Human atrial repolarization: effects of sinus rate, pacing and drugs on the surface electrocardiogram

OBJECTIVES

We studied the effects of rate and some cardioactive drugs on the atrial surface electrocardiogram (ECG).

BACKGROUND

In atrioventricular block, atrial surface ECG is unmasked. The effect of rate alone permits detection of the effect of other exogenous stimulations such as drugs in the presence of rate alterations.

METHODS

High fidelity, high gain ECG leads I, II and III were recorded from 51 patients with heart block. Durations of P and Ta waves and the total PTa interval were measured from nonconducted atrial events.

RESULTS

No relationship was found between sinus cycle length and PTa, P or Ta in 31 patients. In 20 patients, progressively decreasing the atrial pacing cycle length from 853 ms to 381 ms resulted in a linear reduction of the PTa interval from 444 to 291 ms (rho = 0.76, slope = 0.24). This was largely due to shortening of Ta. A linear rate correction formula was derived: corrected PTa = PTa - 0.24 (PP - 1000). Atropine (0.02 mg/kg) shortened the PP interval (p < 0.001) and the PTa interval (p < 0.01). Propranolol (0.1 mg/kg) prolonged the PP interval (p < 0.001) but did not alter the PTa interval. Neither disopyramide (2.0 mg/kg) nor flecainide acetate (2.0 mg/kg) altered the PP interval, but both prolonged the PTa interval (p < 0.001). This was largely due to P wave lengthening after flecainide (p < 0.001) and to Ta prolongation after disopyramide (p < 0.001).

CONCLUSIONS

In heart block, PTa, P and Ta waves can be measured reliably. The effects of pacing and some antiarrhythmic drugs on the atrial myocardium are similar to those known at the ventricular level.

[A randomized double-blind trial comparing cibenzoline and disopyramide in the prevention of recurrences of atrial tachyarrhythmia]

The aim of this multicenter, randomised, double-blind trial was to compare the efficacy and tolerance of oral disopyramide (D: 250 mg slow release twice daily) compared with cibenzoline (C: 130 mg twice daily) in the prevention of recurrences of atrial arrhythmias over a 6 month period. Sixty patients (mean age: 62 +/- 14 years; 37 men, 23 women; cardiac disease in 60% of cases) were randomised to two groups: C (N = 31) and D (N = 29). The commonest arrhythmia was atrial fibrillation (83%). The arrhythmia was recent (< 3 months) in 41% of patients and present for more than one year in 38% of patients. Sixteen patients of Group C (52%) and 11 of Group D (38%) had recurrences after an average of 79 +/- 58 days for Group C and 58 +/- 40 days for Group D (p = NS). The probability of absence of recurrence at 6 months was 36 +/- 11% in Group C and 55 +/- 10% in Group D (p = NS). Four patients in Group C (13%) and 13 patients in Group D (45%) had at least one unwanted side-effect (p = 0.009). Treatment was stopped because of side-effects in 2 patients in group C (6%) and 6 patients in Group D (21%). These results show that cibenzoline has a comparable efficacy for the prevention of recurrence of atrial tachyarrhythmia and is significantly better tolerated than disopyramide. This differences is mainly related to the marked anticholinergic effects of disopyramide.

Evolution of changes in the ventricular rhythm during paroxysmal atrial fibrillation

