Intravenous amiodarone is effective for the treatment of recurrent, life-threatening ventricular tachyarrhythmias.

No abstract

Intravenous amiodarone is a relatively safe therapy for ventricular tachyarrhythmias refractory to other medications.

Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Adenosine in graded doses up to 12 mg rapidly and effectively terminates acute episodes of paroxysmal supraventricular tachycardia in which the atrioventricular node is an integral part of the re-entrant circuit. The overall efficacy of adenosine is similar to that of verapamil, but its onset of action is more rapid. Adverse reactions to adenosine are common but are minor and brief.

CVT-510 promptly prolongs AV nodal conduction and does not affect sinus rate or blood pressure. Selective stimulation of the A(1)-adenosine receptor by CVT-510 may be useful for immediate control of heart rate in atrial fibrillation/flutter and to convert paroxysmal supraventricular tachycardia to sinus rhythm, while avoiding vasodilatation mediated by the A(2)-adenosine receptor, as well as the vasodepressor and negative inotropic effects associated with beta-adrenergic receptor blockade and/or calcium channel blockers.

No abstract

Identification of regional myocardial ischemia by TQ-ST segment mapping, while comnmonly used, is relatively imprecise and nonspecific. In 41 open-chest dogs we examined whether monophasic action potentials (MAPs) recorded from the myocardial surface by means of a new contactelectrode technique could be used to more precisely and specifically index regional myocardial ischemia. After ligation of the left anterior descending coronary artery (LAD), epicardial and endocardi-al MAPs from the ischemic region demonstrated shortening of plateau duration followed by a progressive loss in amplitude to 48 ± 8% and in maximum upstroke velocity (dV/dtmax) to 9 2% of control (n = 7). Regional hyperkalemia produced by intracoronary injection of potassium chloride also resulted in regional decreases in duration, amplitude, and dV/dtmax of the MAP. Similar to previously reported effects on transmembrane action potentials, ischemia-or hyperkalemia-induced loss in MAP amplitude was due to decreases in both diastolic (negative) and systolic (positive) potential and paralleled TQ segment depression and "true" ST segment elevation in unipolar direct current-coupled electrograms recorded from an adjacent site. In eight canine hearts we compared the abilities of MAP recordings and TQ-ST segment measurements in defining a region of myocardial ischemia. Transmural ischemia with a sharp flow border was produced by LAD ligation and distal embolization with dental rubber. One hour later simultaneous MAP and TQ-ST mapping was performed in each dog at 45 to 65 epicardial sites inside and outside the ischemic region. TQ-ST voltage was significantly increased 10 to 20 mm outside the visible cyanotic border, reaching a maximum just inside the border and decreasing progressively toward the center of the ischemic region to values not significantly different from those from sites 10 mm outside the ischemic border. In contrast, MAP amplitude and dV/dtmax were normal up to 5 to 10 mm outside the cyanotic border, decreased sharply across a lateral transition zone of only 8 mm to 8.7 + 2.3% and 4.3 + 0.9% of control, respectively, at sites 4 to 6 mm inside the border, and were uniformly abnormal across the entire ischemic region. Recordings made 3 hr after LAD ligation revealed an overall decline in the magnitude of TQ-ST, making definition of the ischemic border by TQ-ST even less precise, whereas the differences between MAPs from normal and ischemic myocardium had become even more pronounced than after 1 hr. Thus, unlike TQ-ST segment measurements, MAP recordings uniquely define ischemic and nonischemic sites and more precisely localize the border of an ischemic region. The similarities between the effects of regional ischemia and potassium chloride administration on MAPs and on transmembrane action potentials, as previously reported, further suggest that MAP recordings provide specific information about local electrophysiologic alterations. Endocardial and epicardial MAP mapping by this technique may allow assessment of the efficacy of int...