Heart rate variability during the first 24 hours of successfully reperfused acute myocardial infarction: paradoxic decrease after reperfusion

Heart rate variability (HRV) was evaluated during the first 24 hours of hospitalization in 36 patients with acute myocardial infarction. Reperfusion was achieved by 60 minutes in 21 patients (group M1) and by 130 minutes in the remaining 15 (group M2). Mean 24-hour HRV measures were not significantly different between groups M1 and M2. Hourly spectral analysis revealed a decrease in total power (0.01 to 1.0 Hz) from 0 to 8 hours to 9 to 16 and 17 to 24 hours in groups M1 (7.04 +/- 0.27 to 6.94 +/- 0.28 and 6.52 +/- 0.18; p = 0.0006) and in group M2 (6.88 +/- 0.30 to 6.57 +/- 0.23 and 6.40 +/- 0.15; p = 0.002). Total power decreased immediately after reperfusion: in group M1 it decreased during the second hour (7.32 +/- 0.96 to 6.42 +/- 1.2; p = 0.001) and in group M2 during the third (7.47 +/- 1.2 to 6.73 +/- 1.4; p = 0.049) and fourth hours (7.47 +/- 1.2 to 6.48 +/- 1.4; p = 0.029). Mean change in total power in the second hour was -11.6% in group M1 and +3.9% in group M2 (p = 0.0001) and in the third hour, +14.5% in group M1 and -8.6% in group M2 (p = 0.006). During the remaining 21 hours, there was no significant difference in hourly change in total power between groups. Similar changes were noted in high-frequency power, but the ratio of low-frequency to high-frequency power was unchanged. In acute myocardial infarction, HRV is higher during the early phase and decreases as hours progress. Reperfusion causes an immediate, transient, and seemingly paradoxic decrease in HRV, probably because of an abrupt decrease in parasympathetic tone.

Acute myocardial infarction. Then and now

Dramatic changes in the management of acute myocardial infarction (AMI) have occurred in the past decade. While previous management strategies were primarily supportive, current strategies focus on achieving and maintaining patency of the infarct-related artery restoring blood flow to jeopardized myocytes, preserving left ventricular function, and preventing recurrences and complications in addition to promoting healing. Restoration of blood flow can be achieved pharmacologically with thrombolytic agents or mechanically with percutaneous transluminal coronary angioplasty (PTCA). Early use of antiplatelet agents and anticoagulants helps maintain patency of the infarct-related arteries and prevents thromboembolic complications. Administration of beta-blockers and angiotensin enzyme inhibitors are more specific means of conserving myocardium and preserving ventricular function. Additionally, several strategies for preventing arrhythmias such as prophylactic lidocaine use and routine long-term suppression of premature ventricular contractions with antiarrhythmic drugs are no longer routinely advocated. Basically, in the era prior to the eighth decade of this century, the primary direction of the therapeutic strategy for AMI was to reduce the oxygen demands in the infarcted myocardium; whereas in the subsequent years, the emphasis shifts to improvement in oxygen delivery, via thrombolysis, PTCA, and coronary artery bypass graft surgery. These interventional changes, when added to greater sophistication in the use of drugs to reduce oxygen demands, resulted in significant lowering of myocardial mortality.

Is ambulatory electrocardiography useful in the evaluation of patients with recent stroke?

