Optimized mapping of slow pathway ablation guided by subthreshold stimulation: a randomized prospective study in patients with recurrent atrioventricular nodal re-entrant tachycardia.

OBJECTIVES: This randomized prospective study sought to assess the value of slow pathway (SP) mapping and ablation guided by subthreshold stimulation (STS) in comparison with a strategy based on conventional criteria. BACKGROUND: Previous studies have demonstrated that STS can be used as a highly specific and sensitive marker for successful SP ablation in the setting of atrioventricular nodal re-entrant tachycardia (AVNRT). Nonetheless, thus far this mapping strategy has not been investigated in contrast with the conventional approach. METHODS: One hundred patients with sustained AVNRT were included. Fifty patients (group A) were randomly assigned to endocardial mapping and SP ablation using currently established criteria. In the other 50 patients (group B), SP ablation was guided by STS mapping. In group B patients, only radiofrequency current (RFC) was applied if additionally constant current STS (up to 5 mA) during AVNRT interrupted the tachycardia due to selective block within the SP. RESULTS: Termination of AVNRT without apparent capture was observed during STS in 47 of 50 group B patients (94%). In all cases, this effect was indicative for successful subsequent SP ablation. The mean number of RFC pulses required for successful SP ablation was significantly lower in patients assigned to the STS-guided strategy (1.6 +/- 1.3 vs. 3.9 +/- 3.4; p = 0.0003). Similarly, the mean procedure duration was shorter in the STS group (156.9 +/- 33.5 vs. 173.2 +/- 49.7 min; p = 0.0221); the fluoroscopy time was comparable between both groups (14.1 +/- 8.7 vs. 16.9 +/- 10.6 min; p = 0.1278). CONCLUSIONS: Subthreshold stimulation is an effective method for detection of target sites for selective SP ablation. This technique helps to minimize the number of RFC pulses without prolongation of the overall procedure and fluoroscopy time required for SP ablation.

Microwave catheter ablation using a clinical prototype system with a lateral firing antenna design.

Microwave has been considered a potentially more effective and more versatile form of energy than radiofrequency. Its feasibility has been tested using various prototype systems and catheter designs. This study assessed the safety and efficacy of a clinically-suitable prototype microwave power supply and catheter system with a lateral-firing antenna design for atrioventricular (AV) junction ablation in canines and to correlate with tissue histopathology. The system consisted of a deflectable catheter with a 6-mm antenna and a thermocouple; and a 2.45-GHz frequency generator with power, time, and temperature controls. AV junction ablations were performed using 75 W energy for up to 60 seconds. Effective heating was confirmed by a rise in catheter temperature to 69.3 +/- 8.8 degrees C. Complete AV nodal block was accomplished in all canines after an average of 4.1 +/- 2.8 applications at 66.8 +/- 7.7 degrees C, and persisted after 28 days in all chronic animals. Lesions were consistent with thermal necrosis, were hemispherical to semi linear in shape and have distinct borders. Acute lesions were 3.4 +/- 1.5 mm wide, 4.8 +/- 2.1 long, and 2.0 +/- 0.9 deep. Chronic lesions showed typical healing and were smaller in size. Ablations did not cause any transvalvular, vascular or other cardiac structural damage, and no coagulum formation was noted on the antenna or catheter tip. Microwave AV junction ablation using this clinical prototype system specifically designed for it was safe and effective. Lesion's depth was limited to 5 mm with 60-second heating while its shape corresponded to the antenna's length. Microwave energy may provide greater versatility for producing discrete or linear ablation.

Patients with valvular heart disease presenting with sustained ventricular tachyarrhythmias or syncope: results of programmed ventricular stimulation and long-term follow-up.

