Cardiac pacemakers and implantable defibrillators in terminal care

The use of cardiac pacemakers and arrhythmia control devices is increasingly common. The presence of a previously placed pacemaker or implantable cardioverter-defibrillator (ICD) in a terminally ill patient may result in medical and ethical issues for the patient, family, and healthcare provider. Two cases are presented to illustrate the complex issues that may arise in the terminally ill with a pacemaker or an ICD. Based on these cases and a review of published data, it is likely that the disabling of a previously placed pacemaker will neither hasten nor prolong the natural history of the underlying illness in most instances. There are uncommon but potentially severe adverse effects of disabling the pacemaker; therefore, pacemakers should generally be left intact in terminally ill patients. It is more difficult to generalize as to whether deactivation of an ICD is appropriate; in this case death may be hastened and the decision concerning an ICD will depend on the specific clinical scenario. Patient and family education regarding palliative care treatment goals and the function of pacemakers and other implanted arrhythmia control devices can help to alleviate anxiety surrounding the impact of this technology at the end of life.

Atrial pacing periablation for prevention of paroxysmal atrial fibrillation

BACKGROUND

This study tested the hypothesis that rate-adaptive atrial pacing would prevent paroxysmal atrial fibrillation (PAF) in patients with frequent PAF in the absence of symptomatic bradycardia.

METHODS AND RESULTS

Patients (n=97) with antiarrhythmic drug-refractory PAF received a Medtronic Thera DR pacemaker 3 months before planned AV node ablation. Patients were randomized to no pacing (n=48) or to atrial rate-adaptive pacing (n=49). After a 2-week stabilization period, patients were followed up for an additional 10 weeks. The time to first recurrence of sustained PAF, the interval between successive episodes of PAF, and the frequency of PAF were compared between the 2 groups in intention-to-treat analysis. Time to first episode of sustained PAF was similar in the no-pacing (4.2 days; 95% CI, 1.8 to 9.5) and the atrial-pacing (1.9 days; 95% CI, 0.8 to 4.6; P=NS) groups. PAF burden was lower in the no-pacing (0.24 h/d; 95% CI, 0.10 to 0.56) than in the atrial-pacing (0.67 h/d; 95% CI, 0.30 to 1.52; P=0.08) group. Paired crossover analysis in 11 patients revealed that time to first PAF was shorter during atrial pacing (1.6 days; 95% CI, 0.6 to 4.9) than with no pacing (6.0 days; 95% CI, 2.4 to 15.0; P=0.13), and PAF burden was greater during atrial pacing (1.00 h/d; 95% CI, 0.35 to 2.91) than with no pacing (0.32 h/d; 95% CI, 0.09 to 1.13; P<0.016).

CONCLUSIONS

Atrial rate-adaptive pacing does not prevent PAF over the short term in patients with antiarrhythmic drug-resistant PAF without symptomatic bradycardia.

Atrial fibrillation detection and R-wave synchronization by Metrix implantable atrial defibrillator: implications for long-term efficacy and safety. The Metrix Investigators

BACKGROUND

The long-term efficacy of atrial fibrillation (AF) detection and R-wave synchronization are critical safety requirements for the development of an implantable atrial defibrillator (IAD) for treatment of AF.

METHODS AND RESULTS

The long-term efficacy of the Metrix IAD for AF detection and R-wave synchronization was tested in 51 patients. The mean duration of follow-up was 259+/-138 days (72 to 613 days). AF detection tests were performed 2240 times during observed operation with 100% specificity and 92.3% sensitivity for differentiation between sinus rhythm and AF; 2219 episodes and their electrograms stored in the device during AF detection were analyzed. The positive predictive value of the AF detection algorithm was 97.4% (lower 95% confidence limit [CL], 94.5%) in the out-of-hospital setting. A total of 242 435 R waves were analyzed for R-wave synchronization. Of these, 49% were marked for synchronized shock delivery, 82% of sinus rhythm and 36% of AF R waves, respectively. All shock markers were properly synchronized and within the R wave (overall synchronization accuracy, 100%; lower 95% CL, 99.999%). Overall, 3719 shocks have been delivered via the IAD with no instance of unsynchronized shock delivery or any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.084% per shock (95% upper CL).

