Effect of a digitalis drug on ventricular premature beats

Predictors of temporary epicardial pacing wires use after valve surgery

Background

Although temporary cardiac pacing is infrequently needed, temporary epicardial pacing wires are routinely inserted after valve surgery. As they are associated with infrequent, but life threatening complications, and the decreased need for postoperative pacing in a group of low risk patients; this study aims to identify the predictors of temporary cardiac pacing after valve surgery.

Methods

A retrospective analysis of data collected prospectively on 400 consecutive valve surgery patients between May 2002 and December 2012 was performed. Patients were grouped according to avoidance or insertion of temporary pacing wires, and were further subdivided according to temporary cardiac pacing need. Multiple logistic regression was used to determine the predictors of temporary cardiac pacing.

Results

170 (42.5%) patients did not have insertion of temporary pacing wires and none of them needed temporary pacing. 230 (57.5%) patients had insertion of temporary pacing wires and among these, only 55 (23.9%) required temporary pacing who were compared with the remaining 175 (76.1%) patients in the main analysis. The determinants of temporary cardiac pacing (adjusted odds ratios; 95% confidence interval) were as follows: increased age (1.1; 1.1, 1.3, p = 0.002), New York Heart Association class III- IV (5.6; 1.6, 20.2, p = 0.008) , pulmonary artery pressure ≥ 50 mmHg (22.0; 3.4, 142.7, p = 0.01), digoxin use (8.0; 1.3, 48.8, p = 0.024), multiple valve surgery (13.5; 1.5, 124.0, p = 0.021), aorta cross clamp time ≥ 60 minutes (7.8; 1.6, 37.2, p = 0.010), and valve annulus calcification (7.9; 2.0, 31.7, p = 0.003).

Conclusion

Although limited by sample size, the present results suggest that routine use of temporary epicardial pacing wires after valve surgery is only necessary for high risk patients. Preoperative identification and aggressive management of predictors of temporary cardiac pacing and the possible modulation of intraoperative techniques can decrease the need of temporary cardiac pacing. Prospective randomized controlled studies on a larger number of patients are necessary to draw solid conclusions regarding the selective use of temporary epicardial pacing wires in valve surgery.

Prediction of appropriate defibrillator therapy in heart failure patients treated with cardiac resynchronization therapy

The necessity of implantable cardioverter-defibrillator (ICD) implantation in patients with systolic heart failure (HF) who undergo cardiac resynchronization therapy (CRT) may be questioned. The aim of this study was to identify patients at low risk for sustained ventricular arrhythmia. One hundred sixty-nine consecutive patients with HF (mean age 60 +/- 12 years, 125 men, 73% in New York Heart Association class III) referred for CRT and prophylactic, primary prevention ICD implantation underwent baseline clinical and echocardiographic assessment and regular device follow-up. The primary study end point was appropriate ICD therapy. During a mean follow-up period of 654 +/- 394 days, 35 patients (21%) had sustained ventricular arrhythmias requiring appropriate ICD therapy. Of the 3 patients who experienced sudden cardiac death, 2 had been treated with appropriate ICD therapy before sudden cardiac death. In a multivariate model, only history of nonsustained ventricular tachycardia (p = 0.001), a severely (<20%) decreased left ventricular ejection fraction (p = 0.001), and digitalis therapy (p = 0.08) independently predicted appropriate ICD therapy. Patients with 0 (n = 46), 1 (n = 36), 2 (n = 73), and 3 (n = 14) risk factors for appropriate ICD therapy had a 7%, 14%, 27%, and 64% and 0%, 6%, 10%, and 43% incidence of appropriate ICD therapy for ventricular arrhythmias and for rapid ventricular tachycardia or ventricular fibrillation, respectively. In conclusion, apart from commonsense considerations (age and significant co-morbidities), ICD addition seems ineffective in CRT patients without nonsustained ventricular tachycardia, digoxin therapy, and severely reduced left ventricular systolic function.

