Identification of sudden death risk factors in acute and chronic coronary artery disease

QT interval in relation to ventricular arrhythmias and sudden cardiac death in postmyocardial infarction patients

Ninety-one consecutive patients below the age of 70 years were subjected to a 60-second resting ECG and 24-hour ambulatory ECG monitoring two weeks and one, three and six months after an acute myocardial infarction. The corrected QT (QTc) interval decreased from the late hospital phase to the investigations three and six months after the infarction (p less than 0.01, less than 0.05). ECG monitorings showing complicated ventricular ectopic beats (multiform, repetitive, R-on-T) were associated with an insignificantly longer QTc than other recordings. Eleven patients suffered a sudden cardiac death during a median follow-up period of 24 months (range 22-27). The QTc intervals in patients who died suddenly were insignificantly longer than in the survivors. Only four patients, who all survived, had a constantly prolonged QTc. After exclusion of tracings during quinidine therapy, a QTc longer than 440 msec was found in 7 (23%) of 31 recordings from patients who suffered a sudden cardiac death compared to 29 (10%) of 287 recordings from the survivors (p less than 0.05). A combination of complicated ventricular ectopic beats and a QT longer than 440 msec was demonstrated in 5 (16%) of 31 and 14 (5%) of 287 recordings from the two groups of patients (p less than 0.05). A trend towards longer QTc intervals was observed in patients with complicated ventricular arrhythmias and in those who died suddenly, but no well defined high-risk groups could be identified.

Assessment, significance and mechanism of ventricular electrical instability after myocardial infarction

The mechanism of reentrant tachycardia was established nearly a century ago, but the relationships between myocardial infarction and predisposition to sudden death were not unravelled until much later. In the latter half of the twentieth century many studies sought to ascertain what variables were predictive of death following myocardial infarction. Approximately one half of all deaths during the year following myocardial infarction are sudden and due to ventricular tachycardia (VT) or ventricular fibrillation (VF). We aimed to utilise non-invasive signal-averaging, along with programmed electrical stimulation of the heart, to determine whether one could predict spontaneous ventricular tachycardia and sudden death late after myocardial infarction. The sensitivity of ventricular electrical instablility (inducible ventricular tachycardia or fibrillation) as a predictor of instantaneous death or spontaneous VT was 86%, and the specificity was 83%. When other variables (delayed ventricular activation at signal-averaging, ejection fraction at gated heart pool scan, ventricular ectopic activity at ambulatory monitoring and exercise testing) were taken into account, inducible VT at electrophysiological study was the single best predictor of spontaneous VT and sudden cardiac death after myocardial infarction. The Westmead studies of Uther et al. in the decade or so from 1980 established programmed stimulation as the best predictor of sudden death after myocardial infarction. Subsequent studies by others have demonstrated a survival advantage of defibrillator implantation in patients with low ejection fraction (and inducible ventricular tachycardia) after myocardial infarction.

Risk stratification using heart rate turbulence and ventricular arrhythmia in MADIT II: usefulness and limitations of a 10-minute holter recording

BACKGROUND

We evaluated the usefulness of heart rate turbulence (HRT) parameters and frequency of ventricular premature beats (VPBs) for risk-stratifying postinfarction patients with depressed left ventricular function enrolled in Multicenter Automatic Defibrillator Trial II (MADIT II).

METHODS

In 884 MADIT II patients, 10-minute Holter monitoring at enrollment was used to evaluate HRT parameters and frequency of VPBs. The primary endpoints were defined as all-cause mortality in patients randomized to conventional treatment and as appropriate therapy for ventricular tachycardia or fibrillation in patients randomized to implantable cardioverter defibrillator (ICD) therapy.

RESULTS

The median turbulence slope was lower in patients who died in comparison to survivors in the conventional arm (2.3 vs 4.5 ms/RR; P < 0.05); but it was not a significant predictor of mortality after adjustment for clinical covariates (age, ejection fraction, beta-blocker use, and BUN levels). There was no association between HRT parameters and arrhythmic events in ICD patients. Conventionally treated patients who died and ICD patients who had appropriate ICD therapy had significantly more frequent VPBs than those without such adverse events. After adjustment for clinical covariates, frequent VPBs>3/10 min were associated with death in the conventional arm (HR = 1.63; P = 0.070) and were predictive for appropriate ICD therapy in the ICD arm (HR = 1.75; P = 0.003).

CONCLUSION

In postinfarction patients with severe left ventricular dysfunction, frequent VPBs are associated with increased risk of mortality and with appropriate ICD therapy. HRT obtained from 10-min Holter ECG showed a trend toward the association with mortality in univariate analysis but HRT parameters were not predictive of the outcome in multivariate analyses.

The prognostic significance of very low frequency ventricular ectopic activity in survivors of acute myocardial infarction. BHAT Study Group

Survivors of myocardial infarction with less than 2 PVC/h on 24-h ambulatory electrocardiography were followed up for an average of 25 months (11 to 40 months) while receiving a placebo (1,222 patients) or propranolol, 180 or 240 mg/day (1,234 patients). Three quarters of the participants with PVCs had an average of less than 2 PVC/h. Only 16 percent did not have any ventricular ectopic activity during the 24 h. Analysis of total mortality according to the number of premature ventricular complexes per hour showed that patients who had PVCs with a very low frequency (less than 0.5/h) had 49 percent higher mortality than patients who did not have any PVC. Patients who had greater than 0.5 PVC/h but less than 1 PVC/h had a statistically significant higher mortality rate, 11.7 vs 4.1 percent (p less than 0.0001) than patients who had no PVC. These data indicate that low ventricular ectopic activity frequency is associated with increased mortality in survivors of acute myocardial infarction.