CONCLUSIONS

The Metrix IAD can appropriately detect AF with a high specificity and sensitivity and reliably synchronize within a suitable R wave for shock delivery to minimize the risk of ventricular proarrhythmia.

Atrial fibrillation: overview of therapeutic trials

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia treated by physicians, and a plethora of therapeutic trials deal with selected aspects of its management. This overview attempts to categorize and summarize the available studies. A key to management of AF is a clinical classification schema that provides a framework for application of the available treatment modalities. Such a classification is provided. Antithrombotic trials have demonstrated the remarkable efficacy of warfarin and more modest effect of acetylsalicylic acid for prevention of stroke; these data are summarized. Cardioversion to restore sinus rhythm is an important aspect of management of AF, particularly of persistent and new onset AF. In this review pharmacological cardioversion is emphasized. The data concerning the use of various drugs for pharmacological cardioversion are reviewed. Many, but not all, agents have been shown to have efficacy in this regard, but efficacy with drugs is lower than that with electrical cardioversion and, in the case of amiodarone, may be delayed. For recurrent AF, the two major rhythm management approaches are maintenance of rhythm and heart rate control. Trials of pharmacological and nonpharmacological therapies for these purposes are reviewed and summarized. Management of AF is an active area of research, and the present review is intended as a foundation upon which new information can be added.

Changes in pacing lead impedance over time predict lead failure

It has been suggested that a decrease in lead impedance may predict pacing lead failure, but there is limited prospective data about the relation of changes in lead impedance over time to lead performance. We monitored changes in lead impedance through implantable pulse generators with real-time telemetry data capability in 105 patients with Medtronic 4012 leads (n = 38) and Medtronic 4004 leads (n = 67). Pacing lead failure was documented by serial ambulatory electrocardiographic monitoring or intensified pacemaker clinic surveillance. A significant decrease in lead impedance was observed in patients with Medtronic 4012 and Medtronic 4004 leads with documented lead failure, whereas lead impedance remained stable over time in patients without documented lead failure. The sensitivity and specificity of a lead impedance decrease of > or =15% to predict lead failure were 69% and 70%, respectively. The sensitivity and specificity of a lead impedance decrease of > or =30% to predict lead failure were 36% and 90%, respectively. The positive and negative predictive values for a lead impedance decrease of > or =15% were 54% and 81%, respectively, and for a lead impedance decrease of > or = 30% were 65% and 73%, respectively. Thus, small decreases in lead impedance may identify failing leads. Serial measurement of pacing lead impedance over time is a useful tool to monitor pacing lead performance.

Antiarrhythmic drug effects on QT interval dispersion in patients undergoing electropharmacologic testing for ventricular tachycardia and fibrillation

The effects of antiarrhythmic drugs on QT interval dispersion as a predictor of antiarrhythmic drug therapy has not been rigorously assessed. This study was performed to determine whether the effects of antiarrhythmic drugs on QT interval dispersion predict antiarrhythmic drug response in patients undergoing electropharmacologic testing for ventricular tachycardiarrythmias. Precordial QT intervals and QT interval dispersions were measured at baseline and during steady-state antiarrhythmic drug therapy in 72 consecutive patients with documented coronary artery disease and remote myocardial infarction presenting with spontaneous sustained ventricular tachyarrhythmias who underwent electropharmacologic studies to assess arrhythmia suppression. QT interval dispersion was similar at baseline in drug responders (42 +/- 21 ms) and drug nonresponders (46 +/- 21 ms), whereas during antiarrhythmic therapy QT interval dispersion was shorter in drug responders (33 +/- 15 ms) than in drug nonresponders (55 +/- 29 ms, p <0.001). QT interval dispersion was shorter in 7 drug responders during their effective drug trials (27 +/- 14 ms) than during their ineffective drug trials (47 +/- 24 ms, n = 9, p <0.05). QT dispersion < or = 50 ms (p <0.002) and a patent infarct-related artery (p <0.003) were independent predictors of antiarrhythmic therapy. The positive and negative predictive value of QT interval dispersion during drug therapy to predict a successful drug response was 32% and 96%, respectively. QT interval dispersion predicted the outcome of electropharmacologic studies independent of infarct-related artery patency. QT interval dispersion >50 ms during drug therapy was associated with ineffective drug therapy.