Changes in the RR interval within episodes of paroxysmal atrial fibrillation (PAF) have not been fully characterized. A database of 177 24-hour Holter recordings were created from patients with PAF in the CRAFT studies. PAF episodes of > or = 1 minute duration containing < or = 20% noise and preceded by > or = 1 minute of sinus rhythm with < or = 20% noise were selected. Sections of each AF episode containing 10 and 25 RR intervals were identified at the onset, middle, and termination of each episode. Descriptive characteristics (mean, SD, and RMSSD of RR intervals) were calculated within each section, and compared using a nonparametric, paired Wilcoxon test. In 25 patients (17 men, 60.6 +/- 12.2 years old), 231 episodes from 44 recordings met the selection criteria. The mean RR interval increased slightly between the onset and mid-portion of AF episodes (565.9 +/- 128.3 vs 580.3 +/- 144.7 ms, P < 0.001). The RR interval at the termination of AF was significantly greater than that at the start (627.1 +/- 156.1 vs 565.9 ms, P < 10-11) or mid-portion (627.1 +/- 156.1 vs 580.3 +/- 144.7 ms, P < 10-13). SD of the RR interval increased significantly between onset and mid-portion (111.1 +/- 60.2 vs 118.2 +/- 66.7 ms, P < 0.001) and more substantially between mid-portion and termination (118.2 +/- 66.7 vs 201.8 +/- 93.7 ms, P < 10-21). During paroxysms of AF, the mean RR interval and the variability of RR intervals increases. Termination of a paroxysm is preceded by a marked increase in RR interval variability.

Disopyramide: a promising new approach to the medical treatment of the hypercyanotic spell complicating tetralogy of Fallot

Under continuous ECG and oxygen saturation (SpO2) monitoring, the following measurements were taken by Doppler echocardiography in 6 consecutive patients with tetralogy of Fallot (TF) before and after intravenous administration of disopyramide (2mg/kg): left ventricular shortening fraction (LVSF); peak velocities in the right ventricular outflow tract (RVOT); diastolic and systolic internal diameters of the right ventricular outflow tract (dRVOT, sRVOT); and systolic blood pressure. SpO2 increased (p<0.01) from 78 to 98 (89 +/- 7, mean +/- standard deviation)% to 86-99 (94 +/- 5)%. LVSF decreased (p<0.05) from 0.34-0.56 (0.42 +/- 0.08) to 0.22-0.54 (0.33 +/- 0.13). The systolic blood pressure fell slightly (p<0.05) from 68-92 (79 +/- 8) to 64-92 (71 +/- 11)mmHg. The sRVOT increased (p<0.05) from 2.1-4.8 (2.7 +/- 1.5)mm to 3.0-8.1 (4.9 +/- 2.4)mm, while RVOT peak velocity decreased (p<0.05) from 2.20-4.88 (3.70 +/- 0.97)m/sec to 2.05-4.07 (2.92 +/- 0.72)m/sec. Disopyramide alleviates hypoxia in patients of TF through its negative inotropic action on right ventricular outflow obstruction.

Age and gender influences on rate and duration of paroxysmal atrial fibrillation

The influence of age and gender on the character of paroxysmal atrial fibrillation (PAD) has not been described.

METHODS

The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing < or = 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test).

RESULTS

236 episodes from 55 recordings in 32 patients (all patients: 61.4 +/- 12.8 years; men (19): 58.5 +/- 12.6 years; women (13) 65.5 +/- 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 +/- 35 beats/min vs 115 +/- 20 beats/min, P = 0.02) and during the remainder of the episode (120 +/- 25 beats/min vs 112 +/- 22 beats/min at the start, P = 0.01, and 116 +/- 26 beats/min vs 108 +/- 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS).

CONCLUSION

PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.

Mechanism of benefit of negative inotropes in obstructive hypertrophic cardiomyopathy

BACKGROUND

Drugs with negative inotropic effect are widely used to decrease obstruction in hypertrophic cardiomyopathy (HCM). However, the mechanism of therapeutic benefit has not been studied.

METHODS AND RESULTS

We used M-mode, two-dimensional, and pulsed Doppler echocardiography to study 11 patients with obstructive HCM before and after medical elimination of left ventricular outflow tract obstruction. We measured 148 digitized pulsed Doppler tracings recorded in the left ventricular cavity 2.5 cm apical of the mitral valve. Successful treatment slowed average acceleration of left ventricular ejection by 34% (P=.001). Mean time to peak velocity in the left ventricle was prolonged 31% (P=.001). Mean time to an ejection velocity of 60 cm/s was prolonged 91% (P=.001). Before treatment, left ventricular ejection velocity peaked in the first half of systole; after successful treatment, it peaked in the second half (P=.001). In contrast, after treatment, we found no change in peak left ventricular ejection velocity. We also found no change in the distance between the mitral coaptation point and the septum, as measured in two planes, indicating no treatment-induced alteration of this anatomic relationship.