New hopes from old drugs: revisiting DNA-binding small molecules as anticancer agents

Most of the anticancer chemotherapeutic drugs that are broadly and successfully used today are DNA-damaging agents. Targeting of DNA has been proven to cause relatively potent and selective destruction of tumor cells. However, the clinical potential of DNA-damaging agents is limited by the adverse side effects and increased risk of secondary cancers that are consequences of the agents' genotoxicity. In this review, we present evidence that those agents capable of targeting DNA without inducing DNA damage would not be limited in these ways, and may be as potent as DNA-damaging agents in the killing of tumor cells. We use as an example literature data and our own research of the well-known antimalarial drug quinacrine, which binds to DNA without inducing DNA damage, yet modulates a number of cellular pathways that impact tumor cell survival.

Digoxin

After 200 years of use, digitalis still appears to have a place in our armamentarium for heart failure and atrial fibrillation despite the proven survival benefits with ACE inhibitors and beta-blockers. Digoxin therapy is inexpensive and well tolerated and may result in considerable savings. Digoxin is the only oral inotrope that does not increase mortality in heart failure patients, particularly if low doses are being used. Digoxin therapy should be used in patients with systolic heart failure who continue to have signs and symptoms despite therapeutic doses of ACE inhibitors or diuretics or in patients with atrial fibrillation with or without heart failure for rate control.

Ventricular arrhythmia in congestive heart failure

The importance of ventricular arrhythmia is based on its association with sudden death. In certain groups of patients, ventricular arrhythmia--primarily runs of nonsustained ventricular tachycardia (NSVT)--is associated with an increased risk for sudden death. Although this relationship has been most often reported in patients with recent myocardial infarction, it has also been recognized in patients with dilated cardiomyopathy, regardless of etiology. Therefore, ventricular arrhythmia is common in patients with CHF due to cardiomyopathy. A number of studies have reported that 70-95% of patients with cardiomyopathy and congestive heart failure (CHF) have frequent ventricular premature beats, and 40-80% will manifest runs of NSVT. Many factors are responsible for ventricular arrhythmia in such patients, including structural abnormalities, electrolyte imbalance, hemodynamic impairment, activation of neurohormonal mechanisms, and pharmacologic therapy. Many studies have reported a high yearly mortality in patients with cardiomyopathy and CHF; greater than 40% of deaths are sudden, most often the result of sustained ventricular tachyarrhythmia. Most studies have noted an association between presence (and frequency) of NSVT and risk of sudden cardiac death in these patients. Unfortunately, other techniques--such as the signal-averaged electrocardiogram and electrophysiologic testing--are not helpful in identifying the individual at risk. Although several drug interventions will reduce mortality from progressive CHF, these drugs have not been shown to reduce sudden death and, indeed, have a variable effect on ventricular arrhythmia. Although NSVT is a marker for increased risk for sudden death, it is uncertain if antiarrhythmic drugs will prevent this outcome. Antiarrhythmic drugs have not been shown to be effective for preventing sudden death, although there are as yet no well-controlled randomized trials. Several studies suggest that amiodarone and beta blockers are beneficial, but this requires confirmation. For patients who have been resuscitated following an episode of sudden death due to a sustained ventricular tachyarrhythmia, antiarrhythmic therapy guided by invasive and noninvasive techniques appears to reduce risk of recurrent arrhythmia. However, the response rate to antiarrhythmic agents is low and side effects are common in patients with CHF. Especially important is the increased risk of precipitating CHF and aggravating the arrhythmia being treated. For many such patients who have had serious ventricular tachyarrhythmia, the automatic implantable cardioverter defibrillator may prove a better option. Other drugs used for management of CHF reduce overall mortality, but not risk of sudden death.