Results of Electrophysiological Testing and Long-Term Follow-Up in Patients Sustaining Cardiac Arrest Only While Receiving Type IA Antiarrhythmic Agents

Therapeutic management of patients sustaining a cardiac arrest while receiving antiarrhythmic agents can be difficult since the role of the drug in possibly facilitating the arrhythmia is often difficult to define. To determine if the response to programmed stimulation could give insight into which patients may have experienced a drug-induced cardiac arrest, we studied 29 patients (61 +/- 9 years) with no prior history of sustained ventricular tachyarrhythmias (VT) who suffered a cardiac arrest only while receiving type Ia antiarrhythmic agents. Patients with documented myocardial infarction, acute ischemia, electrolyte abnormalities, or torsade de pointes were excluded from the study. Twenty-four patients had coronary artery disease with prior myocardial infarction (ejection fraction 28% +/- 9%) and five patients had idiopathic dilated cardiomyopathy (ejection fraction 31% +/- 6%). During baseline electrophysiological testing, 19 patients (66%) had inducible sustained ventricular arrhythmias: uniform VT, n = 14 (group I), polymorphic VT or ventricular fibrillation, n = 5 (group II). Ten patients (group III) had no inducible sustained ventricular arrhythmias. To determine if rechallenge with a type Ia agent could facilitate induction of a sustained ventricular arrhythmia in group III, eight patients underwent ten electrophysiological studies during therapy with either procainamide or quinidine. Only two patients developed sustained VT in response to programmed stimulation. Patients in groups I and II received therapy guided by electrophysiological testing, including antiarrhythmic agents alone (n = 8), subendocardial resection (n = 4), or an implantable cardioverter defibrillator (n = 7). Patients in group III received antiarrhythmic agents empirically (n = 3), or for treatment of atrial tachyarrhythmias (n = 2) or nonsustained VT (n = 1). In addition, four patients in group III received an implantable cardioverter defibrillator. During a mean follow-up of 28 +/- 27 months (range: 1 day-84 months) 13 patients died suddenly or received a defibrillator shock preceded by syncope or presyncope: group I: n = 5; group II: n = 2; group III: n = 6.

IN CONCLUSION

(1) most patients sustaining a cardiac arrest only in the presence of type Ia antiarrhythmic agents have inducible sustained VT in the absence of antiarrhythmic agents, and (2) the risk of recurrent VT persists in patients without inducible sustained arrhythmias in the drug-free state, regardless of whether they manifest inducible arrhythmias after rechallenge with a type Ia agent.

Anti-arrhythmic properties of the alpha-adrenoceptor blocking drug indoramin

1. The anti-arrhythmic properties of the alpha-adrenoceptor blocking drug indoramin were compared with the effect of disopyramide and placebo in a randomised, single-blind, cross-over study. Two doses of indoramin were tested, 25 mg and 50 mg and the dose of disopyramide was 150 mg. All treatments were administered three times daily. 2. Forty patients with benign ventricular arrhythmia were studied. 3. Assessment was by 24 h ambulatory electrocardiography at entry and at the end of each 2 week treatment period. 4. Indoramin was found to have a significant anti-arrhythmic effect compared with placebo, but only at the higher dose tested. 5. The anti-arrhythmic effect was less than that achieved with disopyramide. 6. The mechanism for this anti-arrhythmic effect is unknown but these results suggest that alpha-adrenoceptor blockade may merit further attention as an anti-arrhythmic treatment.

Coronary revascularization: influence on ventricular arrhythmias

Myocardial ischemia may cause severe cardiac arrhythmias. In the present study, the influence of revascularization on ventricular arrhythmias was investigated. A total of 68 patients (61 male, 7 female; mean age 53 years) with coronary artery disease was divided into three groups: Group A (21 patients) underwent percutaneous transluminal coronary angioplasty (PTCA); Group B (37 patients) had coronary artery bypass grafting (CABG); and Group C were 10 patients who served as controls, who had simple coronary angiography. All patients had a Holter ECG on the day before angiography. PTCA patients and controls were restudied on the day after the procedure, while in Group B, Holter ECG was repeated three weeks after surgery. Groups A and B were again studied 18 months after the first Holter ECG. The PTCA group showed a slight reduction in complex arrhythmias immediately following PTCA, which increased again after 18 months; the CABG group, however, revealed a significant increase in complex arrhythmias three weeks after bypass surgery, but a decrease after 18 months. There was no significant change in the control group before or after angiography. Thus, successful revascularization has no influence on ventricular arrhythmias after 18 months.

