Effects of procainamide and lidocaine on defibrillation energy requirements in patients receiving implantable cardioverter defibrillator devices

INTRODUCTION

In acute canine studies, lidocaine, but not procainamide, increases defibrillation energy requirements. We evaluated the effects of lidocaine or procainamide on defibrillation energy requirements in 27 patients undergoing intraoperative testing for implantable cardioverter defibrillator device placement.

METHODS AND RESULTS

Patients were tested off antiarrhythmic drugs and again following either lidocaine (200 to 250 mg loading and 3 mg/min maintenance infusions) or procainamide (1 gm loading and 3 to 4 mg/min maintenance infusions). The defibrillation testing protocol consisted of initial testing at 15 J, followed by higher or lower energies to determine the lowest energy producing three consecutive successful defibrillations. Overall, the mean defibrillation energy increased from 14 +/- 5 J to 18 +/- 7 J during lidocaine (plasma concentration 5.1 +/- 1.6 micrograms/mL; P < 0.02) but were similar at baseline (12 +/- 5 J) and during procainamide infusion (13 +/- 6 J) (plasma concentration: procainamide 10.7 +/- 7.2 micrograms/mL; N-acetyl procainamide 1.0 +/- 0.4 micrograms/mL). A positive linear correlation was found between lidocaine plasma concentration and percent change in defibrillation energy (lidocaine: r = 0.61; P = 0.01). Procainamide raised the defibrillation energy in three patients, two with supratherapeutic plasma concentrations. The increase in defibrillation energy equaled or exceeded 25 J in four patients after lidocaine and in one patient after procainamide.

CONCLUSION

The data suggest that at high plasma concentrations, lidocaine and procainamide adversely affect defibrillation energy requirements consistent with an adverse, concentration-dependent effect of sodium channel blockade on defibrillation energy requirements in patients.

A randomized, prospective comparison of anterior and posterior approaches to radiofrequency catheter ablation of atrioventricular nodal reentry tachycardia

BACKGROUND

Two different techniques have been developed for radiofrequency catheter ablation of typical atrioventricular nodal reentry (AVNRT). Lesions made anteriorly near the apex of the triangle of Koch usually eliminate fast pathway function, whereas lesions made posteriorly near the ostium of the coronary sinus selectively affect slow pathway function. The current study compares the safety, efficacy, and electrophysiological effects of these two techniques in a prospective, randomized fashion.

METHODS AND RESULTS

Fifty consecutive patients with typical AVNRT were randomly assigned to receive radiofrequency lesions either anteriorly (n = 22) or posteriorly (n = 28). If the initial approach failed to eliminate inducibility of AVNRT after 1 hour or 10 applications of radiofrequency energy, the alternative ablation technique was used. Patients underwent repeat electrophysiological testing 48 hours and 3 months after ablation. The primary success rates of the anterior and posterior techniques were similar (55% versus 68%, p = NS). All of the patients who failed the initial approach were successfully treated by the alternative technique without developing high-grade atrioventricular block. One patient developed right bundle branch block during an anterior lesion, and another patient developed complete atrioventricular block as the result of a posterior lesion.

CONCLUSIONS

The posterior approach to radiofrequency catheter modification of the atrioventricular node is as effective as the anterior approach, and both techniques are associated with a low risk of complications. As long as AVNRT persists, it appears safe to cross over from one technique to the other.

Temperature monitoring during radiofrequency catheter ablation of accessory pathways

BACKGROUND

Animal studies have suggested that the temperature of the electrode-tissue interface during radiofrequency catheter ablation accurately predicts lesion size. The purpose of the current study was to evaluate the utility of continuous temperature monitoring during radiofrequency catheter ablation in patients with Wolff-Parkinson-White syndrome.