The relative effects of digoxin and diltiazem upon ventricular ectopic activity in patients with chronic atrial fibrillation

In eight patients with chronic atrial fibrillation, treatment with digoxin (plasma drug concentration 1.3 to 2.0 nmol l-1) was associated with a significantly higher incidence of ventricular premature beats (VPBs) (mean 22.8 h-1) than diltiazem 120 mg three times daily (mean 6.8 h-1) (P less than 0.05). Seven out of the eight patients showed an increase in numbers of VPBs recorded over 24 h during treatment with digoxin when compared with diltiazem. The clinical importance of these results is unclear, but atrial fibrillation and ischaemic heart disease frequently co-exist, and increases in ventricular ectopy may predispose to serious ventricular arrhythmias following myocardial infarction.

Concentration response relationships of amiodarone and desethylamiodarone

Twelve patients with frequent ventricular premature depolarizations (VPDs) received amiodarone, 600 mg/day, for up to 8 weeks. On days 0, 1, 4, 8, 15, 22, 36, and 57 of treatment, 24-hour ambulatory ECGs were obtained, and multiple blood samples were taken for determination of amiodarone and desethylamiodarone plasma concentrations. All patients had at least 75% suppression of VPDs. The mean duration of therapy before the onset of antiarrhythmic effect was 13.2 days (range 1 to 36 days). Trough amiodarone and desethylamiodarone plasma concentrations at the time of onset of antiarrhythmic effect were 0.86 +/- 0.48 mg/L and 0.23 +/- 0.15 mg/L, respectively. Sixty-seven percent of patients responded at amiodarone concentrations below 1.0 mg/L. For each patient there was a progressive decrease in frequency of VPDs as both amiodarone and desethylamiodarone concentrations increased. Regression modeling indicated that both amiodarone and desethylamiodarone plasma concentrations explained significant variability in the frequency of VPDs, and amiodarone and desethylamiodarone plasma concentrations were highly correlated with each other. There was a trend for desethylamiodarone to explain more variability in frequency of VPDs than amiodarone.

Chronic ventricular arrhythmias: which drug for which patient?

Many agents, including a number of drugs recently approved by the Food and Drug Administration, are now available for the treatment of chronic ventricular arrhythmias. The so-called first-generation agents--quinidine, procainamide and disopyramide--have been used in large numbers of patients for many years, and the safety and efficacy profiles of these drugs are well established. The "second-generation" antiarrhythmic agents recently approved by the Food and Drug Administration offer promising new alternatives; however, their safety and efficacy profiles have yet to be confirmed for broad populations over extended periods of time. Although it is recognized that the choice of agent for treatment of a particular patient is a "therapeutic trial," with an unpredictable outcome of efficacy and adverse effects, certain "descriptors," such as patient age or co-existing medical conditions, are often helpful in determining which agent is most likely to be clinically effective, and which agents are most likely to produce adverse effects. When other medical conditions such as hepatic or renal failure are present, the appropriate choice of drug and dosage is required for optimal management of the arrhythmia and for prevention of overdosage, exacerbation of other medical problems and deleterious interactions. Combination therapy with multiple antiarrhythmic agents is often quite effective for increasing arrhythmia control without increasing adverse effects. However dosage modifications are often necessary when an antiarrhythmic drug is given in conjunction with another such agent, or with agents that also have electrophysiologic activity or modify metabolic or elimination functions. The following report is one clinician's approach for optimizing efficacy and minimizing toxicity while using the difficult class of drugs called antiarrhythmic agents. It will encourage the use of certain drugs before others, based on considerations of efficacy, safety, ease of administration, follow-up, and other factors.

Left ventricular dysfunction and altered autonomic activity: a possible link to sudden cardiac death

There is now a growing body of clinical evidence that suggests a strong association between left ventricular dysfunction and sudden cardiac death in patients recovering from myocardial infarction. The mechanisms underlying this association remain to be determined. Alterations within the autonomic nervous system may represent one factor that links an impairment in cardiac function to an increased mortality. Since ventricular dysfunction would tend to reduce stroke volume, an increased sympathetic and/or decreased parasympathetic efferent activity may compensate for this fall in stroke volume by increasing heart rate and/or the force of contraction (inotropic state) in an attempt to maintain a more normal cardiac output. Similar changes in autonomic activity are, in fact, known to increase the vulnerability to ventricular fibrillation. Therefore, I propose that myocardial infarction induces changes in cardiac function which in turn elicits autonomic efferent changes. As a consequence of these compensatory reflex changes the heart becomes less electrically stable and thereby more prone to lethal arrhythmias.