BACKGROUND: Programmed ventricular stimulation is commonly used to guide therapy in post-myocardial infarction patients with sustained monomorphic ventricular tachycardia (VT) or ventricular fibrillation (VF). In patients with valvular heart disease presenting with spontaneous VT, VF, or syncope, the usefulness of this technique is still unclear. The aim of the study was to analyze whether programmed ventricular stimulation was helpful in guiding therapy and determining prognosis in 97 patients with valvular heart disease presenting with VT (60%), VF (18%), or syncope (22%). METHODS AND RESULTS: Patients were classified as having either predominant ventricular pressure or volume overload or no significant pressure or volume overload. Overall, sustained VT or VF was inducible in 38 (39%) and 19 (20%) patients, respectively. Forty-six (47%) patients were discharged on antiarrhythmic drugs, 29 (30%) received an implantable cardioverter-defibrillator, and 22 (23%) remained without therapy. With serial drug testing, inducibility was completely or partially suppressed in 18 (19%) and 9 (9%) patients, respectively. During a mean follow-up of 51 months (n=97), 17 patients (18%) died (sudden death, n=7; heart failure, n=4; noncardiac causes, n=6). One-, 2- and 3-year event-free survival for sudden death, sustained VT, or VF was 77%, 68%, and 61%, respectively. Only inducibility of VT during baseline study (P<.0003) and left ventricular volume overload (P<.008) were significant predictors of arrhythmic events. Recurrence of arrhythmic events occurred in 56% and 56% of patients with complete or partial suppression of inducibility during serial drug testing as well as in 10 of 19 (53%) patients without a change in inducibility. CONCLUSIONS: Although programmed ventricular stimulation seems to predict adverse outcome, serial drug testing is unreliable in guiding therapy. The type of workload imposed on the ventricles influences outcome, being worse in patients with left ventricular volume overload. Therefore, implantation of a cardioverter-defibrillator should be considered early for the management of these patients.

In vitro and in vivo results of transcatheter microwave ablation using forward-firing tip antenna design.

This study was designed to test a microwave (MW) ablation system using approximately 2,450 MHz of energy and a deflectable catheter with forward-firing tip antenna, an early clinical prototype system. In vitro three-dimensional thermal mapping of single and double helix antenna designs was performed. Quantitative measurements of antenna radiation were recorded on tissue phantoms equipped with temperature sensors distributed radially and outwardly. In vivo testing consisted of closed-chest AV junction ablation in three dogs. Thermal mapping showed hemispherical heat distribution from the tip antenna. For the double helix design, this distribution was measured at 8.4-mm diameter with a maximum temperature of 61.62 degrees C. As expected, the single helix design produced less heating with a measured diameter of 6.4 mm and maximum temperature of 55.90 degrees C. The in vivo study produced lesions of geometry and size concordant with these heating patterns. MW ablation produced bundle branch block in one dog and complete AV nodal block in the remaining two, without transvalvular or other structural damage. The histopathology of the lesions was typical of a thermal burn showing hemorrhage and coagulative necrosis with clearly demarcated borders. We conclude that, using this early clinical prototype system with a deflectable catheter and a forward-firing tip antenna design, MW heating can produce a moderate-size lesion and is safe and effective for cardiac ablation.

Temperature-controlled radiofrequency catheter ablation of manifest accessory pathways.

