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Emergency Cardiac Pacing

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Emergency cardiac pacing may be instituted either prophylactically or therapeutically. Prophylactic indications include patients with a high risk for AV block. Therapeutic indications include symptomatic bradyarrhythmias and overdrive pacing. Transcutaneous and transvenous are the two techniques most commonly used in the ED.

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Because it can be instituted quickly and noninvasively, transcutaneous pacing is the technique of choice in the ED when time is of the essence. Transvenous pacing should be reserved for patients who require prolonged pacing or have a very high (>30%) risk for heart block.

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EMERGENCY TRANSVENOUS CARDIAC PACING The technique can be performed in less than 20 minutes in 72% of patients and in less than 5 minutes in 30%. Transcutaneous cardiac pacing (TCP) has become the mainstay of emergency cardiac pacing and is often used pending placement of a transvenous catheter or to determine whether potentially terminal bradyasystolic rhythms will respond to pacing.

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Bradycardias Sinus Node Dysfunction: may be manifested as sinus arrest,sick sinus syndrome or sinus bradycardia is a common indication for elective permanent pacing, it is seldom cause for emergency pacemaker insertion. 17% percent of patients with AMI will experience sinus bradycardia (occurs more frequently with inferior > anterior infarction)

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Bradycardias Asystolic Arrest: Transvenous pacing in an asystolic or bradyasystolic patient has little value and is not recommended Cardiac pacing may be used as a last-ditch effort in bradyasystolic patients but is rarely successful and is not considered standard practice. Given the continued emphasis on the importance of maximizing chest compressions during CPR, interrupting CPR to institute emergency pacing is not recommended

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Bradycardias AV Block: In symptomatic patients without myocardial infarction (MI) and in asymptomatic patients with a ventricular rate lower than 40 beats/min, pacemaker therapy is indicated. AV block occurring during anterior infarction is believed to result from diffuse ischemia in the septum and infranodal conduction tissue. Because these patients tend to progress to high-degree block without warning, a pacemaker is often placed prophylactically

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Bundle Branch Block and Ischemia Bundle branch block occurring in AMI is associated with a higher mortality rate and a greater incidence of third degree heart block than is uncomplicated infarction. Because of the increased risk, consider pacing for the following conduction blocks: New-onset LBBB RBBB with left axis deviation or other bifascicular block Alternating bundle-branch block

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Tachycardias Hemodynamically compromising tachycardias are usually treated by medical means or electrical cardioversion Supraventricular dysrhythmias,with the exception of AF, respond well to atrial pacing. By overdrive pacing the atria at rates 10 to 20 beats/min faster than the underlying rhythm, the atria become entrained, and when the rate is slowed, the rhythm frequently returns to normal sinus. Overdrive pacing is especially useful for arrhythmias with recurrent prolonged QT intervals such as those seen with quinidine toxicity or torsades de pointes Transvenous pacing is also useful in patients with digitalis-induced dysrhythmias, in whom direct current cardioversion may be dangerous

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Cardiac Pacing for Drug-Induced Dysrhythmias Tachycardic rhythms from amphetamines, cocaine, anticholinergics, cyclic antidepressants,theophylline, and other drugs do not benefit from cardiac pacing Severe bradycardia and heart block often accompany overdose of digitalis preparations, -adrenergic blockers, and CCB Cardiac pacing is not generally effective for serious toxin- induced bradycardias

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Contraindications The presence of a prosthetic tricuspid valve is generally considered to be an absolute contraindication to transvenous cardiac pacing Severe hypothermia will occasionally result in ventricular fibrillation when pacing is attempted Rapid and careful rewarming is often recommended first, followed by pacing if the patients condition does not improve.

