Evaluation of the effect on cardiac repolarization (QTc interval) of oncologic drugs

The 12-lead electrocardiograph (ECG) is the standard safety measurement used in clinical trials to identify drug-induced cardiac adverse effects. Drug-induced prolongation of the QTc interval (the measure of cardiac repolarization change), when excessive and in conjunction with the right risk factors, can degenerate into a polymorphic ventricular tachycardia called torsades de pointes and has become a new focus for new drug development. The assessment of an ECG in clinical practice using machine-defined QTc duration is intrinsically unreliable. Current regulatory concepts have focused on the need for measuring ECG intervals using manual techniques using digital processing in a central ECG laboratory. The QT interval is subject to a large degree of spontaneous variability requiring attention to basic clinical trial design issues such as sample size (use as large a cohort as possible), frequency of measurements taken (at least three to six ECGs at baseline and at many time points on therapy with pharmacokinetic samples if possible), and their accuracy. Since most oncologic products are cytotoxic, a Thorough or Dedicated ECG Trial cannot be conducted and in the usual trail, especially in phase I, all changes seen on the ECG will be attributed to the new oncology drug. For most nononcologic drugs, there is regulatory guidance on how much an effect on QTc duration might be related to the risk of cardiac toxicity. For oncology products, the central tendency magnitude and proportion of outliers needs to be well defined to construct a label if the risk-benefit analysis leads to marketing approval. Clinical cardiac findings such as syncope, ventricular tachyarrhythmias, and other cardiac effects will be important in this analysis.

Cardiac Repolarization and the Safety of New Drugs Defined by Electrocardiography

A compelling assessment of both short- and long-term cardiac safety is increasingly emphasized before regulatory marketing approval. In that context, cardiac adverse effects that were otherwise unexpected become manifest when large numbers of subjects are treated after market approval, many of whom take multiple medications, have co-morbidities, and are subject to other conditions that were not represented in the original clinical trial population. Since 2005, dedicated, robust, and well-controlled electrocardiogram (ECG) trials are required, usually conducted in Phase II, to define the cardiac risk of a new therapy before large-scale Phase III trials are conducted or marketing is approved.

Effects of supratherapeutic doses of ebastine and terfenadine on the QT interval

AIMS

The objective of this study was to compare the effects of high doses of ebastine with terfenadine and placebo on QTc.

METHODS

Thirty-two subjects were randomly assigned to four treatments (ebastine 60 mg x day(-1), ebastine 100 mg x day(-1), terfenadine 360 mg x day(-1), placebo) administered for 7 days. Serial ECGs were performed at baseline and day 7 of each period. QT interval was analysed using both Bazett (QTcB) and Fridericia (QTcF) corrections.

RESULTS

Ebastine 60 mg (+ 3.7 ms) did not cause a statistically significant change in QTcB compared with placebo (+ 1.4 ms). The mean QTcB for ebastine 100 mg was increased by + 10.3 ms which was significantly greater than placebo but was significantly less (P < 0.05) than with terfenadine 360 mg (+ 18.0 ms). There were no statistically significant differences in QTcF between ebastine 60 mg (-3.2 ms) or ebastine 100 mg (1.5 ms) and placebo (-2.1 ms); although terfenadine caused a 14.1 ms increase which was significantly different from the other three treatments. The increase in QTcB with ebastine most likely resulted from overcorrection of the small drug-induced increase in heart rate.

CONCLUSIONS

Ebastine at doses up to five times the recommended therapeutic dose did not cause clinically relevant changes in QTc interval.

Cardiac effects of ebastine and other antihistamines in humans

The electrocardiographic effects of ebastine and its active metabolite, carebastine, have been studied alone and in relevant drug-interaction studies in various patient populations. The overall cardiac tolerability of ebastine is excellent. In ebastine dose-ranging studies in adults and children, there were no meaningful dose-related changes in the QTc interval. At high doses of ebastine (5 to 10 times the recommended dose), a modest 10.3 msec increase in QTc was observed. Recommended doses of ebastine had no meaningful effect on QTc in the elderly or in patients with renal or hepatic insufficiency. Interaction studies involving ebastine with ketoconazole revealed a significant increase in the serum ebastine concentration and in the elimination half-life of ebastine, with a modest 18.1 msec increase in QTc (approximately 10 msec above ketoconazole alone) and a plateau QTc-ebastine relationship at higher ebastine levels. Similar, though more minor, QTc findings were observed during coadministration of ebastine with erythromycin. No QTc effects were noted when ebastine was administered with theophylline, and the QTc was similar when ebastine was administered with or without food. These findings indicate that ebastine is well tolerated and, in contrast to terfenadine and astemizole, has no clinically meaningful effect on the QTc interval even at high serum concentrations. As with other 'safe' antihistamines, which have shown similar modest increases in QTc when coadministered with ketoconazole, caution should be exercised when administering ebastine to patients having the long QT syndrome or hypokalaemia, and in patients receiving azole antifungals or macrolide antibacterials.

The effect of terfenadine on the cardiac pharmacodynamics of sparfloxacin

This double-masked, randomized, placebo-controlled study was conducted to assess the effect of concomitant administration of terfenadine and sparfloxacin on the electrocardiographic (ECG) QT(c) interval in healthy volunteers, before the removal of terfenadine from the market. Eighty-eight men (aged 18 to 49 years, weighing 60.0 to 98.6 kg) with no clinically relevant ECG abnormalities received placebo, sparfloxacin (400 mg on day 1, 200 mg daily on days 2-4), terfenadine (60 mg BID), or the combination of sparfloxacin and terfenadine. After each dose, serial blood samples and ECG measurements were collected to determine sparfloxacin pharmacokinetic and pharmacodynamic variables. The area under the concentration-time curve and maximum concentration for sparfloxacin were approximately 16% less on day 4 compared with day 1, reflecting the higher plasma level after the 400-mg loading dose compared with that after the maintenance dose of 200 mg daily. Concomitant administration of terfenadine had no effect on these pharmacokinetic variables. When compared with the placebo-adjusted increases in QTc interval in the sparfloxacin (19 milliseconds on day 1 and 14 milliseconds on day 4) and terfenadine (2 milliseconds on day 1 and 7 milliseconds on day 4) treatment groups, the placebo-adjusted increases in QTc interval in the volunteers treated with the combination of sparfloxacin and terfenadine (18 milliseconds on day 1 and 22 milliseconds on day 4) were considered to be additive (no statistically significant interaction). Thus there are no apparent pharmacokinetic or dynamic QTc interactions between terfenadine and sparfloxacin. However, sparfloxacin should be administered with caution to patients receiving concomitant medications known to prolong the QTc interval.