Clinical use of digitalis materials

Digitalis is a drug widely used in modern medicine for the control of ventricular response in atrial fibrillation and the treatment of congestive heart failure (CHF). Recently, the use of digitalis for the treatment of CHF in patients in sinus rhythm has become quite controversial. The findings of several clinical studies suggest a small but definite hemodynamic or clinical improvement in patients treated with digitalis. These effects are limited by the onset of toxicity, which is at least partially mediated via the central nervous system. If the inotropic effect of the drug could be separated from the central nervous system effect, much higher doses of digitalis could be tolerated and presumably a greater therapeutic effect could be obtained.

Absence of cardioversion-induced ventricular arrhythmias in patients with therapeutic digoxin levels

To determine the incidence of cardioversion-induced ventricular arrhythmias in patients with therapeutic serum levels of digoxin, 19 patients (average age [+/- standard deviation] 61 +/- 12 years) undergoing elective direct current cardioversion for atrial fibrillation were studied. Only patients with therapeutic serum digoxin levels (range 0.5 to 1.9 ng/ml; mean 1.1 +/- 0.5) at the time of cardioversion were included. Patients with acute myocardial ischemia or unstable angina, serious electrolyte disturbance or those requiring class I antiarrhythmic agents for control of ventricular or supraventricular arrhythmias were excluded. Ambulatory electrocardiograms were recorded for 24 hours before and 6 hours after cardioversion. No patient developed malignant ventricular arrhythmias (ventricular triplets or tachycardia) in the immediate 3 hour period after cardioversion. Furthermore, there were no significant (p less than 0.05) differences in the frequency of ventricular premature beats or couplets before and after cardioversion. To determine whether the level of serum digoxin or the strength of the applied shock had a significant effect on the development of postcardioversion arrhythmias, the change in frequency of single premature ventricular beats after cardioversion was compared with the serum digoxin level (ng/ml) and the applied energy level (joules) by means of linear regression analysis. There was no significant (p less than 0.05) relation between these variables. These findings suggest that patients with therapeutic serum levels of digoxin may safely undergo cardioversion without the concomitant use of class I antiarrhythmic agents.

Comparison of the canine tissue distribution of digoxin after acute and chronic administration: implications for digitalis therapy

Digoxin is often used as an antiarrhythmic and inotropic agent. It produces significant neuroexcitatory responses that influence both its therapeutic and toxic effects. Patients receiving digoxin can be separated into 2 groups: those who receive it acutely and those who receive it chronically. The therapeutic and toxic responses to digoxin vary between these groups. The neural tissue distribution of digoxin was compared in dogs after both acute and chronic injections. Acute administration of digitalis in this study was associated with preferential uptake of digoxin into peripheral sympathetic nerves. Chronic administration was associated with continued selective uptake into the central nervous system despite decreasing serum levels. Therefore, acute (experimental or suicidal) or chronic (maintenance) digoxin administration produces different neural responses. The peripheral sympathetic nervous system will be the primary area of interaction with acute digoxin administration and the central nervous system will have a greater involvement with chronic digoxin administration. Our results indicate that the uptake of digoxin into the peripheral nervous system and central nervous system depends upon the duration of digoxin administration. The time course of digoxin accumulation influences both its therapeutic and toxic actions.