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Pacing Generator An amperage control allows the operator to vary the amount of electrical current delivered to the myocardium increase the output improves the likelihood of capture By increasing the sensitivity, one can convert the unit from a fixed-rate (asynchronous mode) to a demand (synchronous mode) pacemaker Decreasing the setting increases the sensitivity and improves the likelihood of sensing myocardial depolarization In the fixed-rate mode,the unit does not sense any intrinsic electrical activity In the full-demand mode, however, the pacemaker senses the underlying ventricular depolarizations, and the unit does not fire as long as the patients ventricular rate is equal to or faster than the set rate of the pacing generator

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Pacing Generator

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Pacing Catheters and Electrodes

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ECG Machine

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Introducer Sheath The introducer set is used to enhance passage of the pacing catheter through the skin, subcutaneous tissue, and vessel wall. The size of the pacing catheter refers to its outside diameter, whereas the size of the introducer refers to its inside diameter. Thus, a 5-Fr pacing catheter will fit through a 5-Fr introducer.

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Site Selection The four venous channels that provide easy access to the right ventricle are the brachial, subclavian, femoral, and internal jugular veins The right internal jugular and left subclavian veins have the straightest anatomic pathway to the RV and are generally preferred for temporary transvenous pacing For subclavian,the infraclavicular approach is most commonly reported for all temporary transvenous pacemaker insertions This route is preferred because of its easy accessibility, close proximity to the heart, and ease in catheter maintenance and stability

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Site Selection

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Final Assessment Assess pacemaker function again, and take a chest film to ensure proper positioning. Ideal positioning of the pacing catheter is at the apex of the right ventricle A 12-lead ECG tracing should be obtained after placement of the transvenous pacemaker. If the catheter is within the right ventricle, a left bundle branch pattern with left axis deviation should be evident in paced beats If an RBBB pattern is noted, coronary sinus placement or left ventricular pacing secondary to septal penetration should be suspected.

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Final Assessment

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Complications Therapy for catheter-induced ectopy during insertion involves repositioning the catheter in the ventricle. This usually stops the ectopy if after repeated attempts it is found that the catheter cannot be passed without ectopy,myocardial suppressant therapy may be used to desensitize the myocardium. Simply pulling the catheter back and repositioning it in the right ventricle can usually treat uncomplicated perforation

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Complications

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TRANSCUTANEOUS CARDIAC PACING May be preferable to transvenous pacing in patients who have received thrombolytic agents or other anticoagulants Although small pediatric electrodes for TCP have been developed, experience with pediatric TCP has been limited Though generally unsuccessful, TCP may be attempted for the treatment of asystolic cardiac arrest. In this setting the technique is efficacious only if used early after the onset of arrest (usually within 10 minutes).

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Pad Placement Take care to avoid placing the electrodes over an implanted pacemaker or defibrillator. Remove any transdermal drug delivery patches if they are in the way. Remove excessive hair if time permits Place the anterior electrode (cathode or negative electrode) as close as possible to the point of maximal impulse on the left anterior chest wall Place the second electrode directly posterior to the anterior electrode

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Pad Placement There is little risk for electrical injury to health care providers during TCP. The power delivered during each impulse is less than 1/1000 of that delivered during defibrillation Inadvertent contact with the active pacing surface results in only a mild shock.

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Pacing Bradycardiac Rhythms Slowly increase the output from minimal settings until capture is achieved Generally, a heart rate of 60 to 70 beats/min will maintain adequate blood pressure Assess electrical capture by monitoring the ECG tracing Assess mechanical capture by palpating the pulse Because of muscular contractions triggered by the pacer, carotid pulses may be difficult to assess, so palpating the femoral pulse may be easier

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Pacing Bradycardiac Rhythms Failure to capture with TCP may be related to electrode placement or patient size. Patients with barrel-shaped chests and large amounts of intrathoracic air conduct electricity poorly and may prove refractory to capture Patients who are conscious or who regain consciousness during TCP will experience discomfort because of muscle contraction. Analgesia with incremental doses of an opioid agent, sedation with a benzodiazepine compound, or both, will make this discomfort tolerable until transvenous pacing can be instituted

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Complications The major potential complication of TCP is failure to recognize the presence of underlying treatable ventricular fibrillation. This complication is primarily due to the size of the pacing artifact on the ECG screen A rare complication of TCP is induction of ventricular Fibrillation. longer impulse durations used in modern devices seem to decrease the chance of inducing ventricular fibrillation

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