Slow pathway catheter ablation of atrioventricular nodal re-entrant tachycardia guided by electroanatomical mapping: a randomized comparison to the conventional approach.

BACKGROUND: Electroanatomical mapping may be expected to improve safety, efficiency and efficacy of selective slow pathway ablation for atrioventricular nodal re-entrant tachycardia (AVNRT). The goal of this prospective randomized study was to compare the efficiency of conventional fluoroscopic and electroanatomical mapping in guiding catheter ablation of AVNRT. METHODS AND RESULTS: Following induction of typical AVNRT, 20 consecutive patients were randomized to either conventional fluoroscopic or electroanatomical (CARTO) mapping to guide slow pathway ablation using a 4mm electrode. Endpoints for ablation were non-inducibility and no more than a single AV nodal echo on aggressive retesting. Acute procedural success was 100% in both groups, with no complications. Although there were no differences in time taken for pre- and post-ablation electrophysiological evaluations, in the electroanatomical group the ablation portion of the procedure showed a substantial reduction in duration (12.6+/-6.8 vs 35.9+/-18.3 min; P< 0.001) and fluoroscopic exposure (0.7+/-0.5 vs 9.6+/-5.0 min; P< 0.001) compared with the fluoroscopic group, reflected in reduced total procedure time (83.6+/-23.6 vs 114+/-19.3 min; P=0.008) and total fluoroscopic exposure (4.2+/-1.4 vs 15.9+/-6.4 min; P< 0.001). Electroanatomical mapping was associated with a lower number (2.7+/-1.6 vs 5+/-2.8; P=0.018), duration (165.3+/-181.6 vs 341+/-177.7s; P=0.013), and total energy delivery (24.3+/-3.1 vs 28.7+/-4.5 watts; P=0.042) of RF applications. There were no acute or long-term (8.9+/-2.2 month) complications or arrhythmia recurrence in either group. CONCLUSIONS: While both conventional and non-fluoroscopic electroanatomical mapping are associated with excellent results in guiding ablation of typical AVNRT, the latter offers significantly shorter procedure and fluoroscopy times, improving the efficiency of the procedure and reducing X-ray exposure.

Long-term follow-up of patients requiring intravenous amiodarone to suppress hemodynamically destabilizing ventricular arrhythmias.

BACKGROUND: Intravenous amiodarone is effective for the acute suppression of recurrent hemodynamically destabilizing ventricular arrhythmias. There are no follow-up data on patients undergoing long-term therapy with intravenous amiodarone. The objective of this investigation was to evaluate long-term outcome. METHODS AND RESULTS: We reviewed the clinical courses of 245 patients given intravenous amiodarone for sustained ventricular tachyarrhythmias. Of the 107 survivors (84% men; mean age 64 years) released from the hospital taking oral amiodarone, 41 were discharged with an empiric prescription for oral amiodarone. For 64 patients a decision regarding further therapy was based on results of an electrophysiologic study. Two patients were treated empirically with oral amiodarone and an implantable cardioverter defibrillator. Clinical variables and survival curves were the same for the empirically treated group and the group whose treatment was based on electrophysiologic findings (P =.89). Survival at 6, 12, and 18 months was 88%, 81% and 71%, respectively, for empirically treated patients, and 83%, 80% and 73%, respectively, for patients whose therapy was directed with an electrophysiologic study. Of the 64 patients who underwent electrophysiologic studies, 33 received an implantable cardioverter defibrillator. The Kaplan-Meier survival curves for patients with and patients without an implantable cardioverter defibrillator were similar (P =.46). CONCLUSIONS: Patients for whom recurrent ventricular tachycardia and fibrillation are suppressed with intravenous amiodarone and who are discharged receiving oral amiodarone have an 80% 1-year survival rate. Although not randomized, our data suggested that among such patients, electrophysiologic testing, implantation of a cardioverter defibrillator, or both may not be necessary. Ascertaining the best management strategy for these patients will require a prospective randomized trial.

Randomized, double-blind comparison of intravenous amiodarone and bretylium in the treatment of patients with recurrent, hemodynamically destabilizing ventricular tachycardia or fibrillation. The Intravenous Amiodarone Multicenter Investigators Group.