METHODS AND RESULTS

Twenty patients with manifest preexcitation were included in the study. The ablation catheter was positioned on the ventricular side of the mitral annulus for left-sided accessory pathways and on the atrial side of the tricuspid annulus for right-sided and septal accessory pathways. A thermistor imbedded in the distal electrode of the ablation catheter allowed continuous temperature monitoring during each energy application. To define the relation between power and temperature, radiofrequency current was applied several times at each site using outputs of 20, 30, 40, and 50 W. The accessory pathways were successfully ablated in each of the 20 patients. Because of marked variability in the efficiency of heating between sites, power output did not predict temperature. However, at any given site, there was a positive dose-response relation between power and temperature. Radiofrequency energy applications on the atrial side of the tricuspid annulus produced lower temperatures than did applications on the ventricular side of the mitral annulus (49 +/- 7 versus 60 +/- 16 degrees C, p = 0.0001). Transient block in the accessory pathways occurred at a mean of 50 +/- 8 degrees C, whereas permanent block was seen at a mean of 62 +/- 15 degrees C (p = 0.0001). Less than half of the applications at outputs < or = 40 W produced temperatures adequate to interrupt accessory pathway conduction. An abrupt rise in impedance caused by coagulum formation occurred only at temperatures between 95 and 100 degrees C.

CONCLUSIONS

Temperature monitoring may facilitate radiofrequency catheter ablation of accessory pathways. By adjusting power output to ensure that adequate but not excessive temperatures have been achieved, a rise in impedance can be avoided and the total number of energy applications and procedure duration may be reduced.

Recurrence of conduction in accessory atrioventricular connections after initially successful radiofrequency catheter ablation

The purpose of this study was to characterize the incidence and clinical features of accessory pathway recurrence after initially successful radiofrequency catheter ablation and to identify variables correlated with recurrence. Radiofrequency ablation was performed with a 7F deflectable tip catheter with a large (4 mm in length) distal electrode. Left-sided accessory pathways were approached through the left ventricle and right-sided pathways by way of the right atrium. Patients were included in the study if 1) they had an initially successful procedure, defined as the absence of accessory pathway conduction immediately after ablation, and 2) had undergone a 3-month follow-up electrophysiologic test or had documented recurrence of accessory pathway conduction. Accessory pathway conduction recurred after initially successful ablation in 16 (12%) of 130 patients. Almost half (7 of 16) of these recurrences were in the 1st 12 h after ablation, and the last occurred after 106 days. Return of delta waves on the electrocardiogram (ECG) or spontaneous paroxysmal supraventricular tachycardia was the initial indication of recurrence in 15 of the 16 patients. Two patients with manifest accessory pathways exhibited recurrence with exclusively concealed accessory pathway conduction. Accessory pathways ablated from the tricuspid anulus (right free wall or septal accessory pathways) had a much higher recurrence rate (24%) than did those on the mitral anulus (6%). Fourteen of 15 patients have had successful repeat accessory pathway ablation after the initial recurrence. After a mean follow-up period of 4 +/- 3 months, there have been no repeat recurrences of any of these accessory pathways. It is concluded that accessory pathway recurrence is infrequent after successful radiofrequency catheter ablation.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the cost of radiofrequency catheter modification of the atrioventricular node and medical therapy for drug-refractory atrioventricular node reentrant tachycardia

The purpose of this study was to determine the charges for radiofrequency catheter modification of the atrioventricular (AV) node in 15 patients with symptomatic AV node reentrant tachycardia despite pharmacologic therapy and to compare these charges with the estimated charges for health care utilization by the same patients before the catheter procedure was performed. There were seven men and eight women with a mean age of 50 +/- 17 years. The mean duration and frequency of symptoms were 16 +/- 9 years and 4.5 +/- 6 episodes/month, respectively. Fourteen of the 15 patients required only one procedure for diagnosis and cure of AV node reentrant tachycardia and 1 patient required two sessions. All patients underwent electrophysiologic study before discharge from the hospital to confirm the short-term efficacy of the procedure. The mean duration of the hospital stay was 3 +/- 1.5 days and the mean total charge/patient expressed in 1991 dollars was $15,893 +/- $3,338 for catheter modification. These total charges consisted of hospital charges of $8,105 +/- $2,466 and physician charges of $7,788 +/- $971. All patients had a successful outcome and required no additional antiarrhythmic therapy. The estimated cost of health care utilization for these 15 patients before cure of AV node reentrant tachycardia was $7,651/patient per year. These estimated costs included charges incurred for emergency room visits, office visits, hospitalizations and antiarrhythmic drug therapy. In conclusion, the results of this study indicate that the annual health care costs incurred by patients who have symptomatic, drug-refractory paroxysmal supraventricular tachycardia caused by AV node reentry are substantial.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the atrioventricular relationship on atrial refractoriness in humans