Features of cardiac arrest episodes with and without acute myocardial infarction in the Coronary Artery Surgery Study (CASS)

Angiographic evidence of coronary artery disease was present in 16,002 patients in the Coronary Artery Surgery Study (CASS) registry. Of these patients, 551 had a history of cardiac arrest before enrollment angiography. Cardiac arrest was a complication of acute myocardial infarction (AMI) in 372 patients (68%). Electrocardiographic documentation of the responsible rhythm was available in 283 patients. Ventricular fibrillation (VF) was present in 112 (60%), ventricular tachycardia (VT) in 41 (22%) and both VT and VF in 26 (14%) patients. Stepwise linear discriminant analysis comparing the 551 cardiac arrest patients with the other 15,451 patients selected left ventricular wall motion score (F = 265), use of digitalis (F = 71), impaired blood supply to any segment (F = 16) and particularly to the anterior wall (F = 11) as discriminating variables associated with cardiac arrest. Patients with cardiac arrest occurring as a complication of AMI were younger (F = 12), had greater impairment of coronary blood supply (F = 7) and were more likely to be on a cholesterol-lowering diet (F = 16) than were patients with arrest remote from infarction. Comparison of patients with VT versus those with VF showed a positive association of VT with age (F = 8), a trend toward worse left ventricular function and presence of a left ventricular aneurysm, but no difference in severity and collateralization of coronary artery disease. It is concluded that cardiac arrest is related to the extent of myocardial damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias as predictors of sudden death

Two methods are available for exploring arrhythmias in cardiac patients who are at risk of sudden death: Holter monitoring and invasive electrophysiology. Despite numerous studies, the predictive value of these techniques, in terms of prognosis, remains poor for many reasons. Neither technique considered individually can give reliable prognostic indications simply because each technique addresses different issues which are only partially involved in the mechanism of sudden death. Invasive electrophysiology, by artificially provoking an arrhythmia, detects the potential substrate which may ultimately lead to lethal arrhythmias. Although this is an important technique it is insufficient because merely identifying the substrate for an arrhythmia does not necessarily mean that arrhythmia will occur. On the other hand, ambulatory ECG allows monitoring of spontaneous arrhythmias which may be considered as potential initiating factors in arrhythmias. However, even if initiating factors and potential substrates are present, they are not sufficient conditions to cause lethal arrhythmias to occur. When there is an opportunity to scrutinize the mechanism of arrhythmias which are indeed lethal, as in sudden death, it appears that the lethal event results from the intervention of a new factor which was either absent or not considered during preceding investigations. In coronary patients, curiously, ischemia more often provokes cardiac arrest or an electromechanical dissociation rather than a ventricular tachycardia or fibrillation. Sudden death is not infrequently of iatrogenic origin, because of the arrhythmogenic effect of powerful antiarrhythmic drugs. More important, ventricular fibrillation often occurs in the setting of a progressively increased sympathetic tone, which explains either the particular seriousness of a previously known arrhythmia or the occurrence of an arrhythmia which was never before observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognosis of ventricular arrhythmias in relation to sudden cardiac death: therapeutic implications

The hypothesis that ventricular arrhythmias represent an independent predictor of sudden cardiac death was examined by analyzing the published data. The frequency and complexity of ventricular arrhythmias increase progressively both with age and severity of heart disease, but no age- or disease-related norms have been established for clinical guidance. Simple and complex arrhythmias, including short runs of ventricular tachycardia, do not increase risk of sudden cardiac death in subjects without heart disease or with heart disease and normal myocardial function. Progression of nonsustained into sustained ventricular tachycardia in such individuals is rare. Simple and complex ventricular arrhythmias are not strong independent predictors of sudden death in survivors of myocardial infarction. In these, the overall incidence of sudden cardiac death averages 3.5 to 5% during the first year, but is about 15 to 20% per year in patients with severely impaired ventricular function. The results of this survey suggest that in patients with well preserved ventricular function, prophylactic use of antiarrhythmic drugs is not indicated, and that treatment of asymptomatic or mildly symptomatic ventricular arrhythmias is not likely to reduce the incidence of sudden cardiac death.

The proarrhythmic effects of antiarrhythmic drugs

Although antiarrhythmic drugs are effective for controlling cardiac arrhythmias, they may also induce or exacerbate them. Case reports have appeared implicating all classes of antiarrhythmic drugs. It is difficult to assess the size of the problem in practice, as it varies with different subgroups of patients, but rates of up to 13% have been found where proarrhythmic effects were actively sought. Their occurrence is affected both by the electrophysiologic characteristics of the drugs and by the arrhythmia substrate. Mechanisms of proarrhythmic effects may be classified according to the electrophysiologic and hemodynamic effects of the drugs. Detection of drug-induced arrhythmias depends on appreciation of the problem by physicians and, although there are few clear predictors, some form of monitoring of antiarrhythmic drug treatment is recommended. Management of such arrhythmias when they occur involves withdrawal of the offending agent, correcting contributory factors, and reassessing the initial arrhythmia and the strategy for its management.

Prognostic significance of ventricular ectopic activity in survivors of acute myocardial infarction

Twenty-four hour ambulatory electrocardiography was performed on 3,290 survivors of acute myocardial infarction participating in the Beta-Blocker Heart Attack Trial (BHAT). History of myocardial infarction before the qualifying event, congestive heart failure and age were independently associated with the frequency and complexity of ventricular premature beats. Of the 1,640 patients randomized to placebo therapy, 163 died (76 suffered sudden death) during a 25 month average follow-up period. Ventricular ectopic activity was an independent predictor of total mortality after taking into consideration 16 other prognostic factors describing past history, risk factors, physical examination and laboratory investigations. Seven categoric definitions of ventricular ectopic activity predicted mortality, with similar odds ratios ranging from 2.27 to 2.69. A reciprocal relation of the sensitivity and specificity of each definition in predicting mortality was observed. Three clinical criteria (ST depression, cardiomegaly and prior infarction) allowed stratification of patients into four subsets with respective mortality rates of 35.5% (three criteria present), 19.0% (two criteria), 11.5% (one criterion) and 4.7% (none). Presence of ventricular ectopic activity (greater than or equal to 10 ventricular premature beats/h or pairs, ventricular tachycardia or multiform complexes) was associated with higher mortality rates in all four risk strata. The relative risk was higher (3.86) in the lowest risk stratum (mortality 2.4% without and 9.1% with ventricular ectopic activity). Thus, in survivors of acute myocardial infarction, ventricular ectopic activity was more pronounced in patients with prior myocardial infarction and congestive heart failure. It predicted mortality independently of other factors. Although mortality ratios were similar for all seven arrhythmia definitions, a reciprocal relation between sensitivity and specificity of the definitions in predicting mortality existed; ventricular ectopic activity was associated with increased mortality in all risk strata, but with a higher risk ratio in the numerically larger, low risk subset.