A review of the cardiac systemic side-effects of antihistamines: ebastine

The cardiac safety of ebastine, a long-acting, non-sedating antihistamine, has been thoroughly assessed in phase I-III clinical studies. Ebastine alone at the recommended doses of 10 mg and 20 mg has no clinically relevant effect on QTc interval in adults and in special patient populations (elderly, children or subjects with hepatic or renal impairment). Ebastine administered at 60 and 100 mg/day (3-5 times the maximum recommended dose) for 1 week had statistically significantly smaller effects (3.7 and 10.3 msec, respectively) on the QTc interval than terfenadine (18 msec) at three times the recommended dose (360 mg/day). The mean QTc interval prolongation observed with ebastine 100 mg/day was small and not clinically meaningful, although the results were statistically significant vs. placebo. The effect of ebastine 60 mg/day was not statistically different from placebo. Steady-state drug interaction studies demonstrated that the co-administration of ebastine 20 mg with ketoconazole or erythromycin produced significant increases in systemic exposure for ebastine, which were accompanied by small increases in QTc (approximately 10 msec above ketoconazole or erythromycin alone). Results from individual studies suggest that, when coadministered with ketoconazole, ebastine produces similar changes in QTc interval measurements compared to loratadine and cetirizine. Pooled data from clinical efficacy trials of ebastine 1-30 mg/day administered for 2-3 weeks showed no clinically relevant cardiac effects as assessed by serial electrocardiographs and Holter monitoring. The overall cardiac safety profile based on currently available information suggests that ebastine, like loratadine and cetirizine, has a lower potential for causing adverse cardiovascular effects than terfenadine.

The cardiac pharmacodynamics of therapeutic doses of sparfloxacin

This double-masked, randomized, placebo-controlled study assessed the cardiac safety of sparfloxacin (as measured by the effect on corrected QT [QTc] interval) at the extremes of the expected therapeutic dosage range. Ninety healthy adult male volunteers with no clinically relevant electrocardiographic (ECG) abnormalities received either placebo or 1 of 3 sparfloxacin regimens consisting of a loading dose on day 1 followed by 3 days of daily dosing at half the loading dose (200/100 mg, 400/200 mg, or 800/400 mg). After each dose, serial blood samples and ECG measurements were obtained to determine the pharmacokinetic and pharmacodynamic variables for sparfloxacin. Increases in the area under the plasma concentration-time curve from time 0 to 24 hours (AUC0-24) for each dosing interval and in the maximum concentration (Cmax) on days 1 and 4 were dose proportional. The steady-state (day-4) values were 6% to 16% lower than the day-1 values. At steady state, the time to C ranged from 2.5 to 3.9 hours across all doses and days studied. The half-life ranged from 18.7 to 20.3 hours. Increases in the placebo-adjusted mean change and mean maximum change in QTc interval were dose related. The placebo-adjusted increases on day 1 were 9, 16, and 28 milliseconds after receipt of the 200/100-mg, 400/200-mg, and 800/400-mg regimens, respectively. The corresponding increases on day 4 were 7, 12, and 26 milliseconds. The placebo-adjusted changes in QTc interval also showed a linear relationship with the AUC0-24 and Cmax of sparfloxacin. In the majority of volunteers (>90%), these increases were within the normal range for the QTc interval (< or = 460 milliseconds).

Effect of single ascending, supratherapeutic doses of sparfloxacin on cardiac repolarization (QTc interval)

This double-masked, randomized, placebo-controlled study was conducted in healthy adult male and female volunteers with no clinically relevant baseline electrocardiographic (ECG) abnormalities to assess the cardiac tolerability margin of sparfloxacin (as measured by the effect on QTc interval) under conditions of potential overdose at up to 4 times the usual therapeutic loading dose. The 23 enrolled volunteers received a sequence of single doses of sparfloxacin (400, 800, 1200, and 1600 mg), 1 dose in each of 4 study periods. Six volunteers received placebo during each period. A 14-day washout separated the periods. Serial blood samples and ECG measurements were collected in each period to determine the pharmacokinetic and pharmacodynamic characteristics of sparfloxacin. The area under the concentration-time curve from time zero to infinity (AUC0-infinity) exhibited dose proportionality. The maximum plasma concentration (Cmax) after the 1200- and 1600-mg doses was lower than would be expected for a linear dose relationship. This was also the case with the mean increase and mean maximum increase in QTc interval. Increases in the QTc interval correlated well with Cmax but not with AUC0-infinity. The time to reach Cmax showed a slight tendency to increase with dose, as did the terminal elimination half-life. Changes in QTc-interval dispersion were similar for both placebo recipients and sparfloxacin-treated volunteers and were of no clinical consequence. At supratherapeutic doses, the extent of sparfloxacin's absorption (AUC0-infinity) was dose independent; however, the rate of absorption was dose dependent, with Cmax increasing substantially less than proportionally to the administered dose. This limited the Cmax of sparfloxacin at supratherapeutic doses and thus the increase in QTc interval. Rechallenge demonstrated that only 2 of 8 subjects had the same degree of QTc-interval prolongation, emphasizing the marked variability in the QTc interval.