This study was designed to determine whether ambulatory electrocardiography in patients with recent stroke would lead to a change in clinical management or outcome and to express these findings in terms of cost benefit. A prospective, consecutive sample of patients (n = 100) with recent stroke referred from the neurology or medical services for ambulatory electrocardiography was identified. Ambulatory electrocardiograms were reviewed to identify patients with potentially important bradyarrhythmias, tachyarrhythmias, or atrial fibrillation. Patients were then followed up without interference with ongoing care to determine whether these findings led to changes in clinical management that might influence patient outcome. Of the 100 patients, 16 had an index "important" arrhythmia. No significant bradyarrhythmias were noted. Nonsustained ventricular tachycardia (> or = 6 complexes) in two patients and supraventricular tachycardia (> or = 10 complexes) in seven patients did not lead to management changes. Four patients had a history of atrial fibrillation who were in sinus rhythm; anticoagulation had been addressed in three; the fourth patient died before the issue could be addressed. Of three patients in atrial fibrillation, there was a history of atrial fibrillation and a decision regarding anticoagulation in each before monitoring. The cost of these 100 ambulatory electrocardiograms was about $55,000. In conclusion, these findings do not support the routine use of ambulatory electrocardiography in the evaluation of patients with stroke.

Ambulatory electrocardiography. A cost per management decision analysis

BACKGROUND

This study evaluated the current clinical use and costs of ambulatory electrocardiographic (AECG) monitoring for arrhythmia detection based on a cost per management decision analysis.

METHODS

Consecutive inpatient and outpatient 24-hour AECGs (n = 650) performed during the calendar year 1991 were retrospectively reviewed for clinical indication, arrhythmia detection, diary information, and whether a management decision that might alter patient outcome was derived from the data. The cost per management decision (based on a representative reimbursement of $550 per AECG) and the cost index (CI) (all tests divided by useful tests) were calculated.

RESULTS

Although arrhythmias were identified in 91% of the patients, management decisions were indicated in only 18% (cost per decision, $2974; CI = 5.4). Management decisions were most often derived from the data in patients being evaluated for arrhythmia therapy (37 of 37 patients; cost per decision, $550; CI = 1). Symptoms and arrhythmias were correlated in only 11 patients (2%). More often typical clinical symptoms were present (26 patients) in the absence of an arrhythmia. Of 101 AECGs following a cerebrovascular event, four had unsuspected atrial fibrillation (cost per decision, $13,888; CI = 25.0). Dizziness or lightheadedness associated with other cardiac symptoms was more likely to lead to a management decision than the same symptoms in isolation (29% vs 7%; P < .05). No patient had central nervous system symptoms correlated with an arrhythmia during the recording period or unsuspected ventricular tachycardia.

CONCLUSION

Ambulatory electrocardiography has a highly variable and indication-dependent effectiveness and cost. The results suggest a strategy for improving the use of AECG based on knowing what testing indications are more likely to lead to useful clinical information.

Frequency and type of electrocardiographic abnormalities in cocaine abusers (electrocardiogram in cocaine abuse)

Electrocardiographic abnormalities of 200 asymptomatic, chronic cocaine abusers (aged < or = 45 years, 69% black) admitted for rehabilitation (group 1) were compared with 38 cocaine abusers treated in the emergency room (group 2), 21 cocaine abusers who died suddenly (group 3), and 425 control subjects from the general population. In group 1, 39% of electrocardiograms were abnormal: Increased QRS voltage was noted in 27%, ST elevation in 22%, ST-T changes in 17%, and prior myocardial infarction in 3%. Increased QRS voltage (35% vs 10%, p = 0.00007) and ST elevation (26% vs 13%, p = 0.0278) were more prevalent in blacks than in whites. With use of Minnesota coding, electrocardiograms in group 1 were compared with those of 141 black and 284 white men (aged < 40 years) from the general population. ST elevation was more prevalent in both black (22% vs 8%, p = 0.00073) and white (15% vs 1%, p < 0.00001) cocaine abusers than in the general population. Compared with group 1, group 2 had higher prevalence of sinus tachycardia (16% vs 1%, p = 0.0002), supraventricular tachycardia (5% vs 0%, p = 0.024), ST-T changes (34% vs 17%, p = 0.0164), and QTc > 440 ms (26% vs 4%, p = 0.00003); mean QTc was also greater among group 2 subjects (427 +/- 38 vs 404 +/- 19 ms, p < 0.0001). In group 3, QTc was > 440 ms in 6 of 8 subjects (75%) with 12-lead electrocardiograms.(ABSTRACT TRUNCATED AT 250 WORDS)

A technique for performing transesophageal echocardiography safely in patients with Zenker's diverticulum

Transesophageal echocardiography was indicated for evaluation of mitral valve pathology in a patient with a Zenker's diverticulum. However, transesophageal echocardiography is potentially dangerous and therefore relatively contraindicated in such patients. Our gastroenterologist directly intubated the esophagus with a fiberoptic endoscope and introduced an overtube through which transesophageal echocardiography was performed without incident.

