Neural and psychologic mechanisms and the problem of sudden cardiac death

Cognitive processes and recovery from heart attack: a review and theoretical analysis

A review of the literature on psychosocial aspects of recovery from heart attack is presented with emphasis on psychological responses experienced by the patient. Several theoretical models have previously been proposed to explain these data: a psychodynamic view stressing the importance of denial as a coping mechanism, and a second perspective emphasizing patients' beliefs about their health status. A third model is proposed based on cognitive appraisal processes (perceived control and predictability) shown experimentally to mediate reactions to stressors in a wide variety of situations. Viewing heart attack as a crisis situation, it is assumed that particular aspects of illness will generally have a less negative impact on physiological and behavioral health outcomes to the extent they are perceived to be predictable and/or controllable. Specific interventions to alter these perceptions are discussed, and mechanisms linking various recovery outcomes are proposed. The validity of this model is examined with reference to existing research and suggestions for future research are made.

Cardiovascular responses to emotional stress (quiz interview) in post-myocardial infarction patients and matched control subjects

In this investigation, 30 male post-myocardial infarction patients and 30 male control subjects matched according to age and occupation were given a 12-minute tape-recorded stress quiz described by Schiffer et al. Cardiovascular responses (electrocardiogram, heart rate, systolic, blood pressure, and diastolic blood pressure) to emotional stimuli were monitored in a laboratory setting at rest before the quiz and at two-minute intervals during the quiz. Heart rate and blood pressure values were significantly higher during the quiz than at rest for both patient and control groups. There was a significantly higher response for diastolic pressure and a significantly lower response for heart rate in the patient group compared with the control group. In the analysis for occupational status in the entire population, systolic pressure was significantly higher for the executives than for non-executives. Subgroup analyses of patients with angina, hypertension and/or ECG changes (N = 12) revealed a significantly higher diastolic pressure response than found in either the patients without these symptoms (N = 18) or in the controls (N = 30). In comparison to exercise test results, the emotional stress test (quiz) elicited somewhat more PVC's but less ST segment depression. These results support previous reports suggesting that emotional stress testing may be a valid tool in the diagnosis of coronary heart disease and in determining the physiological mechanisms which underlie the association between emotional stress and coronary heart disease.

Retirement and coronary mortality

Information on several variables, including occupational history and various coronary risk factors, was collected from the wives of 568 married men who died of coronary heart-disease (CHD) and an equal number of matched control subjects. The crude matched-pair relative risk of fatal CHD among men who retired compared with non-retirees was 2.9 (95% confidence limits from 1.9 to 4.9). After adjustment for age and history of hospitalisation for myocardial infarction by means of a paired multiple-logistic regression analysis the relative risk was reduced to 1.8 (range 1.0 to 3.3). These data suggest that retirement and subsequent coronary mortality may be linked.

Ethmozin, a new antiarrhythmic drug for suppressing ventricular premature complexes

Ethmozin, a phenothiazine derivative, is an antiarrhythmic drug synthesized in the USSR. Preliminary data suggest that it is effective against a diversity of ectopic arrhythmias. The present study, carried out in the USSR, was designed to assess efficacy and patient tolerance of this new drug. Thirty-seven patients with chronic, persistent, frequent and symptomatic ventricular premature complexes (VPCs) were studied. VPCs were exposed by means of 24-hour ambulatory monitoring and exercise stress testing. Two drug schedules were used. Group 1, consisting of 11 patients, received 225 mg/day of ethmozin, while group 2, consisting of 26 patients, received 600 mg/day. Acute drug testing with a single large dose of ethmozin was followed by multiple dosing for a minimum of 4 days. Placebo was given in a single-blind fashion only to responders. Only two patients in group 1 had a significant reduction in VPCs as evaluated by both monitoring and exercise testing. Fourteen patients in group 2 (54%) showed striking suppression of VPCs. Mild and transiet effects were encountered in only four of the 37 patients. We conclude that ethmozin appears to be a well-tolerated, relatively effective agent for controlling VPCs.