OBJECTIVES: The primary objectives of this study were to assess the feasibility of temperature-controlled radiofrequency catheter ablation of left and right sided manifest accessory pathways in patients with Wolff-Parkinson-White syndrome and to gain more insights into biophysical aspects of temperature-controlled catheter ablation in humans. BACKGROUND: The electrode-tissue interface temperature and other biophysical parameters are among important variables determining the efficacy and safety of radiofrequency ablation of accessory pathways. Experimental studies have shown that radiofrequency-induced tissue necrosis can be accurately predicted by monitoring of catheter tip temperature. METHODS: 38 consecutive patients (14 f, 24 m; aged 42 +/- 12 years) with anterograde conducting accessory pathways (left sided: n = 22; right sided: n = 16) underwent temperature-controlled radiofrequency ablation (HAT 200S, Dr Osypka, Germany). The electrode temperature was monitored via a thermistor embedded into a 4 mm catheter tip. Power output was adjusted automatically during energy delivery in a closed loop system (preselected temp.: 70.1 +/- 5.8 degrees C). RESULTS: Accessory pathway conduction was successfully abolished in all patients after the delivery of 2.3 +/- 2.1 radiofrequency pulses (range: 1-9, median: 2). Interruption of the accessory pathway as evidenced by loss of preexcitation occurred after 5.9 +/- 5.4 s. At the time of the interruption of the accessory pathway the catheter tip temperature measured 54.2 +/- 11.2 degrees C in patients with left and 44.9 +/- 5.0 degrees C in patients with right sided accessory pathways, respectively (P < 0.008). Higher temperature levels during left sided applications did not shorten the time it took for the effect to appear (left sided accessory pathway: 7.5 +/- 6.3 s, right sided accessory pathway: 3.7 +/- 2.9 s; ns). The catheter tip temperature was significantly higher during left compared to right sided applications after 5 (52.1 +/- 3.1 degrees C vs 47.2 +/- 4.3 degrees C) and 10 s (61.5 +/- 6.2 degrees C vs 52.7 +/- 4.2 degrees C) following initiation of the impulse (P < 0.005). Power output and delivered energy did not differ significantly at the time of accessory pathway abolition. Peak values of delivered power (45.1 +/- 10.9 W vs 41.3 +/- 10.6 W; P < 0.05) and total delivered energy (2452 +/- 1335 J vs 1392 +/- 762 J; P < 0.02) were significantly higher in the group of right sided pathways compared to left sided applications. The peak temperature measured 77.1 +/- 13 degrees C during effective and 69.9 +/- 14 degrees C during ineffective energy applications (P < 0.05). The time it took for the effect to appear was significantly longer in transiently effective pulses (10.4 +/- 7.2 s) compared to permanently effective applications (5.9 +/- 5.4 s; P < 0.02). Despite temperature control, an abrupt rise in impedance was observed in 10 of 89 (11%) energy applications. No procedure-related complications occurred. CONCLUSIONS: Temperature-controlled radiofrequency ablation of manifest accessory pathways is highly effective and safe. The temperature response is faster and significantly higher in left-sided energy applications compared to right-sided pulses. Peak temperature levels measured at the electrode tip are significantly higher during effective than ineffective pulses. Sudden rises in impedance are not completely prevented during temperature-controlled radiofrequency ablation of accessory pathway, although no procedure-related complications were noted in this patient cohort.

Comparison of the results of programmed ventricular stimulation from the right ventricular apex and outflow tract: a randomized, prospective study.

OBJECTIVE: The aim of this prospective study was to analyse the yield of programmed ventricular stimulation at the right ventricular apex compared with the outflow tract. METHODS: A stepwise randomized cross-over protocol of programmed ventricular stimulation with alternating stimulation at both sites was used in 66 patients who were studied because of sustained ventricular tachycardia (n = 30), ventricular fibrillation (n = 7), or non-sustained ventricular tachycardia and/or syncope (n = 29). RESULTS: There were no significant differences between the results of stimulation from either right ventricular site with regard to the presence or absence of structural heart disease, spontaneous arrhythmia, ejection fraction or effective refractory periods. Overall, monomorphic ventricular tachycardia was inducible in 33 patients (50%); in 25 patients (75.8%), this arrhythmia was induced from both sites. However, in only 17 of these 25 patients (68%) did the induced monomorphic ventricular tachycardias have the same morphologies and similar (+/- 50 ms) cycle lengths. Ventricular fibrillation was inducible in 11 patients (17%), mostly by three extrastimuli (n = 8; 73%). CONCLUSIONS: (1) stimulation from at least two right ventricular sites is desirable because of their independent contribution to the induction of ventricular tachyarrhythmias, (2) the non-inducibility or inducibility at one ventricular site does not predict the effect at another stimulation site, (3) the effective refractory period at the right ventricular apex and outflow tract do not differ, (4) the inducibility of multiple ventricular tachycardia morphologies emphasizes the importance of documenting the cause of spontaneous arrhythmias with multiple electrocardiographic leads to ensure the correct interpretation of arrhythmias induced by programmed stimulation, (5) clinical or haemodynamic features cannot predict whether one or more stimulation sites will be required for induction of ventricular tachycardia. These results are important for the diagnostic evaluation and assessment of pharmacological or non-pharmacological interventions.

Comparison and combination of late potentials and spectral turbulence analysis to predict arrhythmic events after myocardial infarction in the Post-Infarction Late Potential (PILP) Study.