Ventricular premature beats on Holter monitoring in patients admitted with chest pain, in whom acute myocardial infarction is not confirmed. The prognostic value and relationship to scars or ischemia on thallium-201 scintigraphy

Ambulatory 24-h Holter monitoring was carried out in 198 patients who had been admitted because of suspected acute myocardial infarction (AMI) due to chest pain, but in whom AMI was not confirmed. During a follow-up period of 12-24 months (median 14 months) 16 cardiac events (i.e., nonfatal AMI or cardiac death) occurred. Ventricular premature beats (VPBs) were found in 65.2% of the patients, complex VPBs in 28.8%. Pairs of VPBs which were seen in 10.0% of the patients were the only important type of VPBs significantly related to an impaired prognosis. Thallium-201 scintigraphy was performed in 144 of the patients. VPBs were significantly related to scar formation (i.e., to permanent defects, but not to ischemia, specifically, to transient defects). It is concluded that ventricular arrhythmias in this patient category indicate presence of chronic ischemic heart disease, and that pairs of VPBs seem to identify patients at risk for cardiac events.

Histopathologic correlates of inducible ventricular tachycardia in two experimental canine models of myocardial infarction

Ventricular tachyarrhythmias are the leading cause of sudden cardiac death. Determination of the substrates conducive to the initiation of ventricular tachyarrhythmias remains an important clinical goal. The purpose of this study was to correlate electrophysiologic and histopathologic parameters conducive to the initiation of sustained ventricular tachycardia using programmed electrical stimulation in two canine models of myocardial infarction. Histopathologic correlates included: infarct pattern (heterogeneous vs. homogeneous morphology), distribution (viable epicardial or endocardial rim), and size. Twenty-one adult dogs were randomly divided into two groups: (1) 12 dogs underwent two-stage, 2-hour occlusion of the proximal left anterior descending coronary artery (LAD); and (2) nine animals had permanent, complete occlusion of the LAD with latex embolization. Using programmed ventricular pacing with two premature ventricular extrastimuli, initiation of ventricular tachycardia was attempted at both 1 and 2 weeks after infarction with the chest closed and opened each time. Electrophysiologic evaluation of the infarct type correlated significantly with the histologic morphology of the infarction (p less than 0.001), the presence of a viable epicardial rim was an extremely important discriminating variable for ability to induce sustained ventricular tachycardia (p = 0.04). The presence of an endocardial rim was not significant (p = 1.0). Infarct size alone was only marginally related to ventricular tachycardia inducibility (p = 0.08). Non-uniform infarcts were more conducive to the initiation of sustained ventricular tachycardia than homogeneous infarcts (p = 0.025). The presence of a large, non-uniform infarct was the best overall discrimination variable for inducibility (p = 0.0002). Thus, in these experimental models, specific infarct morphologies correlate significantly with susceptibility to inducible sustained ventricular tachyarrhythmias.

Long-term prognostic significance and electrophysiological evolution of intraventricular conduction disturbances complicating acute myocardial infarction

Fifty-nine patients with post-infarctional, isolated intraventricular conduction disturbances (IVCD) who survived the acute stage of myocardial infarction were followed up after hospital discharge for a mean period of 11.4 +/- 4.8 months. Fourteen patients (24%) had HV interval prolongation (greater than 55 ms) during AMI (group A), and 45 patients had normal HV intervals (76%, group B). His bundle recordings were repeated during follow-up in 48 survivors after a mean period of 7.2 +/- 0.7 months. Infranodal conduction delay in the acute stage of infarction was correlated with a higher incidence of heart failure during AMI (78% of patients in group A vs 22% in group B, p less than 0.001), and with higher rate of cardiac mortality during follow-up (50% in group A vs 13% in group B, p less than 0.01). Survivors of group A showed a higher functional NYHA class, a higher incidence of CHF, and a higher prevalence of complex ventricular arrhythmias at Holter monitoring. No statistically significant difference in late sudden death was evident between the two groups of patients, and the global incidence of late AV block was 2%. At repeat His bundle recording no significant change (greater than 5 ms) in HV interval could be demonstrated in comparison to the acute phase recording, neither in patients with prolonged nor in patients with normal HV time. We conclude that HV prolongation in patients with isolated, post-infarctional IVCD is correlated with a worse prognosis, both during acute infarction and during the follow-up period, which presumably reflects wider anatomic damage in comparison to patients with normal HV time. The low incidence of late AV block and the electrophysiological demonstration of the stability of infranodal conduction several months after AMI indicate that these patients do not require permanent prophylactic pacing after acute myocardial infarction.