BACKGROUND: After several days of loading, oral amiodarone, a class III antiarrhythmic, is highly effective in controlling ventricular tachyarrhythmias; however, the delay in onset of activity is not acceptable in patients with immediately life-threatening arrhythmias. Therefore, an intravenous form of therapy is advantageous. This study was designed to compare the safety and efficacy of a high and a low dose of intravenous amiodarone with bretylium, the only approved class III antiarrhythmic agent. METHODS AND RESULTS: A total of 302 patients with refractory, hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation were enrolled in this double-blind trial at 82 medical centers in the United States. They were randomly assigned to therapy with intravenous bretylium (4.7 g) or intravenous amiodarone administered in a high dose (1.8 g) or a low dose (0.2 g). The primary analysis, arrhythmia event rate during the first 48 hours of therapy, showed comparable efficacy between the bretylium group and the high-dose (1000 mg/24 h) amiodarone group that was greater than that of the low-dose (125 mg/24 h) amiodarone group. Similar results were obtained in the secondary analyses of time to first event and the proportion of patients requiring supplemental infusions. Overall mortality in the 48-hour double-blind period was 13.6% and was not significantly different among the three treatment groups. Significantly more patients treated with bretylium had hypotension compared with the two amiodarone groups. More patients remained on the 1000-mg amiodarone regimen than on the other regimens. CONCLUSIONS: Bretylium and amiodarone appear to have comparable efficacies for the treatment of highly malignant ventricular arrhythmias. Bretylium use, however, may be limited by a high incidence of hypotension.

Dose-ranging study of intravenous amiodarone in patients with life-threatening ventricular tachyarrhythmias. The Intravenous Amiodarone Multicenter Investigators Group.

BACKGROUND: Oral amiodarone effectively suppresses ventricular arrhythmias; however, full activity may take days or weeks. In patients with frequent, life-threatening ventricular arrhythmias, this delay is not acceptable. Thus, in these patients, the speed and dosing accuracy of an intravenous formulation would be beneficial. The goal of this study was to demonstrate the efficacy of intravenous amiodarone in patients with refractory, recurrent hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation by determining a dose response among three regimens. METHODS AND RESULTS: A total of 342 patients were enrolled at 46 medical centers in the United States. Patients received one of three randomized, double-blind dose regimens delivering 125, 500, or 1000 mg during the first 24 hours. Supplemental infusions (150 mg) of intravenous amiodarone could be given to treat breakthrough ventricular arrhythmias. The key efficacy end points were the arrhythmia event rate, time to first arrhythmic event, and number of supplemental infusions administered. The event rate decreased with increasing doses: median values were 0.07, 0.04, and 0.02 events per hour for the 125-, 500-, and 1000-mg dose groups, respectively, representing a significant decrease from baseline event rates (P = .043), and approached significance in the overall test for trend (P = .067). There was a significant dose-related increase in the time to first event (trend test P = .025) and a significant dose-related decrease in the number of supplemental boluses per hour (trend test P = .043). Hypotension was the most common (26%) treatment-emergent adverse event during intravenous amiodarone therapy; there was no dose-response relationship. Seventy-eight percent of the patients survived to at least 48 hours. CONCLUSIONS: Intravenous amiodarone is effective for the treatment of recurrent, life-threatening ventricular tachyarrhythmias.

Virtual cathode effects during stimulation of cardiac muscle. Two-dimensional in vivo experiments.

