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The Intensive Care Manual - part 6

Không giống như các hoạt động tâm nhĩ gây mất trật tự trong rung, nó được chấp nhận rằng đối với hầu hết các trường hợp của rung tâm nhĩ lâm sàng gặp, xung điện lưu thông xung quanh trong tâm nhĩ phải trong một vòng lặp lớn. | 8 Cardiac Arrhythmias 195 FIGURE 8-4 Twelve-lead ECG from a patient with atrial fibrillation and a controlled ventricular response. Note the chaotic baseline without defined atrial activity. There is a suggestion of a more organized pattern in the V1 lead but this is not seen in other leads. The ventricular response is characteristically irregularly irregular. 196 The Intensive Care Manual Atrial flutter has also been extensively studied electrophysiologically. Unlike the disorderly atrial activities in fibrillation it is now well-accepted that for most instances of clinically encountered atrial flutter the electrical impulse circulates around in the right atrium in one large loop. Because atrial flutter is more organized than atrial fibrillation it displays more organized atrial activities of larger amplitude on ECG. Atrial flutter usually has an associated sawtooth pattern which represents revolving atrial activities and is best appreciated in the inferior limb leads 2 3 and aVF Figure 8-5 . In typical atrial flutter the reentrant circuit usually has a well-defined cycle length at about 300 beats min. Often there is a 2 1 AV conduction pattern during atrial flutter leading to a consistently regular ventricular response of 150 beats min. Many of the impulses of a SVT can be transmitted down to the ventricle via the AV junction especially when AV conduction is enhanced by release of catecholamines. The rapid ventricular rate is usually the main problem associated with atrial arrhythmias in the ICU. The fast rates are especially troublesome for patients who have underlying CAD or ventricular hypertrophy because ischemia and significant hemodynamic compromise can occur rapidly. The goal of therapy in the care of patients with atrial arrhythmia is stabilization of hemodynamics and ventricular rate control. During sustained atrial arrhythmias in a patient with stable blood pressure AV nodal blocking agents such as beta blockers calcium channel blockers and digoxin are