Evaluation of patients with chest pain after cocaine use

Role of voltage-gated sodium, potassium and calcium channels in the development of cocaine-associated cardiac arrhythmias

Cocaine is a highly active stimulant that alters dopamine metabolism in the central nervous system resulting in a feeling of euphoria that with time can lead to addictive behaviours. Cocaine has numerous deleterious effects in humans including seizures, vasoconstriction, ischaemia, increased heart rate and blood pressure, cardiac arrhythmias and sudden death. The cardiotoxic effects of cocaine are indirectly mediated by an increase in sympathomimetic stimulation to the heart and coronary vasculature and by a direct effect on the ion channels responsible for maintaining the electrical excitability of the heart. The direct and indirect effects of cocaine work in tandem to disrupt the co-ordinated electrical activity of the heart and have been associated with life-threatening cardiac arrhythmias. This review focuses on the direct effects of cocaine on cardiac ion channels, with particular focus on sodium, potassium and calcium channels, and on the contributions of these channels to cocaine-induced arrhythmias. Companion articles in this edition of the journal examine the epidemiology of cocaine use (Wood & Dargan) and the treatment of cocaine-associated arrhythmias (Hoffmann).

Increased TIMI frame counts in cocaine users: a case for increased microvascular resistance in the absence of epicardial coronary disease or spasm

BACKGROUND

Cocaine produces adverse cardiovascular effects, some of which cannot be explained by epicardial coronary artery disease (CAD) or spasm.

HYPOTHESIS

The hypothesis of this study was that cocaine users would have increased coronary microvascular resistance, even in the absence of recent myocardial infarction (MI), CAD, or spasm.

METHODS

Microvascular resistance was assessed by the corrected Thrombolysis in Myocardial Infarction (TIMI) frame count (cTFC) method in a consecutive series of 59 cocaine users without acute or recent MI or angiographically significant epicardial stenosis (> 50%) or spasm. The cTFCs in these patients were compared with 21 normal controls and with published normal cTFC values.

RESULTS

The cTFC was significantly elevated (by 26-54%) in cocaine users. The cTFCs in the left anterior descending (LAD), circumflex (LCx), and right coronary (RCA)arteries in cocaine users were 30.0 +/- 10.9,34.1 +/- 11.5, and 28.6 +/- 11.8, respectively, compared with values in normal controls of 21.3 +/- 4.3 (p = 0.001), 24.4 +/- 7.2 (p = 0.001), and 22.7 +/- 5.1 (p = 0.04), respectively, and published normal cTFC values (all p < 0.01). An abnormally high cTFC was present in 61% of patients in the LAD, 69% in the LCx, and 47% in the RCA.

CONCLUSIONS

Markedly decreased coronary blood flow velocity, indicating increased microvascular resistance, is present in cocaine users, even in the absence of acute or recent MI, or significant epicardial CAD or spasm. Increased microvascular resistance may explain many important cardiovascular manifestations of cocaine use and has therapeutic implications. Slow coronary filling may also suggest the possibility of cocaine use in patients in whom it was not otherwise suspected.

Cocaine-associated chest pain

Current estimates establish that more than 30 million people in the United States use cocaine. Cardiovascular complaints commonly occur among patients who present to emergency departments(EDs) after cocaine use, with chest pain the most common complaint in several studies. Although myocardial ischemia and infarction account for only a small percentage of cocaine-associated chest-pain, physicians must understand the pathophysiology of cocaine and appropriate diagnostic and treatment strategies to best manage these patients and minimize adverse outcomes. This article reviews the pharmacology of cocaine, its role in the pathogenesis of chest pain with specific emphasis on inducing myocardial ischemia and infarction, and current diagnostic and management strategies for cocaine-associated chest pain encountered in the ED.

2000 ACC/AHA guidelines for the management of patients with unstable angina and non-ST-segment elevation myocardial infarction: a practical summary for emergency physicians

There have been numerous significant clinical advances in both the diagnosis and therapy of acute coronary syndrome during the past several years. Even the term "acute coronary syndrome" is a recent creation meant to expand clinical attention in patients with chest pain of coronary origin beyond identification of ST-segment elevation myocardial infarction and prompt initiation of reperfusion therapy and to include the evaluation and management of those patients with unstable angina (UA) or myocardial injury that does not cause ST-segment elevation. Many of these advances have been studied and first implemented outside the emergency department, leading some emergency physicians to be slow to embrace them, and leaving others without a viable practical option to use them outside of the cardiac catheterization laboratory or the coronary care unit. In September 2000, the American College of Cardiology and the American Heart Association issued practice guidelines for the care of patients with UA and non-ST-segment elevation myocardial infarction. The guidelines specifically address the diagnosis and management of UA and non-ST-segment elevation myocardial infarction in the ED, suggesting evidence-based standards for risk stratification, for the use of biologic markers of myocardial damage and other adjunctive diagnostic tests, and for the appropriate use of antiplatelet and antithrombin therapeutic agents. This article provides an overview of the ED-pertinent analyses and recommendations from the 93-page document. A commentary on the implementation of these recommendations in the ED follows in a separate article.

Prevention of suboptimal beta-blocker treatment in patients with myocardial infarction

OBJECTIVE

To review the published data and clinical guidelines on the use of beta-blockers in myocardial infarctions (MIs) and contrast that with actual clinical practice.

DATA SOURCES

A MEDLINE search (January 1970-June 1999) was performed to identify all relevant articles. References from these articles were also evaluated for review if deemed important.

DATA SYNTHESIS

Intravenous and oral beta-blockers have been proven to improve outcomes in patients with MIs in numerous clinical trials. In current clinical practice, only 15% of MI patients receive intravenous beta-blockers and long-term beta-blocker therapy is used in <40% of patients without contraindications. However, they could be safely administered to 40% and 70% of these patients, respectively. Furthermore, most of these patients are receiving doses far below those found beneficial in clinical trials. Many of the real and perceived contraindications to beta-blockers are reviewed to allow the practitioner to identify patients who are incorrectly excluded from beta-blocker therapy. Also discussed are special clinical situations in which the benefits observed during clinical trials may not apply.

CONCLUSIONS

Beta-blockers are valuable drugs in the treatment of peri- and post-MI. In clinical practice, most patients are not treated or are inadequately treated with beta-blockers. Pharmacists should ensure that such patients actually have an absolute contraindication or unusual situation where therapy is not firmly indicated. Patients without absolute contraindications warrant titration to specific target doses or a target heart rate of 55-60 beats/min.