We have found that when suprathreshold cathodal stimuli were applied to the epicardium of canine ventricle, impulse propagation originated at a "virtual cathode" with dimensions greater than those of the physical cathode. We report the two-dimensional geometry of the virtual cathode as a function of stimulus strength; the results are compared with the predictions of an anisotropic, bidomain model of cardiac conduction recently developed in our laboratories. Data were collected in six pentobarbital-anesthetized dogs by using a small plaque electrode sewn to the left ventricular epicardium. Arrival times at closely spaced bipolar electrodes oriented radially around a central cathode were obtained as a function of stimulus strength and fiber orientation. The dimensions of the virtual cathode were determined by linear back-extrapolation of arrival times to the time of stimulation. The directional dependence of the conduction velocity was consistent with previous reports: at 1 mA, longitudinal (0 degree) and transverse (90 degrees) velocities were 0.60 +/- 0.03 and 0.29 +/- 0.02 m/sec, respectively. At 7 mA, the longitudinal velocity was 0.75 +/- 0.05 m/sec, whereas there was no significant change in the transverse velocity. In contrast to conduction velocity, the virtual cathode was smallest in the longitudinal orientation and largest between 45 degrees and 60 degrees. Virtual cathode size was dependent on both orientation and stimulus strength: at 0 degree, the virtual cathode was small (approximately 1 mm) and relatively constant over the range of 1-7 mA; at oblique orientations (45 degrees-90 degrees), it displayed a roughly logarithmic dependence on stimulus strength, approximately 1 mm at 1 mA and approximately 3 mm at 7 mA. The bidomain, anisotropic model reproduced both the stimulus strength and the fiber-orientation dependence of the virtual cathode geometry when the intracellular and extracellular anisotropies were 10:1 and 4:1, respectively, but not when the two anisotropies were equal. We suggest that the virtual cathode provides a direct measure of the determinants of cardiac activation; its complex geometry appears to reflect the bidomain, anisotropic nature of cardiac muscle.

Adequate heparinization during PTCA: assessment using activated clotting times.

Heparinization during PTCA is often done empirically with an initial 10,000 unit bolus of heparin and subsequent additional boluses as deemed necessary to prevent thrombus formation and fibrin deposition. However, the initial 10,000 unit bolus may not result in adequate systemic anticoagulation in every patient, exposing some patients to risk of thrombus at the angioplasty site and subsequent reocclusion. In this non-randomized study, we assessed systemic coagulation during PTCA by retrospectively analyzing activated clotting times obtained in 108 consecutive patients. All patients had normal baseline prothrombin times and activated partial thromboplastin times. Patients who were on heparin prior to PTCA were excluded. Based on data from studies on heparinization during extracorporeal bypass an activated clotting time (ACT) of greater than 300 seconds was required. Twelve patients (11%) were observed to have activated clotting times of below 300 seconds after an initial 10,000 unit bolus of heparin. These patients required an additional 3,000-10,000 units of heparin to have systemic anticoagulation during PTCA. Symptoms of stable or unstable angina had no significant effect on heparin requirement, although there was a trend toward greater heparin resistance in unstable angina. We conclude that it is important to monitor the status of anticoagulation during PTCA, for 11% of patients undergoing PTCA require additional initial heparin bolus to achieve an ACT greater than 300 seconds and to be effectively anticoagulated. Careful monitoring of heparinization during PTCA may reduce the incidence of thrombosis.

Mexiletine and tocainide: a comparison of antiarrhythmic efficacy, adverse effects, and predictive value of lidocaine testing.

Thirty patients received one of the lidocaine analogues--mexiletine or tocainide--orally for treatment of symptomatic ventricular arrhythmias. Crossover to the other analogue was allowed if initial drug treatment was unsuccessful, and the controlled use of other marketed oral antiarrhythmic agents was permitted. After follow-up of 7 +/- 3 months (SD), mexiletine was successful in 5 of 13 patients initially and in 5 of 14 patients who failed to respond to tocainide. Tocainide was successful in 1 of 17 patients initially and in 2 of 7 who did not respond to mexiletine. Combination therapy was used in nearly half of all ultimately successful drug trials. A common cause of drug trial failure for both drugs was the occurrence of adverse effects that frequently appeared well after hospital discharge. Response to lidocaine was a sensitive but nonspecific predictor of clinical outcome with mexiletine or tocainide that helped to identify drug-resistant patients. Finally, although mexiletine provided effective antiarrhythmic therapy more often than tocainide, response to one lidocaine analogue did not predict response to the other.

Efficacy and toxicity of amiodarone for the treatment of supraventricular tachyarrhythmias.