Electrophysiologic studies of perphenazine and protriptyline in a patient with psychotropic drug-induced ventricular fibrillation

A 51 year old woman sustained ventricular fibrillation while receiving perphenazine and protriptyline. After successful resuscitation and clinical stabilization, cardiac electrophysiologic studies were performed before and after the administration of each of these medications. Perphenazine widened the ventricular echo zone and facilitated induction of short salvoes of ventricular tachycardia (repetitive ventricular response). Protriptyline also widened the ventricular echo zone and allowed easy induction of long runs of ventricular tachycardia. Both psychotropic agents increased the incidence of ventricular dysrhythmias in this patient. The electrophysiologic study is a useful technique in determining the interaction between psychotropic drugs and life-threatening arrhythmias; it may provide a means of identifying the patients with cardiac disease in whom administration of these agents may be fatal.

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.

Sudden unexpected cardiac death--a practical approach to the forensic problem

Sudden cardiac death can usually be resolved by the pathologist into ischaemic heart disease, non-vascular cardiac disease such as aortic stenosis or hypertrophic obstructive cardiomyopathy and infrequently a morphologically normal heart on naked eye examination. When ischaemic heart disease is present one third of cases have a recent occlusive coronary artery thrombosis. Two thirds of patients have coronary stenosis only; the minimum degree of disease reasonably associated with sudden death is one area of 85% stenosis. The majority of patients, however, have multiple areas of stenosis. The predominant causes of non-ischaemic sudden death are severe LV hypertrophy, hypertrophic obstructive cardiomyopathy and the prolapsing mitral valve syndrome. Where the heart and coronary arteries are morphologically normal, review of any previous ECG's, a family history and histological examination of the myocardium and conduction system may reveal a cause or at least allow a reasonable assumption of cardiac arrhythmia to be made. Sudden unexpected death where the circumstances strongly suggest a cardiac cause may pose problems for the pathologist. Ischaemic heart disease (coronary atherosclerosis) is undoubtedly the most frequent cause but even when this is so the detailed pathology is controversial. It is when coronary artery disease is conspicuously absent, often in young individuals previously in good health, that a problem exists. Sudden death in infancy (cot death) is a different entity with its own problems and is not here discussed further.

Ventricular arrhythmias during exercise testing, jogging, and sedentary life: a comparative study of healthy physically active men, healthy sedentary men, and men with previous myocardial infarction

The occurrence of ventricular arrhythmias during exercise testing, jogging, and sedentary life with and without preceding exercise was studied with the aid of ambulatory electrocardiographic monitoring in healthy physically active men, healthy sedentary men, and men with previous myocardial infarction (15 men in each group). Ventricular premature beats of the same grade were found during exercise testing and jogging in ten of the 15 healthy physically active men, in ten of the 15 healthy sedentary men, and in eight of the 15 men with previous myocardial infarction. When unifocal ventricular premature beats were omitted, the corresponding figures were 14/15, 11/15, and 15/15, respectively. Healthy physically active men had less ventricular arrhythmias in all of the tested situations. The greatest number and also the highest grades of ventricular arrhythmias during the exercises were found in healthy sedentary men, whereas the men with previous myocardial infarction had ventricular arrhythmias more during sedentary life.

