Prediction of coronary events following myocardial infarction using a discriminant function analysis

Effect of pharmacological wash-out in patients undergoing exercise testing after acute myocardial infarction

STUDY OBJECTIVES

Pharmacological therapy can reduce diagnostic and prognostic accuracy of exercise stress testing. However, the risk of withdrawing drugs early after myocardial infarction (MI) has not been established. We assessed safety and clinical implications of drug withdrawal in patients undergoing stress testing after uncomplicated MI.

METHODS

A total of 362 MI patients underwent ECG Holter recording before and after withdrawing beta-blockers, calcium-antagonists and nitrates. QRS (QRS/h) and ventricular premature beats (VPB/h) count per hour, repetitive ventricular arrhythmias, ST segment changes and patient complaints were evaluated for reproducibility using kappa statistics and Bland-Altman method.

RESULTS

No major complications occurred. Forty-three patients complained of >1 symptom on and 37 off therapy. QRS/h and VPB/h count were significantly (p<0.0001) higher off therapy but correlated with the corresponding values on therapy. A mean heart rate increase of 8 beats/min (agreement range -8 to +14 beats/min) and a five-fold increase in VPB/h (agreement range -141 to +151) were observed after withdrawing therapy. Repetitive ventricular arrhythmias and ST changes were also more frequent off therapy but intra-patient reproducibility was poor: kappa 0.12 (95% confidence interval (CI) -0.01 to 0.25) for arrhythmias, -0.02 (95% CI -0.46 to 0.39) for ST depression and -0.01 (95% CI -0.66 to 0.64) for ST elevation.

CONCLUSIONS

The withdrawal of therapy is well tolerated soon after uncomplicated MI; however, a generic but not individual risk of ventricular arrhythmias and/or transient myocardial ischemia has to be taken into account.

Evaluation of the Appropriateness of Pacemaker Mode Selection in Bradycardia Pacing:

Although guidelines for selection of the appropriate pacing mode have been published, little data is available on how closely these are followed in the clinical setting. All 738 patients (men 412, women 326; age 73.4 +/- 0.46 years; range 19-101 years) who underwent pacemaker implantation from 1996 to 2000 were reviewed to determine if the appropriate mode was selected based on the ACC/AHA guidelines with the data collected prospectively. Demographic, investigational, and implantation data including the presence of sinus disease and/or atrioventricular block, diagnosis, indication for pacing, ACC/AHA class indication for device therapy, recommended ACC/AHA mode, implanted mode, and reason for not using the recommended mode were entered into an SPSS data base. Of 738 patients, 708 were cross-tabulated for a match to the guidelines of which 358 (50.6%) had a mode selected that did not conform. The reasons were advanced physical disability (16%), physician choice without identifiable reason (21%), rate modulation selected without identifiable indication (16%), DDD implanted instead of VDD (25%), advanced age (9%), rare need for pacing (6%), a need for specific device features (5%), and unstable stimulation thresholds or difficult venous access (2%). In the treatment of bradyarrhythmias, deviation from the ACC/AHA indicated mode occurred in a substantial proportion of pacing system implantations. However, in many, the deviation appeared appropriate considering the patient's clinical status. Nevertheless, in a smaller proportion of patients the deviation appeared inappropriate requiring rectification. The two outstanding categories were: (1) elderly denied a dual chamber system with no clinical explanation and (2) selection of rate-modulated devices without any indication of chronotropic incompetence.

Clinical utility of ST-segment depression in lead AVR in acute myocardial infarction

The present study evaluated the prevalence and significance of ST-segment depression (STD) in lead aVR on the admission 12-lead electrocardiogram in 307 consecutive patients with an acute myocardial infarction (AMI) with ST-segment elevation. STD in aVR was present in a significantly higher proportion of patients with inferior/posterior AMIs. Within inferior/posterior AMIs those with STD in aVR had significantly more concomitant STD in V(1), V(2), V(3) and more concomitant STesegment elevation in V(5), V(6) and right precordial leads. These data suggests that STD in aVR may point to a coronary artery with a large area of supply as the culprit vessel responsible for the AMI.

Effectiveness of a planned strategy using cardiac rehabilitation nurses for the management of dyslipidemia in patients with coronary artery disease

BACKGROUND

Firm evidence exists for reduction in mortality and morbidity by lipid-lowering therapy in patients with coronary artery disease (CAD), yet a significant proportion remain untreated. This prospective study determined the effectiveness of a planned strategy of management using a cardiac rehabilitation nurse in achieving (1) lower 6-month low-density lipoprotein (LDL) levels and (2) a higher proportion of patients on pharmacologic therapy.