Lack of effect of azelastine and ketoconazole coadministration on electrocardiographic parameters in healthy volunteers

Azelastine, an antihistamine with additional pharmacologic properties, was evaluated for a possible influence on pharmacokinetic and electrocardiographic parameters due to its coadministration with CYP3A4 inhibitor ketoconazole (200 mg every 12 hrs). Twelve volunteers entered this three-period, open-label study. Electrocardiographic parameters (PR, QRS and QTc intervals and U-wave morphology) were monitored after 14 days of azelastine HCl (4.4 mg every 12 hrs), after 7 days of either azelastine/ketoconazole or azelastine/placebo, and after a 21-day washout period, which was then followed by a 7-day administration of ketoconazole alone. None of the treatments resulted in meaningful alterations of electrocardiographic variables. Pharmacokinetic parameters could not be estimated because ketoconazole metabolites interfered with azelastine assay procedures. In vitro tests with human liver microsomes were used to characterize azelastine's inhibition spectrum. Azelastine did not inhibit CYP3A4 activity but it did inhibit CYP2D6 and CYP2C19 activity with Ki values exceeding maximum plasma concentration by 120 to 800-fold. Therefore, in vitro tests and the absence of electrocardiographic effects suggests azelastine can be safely administered with CYP3A4 inhibitors.

Oral bropirimine immunotherapy of carcinoma in situ of the bladder: results of a phase II trial

OBJECTIVES

Bropirimine is an orally administered immunostimulant that has been shown to have activity against carcinoma in situ (CIS) of the bladder. To further assess this potential activity, bropirimine was administered to 42 patients for bladder CIS in a Phase II trial.

METHODS

Patients were treated with bropirimine 3.0 g/day by mouth for 3 consecutive days each week up to 1 year. Cystoscopy with biopsies and bladder wash cytology were performed quarterly.

RESULTS

Twenty (61%) of 33 evaluable patients converted malignant biopsies and bladder wash cytology to negative, including 6 (50%) of 12 who failed prior bacillus Calmette-Guérin (BCG) immunotherapy, 14 (67%) of 21 who had not received prior BCG therapy, and 12 (80%) of 15 with primary CIS. Median response duration exceeds 21 months. Four of the 20 responders did have a papillary tumor recurrence at 3 to 15 months, all Stage Ta or T1. Mild toxicity (grade I or II) suggestive to interferon induction or administration occurred in one third of patients. Headache, transient hepatic enzyme elevations, skin rash, and arthralgias each occurred in 5% to 14% of the patients, with nausea or emesis in 21%. Grade 1 tachycardia/palpitations or chest pain each were noted in 5%.

CONCLUSIONS

Oral bropirimine can induce remission of bladder CIS with acceptable toxicity at 3.0 g/day. Bropirimine may be a valuable alternative to cystectomy for some failures of BCG therapy and may have the potential to replace BCG as front-line therapy because of its ease of administration.

Systemic concentrations of salbutamol and HFA-134a after inhalation of salbutamol sulfate in a chlorofluorocarbon-free system

The objective of this study was to determine if salbutamol was absorbed from a new salbutamol sulfate chlorofluorocarbon (CFC)-free metered-dose inhaler (MDI). Measurement of HFA-134a, the CFC-free propellant, was included to provide proof of delivery of this MDI. Eight healthy men received two inhalations (90 micrograms salbutamol base equivalents per inhalation ex adapter) from the CFC-free inhaler (MDI A) in period 1 and from a reference CFC inhaler (MDI V) in period 2. Eight postdose samples were collected for the determination of salbutamol serum levels over a 4-h period. Salbutamol levels were not quantifiable in most samples. Four subjects given MDI A and two given MDI V had a few transient salbutamol levels, which occurred in the first hour after dosing, within a narrow range of 1-2 ng/ml and close to the lower limit of detection (1 ng/ml). No pharmacokinetic analyses were possible. Blood samples were also collected after MDI A for propellant quantitation. HFA-134a levels were seen in all subjects, verifying absorption. We conclude that the transient salbutamol serum levels can be attributed to the two-inhalation dose and not to either propellant system.

Overview of electrocardiographic and cardiovascular safety data for sparfloxacin. Sparfloxacin Safety Group

During the preclinical development of sparfloxacin, prolongation of the electrocardiographic QT interval was observed in dogs. Subsequently, the effect of sparfloxacin on the QTc interval in man was studied in Phase I studies in healthy volunteers. An independent Safety Board was established to evaluate the electrocardiograms, provide an assessment of the clinical consequences of prolongation of the QT interval, and advise on the design of current and future studies. Results of Phase I and Phase III studies have been consistent and indicate that the increase in QTc interval associated with sparfloxacin is moderate (3% on average) and that patients with renal or hepatic impairment are not at increased risk. Few serious adverse cardiovascular events have been reported during post-marketing surveillance of sparfloxacin and all have occurred in patients with an underlying cardiac condition.

Dose-response relation between terfenadine (Seldane) and the QTc interval on the scalar electrocardiogram: distinguishing a drug effect from spontaneous variability

The primary goal of this investigation was to describe the effect of terfenadine on the QT interval corrected for heart rate (QTc) of the scalar electrocardiogram (ECG). The design was double-blind, four-period crossover, dose escalation, which involved 28 normal healthy volunteers and 28 patients with stable cardiovascular disease. At baseline, the normal subjects had a mean QTc interval of 407 msec, whereas the patients with cardiovascular disease had a mean QTc interval of 417 msec (p<0.01). The largest increase in mean QTc on terfenadine was 24 msec in a normal subject and 28 msec in a patient with cardiovascular disease. The longest average QTc observed was 449 msec and 501 msec in any normal subject and patient with cardiovascular disease, respectively. Compared to baseline, terfenadine 60 mg twice daily is associated with a QTc increase of 6 msec in normal subjects and a 12 msec increase in patients with cardiovascular disease (p<0.01 vs baseline; p>0.05 when the two populations were compared). Although the QTc increase from baseline are statistically significant, the magnitude of the spontaneous variability in QTc in the same patients is much greater. Because 40 ECGs were obtained while taking placebo in each participant, the spontaneous variability in QTc interval with placebo was also described. Only one of the 28 normal subjects had a mean baseline QTc=440 msec, yet 14 of the 28 normal subjects had at lease one of the 40 placebo ECGs with a QTc=440 msec. The 28 patients with cardiovascular disease had a mean QTc at baseline of 417 msec; yet 20 of 28 had at lease one ECG on placebo with a QTc interval = 440 msec. On the average, the QTc fluctuated 56 msec in each patient during placebo administration. From the observed placebo variability, we calculated that an increase in QTc of=35 msec while receiving drug therapy is likely to represent a drug effect at the 95% confidence interval.