Cardiovascular manifestations of cocaine abuse. A case of recurrent dilated cardiomyopathy

The medical complications of cocaine abuse are being encountered by clinicians with increasing frequency. The cardiovascular manifestations of cocaine abuse include chest pain, myocardial ischemia and infarction, congestive heart failure, arrhythmias, infective endocarditis, and aortic dissection. The pathogenesis of these cardiovascular complications has not been fully elucidated but may be related to a combination of the sympathomimetic and membrane anaesthetic effects of cocaine. We present these concepts in a case discussion format.

Future evaluation of antiarrhythmic therapy

The expansion of antiarrhythmic therapy beyond pharmacologic agents to include surgery, devices, and ablation procedures, plus the reaffirmation by the Cardiac Arrhythmia Suppression Trial (CAST) of the need for concurrent placebo-controlled trials to establish a mortality benefit, have resulted in the need to consider the requirements for evaluating therapy. Pharmacologic therapy may be used in three ways: (1) primary; (2) alternative; and (3) adjunctive. To accurately identify a mortality benefit from primary therapy, a placebo-controlled study is necessary. In contrast, control of symptoms may be identified without the same rigorous demands. Current data are limited by the absence of true negative controls for most interventions that claim a possible mortality benefit. Alternative therapy provides a choice between equally effective therapies, neither of which has necessarily been documented to have a mortality benefit. Adjunctive therapy is that which is used for control of symptoms, whereas another therapy is used to provide a presumed or proved mortality benefit. For any of these approaches, therapy must be further evaluated in terms of four modifying variables: (1) impact of therapy on the basis of both its efficacy and efficiency; (2) interpretation of outcome data based on analysis of competing risks; (3) measurement of efficacy in terms of extension of life; and (4) analysis of outcome as the equilibrium between antiarrhythmic benefit and proarrhythmic risk. With these approaches a rational analysis of the effect of therapy and its cost-based benefit can be achieved.

Sudden cardiac death: epidemiology, transient risk, and intervention assessment

PURPOSE

To integrate information from the various disciplines that contribute to the understanding of the cause and prevention of sudden cardiac death: identification of new approaches from applied clinical epidemiology; identification and control of transient risk factors; and evaluation of the results of interventions.

DATA SOURCES

A broad range of research reports and interpretations of data from English-language journal articles and reviews, published primarily between 1970 and 1993. The fields of study included epidemiology, experimental electrophysiology, clinical observations, and interventions.

STUDY SELECTION

Continuous literature surveys, done in relation to ongoing clinical and experimental research on sudden cardiac death since 1972.

DATA EXTRACTION

Included on the basis of relevance to the topics discussed and with confirmation of data and concepts by more than one investigator when available.

DATA SYNTHESIS

Information from several disciplines was integrated by the authors to synthesize new ways to view the problem of sudden cardiac death. Quantitative information was used primarily to derive qualitative statements about new perspectives on sudden cardiac death.

CONCLUSIONS

Progress in the prevention of sudden death will require development of new approaches, including epidemiologic techniques to address risk characteristics specific to the problem; characterization of triggering events and identification of specific persons at risk for responding adversely to these events; and methods of evaluating outcomes appropriate to the nature of sudden cardiac death.