Atrial arrhythmias occur frequently in the setting of increased atrial size and pressure. This may result from contraction-excitation feedback. The objective of this study was to investigate the effect of alterations in atrial pressure, induced by varying the atrioventricular (AV) interval, on atrial refractoriness, and on the frequency of induction of atrial fibrillation. Twenty-seven patients without structural heart disease participated in the study. In each patient the atrial effective (ERP) and absolute refractory period (ARP) were measured during AV pacing at a cycle length of 400 msec and AV intervals of 0, 120, and 160 msec. The ERP was defined as the longest extrastimulus coupling interval that failed to capture with an extrastimulus current strength of twice the stimulation threshold. The ARP was defined in a similar manner with an extrastimulus current strength of 10 mA. The ERP and ARP were determined during continuous pacing using the incremental extrastimulus technique. A subset of patients had the pacing protocol performed during autonomic blockade. As the AV interval was increased from 0 to 160 msec, the peak right atrial pressure decreased from 16 +/- 4 mmHg to 7 +/- 3 mmHg and the mean right atrial pressure decreased from 7 +/- 3 mmHg to 3 +/- 22 mmHg (P less than 0.001). The atrial ERP and ARP did not change with alterations in the AV interval. There was no difference in the frequency of induction of atrial fibrillation. Similar results were obtained during autonomic blockade. These findings suggests that the phenomenon of contraction-excitation feedback may not be of importance in the development of atrial arrhythmias in patients without structural heart disease.

Dose-dependent inhibition of stretch-induced arrhythmias by gadolinium in isolated canine ventricles. Evidence for a unique mode of antiarrhythmic action

Transient diastolic dilatation of the isolated canine left ventricle predictably elicits arrhythmias. To test the hypothesis that such arrhythmias may be mediated by sarcolemmal stretch-activated channels, we attempted to inhibit stretch-induced arrhythmias with gadolinium (Gd3+), a potent stretch-activated channel blocker. In experiments with six isolated canine hearts, left ventricular volume was increased for 50 msec during early diastole and then returned to initial volume by a computerized servopump. The stretch volume was adjusted to yield a probability of eliciting a stretch-induced arrhythmia of 95 +/- 2% before treatment with Gd3+. When Gd3+ (1-10 microM) was administered, dose-dependent suppression of stretch-induced arrhythmias was observed. The probability of a stretch-induced arrhythmia was reduced to 13 +/- 10% (p less than 0.05) with 10 microM Gd3+. Washout of Gd3+ completely reversed this effect. Since Gd3+ is known to be a calcium channel antagonist, we compared the effect of Gd3+ on stretch-induced arrhythmias with that of verapamil and nifedipine. These calcium channel blockers produced no demonstrable inhibition of stretch-induced arrhythmias when administered at concentrations (1 microM) that substantially depressed left ventricular pressure development. Thus, our results indirectly implicate stretch-activated channels in the genesis of stretch-induced arrhythmias and provide preliminary evidence for a potential new mode of antiarrhythmic drug action--blockade of stretch-activated channels.

Doppler echocardiography in pericardial disease

In conclusion, an understanding of the physiology of cardiac tamponade and pericardial constriction allows accurate interpretation of the changes in SVC and transatrioventricular valve Doppler flow velocities that characterize each abnormality. Meticulous attention to detail in obtaining the studies is essential for accurate diagnosis, because relative changes in flow velocities during respiration may be obscured or misinterpreted if poor-quality data are obtained. In our laboratory, SVC Doppler studies have proved to be the most technically feasible in patients with cardiac tamponade, but transvalvular studies provide important complementary data and are critical in constrictive pericarditis. Hepatic vein Doppler offers an alternative approach to the analysis of systemic venous return, particularly in stable patients with dilated hepatic veins. These studies must always be interpreted with attention to possible confounding variables such as previous pericardiotomy, significant tricuspid regurgitation, severe chronic lung disease, or restrictive cardiomyopathy. As physiologic rather than anatomic indicators, they are a valuable addition to echocardiography in assessing the hemodynamic significance of pericardial abnormalities.

Snuff-induced hypertension in pheochromocytoma

The dipping of snuff provoked paroxysmal hypertension that induced myocardial ischemia in a 69-year-old woman with pheochromocytoma. The diagnosis of her tumor was delayed by a report of a falsely low urine metanephrine level, resulting from interference with the metanephrine assay by meglumine present in the urine because of contrast coronary angiography performed on the day of urine collection.