Relationship of specific coronary lesions and regional left ventricular dysfunction to prognosis in survivors of sudden cardiac death

We prospectively evaluated the relationship of specific coronary arterial and left ventricular segments to subsequent clinical outcome in 80 persons who were survivors of sudden cardiac death and had failed conventional antiarrhythmic therapy. There were 68 men and 12 women with an average age of 51 years who were treated with investigational antiarrhythmic agents, rendered asymptomatic, and followed for 16 +/- 14 (SD) months. At the end of the study 48 patients (60%) were alive and asymptomatic while 32 (40%) had experienced either recurrent syncope (five) or sudden cardiac death (27). The independent relationship of clinical and angiographic variables was performed in a univariate fashion using a Kaplan-Meier survival analysis and then multivariate logistic analysis was used to simultaneously consider all clinical and arteriographic variables. The results reconfirmed the importance of ejection fraction and left ventricular filling pressure on outcome. However, coronary arterial and left ventricular segmental analyses provided additional predictive power. Specifically, the survival outcome was found to be inversely related to the degree of proximal left anterior coronary (LAD) arterial narrowing: at 1 year 90% of patients with minimal LAD narrowing were alive/asymptomatic in contrast with 70% who had partial and 40% who had complete proximal LAD obstruction (p less than 0.005). Analysis of the posterobasal left ventricular segment wall motion demonstrated that 100% of patients with minimal dysfunction were alive/asymptomatic at 1 year, whereas only 52% of patients with severe dysfunction were alive (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed electrical stimulation in patients with high-grade ventricular ectopy: electrophysiologic findings and prognosis for survival

The significance and treatment of ventricular premature beats (VPBs) in patients without sustained ventricular tachycardia (VT), sudden death, or syncope remains unclear. We undertook a prospective study of programmed electrical stimulation (up to two extrastimuli and burst pacing) in 73 patients (age 60 +/- 10 years) with high-grade VPBs who had no evidence of sustained VT, sudden death, or syncope as determined by 48 hr of monitoring in the cardiac care unit and 48 hr Holter monitoring. Fifty-six patients (76.7%) had atherosclerotic heart disease, 10 (13.7%) had cardiomyopathy or valvular heart disease, and seven (9.6%) had no evident heart disease. Thirty-seven patients (50.7%) had Lown grade IVB VPBs, 30 (41.1%) had Lown grade IVA VPBs, and six (8.2%) had Lown grade III VPBs. Programmed electrical stimulation identified two groups of subjects: group 1 comprised 20 patients (27%) in whom VT or ventricular fibrillation was induced, group 2 comprised 53 patients (73%) in whom no ventricular arrhythmia or only two to four repetitive ventricular responses were induced. There was a significant difference between the presence of atherosclerotic heart disease, old myocardial infarction, and ejection fraction of less than 40% in group 1 compared with group 2. However, there was no significant difference in the grade of VPBs between the two groups. Seventeen of 20 patients from group 1 were placed on antiarrhythmic therapy (defined by programmed electrical stimulation), whereas group 2 patients were randomly assigned to prophylactic antiarrhythmic therapy. A total of 70 patients were followed up for 30 +/- 15 months. The incidence of sustained VT and/or sudden death (31.5% vs 2%; p less than .001) was significantly higher in group 1 compared with group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiform ventricular ectopic rhythm by combined parasystolic and reentrant activities

Multiform ventricular ectopic rhythm (MVER), i.e., at least two QRS configurations of ventricular ectopic beats (VEBs), was assessed by 24-hour ambulatory ECG recording in four patients with ventricular parasystole (VP). In two of these four patients, VEBs with fixed coupling to the preceding impulses coexisted with VP beats of different configuration. In case no. 1, the VEBs had an identical coupling interval to sinus beats and VP beats, suggesting a mechanism of reentry elicited from both dominant pacemakers. In case no. 2, an intermittent form of VP due to type II second-degree entrance block was present. In this patient, the VEBs were coupled to sinus beats and to sinus-VP fusion beats and appeared to be dependent on the sinus beats reaching the VP focus. A mechanism of reentry determined by the penetration of sinus beats into the VP area, with prematurity-dependent aberrancy of VEBs, was suggested for the coupled VEBs in this patient. These observations suggest that the coexistence of an automatic ventricular ectopic focus and of a reentrant activity determined by, or elicited from, an area of automaticity may constitute the underlying mechanism of MVER in some patients.

Relation of ventricular premature beats to underlying heart disease

The relation between ventricular premature beats (VPBs) and physiologic disease was investigated in 305 patients who had 24-hour Holter monitoring tests, cardiac catheterization and angiography. Both frequency and Lown class of VPBs were measured. Analyses showed that occurrence of VPBs at an average frequency of more than 2 per hour or occurrence of complex VPBs (Lown class greater than 2) have the highest association with the presence and severity of cardiac disease. Using these criteria, VPB severity was then compared with extent of ventricular wall motion abnormality (right anterior oblique projection segments), ejection fraction, end-diastolic pressure, category of disease (normal, coronary artery disease [CAD], valvular heart disease, dilated cardiomyopathy), age and severity of CAD (major coronary arteries with greater than 75% diameter reduction). Severe VPBs defined either by complexity or frequency were significantly correlated with extent of wall motion abnormality, ejection fraction, category of disease and age. Severe VPBs were not significantly correlated with end-diastolic pressure or severity of CAD. Discriminant analysis then showed that in addition to wall motion abnormality and ejection fraction, category of disease and age are independently correlated with VPB severity.