Ventricular late potentials detected at the end of the QRS complex by the signal-averaged ECG have been shown to predict arrhythmic events after acute myocardial infarction. Spectral turbulence analysis is a novel technique for detecting abnormalities of cardiac electric activation inside the QRS complex. The purpose of this study was to combine these two analysis methods in order to increase the predictive power of the signal-averaged ECG in post-infarction patients. The study comprised a prospective series of 778 males under 66 years of age who survived the acute phase of myocardial infarction. Signal-averaged ECG recordings were performed before hospital discharge 2 to 3 weeks after infarction. The original Simson method was used for recording and analysing the time-domain signal-averaged ECG. Spectral turbulence analysis was performed using the same averaged vector magnitude QRS complexes (Del Mar Avionics). During the follow-up period of 6 months, 33 patients (4.2%) had an arrhythmic event (sustained monomorphic ventricular tachycardia in 13 cases, ventricular fibrillation in eight cases and sudden cardiac death in 12 cases). The predictive power of late potentials in the time domain, spectral turbulence analysis and their combinations were tested together with clinical variables using the Cox regression method.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical implications of pleomorphic ventricular tachycardias on oral sotalol therapy.

In 90 consecutive patients with coronary artery disease and sustained monomorphic ventricular tachycardia, who were treated with oral sotalol and underwent programmed stimulation to determine drug effectiveness, the influence of sotalol on induced ventricular tachycardia morphology was retrospectively examined. In 54 patients (60%) sotalol rendered the tachycardia non-inducible. However, contrary to drug-testing with class I antiarrhythmic agents, induction of multiple morphologies at baseline study did not predict failure of subsequent drug-testing with sotalol. In the remaining 36 patients (40%), in whom sotalol did not modify inducibility, 21 patients (i.e. a total of 23%) manifested at least one new morphology during electropharmacological testing on sotalol. This effect was independent of the degree of left ventricular dysfunction, infarct location and numbers of morphologies at baseline, but corresponded with drug-induced changes in refractoriness. This observation may be related to a proarrhythmic effect of sotalol. Slowing of ventricular tachycardia rate and changes in morphology may have implications in patients receiving implantable cardioverter-defibrillators or those undergoing ablative procedures.

Are there gender differences in patients with coronary artery disease presenting with spontaneous sustained ventricular tachycardia and ventricular fibrillation?

The incidence of coronary artery disease (CAD) is greater in men than in women. The aim of the study was to analyze whether any gender-related differences in patients with CAD and documented spontaneous sustained ventricular tachyarrhythmias exist, and which parameters influence the induction of sustained ventricular tachyarrhythmias. The data of 250 patients [43 women (17.2%) and 207 men (82.8%)] with spontaneous sustained ventricular tachycardia [n = 190 (76%)] and fibrillation [n = 60 (24%)] who underwent coronary and left ventricular angiography, electrophysiological study, and signal-averaging electrocardiogram (ECG) form the basis of this analysis. No gender-related differences could be observed in age, number of diseased coronary arteries, history, location and number of myocardial infarctions, presence of left ventricular aneurysm, ejection fraction, type of spontaneous or induced arrhythmias, right ventricular effective refractory period, and signal-averaged ECG parameters. Age, presence of previous myocardial infarction, and ejection fraction were significant predictors (p < 0.001) of inducibility of sustained ventricular tachyarrhythmias. Once CAD has begun, female and male patients present similar clinical and electrophysiologic characteristics. Thus, both genders should benefit similarly from diagnostic and therapeutic approaches if they are referred to the hospital or to invasive interventions at similar intervals in the course of their illness.

Localization and radiofrequency catheter ablation of left-sided accessory pathways during atrial fibrillation. Feasibility and electrogram criteria for identification of appropriate target sites.

