How many seconds does it take for the ventricular conduction system to deliver an electrical impulse quizlet?
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the following: Sinus tachycardia often does not cause symptoms. As the heart rate increases, the diastolic
filling time decreases, possibly resulting in reduced cardiac output and associated symptoms (refer to Table 17-1). If the rapid rate persists and the heart can no longer compensate for the decreased ventricular filling, the patient may develop acute pulmonary edema or cardiac ischemia. TREATMENT Atrial fibrillation causes a rapid, disorganized, and uncoordinated electrical activity within the atria. Atrial fibrillation may be transient, starting and stopping suddenly and occurring for a very short time
(paroxysmal), or it may be persistent, requiring treatment to terminate the rhythm or to control the ventricular rate. The erratic atrial contraction promotes formation of thrombi within the atria, increasing the risk for an embolic event such as stroke (brain attack). Atrial fibrillation is usually associated with advanced age, valvular heart disease, CAD, hypertension, heart failure, cardiomyopathy, diabetes, hyperthyroidism, pulmonary disease, chronic lung disease, and surgery (especially
open heart surgery). Physiological stressors such as hypoxia, infection, and hypoglycemia, as well as caffeine and sympathomimetic drugs are also associated with atrial fibrillation. Sometimes atrial fibrillation occurs in people without any underlying pathophysiology. TREATMENT Warfarin is indicated if the patient with atrial fibrillation is at high risk for stroke (i.e., >75 years of age or has hypertension, diabetes, heart failure, or history of stroke). If immediate anticoagulation is necessary, the patient may be placed on heparin until the warfarin level is therapeutic. Pacemaker implantation or catheter ablation is sometimes indicated for patients who are unresponsive to medications. Catheter ablation is an invasive procedure during which high-frequency radio waves are applied to destroy the tissue at the site of the arrhythmia. Ablation procedures are usually performed in electrophysiologic labs and are similar to other types of heart catheterization. During a catheter ablation, long, thin, flexible tubes are placed in the heart via the vascular system. A diagnostic catheter determines where the abnormal tissue that is causing the arrhythmia is located. High-frequency energy is sent into the tissue, creating a lesion or scar. The area is now ablated (destroyed), thus facilitating normal electrical conduction. Several approaches are effective in preventing the occurrence of postoperative atrial fibrillation, including preoperative administration of a beta blocker or immediate postoperative administration of IV amiodarone Ventricular tachycardia (VT) is defined as three or more consecutive ventricular beats, occurring at a rate exceeding 100 bpm. The causes are similar to those of PVC. Ventricular tachycardia is usually associated with CAD and may precede ventricular fibrillation. Untreated ventricular tachycardia can deteriorate into ventricular fibrillation, a lethal arrhythmia. The patient can experience a range of symptoms related to decreased cardiac output, such as hypotension or syncope, pulselessness, and unresponsiveness. Some patients may be asymptomatic. The patient's tolerance for this rapid rhythm depends on the ventricular rate and underlying disease. Several factors determine the initial treatment, including the following: identifying the rhythm as monomorphic (having a consistent QRS shape and rate) or polymorphic (having varying QRS shapes and rhythms); determining the existence of a prolonged QT interval before the initiation of VT; and ascertaining the patient's heart function. If the patient is stable, continuing the assessment, especially obtaining a 12-lead ECG, may be the only action necessary. Amiodarone administered IV is the antiarrhythmic medication of choice for a stable patient with VT. Cardioversion is the treatment of choice for monophasic VT in a symptomatic patient. Atrial fibrillation should be suspected as the cause of a wide complex tachycardia with an irregular rhythm, and it should be treated appropriately. Torsades de pointes (Fig. 17-14) is a polymorphic VT usually preceded by a prolonged QT interval (Sommargren & Drew, 2007). Risk factors for torsades de pointes are described in Box 17-5. Because this rhythm is likely to cause the patient to deteriorate and become pulseless, immediate treatment is usually required. Magnesium has frequently been used to treat torsades, but its use has not been proven effective. Any type of VT in a patient who is unconscious and without a pulse is treated in the same manner as ventricular fibrillation: immediate defibrillation is the action of choice. Ventricular fibrillation is a rapid, disorganized ventricular rhythm that causes ineffective quivering of the ventricles. No atrial activity is seen on the ECG. Causes of ventricular fibrillation are the same as for VT; it may also result from untreated or unsuccessfully treated VT. Clinical manifestations include absence of an audible heartbeat, a palpable pulse, and respirations. Cardiac