Telemetry-documented, pace-terminable ventricular tachycardia in patients with ventricular fibrillation

The follow-up prevalence of electrogram-confirmed spontaneous ventricular tachycardia with a cycle length of >280 ms (53%) exceeds the prevalence of ventricular fibrillation (23%) in patients whose only spontaneous arrhythmia before implantable cardioverter defibrillator implantation was ventricular fibrillation. Antitachycardia pacing therapy safely terminates most (89%) of these slower ventricular tachycardia episodes, recommending the use of tiered-therapy devices and anticipatory activation of ventricular tachycardia detection and treatment algorithms for ventricular fibrillation patients who receive an implantable cardioverter defibrillator.

Definition of predicted effective antiarrhythmic drug therapy for ventricular tachyarrhythmias by the electrophysiologic study approach: randomized comparison of patient response criteria

OBJECTIVES

We sought to compare efficacies of therapy for ventricular tachyarrhythmias selected by programmed stimulation using two different patient response efficacy criteria: <5 versus <16 repetitive ventricular responses.

BACKGROUND

Therapy selection for ventricular tachyarrhythmias by programmed stimulation requires definition of a patient response that predicts long-term efficacy. Such definitions have not been previously compared prospectively.

METHODS

Patients with sustained ventricular tachyarrhythmias were randomized to therapy selection using either the <5 or <16 repetitive response criterion of predicted effective therapy. The primary end point was sudden death or recurrence of ventricular tachyarrhythmia requiring intervention.

RESULTS

Predicted effective drug therapy was found for 23 (34%) of 68 patients randomized to the <5 criterion and 29 (36%) of 81 patients randomized to the <16 criterion (p = NS). Definition of therapy required 3.0 +/- 1.6 drug trials (mean +/- SD) in patients randomized to the <5 criterion and 2.9 +/- 1.8 trials in patients randomized to the <16 criterion (p = NS). Patients randomized to the <5 criterion had a lower 2-year probability of the primary end point (0.20 +/- 0.05) than did patients randomized to the <16 criterion (0.33 +/- 0.05, one-tailed p = 0.004). The advantage of the <5 criterion was also seen in subgroup analyses involving patients with and without an initial drug efficacy prediction.

CONCLUSIONS

The programmed stimulation approach to the selection of antiarrhythmic therapy for ventricular tachyarrhythmias using a patient response criterion of <5 repetitive ventricular responses results in a lower probability of recurrence of ventricular tachyarrhythmia than does use of a <16 repetitive response criterion.

Effect of coronary angioplasty on precordial QT dispersion

Dispersion of the QT interval is a measure of inhomogeneity of ventricular repolarization. Because ischemia is associated with regional abnormalities of conduction and repolarization, we hypothesized that the surface electrocardiographic interval dispersion would increase in patients with symptomatic coronary artery disease in the absence of myocardial infarction and that successful revascularization would reduce QT interval dispersion. Thirty-seven consecutive patients with ischemia due to 1-vessel coronary artery disease without prior myocardial infarction who underwent percutaneous transluminal coronary angioplasty (PTCA) were evaluated. Standard 12-lead electrocardiograms were performed 24 hours before, 24 hours after, and late (>2 months) after PTCA. Precordial QT interval dispersions were determined from differences in the maximum and minimum corrected QT intervals. Mean QT interval dispersion before PTCA was 60 +/- 9 ms, immediately after PTCA 23 +/- 14 ms (p <0.001), and late after PTCA 29 +/- 18 ms (p <0.001 vs before PTCA). The shortest precordial QT interval increased immediately after PTCA (367 +/- 40 vs 391 +/- 39 ms; p <0.02) and then remained stable late after PTCA (376 +/- 36 ms, p = NS vs immediately after PTCA). Symptomatic recurrent ischemia in 8 patients with documented restenosis increased QT interval dispersion (56 +/- 15 ms [p <0.01] vs 25 +/- 14 ms immediately after PTCA), which decreased again after successful repeat PTCA (22 +/- 13 ms [p <0.01] vs before the second PTCA). QT interval dispersion decreases after successful coronary artery revascularization and increases with restenosis. Therefore, QT interval dispersion may be a marker of recurrent ischemia due to restenosis after PTCA.