OBJECTIVES: The purpose of the present study was to assess the feasibility of and electrophysiologic criteria for successful radiofrequency catheter ablation of left-sided accessory pathways during atrial fibrillation in patients with Wolff-Parkinson-White syndrome. BACKGROUND: The onset of recurrent or sustained atrial fibrillation can complicate or significantly prolong accessory pathway catheter ablation procedures. METHODS: We studied 19 consecutive patients (mean age [+/-SD] 44 +/- 16 years) with Wolff-Parkinson-White syndrome who had ongoing atrial fibrillation with rapid anterograde conduction over the accessory pathway (mean ventricular rate [+/-SD] 173 +/- 26 beats/min, range 130 to 220) at the beginning of the localization procedure during radiofrequency catheter ablation. Localization and ablation of the accessory pathway were performed with a 7F deflectable catheter (4-mm tip) that was placed underneath the mitral valve annulus. The electrophysiologic criteria from unipolar and bipolar local electrograms were compared for successful (n = 18) and unsuccessful (n = 39) sites. RESULTS: The accessory pathways were localized in the left posteroseptal (n = 6), posterior (n = 1), posterolateral (n = 7) and lateral (n = 5) regions and successfully ablated during atrial fibrillation in 18 (95%) of 19 patients with a mean of 3 +/- 2 radiofrequency pulses (range 1 to 8, median 2). Presence of an accessory pathway potential (94% vs. 44%), early activation time of the ventricular electrogram (-3.2 +/- 9.2 vs. -15.3 +/- 12.6 ms) and recording of atrial activation (88% vs. 61%) from the ablation catheter were helpful in identifying successful sites (p < 0.001, p < 0.001 and p < 0.05, respectively, compared with unsuccessful sites). In addition, the ventricular activation time in relation to the intrinsic deflection of the unipolar electrogram was significantly earlier at successful than unsuccessful sites (18.1 +/- 4.8 vs. 24.4 +/- 6.6 ms, p < 0.01). A QS complex on the unipolar electrogram was observed at 96% of successful sites and at 94% of unsuccessful sites (p = 0.74). Multivariate logistic regression analysis revealed that the presence of an accessory pathway potential (p < 0.002) and early ventricular activation time in relation to the onset of the QRS complex (p < 0.001) were independent predictors of ablation success. CONCLUSIONS: Localization and radiofrequency catheter ablation of left-sided accessory pathways is possible in patients with sustained atrial fibrillation and rapid anterograde conduction over the accessory pathway during the ablation procedure. The electrophysiologic criteria described here can be used to reliably identify successful sites for radiofrequency ablation.

Dispersion of ventricular refractoriness in experimental myocardial infarction: effect of sotalol.

UNLABELLED: Dispersion of refractoriness may contribute to the propensity for reentrant arrhythmias. This study was performed to assess the effect of sotalol on the dispersion of refractoriness in experimental myocardial infarction. In 9 mongrel dogs, 14 days after induction of myocardial infarction by an occlusion reperfusion technique, programmed ventricular stimulation and epicardial mapping were performed before and during (3 mg/kg + 0.5 mg/kg per hour) sotalol administration. To assess the spatial distribution of refractoriness, ventricular fibrillation (VF) intervals were analyzed. The rationale for this method is that, during VF, when multiple reentrant wavelets are present, cells are excited as soon as they recover from previous activation. The coefficient of variation (standard deviation x 100) served as an index of spatial distribution of refractoriness. RESULTS: VF was induced before sotalol in 7 dogs and in 5 of 7 during sotalol administration. The mean value of the index VF intervals decreased from 19.8 +/- 2.3 at baseline to 15.8 +/- 2.6 during sotalol (P = 0.011), indicating a more homogeneous distribution of refractoriness. Thus, the antiarrhythmic effects of sotalol may be mediated by its action on the dispersion of refractoriness.

QRS alterations in body surface potential distributions during percutaneous transluminal coronary angioplasty in single-vessel disease.

