Natural history of potentially lethal ventricular arrhythmias in patients treated with long-term antiarrhythmic drug therapy

Cardiac effects of quinidine on guinea-pig isolated perfused hearts after in vivo quinidine pretreatment

1 Experimental and clinical studies suggest that class I and class III antiarrhythmic drugs may be subject to pharmacological tolerance during long term treatment, leading to loss of therapeutic effectiveness. 2 The aim of this study was to ascertain whether prolonged in vivo treatment with the Class Ia agent quinidine can modify cardiac (electrical and mechanical) responses to the drug. 3 A group of guinea-pigs (n = 7) was treated intraperitoneally (q.d.) for 6 days with 75 mg kg-1 quinidine sulphate. Preliminary pharmacokinetic experiments indicated that this dose could attain Plasma concentrations similar to those that are therapeutic in man (2-5 mg l-1). A control group (n = 7) received a saline solution for the same period. 4 Twenty-four hours after the last administration hearts were removed and retrogradely perfused at constant flow (stimulation frequency: 2.5 Hz). The following parameters were measured: maximal derivative of intraventricular pressure (dP/dtmax); coronary perfusion pressure (Cp); PR, QRS and JT intervals, on surface ECG. The effects of quinidine on these parameters were measured at different concentrations (2, 4, 8, 12, 16, 20 microns) and compared in the two experimental groups. 5 In the group quinidine decreased in a dose-dependent manner dP/dt and increased PR and QRS intervals. JT interval was increased at the lowest concentrations and decreased at the highest (biphasic effect). Cp did not change significantly. 6 In the pretreated group quinidine qualitatively produced the same effects on dP/dt and ECG intervals as in control group. Also the magnitude of these effects was not significantly different between the two groups. In contrast with findings in control experiments. Cp was significantly decreased by increasing quinidine concentration. Mean baseline Cp was higher in pretreated than in the control group (though not significantly, P = 0.072) and quinidine addition abolished this difference. Thus, it is suggested that quinidine withdrawal induced a rebound increase in coronary tone, due to the unmasking of vasoconstrictor homeostatic mechanisms elicited by the in vivo vasodilating effect of the drug. 7 In conclusion, our data do not support the possibility that tolerance ensues during long term quinidine treatment, at least as far as electrophysiological and contractility effects are concerned. Further experimental work is needed to explain the appearance of a coronary vasodilating effect in pretreated hearts.

Dependency of premature ventricular contractions on heart rate

To identify a method for characterizing the dynamic behavior of ventricular arrhythmias at different heart rates, 201 consecutive patients with frequent premature ventricular contractions (PVCs) underwent two 24-hour electrocardiographic monitoring periods. The percentage of PVCs for each cycle length was calculated and then analyzed by linear regression analysis. On the basis of the significance of the p value, and the positive or negative value of the slope, we identified three trends: a tachycardia-enhanced pattern (p < 0.01, slope negative), a bradycardia-enhanced pattern (p < 0.01, slope positive), and an indifferent pattern (p > 0.01). During the first monitoring period, a tachycardia-enhanced pattern was present in 56 patients (28%), a bradycardia-enhanced pattern was present in 49 patients (24%), and an indifferent pattern was present in 96 patients (48%). This relationship was reproducible in 41 of the patients with a tachycardia-enhanced pattern (73%), in 29 of the patients with a bradycardia-enhanced pattern (59%), and in 70 patients with an indifferent pattern (72%). In conclusion, it is possible to identify a spontaneous trend between the incidence of ventricular arrhythmias and the length of the preceding cardiac cycle that seems to remain stable over time.

Holter triage ambulatory ECG analysis. Accuracy and time efficiency

Triage ambulatory electrocardiographic (ECG) analysis permits relatively unskilled office workers to submit 24-hour ambulatory ECG Holter tapes to an automatic instrument (model 563, Del Mar Avionics, Irvine, CA) for interpretation. The instrument system "triages" what it is capable of automatically interpreting and rejects those tapes (with high ventricular arrhythmia density) requiring thorough analysis. Nevertheless, a trained cardiovascular technician ultimately edits what is accepted for analysis. This study examined the clinical validity of one manufacturer's triage instrumentation with regard to accuracy and time efficiency for interpreting ventricular arrhythmia. A database of 50 Holter tapes stratified for frequency of ventricular ectopic beats (VEBs) was examined by triage, conventional, and full-disclosure hand-count Holter analysis. Half of the tapes were found to be automatically analyzable by the triage method. Comparison of the VEB accuracy of triage versus conventional analysis using the full-disclosure hand count as the standard showed that triage analysis overall appeared as accurate as conventional Holter analysis but had limitations in detecting ventricular tachycardia (VT) runs. Overall sensitivity, positive predictive accuracy, and false positive rate for the triage ambulatory ECG analysis were 96, 99, and 0.9%, respectively, for isolated VEBs, 92, 93, and 7%, respectively, for ventricular couplets, and 48, 93, and 7%, respectively, for VT. Error in VT detection by triage analysis occurred on a single tape. Of the remaining 11 tapes containing VT runs, accuracy was significantly increased, with a sensitivity of 86%, positive predictive accuracy of 90%, and false positive rate of 10%. Stopwatch-recorded time efficiency was carefully logged during both triage and conventional ambulatory ECG analysis and divided into five time phases: secretarial, machine, analysis, editing, and total time. Triage analysis was significantly (P < .05) more time efficient for the machine, analysis, and total time phases and required significantly more time in the editing phases. The triage analysis was limited by the inability of the automatic methodology to detect a specific VT waveform contained on one tape. This result which caused substantial loss of sensitivity for VT, emphasizes the necessity for careful quality control and editing of all automatic Holter analysis methods.