Prediction of cardiac death in patients with a very low ejection fraction after myocardial infarction: a Cardiac Arrhythmia Suppression Trial (CAST) study

The Cardiac Arrhythmia Suppression Trial (CAST) database was analyzed with a Cox proportional hazards regression model to predict the mortality of patients with very poor left ventricular systolic function (ejection fraction < or = .20). Predictors of total death or cardiac arrest were (relative risk), QRS duration (1.10/10 msec increase), coronary artery bypass grafting (0.38), basal heart rate (1.26/10 min-1 increase), diastolic blood pressure (0.79/10 mm Hg increase), diabetes mellitus (1.59), EF (0.94/1 U increase), and ease of suppression (the ability to suppress ambient ventricular ectopy on the lowest dose of the first randomly chosen CAST drug) (0.64). Predictors of arrhythmic death or arrhythmic cardiac arrest included thrombolysis (0.44), coronary artery bypass grafting (0.38), diuretic use (1.71), heart rate (1.21/10 min-1 increase), calcium channel blocker use (1.69), and QRS duration (1.10/10 msec increase). Thus easily measurable clinical and laboratory variables help predict prognosis in this clinically important subgroup. The pathophysiologic basis for and the clinical implications of the ease of ventricular arrhythmia suppression correlating with prognosis requires further study.

Effects of food on the bioequivalence of different verapamil sustained-release formulations

Previously, clinical studies comparing generic and reference formulations of sustained-release (SR) verapamil tablets revealed significant increases in the PR interval in subjects given the generic formulation in the presence of food. To determine the mechanisms underlying these differences in pharmacodynamics, the present analyses examined the pharmacokinetics of these formulations in the presence and absence of food. After single or multiple doses in fasting subjects, AUCs, Cmaxs, and tmaxs were similar, suggesting that these formulations were bioequivalent in the fasted state. However, the generic formulation exhibited a higher AUC(0-6) in fed subjects, suggesting that this formulation may be absorbed more rapidly than the reference formulation when given with food. Analysis of AUC(0-6) showed that 34% of the subjects receiving the generic formulation exhibited rapid absorption, compared with only 8% receiving the reference formulation. Significant increases in the PR interval were seen in nine fed subjects receiving the generic formulation compared with two receiving the reference formulation. Similarly, three fed subjects receiving the generic drug who were rapid absorbers exhibited first-degree heart block, whereas this conduction disturbance was seen in only one fed subject receiving the reference formulation. Thus, increased conduction disturbances seen in subjects given the generic formulation with a meal likely reflect more rapid absorption of this formulation in the presence of food, resulting in an increase in the ratio of more potent to less potent enantiomers of verapamil in the systemic circulation.

New insights into the definition and meaning of proarrhythmia during initiation of antiarrhythmic drug therapy from the Cardiac Arrhythmia Suppression Trial and its pilot study. The CAST and CAPS Investigators

OBJECTIVES

This study was undertaken to determine the characteristics of worsening ventricular arrhythmia during antiarrhythmic drug titration.

BACKGROUND

Proarrhythmia is an evolving concept in cardiology. Its definition, incidence and clinical significance in various patient settings require refinement.

METHODS

The impact of early proarrhythmia was analyzed in 3,840 patients in the Cardiac Arrhythmia Suppression Trial (CAST).

RESULTS

Drug therapy did not affect the incidence of new, sustained but nonfatal ventricular tachycardia (placebo 0.5%, active drug 0.4%). Nevertheless, there was a threefold increase in arrhythmic death (placebo 0.5% vs. active drug 1.6%). The incidence of increased ventricular premature depolarizations was equivalent (3% to 5%) for the three study drugs and indistinguishable from that seen with placebo. Patients with increased ventricular premature depolarizations on the first drug tested had fewer at baseline (65 +/- 94 vs. 137 +/- 260 per hour; mean +/- SD) (p < 0.01). When increased ventricular premature depolarizations occurred with the first drug, they were much more likely also to be present with the second drug (for example, 42% vs. 5%, p < 0.001). Increased ventricular premature depolarizations during initiation of therapy independently predicted increased risk of subsequent arrhythmic death (independent relative risk 2.34, p = 0.0053) in the absence of continued antiarrhythmic drug therapy.

CONCLUSIONS

The overall incidence of early worsening of arrhythmia in the present study was low. In the absence of placebo control, the incidence of proarrhythmia will be overestimated. Increased ventricular premature depolarizations had characteristics that suggest they often represent spontaneous variability rather than proarrhythmia. The main finding is that markedly increased ventricular premature depolarizations during drug titration predict long-term increased risk of arrhythmic death in this patient population despite absence of long-term antiarrhythmic drug therapy.

Relations of QTc prolongation on the electrocardiogram to torsades de pointes: definitions and mechanisms

Antiarrhythmic drug-induced ventricular tachyarrhythmias have traditionally been identified on the basis of prolongation of the QT interval and the appearance of undulating peaks of sequential QRS complexes and T waves that give the tachycardia a "twisting" aspect (so-called torsades de pointes). It is now understood, however, that a precise lengthening of the QT interval is not a necessary or sufficient criterion for the development of torsades de pointes associated with drug therapy. Indeed, not all agents that have been linked with torsades de pointes cause significant lengthening of the QT interval. Moreover, sufficiently accurate determination of QT interval duration to judge a prolongation is confounded by a number of difficulties, including considerable intraindividual variability. It is possible that the development of abnormal giant U waves may be involved in the genesis of these tachyarrhythmias. Such U waves are believed to represent the summation of early afterdepolarizations occurring throughout the myocardium. The prepause ventricular rate determines the amplitude of the U wave, and larger U waves give rise to longer and faster runs of ventricular tachycardia. These arrhythmias tend to be self-perpetuating in a bigeminal feedback pattern. At present, our knowledge base about the relation of the QT interval and torsades de pointes is grossly incomplete. More basic and clinical data are required before hard clinical judgments can be made with any precision.