Effects of acetyl-strophanthidin on left ventricular function and ventricular arrhythmias

Digitalis drugs can suppress ventricular arrhythmias. It is uncertain whether this effect results from improved left ventricular (LV) function. We utilized radionuclide scanning techniques to evaluate changes in LV ejection fraction (EF) after an infusion of acetyl-strophanthidin in 43 patients with frequent ventricular premature beats (VPBs) (44 to 2400/hr). Acetyl-strophanthidin suppressed ventricular arrhythmia in 17 patients, but LVEF increased in only six of these patients (57% to 67%), while it was unaltered in 11 patients (28% to 30%). In 26 patients ventricular arrhythmia was not suppressed. Fifteen of these patients had an increase in LVEF (60% vs 71%), while this was unchanged in 11 patients (27% vs 29%). Thus no correlation was observed between the positive inotropic and antiarrhythmic action of acetyl-strophanthidin on ventricular arrhythmia and LVEF. We conclude that the suppression of VPBs by acetyl-strophanthidin is independent of the drug's effects on LV function. Evidence is reviewed suggesting that the antiarrhythmic effect of acetyl-strophanthidin on ventricular ectopic activity is due to its vagotonic action.

Effects of oral digoxin on ventricular ectopy and its relation to left ventricular function

The ventricular antiarrhythmic properties of oral digoxin were examined in 13 patients with chronic ventricular ectopy using serial 24-hour electrocardiographic monitoring. Mean premature ventricular complex frequency (per 1,000 normal beats) decreased from 56 +/- 47 during the placebo period to 40 +/- 27 (p = not significant [NS]) and 25 +/- 17 (p less than 0.05) during daily administration of digoxin, 0.25 and 0.375 mg. Digoxin had no significant effect on the qualitative occurrence of complex ventricular arrhythmia patterns (multiformity, bigeminy, couplets, ventricular tachycardia). Radionuclide left ventricular (LV) ejection fraction was measured during the placebo period. Seven patients had normal (ejection fraction greater than 50%) and 6 abnormal global LV performance. In the normal group, the mean premature ventricular complex frequency decreased from 69 +/- 58 to 20 +/- 18 (p less than 0.05) and the mean couplet frequency decreased from 0.59 +/- 0.85 to 0.07 +/- 0.06 (p less than 0.04) during the placebo and 0.375 mg digoxin dosing periods, respectively. In contrast, no significant changes in either variable occurred after digoxin in subjects with depressed LV function. This study indicates that oral digoxin is moderately effective in suppressing premature ventricular complexes, and that its effects are greatest in patients with normal overall LV performance.

Pharmacologic treatment of cardiac arrhythmias: 25 years of progress

This review of practical and theoretical advances in antiarrhythmic drug therapy consists of four parts. Part 1, on clinical applications, compares the approaches to treatment 25 years ago with those of today, examines the current status of antiarrhythmic drugs used 25 years ago, reports on drugs approved for clinical use during the past 25 years, reviews new experimental drugs and suggests an approach to classification of antiarrhythmic drugs. Part 2 summarizes the contributions of cellular electrophysiology to the understanding of drug action, with emphasis on the drug-induced block of the voltage- and time-dependent properties of the rapid sodium channel. The subsequent section contains a brief discussion of the impact made by the new knowledge and the new diagnostic technology on the contemporary practices. The main conclusions are 1) that the more rational approach to treatment has benefited proportionately more patients with supraventricular than with ventricular arrhythmias, and 2) that new advances have made it possible to design successful treatments for certain patients with problems that could not be resolved in the past.