Loss of efficacy during long-term cifenline therapy: development of antiarrhythmic resistance?

OBJECTIVE

To describe the possible development of antiarrhythmic resistance to cifenline, an investigational Class I agent.

METHODS

Forty patients with chronic ventricular premature depolarizations (VPDs) underwent dose-ranging studies with cifenline, an investigational Class I antiarrhythmic agent. Patients had a minimum of 30 VPDs/h detected by ambulatory electrocardiographic (ECG) monitoring over a 48-hour baseline placebo lead-in period. Twenty-two patients (55 percent) who initially responded received long-term cifenline therapy. Ambulatory ECG monitoring over 24 hours was repeated during active cifenline therapy at three-month intervals and during placebo reintroduction at six-month intervals.

RESULTS

After an average follow-up of 28 months, VPD frequency during cifenline therapy was similar to that during initial baseline placebo therapy in 8 of the 22 patients (36 percent) who initially responded. Placebo reintroduction following cifenline failure showed a VPD frequency similar to that with active therapy. All patients had further cifenline dosage increases without success. Plasma cifenline concentrations increased in all patients and were in the high therapeutic range. All 8 patients were switched to other Class I antiarrhythmic agents with successful VPD suppression during treatment with the first alternative drug.

CONCLUSIONS

We conclude that antiarrhythmic resistance occurred with cifenline in these patients as (1) initial efficacy was established for a minimum of two years, (2) VPD frequency was similar during cifenline therapy and placebo reintroduction, (3) cifenline therapy failure continued despite further dosage titration, and (4) alternative Class I antiarrhythmic therapy was successful in all patients. Repeat intermittent ambulatory ECG monitoring is necessary not only to assess the continued need for antiarrhythmic drug therapy, but also to establish continued long-term efficacy.

Moricizine: a new agent for the treatment of ventricular arrhythmias

Over the last several years, a number of new antiarrhythmic agents have come into use. One of these promising new drugs, moricizine hydrochloride (Ethmozine), is now available for use in this country. Although similar in some aspects to both quinidine and lidocaine, Moricizine hydrochloride is in many ways unique. The purpose of this review is to summarize the pharmacologic and physiologic effects of moricizine and to outline its clinical use.

Effect of quinidine or procainamide versus no antiarrhythmic drug on sudden cardiac death, total cardiac death, and total death in elderly patients with heart disease and complex ventricular arrhythmias

A prospective study correlated the effect of quinidine or procainamide versus no antiarrhythmic drug on sudden cardiac death, total cardiac death and total death in 406 elderly patients with heart disease and asymptomatic complex ventricular arrhythmias detected by 24-hour ambulatory electrocardiograms. Of 397 patients treated with quinidine, 184 (46%) developed adverse effects during the first 2 weeks of therapy and were given no further antiarrhythmic therapy. Of 9 patients treated with procainamide, 2 (22%) developed adverse effects during the first 2 weeks of therapy and were given no further antiarrhythmic therapy. Adverse effects developed during long-term therapy in 6 patients (2%) receiving quinidine and in 3 patients (33%) receiving procainamide. Mean follow-up was 24 +/- 15 months in both groups. Sudden cardiac death, total cardiac death and total death occurred in 21, 43 and 65% of patients receiving quinidine or procainamide, respectively, and in 23, 44 and 63% of patients receiving no antiarrhythmic drug, respectively (difference not significant). Survival by Kaplan-Meier analysis showed no significant difference between the 2 groups for sudden cardiac death, total cardiac death or total death through 4 years. Patients with abnormal left ventricular ejection fraction had a 3.4 times higher incidence of sudden cardiac death, a 2.4 times higher incidence of total cardiac death and a 1.4 times higher incidence of total death than patients with normal left ventricular ejection fraction. These data showed no significant difference in sudden cardiac death, total cardiac death or total death between patients treated with quinidine or procainamide or with no antiarrhythmic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Noncardiac adverse effects and organ toxicity of moricizine during short- and long-term studies

To determine the tolerance and safety of moricizine, the incidence and nature of its noncardiac adverse effects and organ toxicity reported during short- and long-term clinical studies were examined. From a pooled data base of 1,256 adult patients and healthy subjects, the most frequent non-cardiac adverse events were gastrointestinal (nausea) and neurologic (dizziness) complaints which occurred in 10 to 15% of patients during short-term (less than 3 months) studies and increased to 20 to 25% during long-term (greater than 12 months) studies. Adverse effects led to discontinuation of moricizine therapy in 116 patients (9%). Organ toxicity consisted predominantly of drug fever, possible thrombocytopenia and elevated liver function tests and was quite low (less than 0.7%) for both short- and long-term studies. Moricizine appears to be a well-tolerated antiarrhythmic drug with low occurrence of noncardiac adverse effects without significant serious organ toxicity.