Reliability of sampling during long-term ECG recordings in the detection of ventricular ectopy and abnormal ST segment depression

Two ambulatory ECG recording-analysis methods were each compared in 10 subjects with a careful hand counted analysis of 16 continuously recorded hr and examined for total VEB count, complex VEB and ST-depression. The sampling method made a 28-sec tape recording every 15 min and was visually coded. The other method (conventional Holter) continuously recorded ECG data and used a dedicated computer with technician editing. Both recorders were simultaneously worn by study participants for 16 hr. Neither method showed a statistically significant difference from the hand counted data or systematic over- or under-estimation of clinically important ECG detections. A probability model is presented which provides a theoretical basis for the success of ECG sampling. Findings from this pilot study indicate electrocardiographic sampling may provide event detection comparable with the more conventional analyses, with considerably less data acquisition. The choice of ambulatory ECG recording mode should be governed by the level of quantification required, specific events to be detected and cost.

Prognostic value of ventricular arrhythmias associated with treadmill exercise testing in patients studied with cardiac catheterization for suspected ischemic heart disease

The prognostic information provided by ventricular arrhythmias associated with treadmill exercise testing was evaluated in 1,293 consecutive nonsurgically treated patients undergoing an exercise test within 6 weeks of cardiac catheterization. The 236 patients with simple ventricular arrhythmias (at least one premature ventricular complex, but without paired complexes or ventricular tachycardia) had a higher prevalence of significant coronary artery disease (57 versus 44%), three vessel disease (31 versus 17%) and abnormal left ventricular function (43 versus 24%) than did patients without ventricular arrhythmias. Patients with paired complexes or ventricular tachycardia had an even higher prevalence of significant coronary artery disease (75%), three vessel disease (39%) and abnormal left ventricular function (54%). In the 620 patients with significant coronary artery disease, patients with paired complexes or ventricular tachycardia had a lower 3 year survival rate (75%) than did patients with simple ventricular arrhythmias (83%) and patients with no ventricular arrhythmias (90%). Ventricular arrhythmias were found to add independent prognostic information to the noninvasive evaluation, including history, physical examination, chest roentgenogram, electrocardiogram and other exercise test variables (p = 0.03). Ventricular arrhythmias made no independent contribution once the cardiac catheterization data were known. In patients without significant coronary artery disease, no relation between ventricular arrhythmias and survival was found.

Prognostic value of exercise thallium-201 imaging in patients presenting for evaluation of chest pain

Accurate prognostic information is important in determining optimal management of patients presenting for evaluation of chest pain. In this study, the ability of exercise thallium-201 myocardial imaging to predict future cardiac events (cardiovascular death or nonfatal myocardial infarction) was correlated with clinical, coronary and left ventricular angiographic and exercise electrocardiographic data in 139 consecutive, nonsurgically managed patients followed-up over a 3 to 5 year period (mean follow-up, 3.7 +/- 0.9), using a logistic regression analysis. Among patients without prior myocardial infarction (100 of 139), the number of myocardial segments with transient thallium-201 defects was the only statistically significant predictor of future cardiac events when all patient variables were evaluated. Among patients with myocardial infarction before evaluation (39 of 139), angiographic ejection fraction was the only significant predictor of future cardiac events when all variables were considered. This study suggests an approach to evaluate the risk of future cardiac events in patients with possible ischemic heart disease.

Programmed electrical stimulation of the heart in coronary artery disease

The induction of ventricular arrhythmia in patients with a history of malignant ventricular arrhythmia by programmed electrical stimulation (PES) is associated with a poor prognosis. However, the incidence and significance of inducible arrhythmia in patients with stable coronary artery disease (CAD) who do not have a history of serious arrhythmia are unknown. We studied 32 such patients (31 men, mean age 55 years) with PES at the time of cardiac catheterization. Fourteen patients (Group I) manifested greater than or equal to 3 extraventricular responses when challenged with 1 to 3 propagated right ventricular extrastimuli during ventricular pacing. Twelve (86%) of these 14 had evidence of left ventricular dysfunction (LVD), defined by a global ejection fraction of less than 50% or regional wall motion abnormalities. The remaining 18 patients (Group II) manifested less than or equal to 2 responses to extrastimulation. Only 4 (22%) of these 18 had LVD. Proximal 3-vessel CAD was more frequent in Group I patients (10 of 14, 71%) than in Group II (7 of 18, 39%). Only 5 patients (4 from Group I and 1 from Group II) demonstrated complex arrhythmia during exercise testing or ambulatory monitoring. The induction of extraventricular responses during PES may serve as an independent marker of electrical instability in the coronary population and is a much more common finding in those with LVD.

Ventricular ectopy: etiology, evaluation, and therapy

Ventricular ectopy occurs commonly. Its significance is related to the degree of complexity and the associated cardiac substrate. Coronary artery disease is the most frequent underlying cause, followed by cardiomyopathy and valvular disease. Symptomatic ventricular arrhythmias require treatment, whereas benign simple ventricular ectopy does not; however, the treatment of asymptomatic high-grade ventricular ectopy remains controversial. Therapy first must be directed toward the cardiac disease. Evaluation of the patient includes Holter monitoring, echocardiography, radionuclide studies, exercise testing, cardiac catheterization, and electrophysiologic testing. Programmed stimulation is useful in the diagnosis and prognosis of ventricular tachycardia, as well as in the evaluation of drug regimen efficacy. After treatment of ischemia and/or failure, specific antiarrhythmic agents, conventional and investigational, alone or in combination, are systematically selected. Should medical therapy alone be insufficient, consideration is given to surgical procedures such as subendocardial resection or ventriculotomy, often in combination with bypass grafting, aneurysmectomy, or valvular replacement. Electronic devices, including pacemakers or automatic internal defibrillators, may also be useful in certain selected cases. Suggested guidelines are proposed for a standardized approach, although therapy for each patient must still be individualized.