Body surface QRS potentials were recorded with 63 chest leads in 20 patients with proximal single-vessel disease located on either the left anterior descending coronary artery (n = 10), the right coronary artery (n = 6), or the left circumflex coronary artery (n = 4) before, during, and after percutaneous transluminal coronary angioplasty. In each case, three consecutive inflations of relatively short duration (37 +/- 14 seconds) were carried out. Electrical activity was displayed as unipolar electrograms and body surface potential maps. The total QRS complex duration decreased in 14 of the 20 patients. Focal conduction disturbances were observed in six cases; all six had left anterior descending coronary artery occlusion and two were also accompanied by a clear shortening of the right epicardial breakthrough time. In these two cases, an initial activation loss seemed to be characteristic, whereas in the other four cases, a rather diffuse slowing of intraventricular conduction, especially during the terminal portion of the QRS, could be observed. Individual and group mean isointegral difference body surface potential maps (during-minus-before dilation) were considered valuable for the interpretation of localized changes in intraventricular conduction during percutaneous transluminal coronary angioplasty, and their individual variations could, at least partly, be explained by the presence or absence of collateral circulation. Two different hypotheses are suggested to account for the QRS complex shortening observed during short-term myocardial ischemic injury: (1) coronary artery occlusion delayed activation of the portion of the septal region that is normally activated early during the QRS, and/or (2) coronary artery occlusion increased the speed of propagation within the ventricles. Both of these hypotheses are discussed in light of earlier clinical and experimental results.

Recurrence and late block of accessory pathway conduction following radiofrequency catheter ablation.

INTRODUCTION: Many issues regarding the recurrence of accessory pathway conduction and the long-term outcome of late block of accessory pathway conduction are still unknown or controversial. METHODS AND RESULTS: Data from 217 patients who underwent an initially successful radiofrequency ablation of accessory pathways and 7 patients with late block of accessory pathway conduction following an initially unsuccessful ablation were analyzed. During a mean follow-up of 19 +/- 11 months, accessory pathway conduction resumed in 21 (10%) of 217 patients following an initially successful ablation and in 6 (86%) of 7 patients with late block of accessory pathway conduction (P < 0.01). After initially successful ablations, the recurrence rates of accessory pathway conduction at 1, 3, and 6 months were 5.9%, 7.4%, and 11.3%, respectively. A late electrophysiologic study at 6 months uncovered recurrence in only 1 of 124 asymptomatic patients, but failed to detect the late recurrence in 2 patients in whom the accessory pathway conduction resumed after more than 6 months. Multivariate analysis revealed that independent predictors for recurrence of accessory pathway conduction were concealed accessory pathway, presence of transient effect of radiofrequency pulse, and more than 5 pulses required for initial cure. Accessory pathway location, length of the tip electrode of the ablation catheter, and repeat radiofrequency pulses ("safety pulses") after effective pulses did not predict resumption of accessory pathway conduction. CONCLUSIONS: After initially successful ablation, the recurrence rates of accessory pathway conduction at 1, 3, and 6 months were 5.9%, 7.4%, and 11.3%, respectively. Late electrophysiologic testing had little prognostic value in asymptomatic patients following successful ablation. Application of "safety pulses" did not prevent recurrence. Late block of accessory pathway conduction did not predict long-term efficacy.

Anisotropic conduction characteristics in ischemia-reperfusion induced chronic myocardial infarction.

OBJECTIVES: Anisotropic properties of cardiac tissue play an important role in initiation and perpetuation of ventricular tachycardia. However, anisotropic conduction properties in different morphologic types of chronic myocardial infarctions as well as frequency dependency still need to be elucidated. In the present study, the characteristics of anisotropic conduction were investigated in situ in the setting of ischemia-reperfusion induced chronic myocardial infarction. METHODS: Myocardial infarction was induced in 12 dogs by a percutaneous transcatheter left anterior descending coronary artery occlusion-reperfusion technique. Four additional dogs served as normal controls. After 14 to 20 days, epicardial mapping was performed using simultaneous unipolar recordings from 240 electrodes of a plaque electrode array placed on the epicardial border zone overlying the infarctions. Constant rate pacing with five cycle lengths (CL) ranging from 500 to 200 ms as well as programmed electrical stimulation (PES) with four basic cycle lengths (BCL) ranging from 430 to 300 ms and single extrastimuli (S2) were performed. RESULTS: Two anatomically different patterns of epicardial surface morphology were analyzed, designated as type I and type II. In seven animals, there was a continuous thin layer of surviving epicardial muscle fibers overlying the infarction (type I). During pacing with CL of 500 vs 200 ms, conduction velocity longitudinal to fiber orientation (theta L) decreased significantly in the infarcted animals compared to control group (10.9% vs 5.2%, p < 0.05) whereas conduction velocity transverse to fiber axis (theta T) decreased to a similar degree in control and infarcted animals (6.9 vs 7.4%, n.s.). After premature stimulation, there was considerably greater reduction in theta L in infarcted animals than in controls (39.8% vs 31.5%, p < 0.05) whereas theta T decreased to a similar extend in infarcted and control animals (22.2% vs 21.4%, n.s.). During constant rate pacing and premature stimulation, no functional conduction block was induced in type I infarctions. In five animals, the transmural infarctions clearly extended to the epicardial surface, but continuous strands of surviving epicardial muscle fibers traversed the area of necrosis (type II). During PES with S2, functional conduction block and areas of very slow conduction were observed in each case. CONCLUSIONS: In ischemia-reperfusion induced chronic myocardial infarctions, different epicardial patterns of morphology were observed. Anisotropic conduction was frequency dependent in the longitudinal but not in the transverse direction. In type I infarctions, functional conduction block was not inducible during PES whereas in type II infarctions, prerequisites for reentrant arrhythmias like functional conduction block and very slow conduction were induced in each case by single extrastimuli.