Acetylcholine antagonism of the electrophysiological effects of isoproterenol on canine cardiac Purkinje fibers

The purpose of these experiments was to determine whether or not acetylcholine modulated the electrophysiological effects of isoproterenol on canine cardiac Purkinje fibers. Conventional microelectrode techniques were used. Predictably, isoproterenol produced shortening of action potential duration; acetylcholine significantly blunted this effect of isoproterenol. Isoproterenol restored excitability to fibers exposed to 22 mM potassium solutions, and acetylcholine abolished this isoproterenol-restored excitability. Both of these antagonistic effects of acetylcholine were blocked by atropine. Acetylcholine alone did not affect action potential duration in polarized fibers or excitability in potassium-depolarized fibers. Furthermore, acetylcholine had no effect on the decrease in action potential duration induced by premature electrical stimulation or by acetylstrophanthidin administration, or on excitability of fibers exposed to a zero sodium, high calcium superfusant. These data demonstrate a direct cellular basis for cholinergic antagonism of the electrophysiological effects of beta-adrenergic stimulation of canine cardiac specialized intraventricular conducting tissue.

Comparison of the effects of sleep, exercise and autonomic drugs on ventricular extrasystoles, using ambulatory monitoring of electrocardiogram and electroencephalogram

Ambulatory monitoring of the electrocardiogram (ECG) and the electroencephalogram (EEG) in 12 untreated patients with frequent ventricular extrasystoles showed a significant decrease in both ventricular extrasystoles and heart rate during sleep. The decrease in ventricular extrasystoles correlated more closely with the change in heart rate than with the level of arousal. During wakefulness, similar changes in ventricular extrasystoles and heart rate could be produced by the intravenous administration of propranolol and, to a lesser extent, by phenylephrine. Exercise produced an initial increase in ventricular extrasystoles, with suppression at higher levels in most patients. Thus, the frequency of ventricular extrasystoles is usually reduced at both extremes of heart rate, and the changes that occur during sleep can be explained by autonomic mediation, with the sympathetic limb of the autonomic nervous system having a greater effect than the vagus.

Limitations of routine long-term electrocardiographic monitoring to assess ventricular ectopic frequency

Variations in the frequency of ventricular premature depolarizations (VPDs) were evaluated with three consecutive 24-hour long-term electrocardiography monitor recordings from 15 clinically stable patients with various cardiac disorders. Mean hourly VPD frequencies ranged from 37--1,801 per hour. Data were subjected to 4 and 5 factor nested analyses of variance. The extent of spontaneous variation in arrhythmia frequency that occurred in individual patients from day to day was 23%, between 8-hour periods within days was 29%, and from hour to hour was 48%. In addition, the variability between repeated three-day monitoring periods over time was quantified in five patients and found to be 37%. This analysis determined that to distinguish a reduction in VPD frequency attributable to therapeutic intervention rather than biologic or spontaneous variation alone required a greater than 83% reduction in VPD frequency if only two-24-hour monitoring periods were compared, and greater than 65% reduction if two 72-hour periods were compared. The limitations of routine 24-hour electrocardiographic monitoring must be considered in diagnostic and therapeutic decision-making.

Roles of psychologic stress and autonomic nervous system changes in provocation of ventricular premature complexes

Neural and psychologic factors have been implicated as risk factors for ventricular arrhythmias and sudden death in man. However, the relation between these factors and arrhythmia has hitherto not been systematically explored. We examined the effect of psychologic stress testing in 19 patients with advanced grades of ventricular arrhythmias. Psychologic stress consisted of mental arithmetic, reading from colored cards and recounting emotionally charged experiences. Such testing induced a significant increase in ventricular premature beat frequency in 11 of 19 patients (P less than 0.05). One patient experienced paroxysms of ventricular tachycardia. In 14 of these 19 patients elicitation of vagal or sympathetic autonomic reflexes failed to induce significant arrhythmia in all but one patient. It is concluded that (1) objective psychologic tests may precipitate ventricular arrhythmia in susceptible patients, and (2) evocation of peripheral autonomic reflexes is an insufficient trigger for enhanced ventricular ectopic activity.