Variability of the QTc interval: impact on defining drug effect and low-frequency cardiac event

Prolongation of the QT interval corrected for heart rate (QTc) can lead to the development of torsades de pointes, a life-threatening form of polymorphic ventricular tachycardia. However, the QTc interval duration exhibits a high degree of spontaneous variability and is not necessarily a direct predictor of the risk of torsades. This observation holds implications for the assessment of the potential proarrhythmic effects of noncardiac pharmacologic agents. To date, the antihistamine terfenadine is the only noncardiac drug that has undergone a comprehensive and systematic evaluation related to the consequences of its causing QTc prolongation. The results suggest that QTc prolongation resulting solely from terfenadine at clinical doses does not have an important impact on clinically relevant endpoints. The risk of serious ventricular arrhythmias with terfenadine using epidemiologic data is the same or less than that associated with traditional first-generation antihistamines. The risk of a clinical cardiac event (QTc prolongation, ventricular arrhythmias, syncope, or sudden death) with terfenadine is similar to that of other antihistamines. Factors associated with increased risk in patients taking terfenadine include significant liver disease, hypokalemia, overdose, and concomitant administration of ketoconazole-like agents or erythromycin; use of terfenadine is relatively contraindicated in these settings. No increased risk of serious arrhythmias has been confirmed in conjunction with the use of terfenadine in patients with cardiac disease.

Indications for antiarrhythmic suppression of ventricular arrhythmias: a definition of life-threatening ventricular arrhythmias

A surprising finding of the Cardiac Arrhythmia Suppression Trial (CAST), reported in 1989, is that well-tolerated and effective antiarrhythmic drugs may also be associated with an increase in mortality due to arrhythmia. Consequently, attention has been focused on the importance of the benefit-versus-risk assessment of such therapy. The benefits of antiarrhythmic therapy are reduction or elimination of arrhythmia-caused symptoms (both hemodynamic and nonhemodynamic) and of the associated risk of death. The risks of such treatment include not only noncardiac adverse effects and organ toxicity, but also early cardiac effects (proarrhythmia, heart failure, and conduction defects), as well as the newly recognized potential for late proarrhythmia or late arrhythmic death. Unfortunately, as the potential benefits of antiarrhythmic therapy increase in patients with poorer left ventricular function (owing to their being at greater risk for sudden death), the effectiveness of suppression decreases and the incidence of life-threatening complications increases. The impact of this benefit-risk profile is that the indication for most currently approved antiarrhythmic drugs needs to be limited to those patients with definite life-threatening ventricular arrhythmias that take the form of sustained ventricular tachyarrhythmias with associated hemodynamic symptoms. Broadening this indication to include patients with probable life-threatening or even possible life-threatening arrhythmias must await the availability of drugs with better benefit-risk profiles.

Diagnostic accuracy of seismocardiography compared with electrocardiography for the anatomic and physiologic diagnosis of coronary artery disease during exercise testing

A multicenter study was performed to compare the diagnostic accuracy of a new technique, seismocardiography, with that of electrocardiography for physiologically and anatomically significant ischemic coronary artery disease (CAD) during exercise stress testing. Five participating centers enrolled 129 patients who had simultaneous seismocardiograms and 12-lead electrocardiograms at the time of their exercise treadmill stress tests. Two different definitions of CAD were used: anatomic and physiologically significant disease. The presence of anatomically significant CAD (> or = 50% diameter stenosis) was documented by coronary angiography. Physiologically significant CAD was defined as present in the same 129 patients when coronary arteriography (> or = 50% diameter stenosis) and thallium-201 scintigraphy (defect on initial postexercise images) were both abnormal. Seismocardiography had a significantly better sensitivity for detecting anatomic CAD than did electrocardiography (73 vs 48%; p < 0.001), without loss of specificity (78 vs 80%; p = NS). Exercise seismocardiography added significant incremental diagnostic information beyond that provided by exercise electrocardiography. Seismocardiography was more sensitive (without less specificity) in women and in patients who did not achieve maximal predicted heart rate. In patients with physiologically significant CAD, the seismocardiogram was also significantly more sensitive (78%) than was the electrocardiogram (55%) (p < 0.02), without loss of specificity (84 vs 74%). Seismocardiography significantly improved sensitivity for the detection of anatomic and physiologic CAD. It is easy to perform and may be a clinically useful adjunct in exercise stress testing.

Drug-induced early and late proarrhythmia

Proarrhythmia is the provocation of a new arrhythmia or the exacerbation of a spontaneously occurring arrhythmia due to drug therapy. A drug's toxic effect may occur early after its initiation, and specific definitions have been offered to detect its presence. Primary and secondary forms of proarrhythmia as well as the type of early proarrhythmic events (fatal, serious, and nonserious) have been recognized. More recently, the concept of a late proarrhythmic event (enhanced arrhythmic death) has been defined using placebo-controlled trials. This late proarrhythmic response is extremely important in defining the benefit versus risk ratio that is the key to proper use of drug therapy.

The relationship of anticoagulation level and complications after successful percutaneous transluminal coronary angioplasty

The degree of anticoagulation and its effect on the frequency of abrupt coronary artery closure, coronary ischemia, bleeding complications requiring transfusion, and death were examined in 336 patients after elective percutaneous transluminal coronary angioplasty (PTCA). All patients received a bolus of 10,000 U of heparin at the beginning of the procedure followed by a continuous infusion of 2000 U/hr. At the conclusion of the procedure the infusion was reduced to 1000 U/hr and continued for 18 to 24 hours at which time the heparin infusion was suspended to allow removal of arterial and venous access sheaths. Partial thromboplastin time (PTT) was examined while patients continued to receive the heparin infusion. There was a variable degree of PTT prolongation in response to a standard dose of heparin with a range of 34 seconds to "greater than 150 seconds." Patients were divided into two groups according to the degree of heparin-induced PTT prolongation: group A included 271 patients with PTT greater than or equal to 3 times the control value, and group B comprised 65 patients with PTT less than 3 times the control value. Ischemic complications were analyzed on day 1 after PTCA and at hospital discharge. Bleeding complications and mortality were examined only at hospital discharge. There was a significant reduction in the incidence of abrupt coronary artery closure in group A on day 1 (1.5% vs 10.7%, p less than 0.001) and at hospital discharge (2.6% vs 10.7%, p less than 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Proarrhythmic effects of antiarrhythmic drugs: evolving concepts