Response to sotalol predicts the response to amiodarone during serial drug testing in patients with sustained ventricular tachycardia and coronary artery disease.

UNLABELLED: It was analyzed whether the response to sotalol can predict the response to amiodarone as evaluated by programmed ventricular stimulation in 30 patients with coronary artery disease and documented recurrent sustained ventricular tachycardia (VT). Programmed ventricular stimulation was performed using 1 or 2 extrastimuli during sinus rhythm and 4 drive cycle lengths at 2 right ventricular sites. If no ventricular tachyarrhythmia was induced, a third extrastimulus was introduced during a paced cycle length of 500 ms. During the control study, VT (mean cycle length 305 +/- 63 ms) was induced in all patients, and the right ventricular effective refractory period (during S1-S1 = 500 ms) was 223 +/- 12 ms. After sotalol, sustained and nonsustained VT were inducible in 22 (73%) and 7 (23%) patients, respectively. One patient did not undergo stimulation on sotalol, because of side effects. After amiodarone, sustained and nonsustained VT were inducible in 23 (77%) and 7 (23%) patients, respectively. The mean cycle length of the induced VT was prolonged after both drugs by 17% (p < 0.001). The effective refractory period was prolonged by 15% (p < 0.001) after sotalol and by 13% (p < 0.001 compared with baseline study; p = NS between both drugs) after amiodarone. Thus, concordant results (effective or ineffective drug) between sotalol and amiodarone were found in 26 patients (87%). IN CONCLUSION: (1) The effects of sotalol and amiodarone on the cycle length of induced VT and on right ventricular effective refractory period were similar; and (2) inability to suppress VT by amiodarone can be predicted from the response to sotalol.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of programmed ventricular stimulation in patients with idiopathic dilated cardiomyopathy and documented sustained ventricular tachyarrhythmias: inducibility and prognostic value in 102 patients.

The role of programmed ventricular stimulation (PVS) in patients at high risk of sudden death related to idiopathic dilated cardiomyopathy (DCM) is still controversial. The possible reason is that most study series have been too small or that only a few patients had documented sustained ventricular tachyarrhythmias. This study therefore, looked at PVS performed in 102 patients with DCM and documented sustained ventricular tachycardia (VT; n = 63) or ventricular fibrillation (VF; n = 39). Sustained VT was induced in 27 of 63 patients (43%) with documented sustained VT and in 14 of 39 patients (36%) with documented VF (ns). VF was induced in nine patients (14%) with a history of sustained VT and in seven (18%) with a history of VF (ns). At a mean follow-up of 32 +/- 15 months, sudden death occurred in 14 (14%) patients, a rate similar in both patients with documented VT and VF (ns). Incidence of sudden death at 36 months was 6% in patients with inducible sustained VT/VF compared to 29% in patients without inducible VT/VF (P < 0.05). A favourable drug regimen (response to drug and no intolerable side effects) was obtained by serial drug testing in 25 of all 102 patients (25%). A cardioverter defibrillator (ICD) was implanted in 32 patients, in 63% of whom discharges were observed during 18 +/- 11 months of follow-up; only one patient (3%) died suddenly. Thus, in patients with DCM, there was no relationship between documented and inducible ventricular tachyarrhythmias, and initiation of sustained VT or VF had little prognostic value for the prediction of subsequent sudden death. Wherever antiarrhythmic drug therapy was of limited value, implantation of an ICD may improve the prognosis of these high risk patients.