Ventricular antiarrhythmic effects of beta-adrenergic blocking drugs: a review of mechanism and clinical studies

Beta-adrenergic blocking drugs are now commonly used in patients with ventricular arrhythmias. This review examines the possible mechanisms of their ventricular antiarrhythmic effect. Actions on the myocardial cell, as well as actions on the central and autonomic nervous system, are reviewed. Many clinical studies have attempted to show the efficacy of beta blockers in controlling ventricular arrhythmia and decreasing the incidence of sudden death after acute myocardial infarction. Although some of these clinical trials tended to show an impact on sudden death, the size of these trials or their design problems do not allow firm conclusions to be made. The Beta Blocker Heart Attack Trial (BHAT) is a placebo-controlled, double-blind, randomized trial of propranolol currently under way in the United States. Important additions to the previous trials include the addition of drug levels to ensure beta-blocking dosage, long-term electrocardiographic monitoring, and a study population of 4200 patients followed for an average of three years. These important design features will be of value in addressing some of the unanswered questions presented in this review.

Evaluation and outcome of emergency room patients with transient loss of consciousness

We identified 198 patients who presented to our emergency room with transient loss of consciousness. Seizures (29 percent of patients) and vasovagal/psychogenic episodes (40 percent of patients) were the most common presumptive causes of loss of consciousness, but the cause of loss of consciousness remained uncertain even at follow-up in 11 +/- 6 months in 13 percent of the patients. The history and physical examinations were sufficient for diagnosis in 85 percent of the patients in whom a diagnosis could be established. These data guided inpatient and outpatient with potentially dangerous causes of loss of consciousness except for one patient who had pulmonary embolism. In selected patient, diagnostic tests such as blood chemistries (three patients), electrocardiograms (four patients) electroencephalograms (three patients), and Holter monitoring (four patients) provided crucial information, and CT scans identified new brain tumors in four patients with focal neurologic presentations. At the time of follow-up, 7.5 percent of patients had suffered either major morbidity or death related to the cause of the index episode of loss of consciousness. Patients with cardiac causes represented a high risk (33 percent) group for such poor outcome, whereas patients who were under age 30, or who were under age 70 and had loss of consciousness on a vasovagal/psychogenic or unknown basis, constituted a low risk (1 percent) subgroup.

Multiformity if induced unifocal ventricular premature beats in human subjects: electrocardiographic and angiographic correlations

Single ventricular premature responses induced by strength-interval pacing were elicited at multiple sites in 30 patients undergoing cardiac catheterization to determine if and under what circumstances unequivocally unifocal stimulated ventricular premature beats could manifest multiformity of the QRS configuration. Multiformity was defined as unifocal responses whose mean frontal axes differed by greater than 15 degrees with or without associated morphologic differences in the horizontal leads. Multiformity occurred in 12 (40 percent) of 30 patients. A statistically significant association was found between multiformity and the presence of a quantitatively defined left ventricle wall motion abnormally (p less than 0.01), prior myocardial infarction (p less than 0.01) and a left ventricular election fraction of less than 0.60 (p less than 0.05). Twelve (67 percent) of the 18 patients without multiformity had coronary artery disease, but only 4 of those 12 had a left ventricular wall motion abnormally or prior myocardial infarction, or both. Multiformity was also dependent on the site of stimulation and on the degree of prematurity. The results of this study indicate that the QRS configuration of early premature beats cannot be relied on as a predictor of their site of origin and multiformity is not necessarily synonymous with multifocality.

Pathologic changes in the cardiac conduction and nervous system in sudden coronary death

The arrhythmogenic substrates for sudden coronary death were studied in 13 autopsied hearts and in 2 left stellate ganglia (surgically excised). Diffuse or segmentary obstruction of nutritional arteries accounted for acute ischemic injury of the conduction system, which was the underlying cause of high-risk bradycardic arrhythmias in one-third of the cases. However, in one-quarter of the cases the survival of anoxia-resistant subendocardial specialized fibers was probably responsible for reentrant lethal tachycardic arrhythmias. In other cases, early infarct damage could have fatal arrhythmias of either type. Intrinsic and/or extrinsic neuropathologic changes, unbalancing the autonomic action on the heart, were often seen to participate in the arrhythmogenic features of sudden coronary death.

Electrophysiologic and hemodynamic studies in patients resuscitated from cardiac arrest

Fifty-two patients resuscitated from cardiac arrest underwent electrophysiologic studies. The earliest documented arrhythmia at the time of initial or recurrent (18 patients) cardiac arrest was ventricular fibrillation (30 patients) or ventricular tachycardia (20 patients); in 2 patients no arrhythmia was documented before defibrillation. Programmed ventricular stimulation revealed inducible arrhythmias in 33 patients (63 percent). Of the 30 patients with ventricular fibrillation as the initial arrhythmia, 13 had inducible arrhythmias--ventricular fibrillation (4 patients), sustained ventricular tachycardia (6 patients) and nonsustained ventricular tachycardia (3 patients). In the 20 patients with ventricular tachycardia as the initial arrhythmia, sustained ventricular tachycardia was initiated in 17 patients and torsade de pointes in 1. Patients with inducible arrhythmias had longer mean A-H and H-V intervals than those without inducible arrhythmias (91.1 versus 76.6 ms and 62.5 versus 50.3 ms, respectively). Prolonged H-V intervals (17 of 33) and intraventricular conduction defects (18 of 33) were more common in patients with than in those without inducible arrhythmias (4 of 19 and 7 of 19, respectively). Mean cardiac index was lower (2.4 versus 3.9 liters/min per m2), left ventricular end-diastolic pressure higher (17.0 versus 9.4 mm Hg), and ejection fraction lower (36.1 versus 57.2 percent) in the group with inducible arrhythmias than in those in whom no arrhythmia could be induced. These data suggest that (1) ventricular tachycardia often precipitates cardiac arrest; and (2) electrophysiologic testing may provide data on which to base therapy in patients resuscitated from cardiac arrest.