METHODS

A cardiac rehabilitation nurse arranged for the lipid profiles and initiated pharmacologic therapy as soon as possible after the diagnosis of CAD. In phase 1, this planned-strategy intervention group (n = 80) was compared with the usual-care control group (n = 189), where the management was left at the discretion of the attending cardiologist with the assignment to the 2 groups based on the weekly on-call rotations of the attending cardiologists in a nonrandomized manner. In phase 2 of the study all patients (n = 366) were enrolled in the planned strategy of management.

RESULTS

There were no significant differences in the baseline lipid values between the control and intervention groups. The 6-month cholesterol and LDL values and the percentage of patients on lipid-lowering medications were significantly better in the intervention group (P =.01). In phase 2 the results obtained in the intervention group were duplicated in a much larger group of consecutive patients. The 6-month (millimoles per liter) results in the control, intervention, and phase 2 groups (respectively) were cholesterol 4.92 +/- 0.06, 4.60 +/- 0.07, 4.30 +/- 0.05; low-density lipoprotein 2.91 +/- 0.06, 2.68 +/- 0.07, 2.4 +/- 0.06; high-density lipoprotein 1.18 +/- 0.07, 1.12 +/- 0.09, 1.10 +/- 0.01; triglycerides 1.89 +/- 0.12, 1.78 +/- 0.09, 1.70 +/- 0.05; and on medications 49%, 83%, and 84%.

CONCLUSION

A planned strategy of management with use of early pharmacologic therapy with a cardiac rehabilitation nurse assigned to obtain and follow lipid profiles and initiate therapy is more effective in controlling dyslipidemia than leaving the management to the cardiologist.

Feasibility and safety of early exercise testing using the Bruce protocol after acute myocardial infarction

OBJECTIVE

To assess the feasibility and safety of exercise testing (ET) using a Bruce protocol (BPR) within three days of an acute myocardial infarction (AMI) with the data obtained from a prospectively managed database.

BACKGROUND

Exercise testing after AMI is usually done between days 4 and 6 and often using a "low-level" protocol. Earlier testing with BPR may allow for efficient triage.

METHODS

Patients were considered for early ET when off intravenous nitroglycerine with no rest angina, uncontrolled cardiac failure or arrhythmias.

RESULTS

Of 300 consecutive AMI patients who underwent an ET, 216 (72.0%; M = 163, F = 53; age mean 59 +/- 0.8 SEM, range 34 to 83 years) had ET within three days of admission. There were 124 (57%) negative, 56 (26%) positive and 36 (17%) indeterminate tests. The maximum heart rate achieved was 116 +/- 1 beats/min (range 64 to 163), which was 72.2 +/- 0.8% of predicted maximum (86.6% on beta-adrenergic blocking agents at ET; exercise duration = 6.7 +/- 0.2 min). Reasons for termination: maximum effort-89 (41%); low-level test target (stage III/IV of BPR)-63 (29%); positive ST segment change-19 (9%); severe chest pain-12 (5.5%); reaching 90% predicted maximum heart rate-6 (3%); nonsustained ventricular tachycardia-1 (0.5%); other-26 (12%). Fourteen (6.5%) patients had minor complications (i.e., drop in systolic pressure, chest pain >5 min) with no cardiac arrests, AMIs or deaths. After the ET, 87 (40%) patients were discharged the same day, 73 (34%) the next day.

CONCLUSIONS

The majority of ETs after an AMI can be done using the Bruce protocol within three days of admission with a very low incidence of complications. This can lead to early triage and potential cost savings.

Feasibility of direct discharge from the coronary/intermediate care unit after acute myocardial infarction

OBJECTIVES

This investigation was designed to determine the feasibility and cost-effectiveness of direct discharge from the coronary/intermediate care unit (CICU) in 497 consecutive patients with an acute myocardial infarction (AMI).

BACKGROUND

Although patients with an AMI are traditionally treated in the CICU followed by a period on the medical ward, the latter phase can likely be incorporated within the CICU.

METHODS

All patients were considered for direct discharge from the CICU with appropriate patient education. The 6-week postdischarge course was evaluated using a structured questionnaire by a telephone interview.