Ambulatory electrocardiography for the detection of pacemaker lead failure

The suboptimal performance of some polyurethane bipolar pacing leads has highlighted concern about the optimal method of monitoring pacemaker lead performance. Since the manifestations of premature lead failure may be initially intermittent, we hypothesized that ambulatory electrocardiography (AECG) would be a more sensitive tool for the detection of pacing lead failure compared to increased pacemaker clinic surveillance. Since the Medtronic safety alerts on the 4012, 4082, and 4004 leads, we have followed 261 patients by serial AECG and 165 patients by increased pacemaker clinic surveillance. Lead failures were identified in 75 patients: 68 in the AECG group (31%) and 7 in the clinic group (4%, P < 0.001). Repeat AECG confirmed the lead failure in 38 (97%) of 39 patients in which it could be done. Pacing lead failure documented by AECG could be confirmed by a subsequent clinic assessment in only 15 (25%) of 60 patients evaluated (P < 0.001). The actuarial survival of the 4012 lead was significantly lower in the AECG group compared to the clinic group (56% vs 87% survival at 8 years, P < 0.002). Similar trends were observed for the 4082 and 4004 leads. AECG is a more sensitive method of surveillance for pacemaker lead function compared to pacemaker clinic assessment. AECG should be incorporated into the routine follow-up of pacemaker patients.

Divergence of endocardial QT interval components during programmed electrical stimulation including observations during induction of sustained ventricular tachyarrhythmias

Measurements were made in 12 normal subjects and during induction of sustained ventricular tachyarrhythmias in 31 patients with remote myocardial infarction. QT interval measurements were made semiautomatically with computer assistance and the total QT interval was divided into early (QT1) and late (QT2) components. QT intervals and QT interval dispersion between two right ventricular endocardial sites were plotted against the degree of prematurity of the last extrastimulus (S2, S3, or S4). In the control group, total QT and QT1 intervals shortened with increasing prematurity of the last extrastimulus (p < 0.001). Slopes (positive) were steeper with faster pacing rates (600, 500, or 400 ms) and more extrastimuli (1 to 3). The relationship between QT2 intervals and prematurity of the last extrastimulus was flat, but the slope was slightly negative (p = 0.05 to < 0.001) and did not vary with changes in pacing cycle length or number of extrastimuli. QT interval dispersion in the control group was minor (95% CI 0-40 ms). During induction of sustained ventricular tachyarrhythmias, total QT and QT1 intervals were longer (y intercepts) than in the control group (p < 0.05 at 400-ms pacing cycle length) and their dispersion was increased (p < 0.05). Generally, QT2 intervals were shorter (p < 0.05 at 600-ms pacing cycle length) during induction of ventricular arrhythmias in comparison with the control group but dispersion was increased (p < 0.05 at 400-ms pacing cycle length). QT intervals and QT interval dispersion show an orderly and predictable relationship with prematurity of the last extrastimulus in normal subjects. These patterns differ during induction of sustained ventricular tachyarrhythmias. Such differences may be exploited to derive clinically predictive and useful measurements.

Increased precordial QTc dispersion predicts ventricular fibrillation during acute myocardial infarction

Electrocardiograms of 19 consecutive patients with acute myocardial infarction complicated by early ventricular fibrillation were compared with those in 19 case-matched patients with acute myocardial infarction not complicated by ventricular fibrillation. The mean precordial QTc interval dispersion in patients with ventricular fibrillation was greater than that of patients without ventricular fibrillation (73 +/- 28 ms vs 30 +/- 12 ms, p < 0.001).

