ACTIVIDADES ACADÉMICAS DIRIGIDAS

or T-wave changes and with a negative stress test and cardiac biomarkers. (Level of Evidence: C)

The use of cocaine can produce myocardial ischemia, thereby leading to UA/NSTEMI.998–1001 _{The widespread use of}

cocaine makes it mandatory to consider this cause, because its recognition mandates special management. Specifically, ini- tial management recommendations for cocaine-induced ACS include NTG and calcium channel antagonists. Assessment for resolution of chest discomfort and ECG changes is then undertaken before fibrinolytic therapy is initiated or angiogra- phy is considered. The use of beta blockers in close proximity (ie, within 4 to 6 h) of cocaine exposure is controversial, with some evidence for harm; thus, when used, the guidelines rec- ommend combination alpha and beta blockade in addition to a vasodilator. There are no data to guide recommendations for beta blockade later after exposure, after cocaine elimination.

The action of cocaine is to block presynaptic reuptake of neurotransmitters such as norepinephrine and dopamine, which produces excess concentrations at the postsynaptic receptors that lead to sympathetic activation and the stimula- tion of dopaminergic neurons.1002 _{There may also be a direct}

contractile effect on vascular smooth muscle.999 _{Detoxification}

is accomplished with plasma and liver cholinesterases, which form metabolic products that are excreted in the urine. Infants, elderly patients, and patients with hepatic dysfunction lack sufficient plasma cholinesterase to metabolize the drug1003 _and

therefore are at high risk of adverse effects with cocaine use.

6.6.1. Coronary Artery Spasm With Cocaine Use

The basis for coronary spasm has been demonstrated in both in vitro1003 _{and in vivo}999,1004–1008 _{experiments in animals and}

humans. Reversible vasoconstriction of rabbit aortic rings has been demonstrated with cocaine in concentrations of 10−3 _{to 10}−8 _{mol per liter. Pretreatment with calcium channel}

blockers markedly inhibits cocaine-induced vasoconstriction. Coronary injection of cocaine produces vasoconstriction in miniswine with experimentally induced nonocclusive athero- sclerotic lesions.1009

Nademanee et al1010 _{performed 24-h ECG monitoring in}

21 male cocaine users after admission to a substance abuse treatment center and found that 8 had frequent episodes of ST-segment elevation, most during the first 2 weeks of with- drawal. In cocaine users with prolonged myocardial ischemia, coronary arteriography can reveal coronary artery spasm with otherwise normal-appearing coronary arteries or with under- lying minimally obstructive coronary atherosclerosis.999,1001,1004

The cocaine-induced increase in coronary vascular resistance is reversed with calcium channel blockers.1005,1011 _Cocaine

increasing thromboxane A2 production and platelet aggrega- tion.1012 _{In addition, reversible combined reduction in protein}

C and antithrombin III has been observed in patients with cocaine-related arterial thrombosis.1013 _{All of these effects}

favor coronary thrombosis.999,1006,1014 _{Coronary thrombosis can}

also develop as a consequence of coronary spasm.

Cocaine users can develop ischemic chest discomfort that is indistinguishable from the UA/NSTEMI secondary to coronary atherosclerosis. The patient who presents with prolonged myocardial ischemia should be questioned about the use of cocaine. In a study by Hollander et al,1015 _the

presence or absence of cocaine use was assessed in only 13% of patients who presented to the ED with chest pain. Table 26 lists the clinical characteristics of a typical patient with cocaine-related chest pain or MI.1001

Most patients who present to the ED with cocaine-associ- ated chest pain do not develop MI.1016 _{MI development has}

been reported to occur only in 6% of such patients.1001

Accelerated coronary atherosclerosis has been reported in chronic users of cocaine1017,1018_{; coronary artery spasm is more}

readily precipitated at sites of atherosclerotic plaques.1004 _Cocaine

causes sinus tachycardia, as well as an increase in blood pres- sure and myocardial contractility, thereby increasing myocardial oxygen demand.1005 _{These increases can precipitate myocardial}

ischemia and UA/NSTEMI in both the presence and absence of obstructive coronary atherosclerosis and coronary spasm.