Amiodarone is an effective agent for all types of supraventricular tachyarrhythmias regardless of mechanism and may, in fact, control a high percentage of supraventricular tachyarrhythmias refractory to conventional antiarrhythmic agents. However, its toxicity should temper enthusiasm for the use of the medication in non-life-threatening arrhythmias. As always, when recommending specific therapies the potential benefit should be weighed in light of the related risk. In patients with life disordering, drug-refractory atrial fibrillation, it seems reasonable to attempt control with amiodarone. Likewise in patients with ectopic atrial tachycardias refractory to conventional agents, this seems reasonable as well. Other and better therapies are available for patients with life-threatening arrhythmias associated with the Wolff-Parkinson-White syndrome. While amiodarone is moderately effective in these patients, the advent of improved surgical techniques and the relatively low risk of an operation make surgery the treatment of choice. The role of IV amiodarone, acutely, in the treatment of supraventricular tachyarrhythmias remains to be defined.

Electrophysiologic effects of intravenous and oral sotalol for sustained ventricular tachycardia secondary to coronary artery disease.

The electrophysiologic effects of intravenous sotalol (1.5 mg/kg load followed by 0.008 mg/kg maintenance, mean dose 150 +/- 23 mg) and oral sotalol (mean dose 583 +/- 204 mg daily) were prospectively evaluated in 16 patients undergoing electrophysiologic evaluation for sustained ventricular tachycardia (VT) secondary to coronary artery disease. Electrocardiographic intervals, indexes of sinus and atrioventricular node function and indexes of atrial and ventricular function were assessed. Inducibility or noninducibility of sustained VT and characteristics of the induced arrhythmia were also evaluated. Intravenous and oral sotalol exerted similar beta-blocking effects, which included significant prolongation of sinus cycle length (baseline 820 +/- 165 ms, intravenous sotalol 1,077 +/- 206 ms, oral sotalol 1,141 +/- 306 ms), AH interval (baseline 126 +/- 43, intravenous sotalol 169 +/- 42, oral sotalol 197 +/- 55 ms) and Wenckebach cycle length (baseline 375 +/- 70, intravenous sotalol 460 +/- 84, oral sotalol 449 +/- 68 ms). Both intravenous and oral sotalol also prolonged repolarization and refractoriness including significant increases in QT interval (baseline 338 +/- 47, intravenous sotalol 417 +/- 35, oral sotalol 450 +/- 70 ms), atrial effective refractory period (baseline 240 +/- 38, intravenous sotalol 330 +/- 71, oral sotalol 299 +/- 26 ms) and right ventricular effective refractory period (baseline 241 +/- 16, intravenous sotalol 289 +/- 35, oral sotalol 291 +/- 22 ms).(ABSTRACT TRUNCATED AT 250 WORDS)

Right ventricular hypertrophy is an important determinant of right ventricular infarction complicating acute inferior left ventricular infarction.

To explore the role of right ventricular hypertrophy and chronic obstructive pulmonary disease in the pathogenesis of right ventricular infarction, 27 consecutive patients with a first inferior left ventricular infarction were prospectively studied. Right ventricular infarction was diagnosed using established hemodynamic criteria. Right ventricular hypertrophy was defined as right ventricular free wall thickness greater than or equal to 5 mm. Patients were classified into two groups: Group I patients with right ventricular infarction (n = 15), and Group II patients without right ventricular infarction (n = 12). The ratio of forced expiratory volume over forced vital capacity (FEV1/FVC) and forced expiratory flow between 25 and 75% expired volume (FEF) as a percent of predicted values were significantly reduced in Group I versus Group II (90 +/- 5 versus 105 +/- 6% and 63 +/- 13 versus 103 +/- 15%, respectively; p less than 0.05). This was associated with increased right ventricular wall thickness (Group I 5.5 +/- 0.3 mm versus Group II 3.9 +/- 0.2 mm, p less than 0.001). Multiple logistic regression analysis demonstrated that right ventricular wall thickness was the strongest predictor of right ventricular infarction (p less than 0.0005). No significant difference was found in the site of right coronary occlusion, collateral blood supply or extent of coronary artery disease between the two groups. These findings suggest that right ventricular hypertrophy predisposes patients with acute inferior myocardial infarction to right ventricular infarction independent of the site or extent of coronary artery disease.