Alterations in heart rate variability and its circadian rhythm in hypertensive patients with left ventricular hypertrophy free of coronary artery disease

Heart rate variability (HRV) and its circadian rhythm were evaluated in 22 patients with treated hypertension and left ventricular hypertrophy in whom coronary artery disease was excluded by stress thallium or angiography. By using 24-hour Holter monitoring, HRV and its spectral components were measured. Findings were compared with 11 age-matched normal controls. The difference between mean R-R intervals during sleep (11 PM to 7 AM) and while awake (9 AM to 9 PM) (73 +/- 33 vs 263 +/- 63 msec, p < 0.0001) and the mean 24-hour SD of the R-R intervals (55 +/- 6.3 vs 93 +/- 11, p < 0.0001) were lower among the hypertensive patients compared with controls. The percentage of difference between successive R-R intervals that exceeded 50 msec, a measure of parasympathetic tone, was also lower among the hypertensive patients (6.8 +/- 7.1 vs 13.6 +/- 8.9, p < 0.002); it increased at night and decreased during the day among the controls, and this circadian rhythm was blunted among the patients. Spectral analysis showed that power in the high-frequency range (0.15 to 0.40 Hz) was lower among the hypertensive patients during 21 of 24 hours but that the difference was statistically significant only during 9 hours (p ranging from < 0.05 to 0.009). Power in the low-frequency range (0.04 to 015 Hz) was lower at night, increased in the morning, and higher during the day among controls; this circadian rhythm was absent among hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute right ventricular infarction mimicking extensive anterolateral wall injury

A patient presented with an acute right ventricular infarction characterized by an electrocardiographic current of injury in both the inferior (2,3,aVF) and anterior precordial leads (V1-V6). Cardiac catheterization demonstrated normal left ventricular wall motion, a codominant circulation, and severe disease of the right coronary artery. We propose that this coronary anatomy explains the injury currents on the electrocardiogram. This case illustrates a rare presentation of right ventricular myocardial infarction mimicking an extensive anterolateral wall injury.

Frequency domain measures of heart rate variability before the onset of nonsustained and sustained ventricular tachycardia in patients with coronary artery disease

BACKGROUND

Low heart rate variability (HRV) is associated with an increased risk of arrhythmic death and ventricular tachycardia (VT). The purpose of this study was to examine whether there is a temporal relation between changes in HRV and the onset of spontaneous episodes of VT in patients at high risk of life-threatening arrhythmias.

METHODS AND RESULTS

Components of HRV in the frequency domain were analyzed before the onset of 28 episodes of nonsustained VT (more than four impulses; duration < 30 seconds) and 12 episodes of sustained VT (> 30 seconds or requiring defibrillation) in 18 patients with coronary artery disease. Seven patients had survived cardiac arrest not associated with acute myocardial infarction, and 11 had a history of sustained VT. All frequency domain measures of HRV, i.e., total power (p < 0.001), high-frequency power (p < 0.05), low-frequency power (p < 0.01), very-low-frequency power (p < 0.01), and ultralow-frequency power (p < 0.05), were significantly lower before the onset of sustained VT than before nonsustained VT. Total power of HRV was also lower during the 1-hour period before the onset of sustained VT than the average 24-hour HRV (p < 0.05). An indirect correlation existed between the length of VT and the total power of HRV analyzed during the 15 minutes before the onset of VT (r = 0.54, p < 0.01). HRV had a trend toward increasing values before the onset of nonsustained VT (p < 0.01) but not before the sustained VT episodes. The ratio between low-frequency and high-frequency powers increased substantially before both nonsustained and sustained VT episodes (p = 0.06 and p = 0.05, respectively). The rate of VT or the coupling interval initiating the VT did not differ significantly between the nonsustained and sustained VT.

CONCLUSIONS

Spontaneous episodes of VT are preceded by changes in HRV in the frequency domain. Divergent dynamics of HRV before the onset of nonsustained and sustained VT episodes may reflect differences in factors that can facilitate the perpetuation of these arrhythmias.