RESULTS

There were 497 patients (men = 353; women = 144; age 63.5 +/- 0.6 years) in the study, with 29 in-hospital deaths and a further 11 deaths occurring within 6 weeks of discharge. The mode length of CICU stay was 4.0 days (mean 5.1 +/- 0.2 days): 1 to 2 (12%), 3 (19%), 4 (21%), 5 (14%), 6 to 7 (19%) and > or = 7 (15%) days, respectively with 87.2% discharged home directly. Of the 425 patients surveyed, 119 (28.0%) indicated that they had made unscheduled return visits (URV) to a hospital or physician's office: 10.6% to an emergency room, 9.4% to a physician's office and 8.0% readmitted to a hospital. Of these URV, only 14.3% occurred within 48 h of discharge. Compared to historical controls, the present management strategy resulted in a cost savings of Cdn. $4,044.01 per patient.

CONCLUSIONS

Direct discharge from CICU is a feasible and safe strategy for the majority of patients that results in considerable savings.

Exercise-induced changes in R wave amplitude and heart rate in normal subjects

An intermittent exercise protocol on a treadmill was used to examine six healthy subjects, and a steady protocol was applied to three of the subjects before and after short-term training. The peak blood velocity in the common carotid artery increased by 73.1% during the intermittent protocol and recovered to resting level within 3 minutes, while the heart rate (HR) remained high even 5 minutes after exercise. R wave amplitude (RWA) increased significantly from 1.40 +/- 0.39 mV at rest to 1.59 +/- 0.33 mV (P < .05) immediately after the start of walking, and decreased gradually to 1.46 +/- 0.36 mV (P < .05) during 3 minutes of walking. Thus, it decreased significantly to 1.31 +/- 0.40 mV (P < .01) during the interphase from exercise to rest, and increased again during recovery or rest periods in the intermittent protocol. The results suggest that an increase in the venous return per heart beat at the start of walking induces the increase in RWA, and that its abrupt decrease at the end of walking induces the decrease in RWA. Subjects with a higher HR response and recovery slopes have smaller abrupt changes in RWA at the interphases between rest and walking. The gradual decrease in RWA during walking may be related to a gradual increase in HR and a gradual decrease in systemic peripheral resistance, and the gradual increase in RWA after walking may be related to a gradual decrease in HR and a gradual increase in systemic peripheral resistance.

Prognostic value of changes in R-wave amplitude during exercise testing after a first acute myocardial infarction

To investigate the prognostic value of exercise-induced changes in R-wave amplitude and their relation to other exercise and angiographic variables, 303 consecutive patients who underwent maximal exercise testing and coronary angiography within 2 months of a first acute myocardial infarction were studied. R-wave amplitude at peak exercise increased or was unchanged in 159 patients (57.4%) and decreased in 118 (42.6%). Increased R-wave amplitude was significantly related to underlying 3-vessel disease (p = 0.0001), the extent of ST-segment depression on exercise (p = 0.0001), and the time to 1 mm ST depression (p less than 0.05). Follow-up information was available in 285 patients (86.4%) at a mean of 4 +/- 1.8 years. Death from cardiac causes occurred in 25 patients (9%); 18 (6.5%) developed recurrent myocardial infarction, and 32 (11.6%) developed angina. Variables with a predictive value for cardiac death were maximal exercise heart rate (p = 0.0005), occurrence of exercise-related supraventricular arrythmia (p = 0.02), and number of diseased vessels (p = 0.02). R-wave changes had no predictive value. No variable had a predictive value for recurrent infarction. Maximal exercise heart rate (p = 0.02) and increased R-wave amplitude (p = 0.0001) were significantly related to the occurrence of angina at follow up. Exercise-related R-wave increases were associated with the presence of angina at follow-up, but had no predictive value for cardiac death or recurrent infarction; their association with subsequent angina appears to reflect an association with more severe underlying coronary disease.

Psychiatric morbidity during the early phase of coronary care for myocardial infarction: association with cardiac diagnosis and outcome

We evaluated the association of psychiatric morbidity during the early phase of admission to a coronary care unit with cardiac diagnosis and subsequent morbidity. Ninety-two patients admitted for the first time for presumed myocardial infarction were evaluated within 48 hours of hospitalization. Anxiety and depressive symptoms and cognitive impairment were rated. Data were collected on cardiac diagnosis and morbidity. Three and 12 months after hospitalization, cardiac morbidity, psychiatric symptoms and psychosocial morbidity were assessed.