Relation of ventricular premature beat suppression to serum quinidine concentraton determined by a new and specific assay

Fourteen patients who were receiving quinidine in doses of 800 to 1800 mg. per day for ventricular arrhythmias underwent Holter monitoring during a steady state dosing interval at a mean of four days after the initiation of quinidine therapy. Serum quinidine concentration, determined by a specific high performance liquid chromatography method, was measured hourly during the dosing interval. Ventricular premature beat (VPB) frequency during quinidine therapy was compared to the baseline VPB frequency. A reduction in VPB frequency of at least 90% was required to substantiate the presence of a therapeutic response to quinidine. In 12 of the 14 patients a therapeutic response to quinidine was present at serum levels ranging from 0.72 to 5.92 micrograms/ml. There was no group correlation between serum quinidine concentration and VPB frequency, but there was a tendency in individual patients for VPB frequency to decrease as serum quinidine level increased. Quinidine toxicity was not observed in these 14 patients. Because of the wide variation in response to quinidine, a serum quinidine concentration that is within the therapeutic range is not necessarily the optimal serum quinidine concentration for an individual patient. The clinician may therefore consider increasing the dose if there is no evidence of quinidine toxicity and the ventricular rhythm disturbance is not adequately controlled.

Cardiovascular complaints. Correlation with cardiac arrhythmias on 24-hour electrocardiographic monitoring

Long-term ambulatory electrocardiographic (Holter) monitoring is frequently used to evaluate patients with various cardiovascular complaints, including palpitations, dyspnea, discomfort in the chest, dizziness, and syncope. In the present study, 518 consecutive 24-hour electrocardiographic recordings were reviewed to determine correlations between cardiac diagnoses, presenting complaints, and specific electrocardiographic abnormalities. Two hundred seventy-four patients (53 percent) had significant arrhythmias; 212 (41 percent) had significant ventricular arrhythmias, and 106 (20 percent) significant atrial arrhythmias, including 44 patients (8 percent) with both. No presenting complaint or cardiovascular diagnosis correlated closely with any specific cardiac arrhythmia. Major arrhythmias, including supraventricular and ventricular tachycardias, often occurred asymptomatically (in 44/54 and 37/40 patients, respectively); however, among 371 patients with accurate historic logs, only 176 (47 percent) had long-term electrocardiographic studies in which their typical symptoms occurred during the monitoring period. Fifty (13 percent) of the 371 patients had concurrence of their presenting complaints with an arrhythmia, and 126 patients (34 percent) had their typical symptoms associated with a normal electrocardiogram, which was helpful in excluding an abnormality of rhythm or conduction as the primary cause for their complaints.

Frequency and complexity of ventricular ectopic beats in the posthospital phase of myocardial infarction

This study is a descriptive report of the occurrence of ventricular arrhythmias in a large, prospectively designed follow-up study of postcoronary patients. Six-hour Holter recordings were obtained on 954 postinfarction patients prior to hospital discharge and at 4 (n = 837), 8 (n = 762), 12 (n = 713), and 24 (n = 487) months post-discharge. Ventricular ectopic beats (VEB) were quantitated by frequency and patterns at each recording, and antiarrhythmic medication usage was recorded. The proportion of patients wtih each VEB frequency (any, less than 9.9/hour, 10 - 19.9/hour, greater than or equal to 20/hour) increased progressively during the 24-month follow-up, with the most significant increase in the interval between baseline and the four-month follow-up recording. Significant (p less than 0.01) associations were found between VEB frequency greater than or equal to 20/hour and almost all VEB patterns for each follow-up; no significant associations were found between VEB prematurity (RR'/QT less than or equal to 1.00) and any of the VEB patterns. Among the survivors, the utilization of diuretics and beta blockers increased (p less than 0.01) and antiarrhythmic agents declined (p less than 0.01) between predischarge and all subsequent follow-up visits. The significance of these findings is discussed.

Evaluation of aortocoronary venous bypass grafting for prevention of cardiac arrhythmias

The influence of ACB on cardiac arrhythmias was examined in 27 patients. Eight-hour Holter monitoring was performed 8 days preoperatively and 100 days postoperatively. Arrhythmias were divided into 3 groups (Class I: NSR +/- occasional APBs; Class II: less than five unifocal VPBs per minute; Class II: more than five VPBs per minute, multifocal VPBs, VPBs in a row or VT). Preoperative classification disclosed that 13 patients (48.1 per cent) were in Class I, six patients (22.2 per cent) were in Class II, and eight patients (29.6 per cent) were in Class III. The corresponding values after surgery were 10 patients (37.0 per cent), 13 patients (48.1 per cent), and four patients (14.8 per cent). These differences were not statistically significant (p less than 0.1). In view of the tendency of arrhythmias of Class III to improve after ACB, we feel that further investigations in this area are needed. At the present time ventricular arrhythmias alone constitute no indication for bypass surgery.