CONCLUSIONS

Medical treatment eliminates mitral-septal contact and obstruction by decreasing left ventricular ejection acceleration. By slowing acceleration, treatment reduces the hydrodynamic force on the protruding mitral leaflet and delays mitral-septal contact. This, in turn, results in a lower final pressure gradient.

Relation between bradycardia dependent long QT syndrome and QT prolongation by disopyramide in humans

BACKGROUND

Recent molecular biological investigations have identified abnormal genes in familial forms of long QT syndrome, but in bradycardia dependent acquired long QT syndrome, no such genetic abnormality has yet been identified.

OBJECTIVE

To investigate the relation between the responses of QT interval to pacing change and to disopyramide.

METHODS

This study included 13 patients with bradyarrhythmia who had undergone pacemaker implantation. The patients were divided into two groups: group I (n = 8), patients with QT prolongation (QT interval > or = 500 ms) during bradycardia; group II (n = 5), patients without QT prolongation (QT interval < 500 ms) during bradycardia. The responses of QT interval caused by the change of pacing rate were determined and compared with the changes of the QT interval after disopyramide administration.

RESULTS

The QT interval in group I was significantly longer than that in group II when the pacing rate was decreased from 110 to 50 beats/min: mean (SD) 451 (16) v 416 (17) ms at 90 beats/min (p = 0.0033), and 490 (19) v 432 (18) ms at 70 beats/min (p = 0.0002), respectively. The QT interval was prolonged significantly by disopyramide in both groups, but the change was more pronounced in group I than in group II: 78 (33) v 35 (10) ms (p < 0.05).

CONCLUSIONS

This study suggests that the patients showing bradycardia dependent QT prolongation are also more markedly affected by disopyramide and that abnormal potassium channel may be the underlying mechanism.

Graphical representation of complex data--diurnal patterns of initiations of atrial fibrillation episodes

A construction of a purpose designed graphical display is demonstrated in a study investigating the circadian distribution of patterns of RR interval sequences preceding episodes of paroxysmal atrial fibrillation (PAF). Based on a comparison with a (80%, 120%) range around the median of preceding 10 RR intervals, each RR interval is classified as normal, short, or long. Classifications of RR intervals in n-tuplets (n = 1, ...,5) preceding PAF episodes are used to compute probabilities of individual types of sequences occurring within 4-hour periods of the day (between 1 am, 5 am, 9 am, 1 pm, 5 pm, and 9 pm). Graphical representation of the data is proposed using a hierarchy of bar graphs. The graphical system has been filled with data of 327 atrial fibrillation episodes recorded in 46 24-hour ECGs in PAF patients. The graphical analysis supports a link between PAF initiation and cardiac autonomic status.

Mid-systolic drop in left ventricular ejection velocity in obstructive hypertrophic cardiomyopathy--the lobster claw abnormality

In many patients with obstructive hypertrophic cardiomyopathy, an abrupt mid-systolic drop in left ventricular ejection velocity can be detected. We analyzed 27 patients with obstructive hypertrophic cardiomyopathy who had 43 echocardiographic examinations (mean gradient 53 +/- 6 mm Hg). Exams showing a mid-systolic drop had higher mean outflow tract pressure gradients (90 +/- 6 compared with 29 +/- 4 mm Hg, p < 0.001). After medical elimination of obstruction, the mid-systolic drop was no longer seen. We measured 105 pulsed-wave Doppler tracings in the left ventricular cavity and compared them with 90 continuous-wave tracings through the outflow tract. There was a close temporal correlation between the nadir of the left ventricular velocity drop and the peak continuous-wave left ventricular outflow tract velocity (r = 0.99). There was also a close temporal correlation between the onset of the fall in pulsed velocity and the onset of M-mode mitral-septal contact (r = 0.95).