Although antiarrhythmic drugs are prescribed to reduce an arrhythmia, they may have the paradoxic effect of actually exacerbating that arrhythmia or causing new or more serious forms. This effect is known as "proarrhythmia." Proarrhythmic events may be segregated into those that occur "early" after therapy (within 30 days) and those that occur "late," after many months of therapy and manifesting as a fatal event (an increased risk of sudden cardiac death). The ability of the physician to predict drug proarrhythmia and its severity depends on the class of antiarrhythmic drug chosen, the type of ventricular arrhythmia to be treated, and the severity of the patient's underlying left ventricular dysfunction. Before the start of antiarrhythmic therapy, the physician must be able to quantitate the degree of proarrhythmic risk so that the benefit/risk ratio of such drug use can be determined.

Early and late proarrhythmia from antiarrhythmic drug therapy

Antiarrhythmic drug therapy is used with the hope of suppressing arrhythmias and therefore decreasing their associated symptoms or prolonging life. Unfortunately, many antiarrhythmic drugs have the opposite effect of exacerbating or provoking arrhythmias, a phenomenon that is termed proarrhythmia when such an event is specifically due to the drug in use. Early proarrhythmic events (within 30 days of initiation of drug use) have been reasonably well characterized and are predicted by either type of drug employed or the nature of the patient's cardiac disease and arrhythmia type. Late proarrhythmic events, as defined by placebo-controlled trials, have now been recognized as an increased risk of arrhythmic death in patients on antiarrhythmic drugs after many months of therapy. Initially, this late proarrhythmic event was identified with encainide and flecainide, but now several new studies have demonstrated that the risk of late proarrhythmia of comparable magnitude may be present in patients subjected to commonly used drugs, such as quinidine, mexelitine, etc. At present, only moricizine and the class II drugs (beta-adrenergic blockers) appear not to have this potential late proarrhythmic response. Therefore, before instituting antiarrhythmic drug therapy, the physician must be able to quantitate the degree of proarrhythmia and other risks of such therapy, as compared to their potential benefit, to define the proper indications for these agents.

Events in the cardiac arrhythmia suppression trial: baseline predictors of mortality in placebo-treated patients

Patients randomized to placebo in the encainide and flecainide arms of the Cardiac Arrhythmia Suppression Trial (CAST) have been found to have a relatively low 1-year mortality rate of 3.9% in comparison with previous studies of patients in the postmyocardial infarction period. To determine the comparability of CAST with previous studies, baseline variables were examined in the 743 patients randomized to placebo in the flecainide and encainide arms of CAST. Twenty-three baseline characteristics were correlated with major outcome events: arrhythmic death (16 events), total mortality (26 events) and congestive heart failure (51 events). On multivariate analysis the risk of new or worsening congestive heart failure was significantly associated with diuretic use, diabetes, high New York Heart Association functional class, age, prolonged QRS duration and low ejection fraction. The risk of arrhythmic death or resuscitated cardiac arrest was significantly associated with an index Q wave myocardial infarction, history of heart failure, use of digitalis, diabetes and prolonged QRS duration. Total mortality or resuscitated cardiac arrest was significantly associated with an index Q wave myocardial infarction, diabetes, ST segment depression, high functional class, prolonged QRS duration and low ejection fraction. The variables at baseline associated with mortality from all causes or arrhythmic death or resuscitated cardiac arrest and heart failure in the CAST placebo-treated patients are similar to those identified in previous postmyocardial infarction studies. Thus, the observation of increased mortality in CAST associated with the administration of encainide and flecainide for suppression of ventricular premature depolarizations is probably applicable to any comparably defined group of patients in the postmyocardial infarction period.

Quinidine-related mortality in the short-to-medium-term treatment of ventricular arrhythmias. A meta-analysis

BACKGROUND

The interim results of the Cardiac Arrhythmia Suppression Trial requires physicians to use a higher threshold for employing antiarrhythmic agents in the treatment of benign or potentially lethal ventricular arrhythmias. Many have managed patients by switching to the traditional class I quinidine despite its known proarrhythmic tendency.

METHODS AND RESULTS

To evaluate the relation between quinidine therapy and mortality in patients with benign or potentially lethal ventricular arrhythmias, we performed a meta-analysis on four randomized double-blind active controlled parallel trials evaluating 1,009 patients in which quinidine (n = 502) was compared to flecainide (n = 141), mexiletine (n = 246), tocainide (n = 67), and propafenone (n = 53). All four trials had similar patient selection, protocols, and methodology (e.g., placebo lead-in and Holter monitoring) but varying lengths of drug exposure. A total of 12 deaths were reported on quinidine and four deaths on the other drugs: two on mexiletine, one on flecainide, and one on tocainide. The statistical analysis of the mortality rates was based on techniques for combining data across separate strata. Based on maximum likelihood estimation, the combined risk of dying on quinidine was statistically significantly higher compared to the other four drugs with a risk difference of 1.6%. The 95% confidence interval was 0-3.1% (p = 0.05). The likelihood ratio test for uniformity of the risk difference across strata showed the trials to be homogeneous (p = 0.88). There was one death recorded for the placebo lead-in period (2 weeks' exposure for 624 patients and 1 week for 385 patients), and seven deaths were reported within 2 weeks on active drug treatment--six on quinidine and one on mexiletine. Furthermore, proarrhythmia was reported in 20 patients on quinidine versus 11 patients on the four other drugs (p = 0.09).

CONCLUSIONS

These data suggest that quinidine may have an adverse effect on mortality as compared to other class I antiarrhythmic agents and that individualized patient selection for the use of this agent be carefully weighed relative to its potential for harm and benefit.