Aortic dissection1019 _{and coronary artery dissection}999,1019

have been reported as consequences of cocaine use. Other reported cardiac complications are myocarditis1018 _and

cardiomyopathy.1020,1021

6.6.2. Treatment

When a patient with or suspected of cocaine use is seen in the ED with chest pain compatible with myocardial isch- emia and ST-segment elevation, sublingual NTG or a calcium channel blockers (eg, diltiazem 20 mg IV) should be admin- istered.999,1008 _{If there is no response, immediate coronary angi-}

ography should be performed, if possible. Fibrinolytic therapy has been successfully employed in patients with MI after cocaine use, although these patients frequently have contra- indications to fibrinolysis, including hypertension, seizures, or aortic dissection. Thus, PCI may be a preferred method

of revascularization in this setting. However, even this thera- peutic strategy is problematic in subjects with cocaine-related MI; those in whom stents are deployed are at substantial risk of subsequent in-stent thrombosis unless double-antiplatelet therapy (ASA and clopidogrel) is ingested regularly and pre- dictably for several months afterward, and those who partake in substance abuse often are unreliable in adhering to such a regimen. Thus, bare-metal stents, which require a shorter duration of dual-antiplatelet therapy, generally are preferred to DES in cocaine abusers. If thrombus is present and PCI is unavailable or ineffective, fibrinolytic agents may be admin- istered if there are no contraindications.1022,1023 _{If catheteriza-}

tion is not available, intravenous fibrinolytic therapy may be considered in patients with ST-segment elevation and clinical symptoms consistent with MI.

If the ECG is normal or shows only minimal T-wave changes and there is a history of chest pain compatible with acute myocardial ischemia, the patient should receive sublin- gual NTG or an oral calcium channel blocker and be observed. After cocaine use, increased motor activity, skeletal muscle injury, and rhabdomyolysis can occur, causing CK and even CK-MB elevation in the absence of MI.1024 _{Troponin I and}

TnT are more specific for myocardial injury and therefore are preferred. Blood should be drawn twice for serum mark- ers of myocardial necrosis at 6-h intervals. If the ECG shows ST-segment changes and the cardiac biochemical markers are normal, the patient should be observed in the hospital in a monitored bed for 24 h; most complications will occur within 24 h.1025 _{If the patient's clinical condition is unchanged and}

the ECG remains unchanged after 24 h, the patient can be dis- charged.1023 _{A shorter observation period of 9 to 12 h, with}

measurement of troponin levels at 3, 6, and 9 h after presenta- tion, also has been validated.1026

Many observers believe that beta blockers are contrain- dicated in cocaine-induced coronary spasm because there is evidence from a single double-blind, randomized, placebo- controlled trial that beta-adrenergic blockade augments cocaine-induced coronary artery vasoconstriction.1027 _Others

believe that if the patient has a high sympathetic state with sinus tachycardia and hypertension, beta blockers should be used.999 _{Labetalol, an alpha and beta blocker, has been advo-}

cated, because it has been shown not to induce coronary artery vasoconstriction1028 _{even though its beta-adrenergic–block-}

ing action predominates over its alpha-adrenergic–blocking activity in the doses that are commonly used.1028 _Therefore,

in cocaine-induced myocardial ischemia and vasoconstric- tion, NTG and calcium channel blockers are the preferred drugs. Both NTG and verapamil have been shown to reverse cocaine-induced hypertension, coronary arterial vasoconstric- tion,1008,1027 _{and tachycardia (verapamil).}

6.6.3. Methamphetamine Use and UA/NSTEMI

Given the rapid increase in methamphetamine abuse, recog- nition of its cardiovascular risk is of mounting importance. Currently, the evidence base for UA/NSTEMI after meth- amphetamine and its treatment is limited to a few publica- tions of case reports and small series.1029–1032 _{These suggest}

that ACS is increasingly common in patients evaluated in the ED for chest discomfort after methamphetamine use and that

Table 26. Clinical Characteristics in the Typical Patient With Cocaine-Related Chest Pain, Unstable Angina, or Myocardial Infarction

Young age, usually less than 40 years Male gender

Cigarette smoker, but no other risk factors for atherosclerosis Chronic or first-time cocaine user

Symptom onset minutes or even several hours after cocaine use Associated with all routes of administration

May occur with small or large doses

Often associated with concomitant use of cigarettes and/or alcohol Reprinted from Progressive Cardiovascular Disease, Pitts WF, Lange RA, Cigarroa JE, Hillis LD. Cocaine-induced myocardial ischemia and infarction: pathophysiology, recognition, and management, 65–76. Copyright 1997, with permission from Elsevier.857

the frequency of other potentially life-threatening arrhyth- mias is not negligible.1030 _{Clinical presentation resembles}

that of cocaine-associated ACS. On the basis of the similari- ties in pathophysiology and these few clinical observations, therapy similar to that of cocaine-induced UA/NSTEMI is recommended pending information more specific to methamphetamine.

6.7. Variant (Prinzmetal's) Angina Recommendations

Class I

1. Diagnostic investigation is indicated in patients with