CONCLUSIONS

The mid-systolic drop in left ventricular velocity is due to impedance to ejection and provides evidence of true obstruction. As left ventricular ejection velocity falls to its mid-systolic nadir because of impedance of ejection, velocity downstream in the left ventricular outflow tract actually rises to its peak. This disparity in the two velocities, deceleration in the left ventricular cavity and acceleration in the left ventricular outflow tract, indicates that the outflow orifice is progressively narrowed over time as the mitral valve is forced into the septum by the rising pressure difference. The obstruction phase is best described as a time-dependent, amplifying feedback loop. The orifice narrows over time because of the rising pressure difference; the pressure difference rises over time because of the narrowing orifice.

Unexplained syncope: clinical management

The management of unexplained syncope begins with the patient's history and physical examination, which are oriented to help separate benign from serious causes. Malignant etiologies are more likely to occur with exertional syncope. Cardiac causes should be considered, particularly cardiomyopathy, postoperative congenital heart disease, right ventricular dysplasia, anomalous coronary artery, pulmonary artery hypertension, myocarditis, long QT syndrome, and Wolff-Parkinson-White syndrome. Neurological and metabolic disorders may underlie a syncope episode. After malignant causes of syncope have been excluded and the diagnosis of neurocardiac syncope has been established, treatment strategies include behavior modification, salt and increased fluids, and pharmacological agents. Efficacious agents include beta-blockers, dysopyramide, fludrocortisones, and alpha agents. Yet, behavior modification alone may be as effective as salt or pharmacological therapy. Because the natural history of neurocardiac syncope in children is spontaneous resolution, it is appropriate to try the simple measures before introducing drug therapy.

The medical therapy of cardioinhibitory syncope in pediatric patients

A small percentage of pediatric patients with neurally mediated syncope will have an asystolic response during upright tilt table testing. The purpose of this study is to evaluate the incidence of asystole during tilt table testing, and to assess the outcome of medical management of such patients. Of 398 patients undergoing evaluation for recurrent syncope between January 1989 and 1994, 18 (4.5%) experienced asystole lasting > or = 5 seconds during baseline tilt test. Patients had experienced a mean of four episodes of syncope, with a mean age at the time of tilt test of 11.1 +/- 4.0 years. The median duration of asystole was 10 seconds (range 5-40 s). Treatment was individualized to increased fluids and salt intake (3 patients), metoprolol (8 patients), pseudoephedrine (4 patients), disopyramide (1 patient), or combination therapy with fludrohydrocortisone (2 patients). During a median duration of follow-up of 31 months, no additional syncope was experienced by 78% of patients. Recurrent syncope in 4 patients was associated with either noncompliance or discontinuation of therapy in 3 patients; in 1 patient, increasing the dose of metoprolol was effective in preventing recurrences. We conclude that young patients with recurrent syncope and asystole during tilt test may be safely and effectively managed with pharmacological therapy, without resorting to pacemaker implantation.

Oral disopyramide in the treatment of recurrent neurocardiogenic syncope

In neurocardiogenic syncope the normal compensatory response on assuming an upright posture is interrupted after several minutes and replaced by a paradoxical withdrawal of sympathetic activity and increased parasympathetic activity. The resulting reduction in blood pressure is severe, sympathetic activity is inhibited, plasma norepinephrine levels do not increase and the heart rate decreases. The defect is a paradoxical interruption of sympathetic excitation associated with parasympathetic excitation, causing profound vasodilatation and bradycardia. Disopyramide has been shown not only to treat the bradycardia but also to control the hypotension.

A case of a coronary artery arising from the pulmonary artery

We present a case of an anomalous origin of the left coronary artery arising from the pulmonary artery in a 60 year old woman with ventricular arrhythmias and ischemic electrocardiographic changes but who had tolerated eleven normal pregnancies and deliveries without complications. No cardiac surgical repair has been performed and she is asymptomatic and has been well controlled with diisopyramide during a ten year follow up.

