrimination of P-wave morphology, such as pace mapping or concealed entertainment, are likely to be imprecise when used in the atria.

Adult↗
PubMed1996

Ventricular rate during atrial fibrillation before and after slow-pathway ablation. Effects of autonomic blockade and beta-adrenergic stimulation.

BACKGROUND: Radiofrequency catheter modification of AV conduction can be used to control the ventricular rate during atrial fibrillation both in the baseline state and during exercise. Slow-pathway ablation has been suggested to be the mechanism for this response. The purpose of this study was to determine the effect of slow-pathway ablation on the ventricular rate in atrial fibrillation during autonomic blockade and sympathetic stimulation in patients with AV nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: Thirty-five patients undergoing slow-pathway radiofrequency ablation for AVNRT were assigned to autonomic blockade (0.2 mg/kg propranolol and 0.04 mg/kg atropine; n = 14) or isoproterenol (2 micrograms/min; n = 21). Atrial fibrillation was induced before and after slow-pathway radiofrequency ablation. During autonomic blockade, the mean ventricular cycle length (448 +/- 34 versus 525 +/- 103 ms, P < .01) and maximum ventricular cycle length (640 +/- 105 versus 798 +/- 226 ms, P = .04) were prolonged after ablation, whereas the minimum ventricular cycle length did not change significantly (361 +/- 42 versus 403 +/- 83 ms, P = .05). During isoproterenol infusion, the mean ventricular cycle length (375 +/- 52 versus 390 +/- 61 ms, P = .2), maximum ventricular cycle length (520 +/- 88 versus 537 +/- 106 ms, P = .3), and minimum ventricular cycle length (307 +/- 59 versus 298 +/- 33 ms, P = .4) did not change significantly after slow-pathway ablation. CONCLUSION: Slow-pathway ablation slows the ventricular rate during atrial fibrillation under conditions of autonomic blockade but not during sympathetic stimulation. Therefore, slow-pathway ablation alone cannot account for the clinical results obtained with radiofrequency modification of AV conduction in patients with atrial fibrillation.

Adult↗
PubMed1996

Response of type I atrial fibrillation to atrial pacing in humans.

BACKGROUND: High-density mapping studies of atrial fibrillation (AF) have suggested the presence of an excitable gap. The purpose of this study was to assess the local and left atrial response to pacing at the high right atrium during type I AF in humans. METHODS AND RESULTS: Pacing was performed at the high right atrium during type I AF in 24 patients in the electrophysiology laboratory. The response to pacing was assessed at cycle lengths 10, 20, 30, 40, and 50 ms less than the mean baseline atrial cycle length. Digitized tracings of the baseline tachycardia and the response to pacing were recorded from the high right atrium and from the distal coronary sinus. Computer analysis of these signals was used to calculate a left atrial electrogram density before, during, and after pacing. Two hundred eight-eight segments of AF with a duration of 3.9 +/- 0.5 seconds (mean +/- SD) were analyzed. Local capture of the right atrium during AF was demonstrated for at least one pacing cycle length in each patient. The left atrial electrogram density was significantly greater than baseline at each pacing cycle length that resulted in local capture, except when pacing at 50 ms less than the mean AF cycle length. There was no significant change in the baseline left atrial electrogram density compared with baseline when pacing did not result in local capture of AF. CONCLUSIONS: Local right atrial capture is often possible by pacing during type I AF and consistently influences the left atrial electrograms recorded in the coronary sinus. These results confirm the presence of excitable tissue in the right and left atria in type I AF.

Adult↗
PubMed1996

Transesophageal echocardiographic evaluation of left atrial appendage function and spontaneous contrast formation after chemical or electrical cardioversion of atrial fibrillation.

Changes in left atrial (LA) appendage pulsed-wave Doppler velocities and changes in grades of spontaneous contrast occur immediately after electrical cardioversion of atrial fibrillation (AF) using transesophageal echocardiography (TEE). The effect of sequential ineffective electrical cardioversion attempts or chemical cardioversion on these parameters is unknown. TEE was performed in 23 patients with chronic AF. Doppler velocities and grades of spontaneous contrast were assessed before and after each cardioversion attempt until sinus rhythm was achieved. Doppler emptying and filling velocities were significantly decreased after electrical (0.39 +/- 0.14 vs 0.27 +/- 0.16 [p = 0.01] and 0.43 +/- 0. 18 vs 0.30 +/- 0.14 m/s [p = 0.01]) or chemical cardioversion to sinus rhythm (0.65 +/- 0.18 vs 0.31 +/- 0.06 [p = 0.03] and 0.64 +/- 0.22 vs 0.44 +/- 0.17 m/s [p = 0.04]). Spontaneous contrast developed in 1 of 3 patients after chemical conversion to sinus rhythm and was present in 11 of 20 patients before electrical cardioversion, developing in 4 patients and intensifying in 2 patients immediately after successful cardioversion. These phenomena were not seen after ineffective electrical or chemical cardioversion attempts. This suggests that restoration of sinus rhythm is in itself responsible for these phenomena, not the method by which sinus rhythm is achieved.

Aged↗