Frequency- and orientation-dependent effects of mexiletine and quinidine on conduction in the intact dog heart.

Myocardial conduction depends on the magnitude of the fast inward sodium current as well as on cardiac fiber orientation, with more rapid propagation along myocardial fibers than across them. Although antiarrhythmic drugs depress the sodium current in a frequency-dependent fashion in vitro, their effects on conduction in the intact ventricle have been less well studied. We therefore evaluated the frequency- and orientation-dependent actions of mexiletine, quinidine, and their combination on epicardial conduction in 24 pentobarbital-anesthetized dogs. These interventions were chosen because the time constant of recovery from sodium-channel blockade by mexiletine in vitro is shorter than that from blockade by quinidine, and because we have previously shown that the combination of these drugs is often clinically effective when single-agent therapy fails. An electrode array that permitted measurement of conduction times in multiple orientations over short segments of epicardium without contamination by rapid Purkinje fiber propagation or by latency or virtual cathode effects at the stimulus site was developed for these studies. In all animals, the atrioventricular node was destroyed by injection of formalin to permit measurements over a wide range of cycle lengths (250 to 1500 msec). In the absence of drugs, conduction in any direction was frequency independent. In the presence of mexiletine, however, frequency-dependent increases in conduction times were found at cycle lengths of 600 msec or less; these changes were significantly greater in orientations for which baseline conduction was rapid. Quinidine, on the other hand, increased conduction times at all tested cycle lengths without significant orientation-dependent effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of left ventricular aneurysm formation after anterior myocardial infarction: a clinical and angiographic study.

To determine factors involved in left ventricular aneurysm formation after transmural anterior myocardial infarction, 79 patients with a first myocardial infarction who underwent cardiac catheterization within 6 months of infarction were evaluated. Patients who had received thrombolytic therapy were excluded. Patients were divided into four groups depending on the status of the left anterior descending artery and the presence or absence of a left ventricular aneurysm: Group I (n = 25): aneurysm with occluded left anterior descending artery; Group II (n = 27): no aneurysm and occluded left anterior descending artery; Group III (n = 23): no aneurysm and patent left anterior descending artery; and Group IV (n = 4): aneurysm with patent left anterior descending artery. Single vessel disease was more common in Group I (aneurysm) compared with Groups II and III (no aneurysm) (chi 2(4) = 12.8; probability value equal to 0.012). Collateral blood supply in the presence of an occluded left anterior descending artery was significantly less in Group I (aneurysm) compared with Group II (no aneurysm) (0.9 versus 2.4, p less than 0.001). The extent of coronary artery disease and collateral blood supply in Groups I and II were directly related (p = 0.012). Neither age, sex nor risk factors for coronary disease correlated with aneurysm formation. At a mean follow-up of 48 months, no differences were observed in the incidence of recurrent angina, new myocardial infarction, embolic events or sudden death. More patients in Group II underwent coronary artery bypass surgery. Total occlusion of the left anterior descending artery in association with inherent poor collateral blood supply is a significant determinant of aneurysm formation after anterior myocardial infarction. Multivessel disease with either good collateral circulation or a patent left anterior descending artery is uncommonly associated with the development of left ventricular aneurysm.

Myocardial abscess with complete heart block complicating anaerobic infective endocarditis.

Myocardial abscess caused by anaerobic infection is rare and usually occurs in cases of myocardial infarction, in which it may be related to areas of low oxygen tension. Bacteroides CDC group F-1 infective endocarditis complicated by an aortic valve ring abscess with resultant complete heart block developed in a patient with steroid dependent systemic lupus erythematosus. The genitourinary system was the presumed source of the infection. Endocarditis developed after an elective abortion, despite antibiotic prophylaxis according to American Heart Association recommendations. This case shows that an anaerobic abscess of the aortic valve ring can affect contiguous vital structures of the conducting system. Immunosuppression may increase the risk of anaerobic infection after genitourinary procedures, and in this situation the recommended antibiotic prophylaxis may be inadequate.