Discrepant drug action of disopyramide on ECG abnormalities and induction of ventricular arrhythmias in a patient with Brugada syndrome

An electrophysiologic study was attempted in a patient who experienced cardiac arrest. Programmed electrical stimulation from the right ventricle, without the use of any drugs, induced ventricular fibrillation (VF) twice. Disopyramide prevented the induction of ventricular arrhythmia by rendering VF to a nonsustained polymorphic ventricular tachycardia when administered at 300 mg/day, and noninducible at 400 mg/day. However, ST-segment elevation and the rSr' pattern in leads V(1-3) characteristic of Brugada syndrome became exaggerated by disopyramide. Disopyramide exerted discrepant action on the electrocardiographic (ECG) abnormalities and induction of VF in this patient, suggesting the efficacy of antiarrhythmic drugs assessed by an electrophysiologic study may be unrelated to ECG abnormalities in cases of Brugada syndrome.

Prolonged asystole induced by head up tilt test. Report of four cases and brief review of the prognostic significance and medical management

Head up tilt is an established test for assessing patients with vasovagal syncope. Prolonged asystole during the test has previously been reported in patients suffering from the malignant form of this syndrome. Little is known about the prognostic significance of this response and there is no consensus about the optimum treatment. Four such patients are reported who were treated pharmacologically. During follow up they remained free from major events and their symptoms were well controlled. Conservative management is the initial method of choice and only if this fails should implantation of a dual chamber permanent pacemaker be considered.

Disopyramide improves the balance between myocardial oxygen supply and demand in patients with hypertrophic obstructive cardiomyopathy

We evaluated the effects of disopyramide in terms of the balance between myocardial oxygen supply and demand in patients with hypertrophic obstructive cardiomyopathy (HOCM). The myocardial oxygen supply was evaluated by measuring coronary flow velocity and the myocardial oxygen demand was assessed by the pressure-volume area (PVA). The time velocity integral of coronary flow did not change significantly (20 +/- 6 to 21 +/- 8 cm), but the peak left ventricular pressure and left ventricular external work decreased significantly (206 +/- 44 to 157 +/- 37 mmHg, P < 0.001; 1.09 +/- 0.33 to 0.80 +/- 0.23 J/beat, P < 0.001) after disopyramide administration. From theoretical analysis using these data, we concluded that disopyramide improves the myocardial oxygen supply-demand balance in patients with HOCM.

Effects of the new class I antiarrhythmic agent Ro 22-9194, (2R)-2-amino-N-(2,6-dimethylphenyl)-N-[3-(3-pyridyl)propyl]propionamide D-tartrate, on ischemia- and reperfusion-induced arrhythmias in dogs: involvement of thromboxane A2 synthase inhibitory activity

We investigated the effects of (2R)-2-amino-N-(2,6-dimethylphenyl)-N-[3-(3-pyridyl)propyl]propionamide D-tartrate (Ro 22-9194), a novel class I antiarrhythmic agent, on myocardial ischemia- and reperfusion-induced arrhythmias in dogs. The incidence of ventricular fibrillation induced by reperfusion after a 30-min coronary ligation was significantly reduced by an i.v. infusion of Ro 22-9194 (10 mg/kg for 5 min before and an additional 20 mg/kg for 30 min during coronary ligation: total, 30 mg/kg) from 73% in the vehicle-treated group to 13%. Ro 22-9194 (20 and 30 mg/kg) also dose-dependently reduced the incidence of ventricular arrhythmias, including ventricular tachycardia and ventricular fibrillation, after coronary reperfusion. Other class I antiarrhythmic agents, mexiletine (15 mg/kg) and disopyramide (7.5 mg/kg), did not inhibit the development of ventricular fibrillation. In in vitro studies, Ro 22-9194, but neither mexiletine nor disopyramide (approximately 10(-3) M), inhibited thromboxane A2 synthase and arachidonic acid-induced aggregation of human platelets (IC50: 1.2 x 10(-5) M and 3.4 x 10(-5) M, respectively). Furthermore, Ro 22-9194 (30 mg/kg) attenuated the increase in venous thromboxane B2 concentrations in the local coronary vein during coronary ligation in dogs. A thromboxane A2 synthase inhibitor, OKY-046 (2.5 mg/kg administered for 5 min before coronary ligation) also showed no evident increases in thromboxane B2 concentrations as well as an antifibrillatory effect. Venous 6-keto-prostaglandin F1 alpha concentrations were not affected by either Ro 22-9194 or OKY-046. These results demonstrate that, unlike mexiletine and disopyramide, Ro 22-9194 protects against reperfusion-induced fatal ventricular arrhythmias in dogs. They also suggest that, in addition to the class I antiarrhythmic effect, the thromboxane A2 synthase inhibitory activity may contribute to the antiarrhythmic properties of Ro 22-9194.