Risk stratification after percutaneous transluminal coronary angioplasty

Approximately 20-30% of patients who undergo elective percutaneous transluminal coronary angioplasty (PTCA) require a second angioplasty within 12 months. A significant proportion of patients develop clinical cardiac events during the first year following the initial procedure. The present investigation was undertaken to establish a statistical model for predicting such events. The study group consisted of 100 patients who underwent elective PTCA at the University of Alberta Hospital. All patients were prescribed nifedipine (10 mg tid) and aspirin (325 mg daily) in addition to other medications determined by the attending cardiologist. The patients were reviewed 10 weeks after the procedure and again at the end of 1 year. The follow-up was completed on 96 patients. Within the first year, forty-five experienced cardiac events (1 death, 5 myocardial infarctions, 4 bypass surgeries, 22 repeat PTCAs). These events occurred in 29 patients. An additional 16 patients experienced significant anginal symptoms. A statistical model based upon the patients' perception of symptoms immediately after the procedure, history of hypertension, vessel subjected to PTCA, ejection fraction pre-PTCA, and occurrence of intimal dissection during PTCA was used to identify patients likely to develop cardiac events. Overall, the model classified 72% of the patients (with and without events). Such a statistical model could be used to identify patients who should be subjected to an enhanced degree of cardiologic surveillance in a rehabilitation program.

Estimation of the risk of death during the first year after acute myocardial infarction from systolic time intervals during the first week

Patients who survived for the first seven days after acute myocardial infarction were followed up for a further 51 weeks. During these 51 weeks there were 123 deaths and 477 eventual survivors. Approximately half of the deaths occurred during the first 3 weeks of follow up. The deaths were predicted with 75% sensitivity and 73% specificity by a discriminant analysis based upon six variables seen during the first 7 days; predictions of death and survival were 55% and 92% accurate respectively. These six variables were, in ascending order of prognostic importance, the occurrence of bundle branch blocks, the administration of a diuretic, the age of the patient, the presence of diabetes mellitus, a previous myocardial infarction, and the ratio of the measured left ventricular pre-ejection and ejection periods. Many other monitored variables, although univariately associated with death, contributed nothing further to the multivariate assessment of mortality risk.

Limitations of a conventional logistic regression model based on left ventricular ejection fraction in predicting coronary events after myocardial infarction

The clinical utility of conventional logistic regression models based on left ventricular ejection fraction (LVEF) for the prediction of cardiac events (death or recurrent infarction) was assessed in 646 postinfarction patients undergoing radionuclide ventriculography at rest and during exercise. The discriminant power of 2 different models (LVEF at rest alone vs LVEF at rest plus LVEF at peak exercise) was quantified in terms of the area under receiver-operating characteristic curves based on knowledge of patient outcome in the year after testing and the logistic probability of that outcome. Although LVEF at rest provided a significant amount of prognostic information (receiver-operating characteristic curve area = 62 +/- 4%, p less than 0.001), several limitations were observed: (1) powerful predictors of risk were uncommon (32% of patients with an LVEF at rest less than 0.20 had a cardiac event, but only 3% of the population had such extreme values); (2) the accuracy of predictions for high risk patients was less than for low risk patients (28 vs 98%, p less than 0.001); (3) addition of exercise LVEF to the model did not improve the accuracy of prediction (receiver-operating characteristic curve area = 68 +/- 4%, p = 0.11); and (4) predictions for individual patients were very imprecise (the 95% confidence interval of percent risk for an LVEF at rest of 0.20 [11 to 36%] overlapped that for an LVEF at rest of 0.60 [0 to 14%]).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise testing after myocardial infarction: relative values of the low level predischarge and the postdischarge exercise test

This study was undertaken to compare the relative values of the low level predischarge exercise test and the postdischarge (6 weeks) symptom-limited test in 518 consecutive patients admitted with an acute myocardial infarction. Of the patients who did not develop significant ST segment depression or angina during the predischarge test, the symptom-limited test also remained negative in 91.5 and 91.9% of the patients, respectively. Similar results were obtained with ST segment elevation and the systolic blood pressure response during the two exercise tests with only 2.1 and 11.4% changing from normal to abnormal, respectively. Discriminant function analysis was done to predict the occurrence of coronary events (unstable angina, reinfarction, cardiac failure, cardiac death) with use of the data from the exercise tests together with other clinical and investigational data. The jackknife method correctly classified 71.9 and 71.4% of the patients with the data from the predischarge exercise test and symptom-limited test, respectively. Combining the data from the two tests improved the overall predictive accuracy to only 75.0%. It is concluded that the routine performance of a symptom-limited test 6 to 8 weeks after infarction does not reveal any significant additional information in those patients who have undergone a predischarge low level exercise test. Thus the 6 to 8 week test should be restricted to selected patients after myocardial infarction.