An "autonomic" classification of antiarrhythmic drugs

An alternative classification schema for antiarrhythmic drugs is proposed based primarily on the autonomic "side effects" of these drugs in addition to their electrophysiologic actions. In this new schema, Class I (local anesthetics) is subdivided into 1A (quinidine-like agents with cholinergic blocking actions) and 1B (agents such as lidocaine without autonomic activity). Class II comprises the digitalis glycosides which have vagotonic effects. Class III contains drugs with antiadrenergic activity, subdivided into IIIA (beta-blockers such as propranolol), IIIB (norepinephrine-release inhibitors such as bretylium) and IIIC (non-specific adrenergic blockers such as amiodarone). Class IV includes the calcium channel blockers. Thus, with the exception of Classes IB and IV, all antiarrhythmics possess important autonomic properties. A possible link between autonomic and electrophysiologic effects is suggested by this schema. Classical pharmacologic theory separates the anticholinergic and membrane-active effects of quinidine-like (1A) drugs. An alternative theory is that the anticholinergic effects of 1A agents are germane to the antiarrhythmic actions of drugs in this class. A unifying hypothesis is that the acetylcholine receptor or a site with similar structure may participate directly in the binding of 1A drugs to the ventricular conduction system. This hypothesis is supported by: 1) the anti-muscarinic effects of all Class 1A agents; 2) previous data showing binding of these agents to atrial cholinergic receptors; 3) prominent His-Purkinje cholinergic innervation; 4) striking structural similarity between cocaine, the prototypical membrane anesthetic, and atropine; and 5) quinidine-like effects of tricyclic antidepressants and phenothiazines which have cholinergic properties. Additional ramifications of this autonomic classification are discussed.

Long-term survival of patients with malignant ventricular arrhythmia treated with antiarrhythmic drugs

The protective effect of antiarrhythmic agents for patients with malignant ventricular arrhythmia (defined as noninfarction ventricular fibrillation or sustained hemodynamically compromising ventricular tachycardia) remains uncertain. We have analyzed survival among 123 such patients (98 males, 25 females, average age 53.6 years) dependent on the abolition of antiarrhythmic drugs of salvos of ventricular tachycardia and R-on-T ventricular premature beats (Lown grades 4B and 5). Over an average follow-up of 29.6 months there were 35 deaths (11.2 percent annual mortality rate) of whom 23 patients succumbed suddenly (8.2 percent annual mortality rate). Among 98 patients in whom antiarrhythmic drugs abolished grades 4B and 5 ventricular premature beats, only 6 sudden deaths occurred for a 2.3 percent annual mortality rate. Of the 25 patients in whom advanced ventricular premature beats were not controlled, 17 died suddenly. Seventy-nine patients had left ventricular studies suitable for analysis. Among 44 patients with left ventricular dysfunction, control of ventricular premature beats was a critical element predicting survival. The annual sudden death rate for the 12 noncontrolled patients with left ventricular dysfunction was 41 percent contrasting with only 3.1 percent for the 32 patients with similar abnormalities in ventricular function in whom advanced ventricular premature beats were abolished. It is concluded that antiarrhythmic drugs can protect against the recurrence of life-threatening arrhythmias in patients who have manifest ventricular fibrillation or ventricular tachycardia and that abolition of certain advanced grades of ventricular premature beats provides an effective therapeutic objective.

Management of patients at high risk of sudden death

Patients who experience malignant ventricular arrhythmias (i.e., ventricular fibrillation or ventricular tachycardia with syncope or with hemodynamic compromise) are at high risk of sudden death. Such patients can now be protected from recurrent arrhythmias by the use of conventional and experimental drugs. Drug therapy must be individualized, and this requires a system of testing to expedite the selection of the most efficacious and least toxic agent. In 85% of these patients, the frequency and advanced grades of ventricular premature beats exposed either by Holter monitoring or by maximal exercise stress testing provide an adequate target for assessing drug action. Only 15% of patients require invasive electrophysiologic studies to guide antiarrhythmic therapy. In 10% of instances, antiarrhythmic drugs cause aggravation of arrhythmias. When drug therapy is individualized, an effective program can be achieved for 80%, with less than a 3% incidence of sudden death annually.