The use of methylphenidate in the treatment of refractory neurocardiogenic syncope

Recurrent neurocardiogenically mediated episodes of hypotension and bradycardia are a common cause of recurrent syncope that can be identified by head upright tilt table testing. While the use of beta-blockers, theophylline, fludrocortisone, disopyramide, and serotonin re-uptake inhibitors can be helpful in preventing further episodes, some patients are unresponsive to or poorly tolerant of these agents. We investigated the use of the central nervous system stimulant and peripheral vasoconstrictor methylphenidate in preventing both tilt induced and spontaneous neurocardiogenic syncope. Seven patients (all women, mean age 31 +/- 15 years) with recurrent syncope and positive head upright tilt induced hypotension/bradycardia (refractory to normal therapy) were placed on methylphenidate 10 mg orally three times per day. Six of the seven patients became both tilt negative and clinically asymptomatic over a 7-month follow-up period. We conclude that methylphenidate may be an effective therapy in patients with recurrent neurocardiogenic syncope refractory to other forms of therapy.

Autonomic and antiarrhythmic drug modulation of ST segment elevation in patients with Brugada syndrome

OBJECTIVES

We examined the modulatory effects of autonomic nervous system and antiarrhythmic drugs on the ST segment in patients with Brugada syndrome to gain an insight into the mechanism of ST segment elevation.

BACKGROUND

Right bundle branch block, ST segment elevation and ventricular tachyarrhythmias define a distinct clinical and electrocardiographic (ECG) syndrome (Brugada syndrome). However, the mechanism of ST segment elevation and the causes of this syndrome are unknown.

METHODS

The study included four patients in whom structural heart or coronary artery disease was excluded by noninvasive and invasive tests. High take-off ST segment elevation of either the coved or saddle-back type in precordial leads V1, V2 and V3 was seen in all patients. Three patients experienced recurrent episodes of syncope or aborted sudden cardiac death, and the remaining patient had palpitation. Autonomic receptor stimulation and blockade and intravenous administration of antiarrhythmic drugs were performed during sinus rhythm while the 12-lead ECG was recorded. Metaiodobenzylguanidine (MIBG) scanning and Holter monitoring were also performed.

RESULTS

Beta-adrenoceptor stimulation by intravenous isoproterenol consistently reduced (> or = 0.1 mV) ST segment elevation at or 80 ms after the J point in all four patients. Selective alpha-adrenoceptor stimulation by intravenous norepinephrine in the presence of propranolol or by intravenous methoxamine consistently augmented, whereas alpha-adrenoceptor blockade reduced, ST segment elevation in three patients. Intracoronary acetylcholine or intravenous edrophonium or neostigmine augmented ST segment elevation without inducing coronary spasm in three of four patients. Class IA antiarrhythmic drugs also consistently augmented (three patients), whereas class IB drugs had no effect on (two patients) ST segment elevation. No abnormality was found on MIBG imaging or heart rate variability in three patients, suggesting that autonomic dysfunction is not a primary disease process. Class IA drugs had no effect on ST segment in three control patients, suggesting that the ST segment elevation seen in patients with Brugada syndrome in response to the drugs is not a nonspecific response.