Right ventricular myocardial infarction in patients with chronic lung disease: possible role of right ventricular hypertrophy.

To determine the relation between right ventricular hypertrophy and right ventricular myocardial infarction in patients with chronic lung disease, the records of 28 patients with chronic lung disease, inferior myocardial infarction and significant coronary artery disease (group I) and 20 patients with right ventricular hypertrophy, chronic lung disease without inferior myocardial infarction or significant coronary artery disease (group II) were reviewed. Chronic lung disease was diagnosed by clinical criteria, chest radiographs and pulmonary function tests. All patients had postmortem examinations. Patients in group I were classified into two subgroups: group Ia (without right ventricular hypertrophy) and group Ib (with right ventricular hypertrophy). Right ventricular wall thickness was 3.3 mm +/- 0.5 in group Ia, 6.0 mm +/- 1.1 in group Ib and 8.8 mm +/- 2.4 in group II (group Ia versus Ib, p less than 0.001; group Ia versus II, p less than 0.001; group Ib versus II, p less than 0.001). Eleven patients (78.6%) in group Ib (chronic lung disease with both right ventricular hypertrophy and inferior myocardial infarction) had right ventricular myocardial infarction compared with only 3 patients (21.9%) in group Ia (chronic lung disease without right ventricular hypertrophy and with inferior myocardial infarction) (p less than 0.008). Isolated right ventricular myocardial infarction occurred in four patients (20%) in group II (chronic lung disease with right ventricular hypertrophy, but without evidence of infarction of the left ventricle or significant coronary artery disease). There was no significant difference in the extent of anatomic coronary disease in groups Ia and Ib.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of infarct size with intracoronary perfluorochemical in a canine preparation of reperfusion.

The effect of low-dose (15 ml/kg) intracoronary perfluorochemical (Fluosol-DA) on infarct size, regional myocardial blood flow, and ventricular function was studied in 20 anesthetized closed-chest dogs subjected to 11/2 hr of proximal left anterior descending occlusion. In this preparation reperfusion was simulated with fibrinolytic therapy. The animals were randomly assigned one of two treatment groups and given 15 ml/kg of either oxygenated intracoronary perfluorochemical (n = 9) or saline (n = 11). Contrast ventriculograms were obtained at baseline, 1 hr after occlusion, and at 24 hr after reperfusion and were analyzed with a radial fractional shortening method. Regional myocardial blood flow was measured with radioactive microspheres. At 24 hr the area at risk was defined in vivo with monastryl blue staining and the area of necrosis was estimated after incubation of left ventricular slices with triphenyltetrazolium chloride. No significant changes were noted in heart rate, blood pressure, pulmonary capillary wedge pressure, or dP/dt during the experimental protocol. Infarct size was significantly reduced (p less than .02) in the perfluorochemical-treated group, both when expressed as a percentage of the total left ventricular mass (7.9 +/- 1.7% vs 14.7 +/- 2.5%) and as a percentage of the area at risk (20.1 +/- 5.0% vs 46.8 +/- 8.5%). This was associated with significant improvement in fractional shortening in the jeopardized zone at 24 hr after reperfusion. Although endocardial blood flow was significantly greater in the central ischemic zone and lateral region at risk immediately after reperfusion in the perfluorochemical-treated group, no difference was found 1 hr after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dieldrin-induced chromosome damage in mouse bone-marrow and WI-38 human lung cells.

Several concentrations of the insecticide dieldrin were tested on in vivo bone marrow cells of STS mice and in vitro human embryonic lung cells of the WI-38 cell line. The insecticide caused pronounced mitotic inhibition and produced a 2 to 3-fold increase in chromosome abnormalities such as breaks and fragments in concentrations as low as 1 mg/kg in STS mice bone marrow cells, and 1 mug/ml in human WI-38 cells. The chemical also produced chromosome interchanges and rings. A few cells from the control groups exhibited breaks and fragments but not exchange figures and rings. Cytotoxic studies using the WI-38 cell line revealed dose-response and time-response reactions to dieldrin. Cell toxicity was most pronounced at the 50 mug/ml treatment level, producing 100 percent cell degeneration within 6 hours.