Digoxin uptake into peripheral autonomic cardiac nerves: possible mechanism of digitalis-induced antiarrhythmic and toxic electrophysiologic actions

It is generally accepted that certain cardiac rhythm disturbances are due to imbalances between the sympathetic and parasympathetic nervous systems. We have provided evidence that digoxin is concentrated in the peripheral nervous system of the heart as well as in the central nervous system. Previous findings have indicated that cardiac glycosides may directly or indirectly affect autonomic neurotransmitters. Therefore the uptake of digoxin into the peripheral cardiac nervous system may play an important role in both the antiarrhythmic and toxic electrophysiologic actions of digoxin.

Valsalva termination of ventricular tachycardia

Nine patients with recurrent ventricular tachycardia (VT) that could be repeatedly terminated by a Valsalva maneuver are described. In two, the tachycardia would cease for only a few seconds and then resume, whereas in seven, the tachycardia could be permanently and reproducibly terminated with a Valsalva maneuver. In all patients the tachycardia ended during the strain phase of the Valsalva maneuver, when blood pressure and radiographic measurement indicated that cardiac dimensions had been reduced dramatically. The speed with which the Valsalva maneuver terminated VT incresed in direct proportion to the strain pressure. Maneuvers such as standing or nitroglycerin, which independently reduce cardiac dimensions, enhanced the potency of the Valsalva maneuvers. Pretreatment with atropine or propranolol in four patients did not alter the response of VT to the Valsalva maneuver. Thus, it appears that a strong Valsalva maneuver can terminate some forms of VT, most likely related to an abrupt reduction in cardiac dimensions.

Digitalis drugs and vulnerability to ventricular fibrillation

The effect of acetylstrophanthidine (AS), a rapid-acting digitalis-like agent, on the ventricular fibrillation (VF) threshold was examined in normal and denervated chloralose-anesthetized dogs. In neurally intact dogs an intravenous bolus of AS (0.075 mg/kg) increased the VF threshold up to a maximum 50% (P less than 0.01) within 30 min after injection. The augmented VF threshold following intravenous administration of AS was not altered by vagotomy. Bilateral stellectomy in vagotomized dogs, as well as carotid sinus and aortic arch denervations, however, prevented the AS induced increase in VF threshold. In neurally intact dogs beta-adrenergic blockade with propranolol (0.25 mg/kg) precluded AS effects. These data suggest that the increase in the VF threshold resulting from AS administration in the normal canine ventricle is due to withdrawal of sympathetic tone mediated via the baroreceptor reflex. The direct effect of AS on the myocardium is to decrease the VF threshold.

Antiarrhythmic drug effect mimicked by spontaneous variability of ventricular ectopy

Twenty patients with frequent ventricular ectopic beats had a 5 1/2 hour ECG rhythm strip recorded. Individual patients showed a marked spontaneous variability from one half-hour to the next in the total number of ectopic beats (-99% to +1100%) and the occurrence of pairs or salvos. Although no patient received antiarrhythmic drugs, some patients showed a spontaneous change in arrhythmia which mimicked either drug suppression or drug-induced worsening of arrhythmias. If an antiarrhythmic drug had been given to these patients after the first half-hour, 65% would have been termed "drug responders," using the criteria of 50% reduction in ectopic beats and elimination of pairs or salvos during any half-hour period in the subsequent three hours. Spontaneous variability in ventricular ectopic beats causes serious problems when using ECG monitoring to evaluate antiarrhythmic drug response in individual patients. The arrhythmias averaged for the entire group remained stable during the recording period. Evaluating antiarrhythmic drugs by examining group response rather than individual patient response minimizes the effect of spontaneous variability.

A mathematical model of parasystole and its application to clinical arrhythmias

A ventricular parasystolic focus capable of generating manifest ectopic beats should not be totally insulated from the electrical events that accompany depolarization in the surrounding tissue; the intrinsic cycle length of the ectopic discharge may be modulated by electrotonic influences transmitted across the zone of "protection." To study the nature of the interaction, response patterns were examined in a mathematical model programmed to simulate an ectopic pacemaker protected, but not divorced from ventricular responses to the normal pacemaker. Computer runs covered a wide range of heart rates, and a wide range of magnitudes of the simulated electrotonic influence. Application of the results obtained in the model to published examples of complex arrhythmias revealed a remarkably close fit to many clinical examples. This findings suggests that many patterns attributed to a re-entrant "extrasystolic" rhythm may, in fact, represent the modulated activity of a parasystolic focus.