CONCLUSIONS

ST segment elevation in patients with Brugada syndrome was augmented by selective stimulation of alpha-adrenoceptors or muscarinic receptors or by class IA drugs but was mitigated by beta-adrenoceptor stimulation or alpha-adrenoceptor blockade. These responses might be explained by postulating the presence of an area of early repolarization or a local "depolarized" area in the ventricle causing ST segment elevation in this syndrome. Because only a small number of patients were studied, these possibilities need further evaluation.

Antiarrhythmic effects of optical isomers of disopyramide on canine ventricular arrhythmias

Disopyramide is an effective class I antiarrhythmic drug and widely used for the treatment of arrhythmias, but it has anticholinergic side effects. In vitro studies demonstrated that dextrorotatory (D-) disopyramide has a stronger anticholinergic action, whereas the levorotatory (L-) isomer has a stronger Na channel blocking action. Because the antiarrhythmic mechanism of disopyramide suppressing digitalis- and two-stage coronary ligation-induced canine ventricular arrhythmias is the drug-induced Na channel block, we examined the antiarrhythmic efficacy of D- and L-disopyramide on two arrhythmia models. On ouabain-induced ventricular tachycardia (VT), L-disopyramide 3 mg/kg decreased the arrhythmic ratio (number of ectopic beats/total heart rate), whereas the same dose of the D-isomer was ineffective and a higher dose (5 mg/kg) was needed to suppress the arrhythmia. The effective plasma concentrations (IC50) decreasing the arrhythmic ratio to 50% of the control were 5.3 and 11.3 mu g/ml for L- and D-disopyramide, respectively. We obtained similar results using 24-h two-stage coronary ligation VT. The IC50 were 8.9 and 22.2 mu g/ml for the L- and D-isomers, respectively. Our results indicate that L-disopyramide is about twice as strong an antiarrhythmic drug as the D-isomer.

Drug-induced narrowing of the width of the zone of entrainment as a predictor of the subsequent non-inducibility of reentrant ventricular tachycardia after an additional dose of an antiarrhythmic drug

BACKGROUND

The efficacy of drugs used to treat inducible monomorphic sustained ventricular tachycardia (VT) has been assessed by investigating their ability to suppress inducibility, but the mechanism of the drug action remains to be determined.

OBJECTIVES

To determine electrophysiological variables that predict inducibility, divided doses of class I antiarrhythmic drugs were given and their effects were analysed, particularly the ability of the final dose to suppress inducibility.

METHODS

The excitable gap was estimated by the zone of entrainment, which was defined as the difference between the cycle length of VT and the longest paced cycle length that interrupted VT during entrainment of VT with rapid pacing at paced cycle lengths in decrements of 10 ms. The cycle length of VT, the block cycle length, and the zone of entrainment were measured in the drug free state and after intermediate and final doses of procainamide, disopyramide, cibenzoline, and mexiletine.

RESULTS

Sustained monomorphic VT with a mean (SD) cycle length of 285 (43) ms was induced in 8 patients. It was entrained and interrupted at the block cycle length of 231 (31) ms. The width of the zone of entrainment was 54 (23) ms. In 8 studies VT was not inducible at final doses of procainamide in 4, cibenzoline in 1, and mexiletine in 3. In another 10 studies (procainamide in 4, disopyramide in 1, cibenzoline in 2, and mexiletine in 3), VT remained inducible at the intermediate dose and at the final dose. The cycle length of VT was prolonged to a similar degree in studies of effective and ineffective drugs, but the cycle length that blocked VT was longer at the intermediate dose of the effective drugs. Consequently, the width of the zone of entrainment was significantly narrowed at the intermediate dose of effective drugs and the width of the zone of entrainment was narrower than when ineffective drugs were given (22 (13) ms v 76 (18) or 75 (37) ms at the intermediate and final doses respectively (P < 0.02).

CONCLUSION

Drugs that narrowed the zone of entrainment were associated with non-inducibility of VT after the final dose of the drug was given. The baseline variables did not predict the responses to class I antiarrhythmic drugs.