arrest and death are imminent. TREATMENT Cardioversion and defibrillation are used to treat tachyarrhythmias by delivering an electrical current that depolarizes a critical mass of myocardial cells. When the cells repolarize, the sinus node is usually able to recapture its role as the heart's pacemaker. One major difference between cardioversion and defibrillation is the timing of the delivery of electrical current. In cardioversion, the delivery of the electrical current is synchronized with the patient's electrical events; in defibrillation, the delivery of the current is unsynchronized. Defibrillation is used in emergency situations as the treatment of choice
for ventricular fibrillation and pulseless VT. Defibrillation is not used on patients who are conscious or have a pulse. It has been established that early defibrillation is the major determinant of survival in cardiac arrest (Field, 2008). The implantable cardioverter defibrillator (ICD) is a device that detects and terminates life-threatening episodes of tachycardia or fibrillation. ICDs are used for patients who have survived sudden cardiac death syndrome, usually caused by ventricular fibrillation, or have experienced symptomatic ventricular tachycardia. Other people at risk of sudden cardiac death include those with dilated cardiomyopathy, hypertrophic cardiomyopathy, arrhythmogenic (capable of inducing an arrhythmia) right ventricular dysfunction, and prolonged QT syndrome. In addition, patients with moderate to severe left ventricular dysfunction, with or without nonsustained VT, are at high risk for cardiac arrest; therefore, prophylactic implantation may be indicated. ICDs may also be implanted in patients with symptomatic, recurrent, medication-refractory atrial fibrillation. A pacemaker is an electronic device that delivers electrical stimulation to the heart to regulate the heart rate when a patient has a slower-than-normal heart rate or conduction disturbance. They may also be used to control some tachyarrhythmias or to treat advanced heart failure that does not respond to medication. Pacemakers may be temporary or permanent. Temporary
pacemakers may be transvenous, transcutaneous, or epicardial. Pacemakers consist of two components: an electronic pulse generator and pacemaker electrodes, or leads. The generator contains the energy source that determines the rate (measured in bpm) and the strength or output (measured in milliamperes [mA]) of the electrical stimulus delivered to the heart. The generator can be programmed to detect the heart's intrinsic electrical activity and to cause an
appropriate response; this component of pacing is called sensitivity and is measured in millivolts (mV). Leads can be threaded through a major vein into the right ventricle (endocardial leads), or they can be lightly sutured onto the outside of the heart and brought through the chest wall during open heart surgery (epicardial wires). The endocardial leads may be temporarily placed with catheters through a great vessel (transvenous wires), usually guided by fluoroscopy. The endocardial and
epicardial wires are connected to a temporary external generator. How many seconds does it take for ventricular conduction system to deliver an electrical impulse?Rationale: The ventricular conduction system delivers the impulse within 0.12 second. The action potential is generated from the sinoatrial node. It travels through the conduction system, including the atrioventricular (AV) node, bundle of His, and the left and right bundle branches.
How much time does ventricular depolarization usually take?QRS complex (ventricular depolarization)
The duration of the QRS complex is normally 0.06 to 0.10 seconds. This relatively short duration indicates that ventricular depolarization normally occurs very rapidly. If the QRS complex is prolonged (> 0.10 sec), conduction is impaired within the ventricles.
Which part of the ECG represents electrical impulse transmission through the ventricles quizlet?The QRS complex represents ventricular depolarization (and atrial repolarization) or the journey through the electrical impulse from the Av-Node through the Purkinje network.
What is the normal PR interval?The P-R Interval
The first measurement is known as the "P-R interval" and is measured from the beginning of the upslope of the P wave to the beginning of the QRS wave. This measurement should be 0.12-0.20 seconds, or 3-5 small squares in duration.
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