The assessment of an antiarrhythmic agent, sustained-release procainamide, with the aid of Holter monitoring

A sustained-release preparation of procainamide (PAD) was evaluated in a double-blind cross-over study. The preparation was found to reduce ventricular ectopic activity in all seven patients who completed the investigation in five patients the effectiveness reached the defined level of significance. A larger clinical trial to assess the long-term use of this preparation in terms of efficacy, safety and convenience is recommended.

Management of patients with malignant ventricular arrhythmias

The patient with recurrent malignant ventricular arrhythmias (ventricular fibrillation or ventricular tachycardia with syncope) presents a complex therapeutic problem. To examine this problem, a study was made of 43 consecutive patients with such arrhythmias (mean age 54 years for the 33 men and 43 years for the 10 women). Arrhythmias were not precipitated by either remediable clinical conditions or acute myocardial infarction. The population was divided into two nonrandomized groups based on the type of therapeutic intervention employed. The 26 patients in Group 1 (20 with ventricular fibrillation, 6 with ventricular tachycardia) were subjected to a systematic attempt to select two independently effective antiarrhythmic drugs. Acute drug testing was followed by drug usage over 48 to 72 hours with drug efficacy determined with use of ambulatory monitoring and exercise stress. The 17 patients in Group 2 (10 with ventricular fibrillation, 7 with ventricular tachycardia) received standard antiarrhythmic therapy based on clinical factors and "therapeutic" blood drug concentrations. Twenty-four of 26 patients in Group 1 (92 percent) demonstrated control of arrhythmias and are alive at a mean follow-up period of 17 months. Of 121 drug tests, 47 (39 percent) were effective, 58 (48 percent) were ineffective and 16 (13 percent) provoked major adverse effects. The most effective combination of drugs involved a beta adrenergic blocking agent, a cardiac glycoside and quinidine. Ten of 17 patients in Group 2 (59 percent) have died after a mean follow-up period of 14.8 months. Elements of a successful management program are outlined.

Neural and psychologic mechanisms and the problem of sudden cardiac death

Brain stimulation can provoke a variety of arrhythmias and lower the ventricular vulnerable threshold. In the animal with acute myocardial ischemia such stimuli suffice to provoke ventricular fibrillation. Vagal neural traffic or adrenal catecholamines are not the conduits for this brain-heart linkage. Accompanying increases in heart rate or blood pressure are not prerequisites for the changes in cardiac excitability. Increased sympathetic activity, whether induced by neural or neurohumoral action, predisposes the heart to ventricular fibrillation. Protection can be achieved with surgical and pharmacologic denervation or reflex reduction in sympathetic tone. With acute myocardial ischemia, augmented sympathetic activity accounts for the early surge of ectopic activity frequently precipitating ventricular fibrillation. Asymmetries in sympathetic neural discharge may also contribute to the genesis of serious arrhythmias. The vagus nerve, through its muscarinic action, exerts an indirect effect on cardiac vulnerability, the consequence of annulment of concomitant adrenergic influence, rather than of any direct cholinergic action on the ventricles. There exist anatomic, physiologic as well as molecular bases for such interactions. Available experimental evidence indicates that environmental stresses of diverse types can injure the heart, lower the threshold of cardiac vulnerability to ventricular fibrillation and, in the animal with coronary occlusion, provoke potentially malignant ventricular arrhythmias. Available evidence indicates that in man, as in the experimental animal, administration of catecholamines can induce ventricular arrhythmia, whereas vagal activity exerts an opposite effect. Furthermore, in certain subjects diverse stresses and various psychologic states provoke ventricular ectopic activity.