A multicenter evaluation of the A&D TM-2420 ambulatory blood pressure recorder

The A&D TM-2420 (A&D Engineering, Milpitas, CA) is an automatic, portable, noninvasive blood pressure (BP) recorder which uses a dual microphone system for the detection of Korotkoff sounds. Its accuracy and clinical performance were assessed in a multicenter study that also addressed issues such as observer agreement and the effects of age, arm circumference, heart rate, posture, and blood pressure level on the observer-device differences. We compared 906 simultaneous, same-arm BP measurements in 151 subjects using the TM-2420 versus two skilled clinicians per site using a teaching stethoscope. The agreement between the TM-2420 and mercury column determinations were within 10 mm Hg for 86 to 91% of systolic readings and 91 to 94% of diastolic readings, depending on the posture; a level of agreement which would receive a 'B+' grade from the recent British Hypertension Society guidelines. The limits of agreement (2 standard deviations about the mean difference) for systolic BP between observers and the TM-2420 tended to be greater for the standing position (-20 to 15 mm Hg) compared to supine (-14 to 12 mm Hg) and seated (-13 to 8 mm Hg) positions. Limits of agreement between the observers and device were not dependent upon age, heart rate, arm size, or blood pressure level. Twenty-four-hour blood pressure monitoring in two of the four centers demonstrated an error code rate of 3.4%, excluding 'retries' that are one of the device's features. These data demonstrate an acceptable level of accuracy and performance of the sixth generation of the TM-2420 for use in clinical practice and research.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of angiotensin converting enzyme inhibition on the incidence of restenosis after percutaneous transluminal coronary angioplasty

To determine whether angiotensin converting enzyme (ACE) inhibition may reduce the incidence of restenosis after percutaneous transluminal coronary angioplasty (PTCA), we retrospectively identified 322 consecutive patients who underwent a successful procedure from June 1988 to December 1989. No patients developed chest pain, ST segment elevation, positive cardiac enzymes, or other evidence of abrupt vessel closure following the PTCA. All patients received intravenous heparin after PTCA and aspirin was begun on the day prior to PTCA. Patients were separated into two groups: those at hospital discharge incidentally treated for hypertension or heart failure with ACE inhibitors (n = 36), and those treated with a drug regimen which did not include ACE inhibitors (n = 286). The two groups were similar with respect to age (61 +/- 13.5 vs. 60 +/- 12.5, p = NS) and other demographic characteristics. Restenosis, defined as the presentation to a physician with symptoms of angina within 6 months of the PTCA and the finding on repeat catheterization of a significant restenosis at the site of the PTCA, occurred in 30% of the patients who were discharged on a drug regimen which did not include ACE inhibitors vs. 3% (p less than .05) in those treated with an ACE inhibitor. Thus, it appears that the use of ACE inhibitors may significantly reduce the incidence of restenosis after successful PTCA.

Determination of antiarrhythmic drug efficacy in the treatment of ventricular arrhythmias

The presence of ventricular arrhythmias mark an individual with underlying structural heart disease as a candidate at high risk for sudden cardiac death. It is still unknown whether suppression of those ventricular arrhythmias by all drugs will in fact prevent sudden cardiac death. Therefore, the efficacy of an antiarrhythmic drug at present must be defined as only its pharmacologic activity that relates to its ability to reduce the frequency of ventricular arrhythmias rather than to a potential beneficial effect on patient outcome. Ventricular arrhythmias can be differentiated using a prognostic classification into those that are benign, potentially lethal, or lethal. Benign and potentially lethal ventricular arrhythmias undergo a high degree of spontaneous variability, and therefore the degree of frequency suppression needed to differentiate drug suppression from spontaneous variability must be carefully considered. It therefore is important to establish the mean ventricular premature complex frequency per hour over at least 24 hours at baseline using quantitative continuous ambulatory electrocardiographic (Holter) monitoring. To eliminate spontaneous variability, a repeat Holter monitoring session after the initiated therapy has reached steady state should show at least a 75% reduction in the mean VPC/hr frequency and at least a 90% suppression in the number of beats in the form of nonsustained ventricular tachycardia (NSVT). Exercise testing is a complementary technique and is best suited for patients with NSVT developing during exercise testing from either a "catecholamine" or an "ischemic" mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose effect of moricizine on suppression of ventricular arrhythmias

To define the pharmacologic properties of moricizine in patients with benign or potentially lethal ventricular arrhythmias, 1,072 patients in the moricizine data base through February 1987 were evaluated. In dose-ranging and titration trials as well as in a cross-study analysis of th entire data base, the minimally effective dose for moricizine was found to be 600 mg/day and the optimal dose range from 600 to 900 mg/day. The dose efficacy relation plateaued beyond 900 mg/day. With use of a 75% reduction in ventricular premature complex frequency as the definition of a drug responder, 391 of 583 patients (67%) with paired Holter monitors demonstrated overall efficacy. The dose onset of moricizine was between 16 and 20 hours and the dose offset was at approximately 24 hours at the point when 50% of the ventricular arrhythmia frequency returned to baseline. Although moricizine was primarily given on a 3-times-a-day regimen during clinical trials, dose interval evaluation suggested that a twice-a-day regimen may produce the same degree of efficacy although there are limited data regarding comparable safety.

Placement of moricizine in the selection of antiarrhythmic drug therapy

The selection of antiarrhythmic drug therapy requires a careful assessment of the benefits of ventricular arrhythmia suppression compared with the risks of antiarrhythmic drug use. Since reduction in sudden cardiac death from ventricular arrhythmia suppression has not been demonstrated, the only indications for antiarrhythmic drug suppression involve the reduction of hemodynamic symptoms such as syncope (a major benefit) or the reduction of nonhemodynamic symptoms such as palpitations or dizziness (a minor benefit). Noncardiac adverse effects and organ toxicity as well as cardiac side effects must be considered when antiarrhythmic drug therapy is initiated. For reduction of nonhemodynamically important symptoms in patients with benign or potentially lethal ventricular arrhythmias, beta blockers are chosen as first-line therapy. Because of moricizine's relatively high effectiveness in suppressing ventricular arrhythmias and its low potential for noncardiac adverse effects and organ toxicity as well as a low incidence of induced proarrhythmia and heart failure, moricizine is selected as the next drug in line. All other class I antiarrhythmic drugs either have been shown to have the potential for increasing sudden cardiac death or have major rates of noncardiac adverse effects or organ toxicity that preclude their use in these patient groups except in special circumstances. In patients with malignant ventricular arrhythmias who present with hemodynamic consequences such as syncope or worse, moricizine also is preferred as an initial drug for consideration. When compared to drugs with class IA and IB action, moricizine has comparable efficacy yet lower rates of noncardiac adverse effects, organ toxicity, proarrhythmia and heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of ventricular arrhythmias by United States cardiologists: a survey before the Cardiac Arrhythmia Suppression Trial results were available

