Q wave

Ascher, E.K. Stauffer, J-C.E. and Gaasch, W.H. Coronary artery spasm, cardiac arrest, transient electrocardiographic Q waves and stunned myocardium in cocaine-associated acute myocardial infarction. 

After an electrical impulse is initiated and conducted, there is a period of time during which cells and fibers cannot be depolarized again. This period of time is referred to as the absolute refractory period (Fig. 6-2),2 and corresponds to phases 1,2, and approximately half of phase 3 repolarization on the action potential. The absolute refractory period also corresponds to the period from the Q wave to approximately the first half of the T wave on the ECG (Fig. 6-2). During this period, if there is a premature stimulus for an electrical impulse, this impulse cannot be conducted, because the tissue is absolutely refractory. 

Acute coronary syndromes Ischemic chest discomfort at rest, most often accompanied by ST-segment elevation, ST-segment depression, or T-wave inversion on the 12-lead electrocardiogram. Furthermore, it is caused by plaque rupture and partial or complete occlusion of the coronary artery by thrombus. Acute coronary syndromes include myocardial infarction and unstable angina. Former terms used to describe types of acute coronary syndromes include Q-wave myocardial infarction, non-Q-wave myocardial infarction, and unstable angina. 

Non-ST-segment elevation A type of myocardial infarction (MI) that is limited to the subendocardial myocardium and is smaller and less extensive than an ST-segment MI. There is usually no pathologic Q-wave on the electrocardiogram in non-ST-segment elevation. 

After a STEMI, pathologic Q waves are seen frequently on the ECG and usually indicate transmural MI. Non-Q-wave MI, which is seen predominantly in NSTE MI, is limited to the subendocardial myocardium. 

The QT interval (measured from the beginning of the Q wave to the end of the T wave of the surface electrocardiogram) reflects the duration of individual action potentials in cardiac myocytes (Figure 3.1) indeed, a prolongation of the action potential duration (APD) of myocytes will result in a prolonged QT interval. 

QT interval time between end of Q wave and start of T wave... 

Acute coronary syndrome For patients with acute coronary syndrome (unstable angina/non-Q-wave Ml) including patients who are to be managed medically and those who are to be managed with percutaneous coronary intervention (with or without stent) or coronary artery bypass graft (CABG), clopidogrel has been shown to decrease the rate of a combined endpoint of cardiovascular death. Ml, or stroke, as well as the rate of a combined endpoint of cardiovascular death. Ml, stroke, or refractory ischemia. 

Prophylaxis of ischemic complications in unstable angina and non-Q-wave Ml- —... 

Unstable angina/Non-Q-wave Ml - The recommended dose is 120 units/kg of body weight (but not more than 10,000 units) subcutaneously every 12 hours with concurrent oral aspirin (75 to 165 mg/day) therapy. Concurrent aspirin therapy is recommended except when contraindicated. Continue treatment until the patient is clinically stabilized. The usual duration of treatment is 5 to 8 days. 

Do not give dalteparin to patients undergoing regional anesthesia for unstable angina or non-Q-wave Ml because of an increased risk of bleeding associated with the dosage of dalteparin recommended for unstable angina and non-Q-wave Ml. 

Cardiovascular - Ang na pectoris aggravated, arrhythmia, arrhythmia atrial, atrial fibrillation, bradycardia, bundle branch block, cardiac failure, extrasystole, heart murmur, heart sound abnormal, hypertension, hypotension. Ml, palpitation, Q-wave abnormality, tachycardia, ventricular tachycardia (5% or less). 

Effects of tissue plasminogen activator and a comparison of early invasive and conservative strategies in unstable angina and non-Q-wave myocardial infarction results of the TIMI IIIB trial. Thrombolysis in myocardial ischemia. Circulation 1994 89 1545-1556. 

Boden WE, O Rourke RA, Crawford MH, et al. Outcomes in patients with acute non-Q wave myocardial infarction randomly assigned to an invasive as compared with a conservative management strategy (VANQUISH). N Engl J Med 1998 338 1785-1792. 

Drug therapy of acute coronary syndromes including unstable angina and non-Q-wave myocardial infarction includes use of aspirin, heparin and anti-ischaemic drugs and is similar in older patients to other age groups. Activation of platelet thromboxane production in the coronary circulation has been demonstrated in unstable angina. The risk of myocardial infarction or death is reduced by approximately 50% by early aspirin therapy in recommended doses of 160-325 mg per day and continued... 

Cohen M, Adams PC, Parry G, Xiong J, Chamberlain D, Wieczorek 1 et al. Combination antithrombotic therapy in unstable rest angina and non-Q-wave infarction in nonprior aspirin users. Primary end points analysis from the ATACS trial. Antithrombotic Therapy in Acute Coronary Syndromes Research Group. Circulation 1994 89(l) 81-8. 

Tirofiban is a synthetic, nonpeptide inhibitor of glycoprotein-(GP)-receptors. Tirofiban has a rapid onset and short duration of action after intravenous administration. Coagulation parameters turn to normal 4-8 hours after the drug is withdrawn. Tirofiban in combination with heparin and aspirin is indicated in the management of patients with unstable angina or non-Q-wave myocardial infarction. 

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