Propafenone pharmacokinetics and pharmacodynamics in patients with sustained ventricular tachycardia

The myocardium accumulation and pharmacodynamics of propafenone were evaluated during intravenous infusion in 6 patients undergoing electrophysiologic study for evaluation of ventricular tachycardia. The myocardial accumulation of propafenone was delayed and resulted in nonlinear arterial concentration-effect relations.

A randomized clinical trial of the noninvasive and invasive approaches to drug therapy for ventricular tachycardia: long-term follow-up of the Calgary trial

Individualized antiarrhythmic drug therapy for patients with ventricular tachyarrhythmias may be selected by the noninvasive approach (suppression of spontaneous ventricular premature beats) or the invasive approach (suppression of ventricular tachyarrhythmias induced at an electrophysiologic study). There is controversy over which approach is superior. From a screened population of 124 patients with symptomatic ventricular tachycardia or ventricular fibrillation, 57 patients with both frequent ventricular premature beats and inducible ventricular tachycardia at baseline were randomized to have chronic therapy selected by either the noninvasive or invasive approach. These patients have now been followed up for a minimum event-free period of 6.5 years. By intention-to-treat, therapy selected by the invasive approach prevented subsequent ventricular tachyarrhythmias better than that selected by the noninvasive approach (6-year probabilities of freedom from symptomatic sustained ventricular tachyarrhythmia recurrence; noninvasive approach, 0.45 +/- 0.10; invasive approach, 0.73 +/- 0.09; p=.02). This advantage of the invasive approach was also evident for the outcome of any ventricular tachyarrhythmia recurrence and for efficacy analyses involving only those patients with a drug-efficacy prediction. We hypothesize that the difference between these results and those of the ESVEM trial are caused, in part, by differences in the characteristics of the enrolled patients and differences in criteria used to define a predicted-effective therapy.

Long-term reproducibility of ventricular tachycardia induction in patients with implantable cardioverter/defibrillators. Serial noninvasive studies

BACKGROUND

Noninvasive electrophysiological studies (EPSs) can be performed in current implantable antitachycardia pacemaker/cardioverter/defibrillators (ICDs). Thus, these devices may be used as tools to study changes in the electrophysiological substrate and ventricular tachycardia characteristics over time.

METHODS AND RESULTS

Fifty-five patients receiving an ICD for treatment of sustained ventricular tachyarrhythmias underwent serial EPSs after implantation of the ICD. Studies were performed before hospital discharge and 1, 3, 5, 9, 12, 18, 24, and 36 months after ICD implantation. Sustained monomorphic ventricular tachycardia (VT) was induced in 37 patients (group 1) at the predischarge EPS, whereas no sustained arrhythmia could be induced in 18 patients (group 2) at baseline. Group 1 patients underwent 165 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 72% of the follow-up EPSs, ventricular fibrillation (VF) was induced during 11% of follow-up EPSs, and no sustained VT or VF was induced during 17% of follow-up visits. Sustained VT was induced at every follow-up EPS in 23 patients (62%), whereas no sustained VT/VF could be induced at least once during follow-up in 14 patients (38%). Clinical or electrophysiological variables did not predict noninducibility during follow-up. However, the probability that a patient would experience spontaneous VT decreased significantly over time in patients in whom VT was not inducible during at least 1 follow-up EPS (P = .05). Group 2 patients underwent 86 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 22% of follow-up EPSs, VF was induced during 19% of follow-up EPSs, and no sustained VT/VF could be induced during 68% of follow-up EPSs. No sustained VT/VF could be induced during every follow-up EPS in 9 patients (50%), whereas sustained monomorphic VT was induced at least once during follow-up in 7 patients (34%). Persistent noninducibility of VT during follow-up was associated with low probability of occurrence of spontaneous VT (11%), whereas inducibility of VT at least once during follow-up was associated with the occurrence of spontaneous VT (89%, P = .003).