Effect of electroconvulsive therapy on cardiac rhythm, conduction and repolarization

Because sympathetic stimulation has been implicated in the genesis of arrhythmias, we studied the effects on arrhythmias of electroconvulsive therapy (ECT). Fifteen psychiatric patients (male: 8, female: 7, age: 19-51, mean: 29.8) without known heart disease underwent 24-hout Holter recordings before, during, and after ECT (25 episodes). All patients were taking psychotropic drugs and received atropine (0.4-1.2 mg, mean: 1.1 mg IV), methohexital, and succinylcholine prior to ECT. Following ECT, mean maximum heart rate increased (106 +/- 3.2 to 142 +/- 6.0 beats/min, p less than .001), PR interval decreased (149 +/- 3.3 to 131 +/- 3.7 msec, p less than .001) and QTc interval increased (132 +/- 6.5 to 454 +/- 9.7 msec, p less than .001) compared to values obtained after atropine administration. Mean PVC or PAC frequently immediately after ECT or per 24 hours did not change significantly (PVC per 24 hours 6.8 +/- 3.2 to 10.4 +/- 6.4, NS; PAC per 24 hours 0.4 +/- 0.3 to 0.3 +/- 0.2, NS) and no complex arrhythmias were noted. Rate and PR changes suggest adrenergic effects of ECT and QTc increase may be due to imbalanced sympathetic discharge. Autonomic stimulation produced by ECT did not induce arrhythmias in these patients without heart disease. The possible antiarrhythmic role of psychotropic agents or premedication is unknown.

Central neurochemical factors related to serotonin metabolism and cardiac ventricular vulnerability for repetitive electrical activity

Sympathetic neural activity modifies cardiac excitability and lowers the threshold of the vulnerable period for ventricular fibrillation. Sympathetic neural traffic to the heart can be diminished by administering serotonin precursors that localize in the central nervous system. In this study anesthetized dogs were injected with either of the serotonin precursors L-tryptophan or 5-hydroxy-L-tryptophan in conjunction with the monoamine oxidase inhibitor pheneizine and the selective peripheral L-amino acid decarboxylase inhibitor carbidopa. Ventricular vulnerability was evaluated by measuring the repetitive extrasystole threshold. A sustained increase of 50 percent in this threshold resulted only with use of biochemical measures that presumably increase serotonin levels in the central nervous system. Thus neuropharmacologic measures affecting central sympathetic activity alter cardiac vulnerability and may protect against ventricular fibrillation.

Derangements of myocardial metabolism preceding onset of ventricular fibrilliation after coronary occlusion

To determine alterations in myocardial metabolism and and hemodynamics that occur within the first 30 minutes after coronary arterial occlusion, before the onset of ventricular fibrillation, measurements were compared in two series of dogs. Series A, 90 dogs that did not manifest ventricular fibrillation after coronary occlusion, were considered a control group. Series B consisted of 28 dogs that had ventricular fibrillation within 30 minutes after occlusion. All had similar comprehensive measurements completed preceding the onset of ventricular fibrillation. The animals in series B (subseuqnt fibrillation) had significantly higher heart rates before and after coronary occlusion. In this series cardiac metabolism of the occluded segment judged by transmyocardial lactate extraction, potassium balance, sodium/potassium ratio and blood pH because grossly more abnormal after coronary occlusion than in series A. In 5 animals whose measurements were obtained within 5 minutes of the onset of ventricular fibrillation, a sudden massive lactate production, potassium loss and increased acidosis of the occluded portion supervened minutes before the onset of the fatal arrhythmia. Animals with ventricular fibrillation had higher intracoronary S-T segment elevation that persisted until the onset of ventricular fibrillation. Measurements of abnormal hemodynamic function (left ventricular end-diastolic pressure, peak systolic pressure and first derivative of left ventricular pressure [DP/dt]) were not associated with an increased incidence of ventricular fibrillation. The study indicates that animals that manifest ventricular fibrillation within 30 minutes after coronary occlusion have higher preocclusion heart rates, a more severe metabolic disorder of the coronary occluded segment and more persistent intracoronary S-T segment elevation compared with animals that do not manifest ventricular fibrillation.