Atrioventricular nodal reentry tachycardia: electrophysiologic comparisons in patients with and without 2:1 infra-His block.

Patients with atrioventricular nodal reentry tachycardia (AVNRT) occasionally may demonstrate a 2:1 infra-His block during tachycardia. However, the electrophysiologic background of this phenomenon has not been established so far. In the present study we compared the electrophysiologic parameters of 10 consecutive patients with a transient 2:1 infra-His block during AVNRT of the common type (Group A) with those of 17 consecutive patients without this phenomenon during tachycardia (Group B). Transient 2:1 infra-His block occurred without termination of the tachycardia in all 10 patients of Group A. The tachycardia sustained despite intermittent or permanent conduction disturbance of the infrahisian tissue in 8 of these 10 patients. In comparison, the electrophysiologic parameters of 17 patients without 2:1 block during AVNRT of the common type (Group B) were analyzed. A significantly longer antegrade (318 +/- 58 ms vs. 259 +/- 50 ms) and retrograde (308 +/- 59 ms vs. 239 +/- 20 ms) AV conduction capacity could be demonstrated in these patients. The tachycardia cycle length did not differ significantly between the two groups, although the mean tachycardia cycle length was 48 ms longer in patients of Group B. These observations demonstrate an advanced conduction capacity in patients with a transient infra-His block during AVRNT of the common type. This study underlines that the reentry circuit in AVNRT is not necessarily dependent on infrahisian tissue.

Signal averaging in patients with coronary artery disease: how helpful is it?

In patients who have survived acute myocardial infarction, the presence of ventricular late potentials using the high resolution signal-averaged ECG indicates areas of slow conduction and delayed activation that may potentially serve as a substrate for malignant ventricular arrhythmias. Although detection of late potentials is technique specific, signal-averaged analysis in the time or frequency domain may be a useful index for risk stratification with regard to ventricular tachycardia or sudden cardiac death. The sensitivity and specificity of late potentials for this purpose may be enhanced by combination with other variables, such as left ventricular ejection fraction and presence of complex ventricular ectopy. Therefore, the presence of ventricular late potentials in postmyocardial infarction patients, particularly in those patients with impaired left ventricular function, identifies those patients who are at high risk of malignant ventricular tachyarrhythmias. However, the strategies for prevention of serious arrhythmia complications during follow-up need to be established. The negative predictive value of late potentials is very high. Thus, the absence of late potentials indicates a low propensity to sustained ventricular tachycardia or sudden death, even in the presence of complex ventricular ectopy. Interventions may therefore not be necessary or should even be avoided. The incidence of late potentials in patients with spontaneous or induced ventricular fibrillation is lower and, if present, less pronounced than in those with sustained monomorphic ventricular tachycardia. This presumably is due to a lower degree of conduction delay, which serves as a substrate for reentry. Therefore, the ability of the signal-averaged ECG to predict a propensity to ventricular fibrillation is limited. Despite these limitations, the signal-averaged ECG may be used as a risk predictor in evaluation of patients after myocardial infarction. Unfortunately, at least as far as time domain analysis is concerned, it cannot be used as an efficacy predictor for response to pharmacologic interventions. Further studies will determine whether other modes of signal-averaged analysis can predict the response to drugs.

The signal-averaged ECG: time-domain analysis.

During the past decade, the high-resolution electrocardiogram as a non-invasive technique for the detection of ventricular late potentials has developed from an experimental method into a routinely applied non-invasive method for risk stratification of patients after myocardial infarction. Meanwhile, several approaches have been developed for the detection of ventricular late potentials including time-domain analysis, frequency-domain analysis and spectrotemporal mapping. Clinical applications are no longer limited to patients after myocardial infarction, but cover a wider spectrum of different cardiac diseases. This review focuses on some methodological aspects as well as on the results and current clinical applications of the analysis of the signal-averaged ECG in the time domain.