CONCLUSIONS

Considerable variability of VT induction is observed over a lengthy period in patients presenting with sustained VT/VF. Persistent noninducibility of VT is associated with a reduced probability of spontaneous VT. These observations suggest that the substrates for inducible and spontaneous VT change in parallel over time.

Quinidine pharmacodynamics in patients with arrhythmia: effects of left ventricular function

OBJECTIVES

This study was undertaken to determine whether quinidine pharmacodynamics are altered in the presence of left ventricular dysfunction.

BACKGROUND

Left ventricular function is an independent predictor of antiarrhythmic drug efficacy. However, the effects of left ventricular dysfunction on the pharmacodynamics of antiarrhythmic drugs have not been studied extensively.

METHODS

Signal-averaged electrocardiograms were obtained and quinidine plasma concentrations measured during 24-h quinidine washout in 22 patients.

RESULTS

Linear quinidine concentration-effect relations were observed for QRS and QT intervals corrected for heart rate. The slopes of the concentration-effect relation describing changes in the corrected QT (QTc) interval were significantly higher in the group with left ventricular ejection fraction > or = 0.35 ([mean +/- SD] 29.5 +/- 11.2 ms/micrograms per ml) than in the group with a low left ventricular ejection fraction (15.7 +/- 9.7 ms/micrograms per ml, p = 0.001). The QRS concentration-effect relations were not different in the two groups. A significant linear correlation was observed between the slopes of the concentration-effect relations describing changes in QTc intervals and left ventricular ejection fraction (r = 0.7, p < 0.001). Nineteen patients with inducible ventricular tachycardia underwent serial electrophysiologic studies for evaluation of quinidine efficacy. Ventricular tachycardia could not be induced during quinidine therapy in eight patients. The slopes of the quinidine concentration-effect relations for QTc intervals were significantly higher in quinidine responders than in nonresponders (p < 0.05).

CONCLUSIONS

The effects of quinidine on ventricular repolarization are linearly related to left ventricular ejection fraction. Quinidine concentration-effect relations describing ventricular repolarization are associated with antiarrhythmic efficacy in patients with ventricular tachycardia.

Antiarrhythmics Versus Implantable Defibrillators (AVID)--rationale, design, and methods

The Antiarrhythmics Versus Implantable Defibrillators (AVID) study compares a strategy of initial treatment with an implantable cardioverter-defibrillator (ICD) to a strategy of initial treatment with an antiarrhythmic drug to prevent death in patients with a history of ventricular fibrillation or hemodynamically compromising ventricular tachycardia, or both. Neither arrhythmia can have been due to a transient or correctable cause. The principle exclusions are a contraindication to amiodarone therapy and inability to undergo ICD implantation. Antiarrhythmic drug therapy includes empiric amiodarone and guided sotalol. The ICDs allowed are advanced generation devices, and most are implanted transvenously. The primary end point of the study is total mortality. Secondary end points are cost and quality of life. The study was designed in 2 phases. The pilot phase enrolled 200 patients between June 1993 and June 1994. Data collected during the pilot phase confirmed that the trial is feasible. An additional 1,000 patients will be enrolled between June 1994 and March 1997. It is anticipated that all 1,200 patients will be followed until September 1998, and will be included in the intention-to-treat analysis.

