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- The transesophageal echocardiography (TEE) machine records the electrocardiogram (ECG) simultaneously with all TEE imagery. This is done so that echocardiographers can correlate echo images throughout systole and diastole. Alterations in rhythm can have sweeping and at times ultimately fatal hemodynamic consequences. Thus, the rapid interpretation of abnormal rhythms and their correction is critical in cardiac anesthesia practice.
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The ECG remains one of the main monitors used by anesthesiologists. It is primarily employed in anesthesia practice to detect heart rate and rhythm changes, and perioperative myocardial ischemia. The ECG detects electrical currents flowing through the body generated by the electrical activity of the heart. ECG leads are positioned throughout the body and provide various perspectives (depending upon where the lead is placed) of the electrical activity of the heart. Examining the ECG in multiple leads provides the anesthesiologist the ability to discern if perceived changes in ECG pattern are widespread (found in multiple leads) or are perhaps less significant (motion artifact). At the end of diastole, the atria contract providing the atrial contribution to the patient's cardiac output generating the "P" wave. Following atrial contraction, the ventricle is loaded awaiting systole. Systole commences at the QRS beginning with isovolumetric contraction following a 120 to 200 milliseconds conduction delay at the AV node. Subsequently, intracavitary pressure builds, the atrioventricular valves (eg, mitral or tricuspid) close, and the arterioventricular valves (eg, aortic, pulmonic) open resulting in ventricular ejection of the stroke volume (SV). The QRS represents the electrical activity generated by the depolarization of the left and the right ventricles. Depolarization proceeds from the AV node through the interventricular septum via the His-Purkinje fibers. The QRS segment lasts approximately 120 milliseconds. Repolarization of the ventricles produces the ST segment and the T wave. Electrolyte abnormalities (eg, hypocalcemia) and drug effects (eg, droperidol) can delay repolarization leading to a prolonged QT interval. This can result in potentially life-threatening ventricular arrhythmias.
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Electrolyte disorders, heart structure abnormalities, and myocardial ischemia can cause aberrations in the patient's baseline ECG without producing an arrhythmia per se (Figure 3–1). Electrolyte abnormalities occur with some frequency perioperatively. Hyperkalemia can present following cardioplegia administration during cardiopulmonary bypass (CPB), following iatrogenic administration, or associated with metabolic acidosis. As the potassium concentration increases, the T wave becomes progressively peaked. Hyperkalemia can ultimately produce broad, complex ventricular activity and asystole. Treatment is with immediate administration of calcium chloride. Glucose and regular insulin are given to lower the potassium concentration.
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