Effects of intravenous disopyramide on coronary hemodynamics and vasodilator reserve in hypertrophic obstructive cardiomyopathy

Disopyramide reduces the subaortic pressure gradients and improves the clinical symptoms of patients with hypertrophic obstructive cardiomyopathy. Changes in coronary hemodynamics and vasodilator reserve in response to this agent have not been evaluated in such patients. To assess the acute effects of intravenous administration of disopyramide on coronary hemodynamics, microvascular dilatory capacity, and balance between myocardial oxygen supply and demand in hypertrophic obstructive cardiomyopathy, we examined 12 patients using an intravascular Doppler catheter and spectral analysis. Intravenous disopyramide 100 mg over 10 min caused mild increases in heart rate and aortic systolic pressure and a significant fall in left ventricular systolic pressure, resulting in a 13% decrease in the product of heart rate and left ventricular systolic pressure (from 1.13 +/- 0.18 x 10(4) before disopyramide to 0.98 +/- 0.17 x 10(4) beats/min x mm Hg 10 min afterwards; p < 0.05) and a reduction in the resting peak systolic pressure gradients of the left ventricular outflow tract. There was a 14% reduction in coronary blood flow (from 93.5 +/- 13.2 to 80.3 +/- 11.6 ml/min; p < 0.05) with an increase in coronary resistance (from 0.94 +/- 0.16 to 1.23 +/- 0.21 mm Hg/ml/min; p < 0.001). The index of coronary vasodilator reserve remained unchanged. These findings suggest that intravenous disopyramide causes a coronary vasoconstrictive effect without significantly changing the coronary microvascular dilatory capacity, but this effect may not be harmful to the balance between myocardial oxygen supply and demand in patients with hypertrophic obstructive cardiomyopathy.

Effects of class IA antiarrhythmic drugs on the reentrant circuit in common human atrial flutter

In 9 patients with the common type of atrial flutter (AF), a zone of slow conduction was observed proximal to the coronary sinus orifice. Class IA antiarrhythmic drugs were administrated intravenously in all 9 patients. AF was converted to sinus rhythm in only 1 patient. In the remaining 8 patients, although IA drugs suppressed conduction velocity, this effect was not preferential with regard to the zone of slow conduction. Conversion of AF to sinus rhythm by rapid pacing was achieved in these 8 patients. At a critical pacing cycle length, AF was interrupted just after conduction block developed in the zone of slow conduction. A progressive decrease in conduction velocity was observed in the zone of slow conduction for several beats just before the onset of conduction block. In conclusion, class IA drugs facilitate the interruption of AF by rapid atrial pacing by inducing conduction block in the zone of slow conduction.

Effects of disopyramide on the atrial fibrillation threshold in the human atrium

The effects of disopyramide on the atrial fibrillation threshold (AFT) in the human atrium were investigated. To evaluate atrial vulnerability, the following electrophysiologic parameters were measured before and after the administration of disopyramide (2 mg/kg) in 12 patients with paroxysmal atrial fibrillation: The right atrial effective refractory period (ERP) and percentage maximum atrial fragmentation (%MAF) were measured by atrial premature stimulation based on a cycle length of 500 ms. The inter-atrial conduction time (ACT) was measured by burst pacing (120/min) for 30 s. AFT was measured by applying a high-frequency (50 Hz) stimulation for 1 s given at the right atrial appendage. AFT was defined as the lowest intensity of electrical current that could induce atrial fibrillation lasting for more than 30 s. Disopyramide significantly reduced %MAF, and prolonged ERP and ACT. AFT was measured in all patients and the mean AFT was 3.1 +/- 1.7 mA. After the administration of disopyramide, AFT significantly increased to 6.1 +/- 3.6 mA. There was a positive correlation between ERP and AFT, and a negative correlation between %MAF and AFT. No correlation was detected between ACT and AFT. In conclusion, disopyramide increased AFT in the human atrium.