To define the practice habits of United States cardiologists and the treatment of ventricular arrhythmias, a random sample of 1,000 of 12,000 cardiologists was sent a pretested questionnaire. After follow-up procedures, 252 responded, of which 18% were academically-based, 29% were hospital-based and 53% were office-based. Attitudes about antiarrhythmic drug therapy for the treatment of ventricular arrhythmias were influenced by the presence and severity of cardiac disease, the presence and severity of cardiac disease, the presence of symptoms and the type of ventricular arrhythmias. In this survey, only 1% of cardiologists treated patients with asymptomatic ventricular premature complexes and no heart disease, but 17% treated such patients if unsustained ventricular tachycardia was present. The treatment rate among cardiologists increased to 38% when coronary artery disease with left ventricular dysfunction was present in patients with asymptomatic ventricular premature complexes. The presence of any cardiac disease and symptomatic ventricular arrhythmias increased the treatment rate to 80 to 100%. Approximately 50% of responding physicians treated patients comparable to the Cardiac Arrhythmia Suppression Trial study population with antiarrhythmic drugs. Beta blockers were the most common antiarrhythmic drug class chosen as the most appropriate initial therapy in new patients with ventricular arrhythmias. Whereas no cardiologists thought that amiodarone was appropriate to initiate in new patients with benign or potentially malignant ventricular arrhythmias, as many as 33 to 43% of cardiologists would use amiodarone for refractory patients with such arrhythmias, a response contradictory to the approved labeling for this drug. Less than one half of cardiologists recognize the high potential organ toxicity for quinidine, procainamide and tocainide.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms and risk factors for proarrhythmia with type Ia compared with Ic antiarrhythmic drug therapy

Proarrhythmia defined as the exacerbation of existing arrhythmias or the genesis of new arrhythmias de novo may result from any antiarrhythmic agent. The two general clinical syndromes of sustained arrhythmias that result appear to have distinct clinical properties that are consistent with the proposed basic mechanisms of arrhythmogenesis. Torsades de points occurs most commonly in association with administration of type Ia antiarrhythmic agents and has characteristics most consistent with triggered activity mediated by early after depolarization. Conversely, incessant, sustained, monomorphic, wide complex ventricular tachycardia occurs most commonly in association with type Ic antiarrhythmic agents and has characteristics most consistent with incessant reentry. These general subdivisions are probably oversimplified, and in fact, much overlap likely exists. In addition, these proposed mechanisms may not apply to other forms of proarrhythmia such as an increased frequency of isolated ventricular premature couplets or repetitive forms. Furthermore, proarrhythmia may also occur during treatment of supraventricular arrhythmias; although some of these described syndromes are consistent with incessant reentry, the clinical syndromes are not sufficiently defined to better characterize potential mechanisms. Further investigation, therefore, is needed to better define the mechanisms in question, but the mechanisms proposed in this article help to provide a rational approach toward understanding and dealing with clinical proarrhythmia.

Prevalence and characteristics of proarrhythmia from moricizine (Ethmozine)

Moricizine was studied in 908 patients with ventricular arrhythmia. Proarrhythmia occurred in 29 (3.2%). When the type of proarrhythmia and the type of ventricular arrhythmia were correlated, no proarrhythmic events occurred in patients with benign ventricular arrhythmia. Three of the 4 deaths due to proarrhythmia occurred in patients with lethal ventricular arrhythmia and 14 of the 15 serious proarrhythmic events occurred in patients with potentially lethal ventricular arrhythmia. The overall proarrhythmia incidence in lethal and potentially lethal ventricular arrhythmias was not different (3.2 vs 3.7%, respectively). Proarrhythmia occurred in patients with more significant structural heart disease or conduction defects at baseline, but was not related to the baseline frequency of ventricular premature complexes. There was no relation between dose of moricizine and incidence of proarrhythmia. All 29 proarrhythmic events occurred within 10 days and 26 of 29 (90%) took place within 7 days of therapy start. Thus, moricizine has a low proarrhythmic potential, especially in patients with lethal ventricular arrhythmias, and may have the best risk/benefit ratio among first-line drugs used in these patients.

Evaluation of antiarrhythmic therapy using Holter monitoring

Premature ventricular complexes and nonsustained ventricular tachycardia mark a person with structural cardiac disease as a high--risk candidate for sudden cardiac death. Such ventricular arrhythmias are considered potentially lethal and should be distinguished from both those that are benign and those that cause hemodynamic consequences (i.e., lethal or malignant arrhythmias). Noninvasive Holter monitoring is the principal technique for detecting and evaluating the presence of potentially lethal ventricular arrhythmias. These arrhythmias undergo a high degree of spontaneous variability. Thus, to define a therapeutic drug effect, a reduction in the frequency of premature ventricular complexes of at least 75% and a reduction in the frequency of nonsustained ventricular tachycardia by at least 90% are required to eliminate the likelihood of spontaneous variability as the cause of this change in the frequency of arrhythmia. To define proarrhythmia, a different algorithm must be applied. When using antiarrhythmic drugs, a quantitative ventricular arrhythmia baseline for both frequency and type of arrhythmia must be established so that after therapeutic intervention repeat Holter monitoring can determine whether efficacy, inefficacy or proarrhythmia had occurred. Holter monitoring clearly reveals differential antiarrhythmic response rates among classes of antiarrhythmic drugs in patients with benign or potentially lethal arrhythmias. However, preliminary data have not clearly defined the relation between antiarrhythmic pharmacotherapy and a reduction in sudden cardiac death. The results of large-scale clinical trials that have only recently been undertaken must be assessed to determine whether sudden cardiac death can be prevented by adequately suppressing potentially lethal ventricular arrhythmias.