Alpha-adrenoceptor responses of an isolated human artery and blood pressure

This cross-sectional study examined responses of the isolated cystic artery to 3 alpha-adrenoceptor agonists and the effects of 2 antagonists in relation to subjects' blood pressures. Potency of the 3 amines studied was: alpha-methylnorepinephrine > norepinephrine > phenylephrine. Responses to clonidine were trivial (< 5% of maximum) and remained < 25% of maximum in the presence of subthreshold concentrations of angiotensin II. A weak trend for increased potency of alpha-methylnorepinephrine was noted in arteries of subjects with higher blood pressures (r = 0.268, p = 0.027). There was no relationship between blood pressure and pA2 for yohimbine. The pA2 for prazosin could not be calculated because of a decline in maximal responses but prazosin was clearly more potent than yohimbine. The decline in maximal responses to norepinephrine and phenylephrine after prazosin treatment was related to subjects' diastolic blood pressures (r = -0.400, p = 0.003). There were no significant relationships between these measurements of vascular responsiveness and a family history of hypertension. There were also no significant relationships between these measurements of vascular responsiveness and plasma norepinephrine levels, alpha 2-adrenoceptor binding or platelets of beta 2-adrenoceptor binding of lymphocytes. The major postjunctional alpha-adrenoceptors in this artery are of the alpha 1 type. The data suggest that differences in potency of alpha-adrenoceptor agonists in relation to blood pressure may be due to differences in the alpha 2-adrenoceptor but are not likely due to a difference in binding to the receptor itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride-quinidine interaction: adverse outcomes

OBJECTIVES

Previous studies have reported beneficial antiarrhythmic effects when selected drugs were combined. The purpose of this study was to assess whether a favorable interaction would occur with amiloride and quinidine.

DESIGN

The antiarrhythmic and electrophysiologic effects of quinidine alone and in combination with amiloride were assessed in 10 patients with inducible sustained ventricular tachycardia. Parallel electrophysiologic studies assessed this drug combination in guinea pig papillary muscle.

RESULTS

None of the patients had adverse effects during quinidine monotherapy. However, seven of 10 patients had adverse responses to the combination treatment: three patients had suppression of inducible ventricular tachycardia during quinidine monotherapy but had sustained ventricular tachycardia induced during combination treatment; three other patients had somatic side effects that resulted in discontinuation of the combination therapy but were absent during quinidine monotherapy; and one patient had 12 episodes of sustained ventricular tachycardia during this combination therapy. The patient had no such response during monotherapy. Surface QRS duration was significantly more prolonged during combination therapy than during monotherapy. Parallel electrophysiologic effects assessed this drug combination in guinea pig papillary muscle. The combination of amiloride (1 mumol/L) and quinidine (10 mumol/L) synergistically decreased the maximum rate of rise of phase 0 of the action potential (Vmax) (43 +/- 12 V/sec) compared with quinidine alone (24 +/- 9 V/sec) because of a greater degree of tonic block of Vmax (14% +/- 6%) as compared to quinidine alone (3% +/- 3%) with no significant change in action potential duration.

CONCLUSIONS

Amiloride exaggerates the effects of quinidine on QRS duration in patients and on Vmax during in vitro study, which implies that the proarrhythmic effect of the combination of amiloride and quinidine may be associated with synergistic increase in sodium channel blockade.

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.

Mortality following ventricular arrhythmia suppression by encainide, flecainide, and moricizine after myocardial infarction. The original design concept of the Cardiac Arrhythmia Suppression Trial (CAST)

OBJECTIVE

To test the hypothesis that in survivors of myocardial infarction, the suppression of ventricular premature depolarizations improves survival free of cardiac arrest and arrhythmic death.

DESIGN

International, prospective, multicenter, randomized, placebo-controlled trial.

SETTING

University and community hospitals.

PATIENTS

A total of 3549 patients with myocardial infarction and left ventricular dysfunction.

INTERVENTION

Administration of encainide, flecainide, moricizine, or placebo to suppress ventricular premature depolarizations.

MAIN OUTCOME MEASURES

Overall survival and survival free of cardiac arrest or arrhythmic death were compared in patients randomized to long-term, active antiarrhythmic drug therapy vs corresponding placebo, using the stratified log rank statistic.

RESULTS

At 1 year from the time of randomization to blinded therapy, 95% of placebo-treated patients vs 90% of active drug-treated patients remained alive (P = .0006). Similarly, at 1 year, 96% of placebo-treated patients vs 93% of active drug-treated patients remained free of cardiac arrest or arrhythmic death (P = .003).

CONCLUSIONS

The suppression of asymptomatic or mildly symptomatic ventricular arrhythmias after myocardial infarction does not improve survival and can increase mortality. Treatment strategies designed solely to suppress these arrhythmias should no longer be followed.