Transvenous and Transcutaneous Cardiac Pacing

Published on 22/03/2015 by admin

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W7 Transvenous and Transcutaneous Cardiac Pacing

Raúl J. Gazmuri

image Before Procedure

Indications

• Treatment of symptomatic bradycardia:

• Sinus bradycardia
• Second- or third-degree atrioventricular block

• Prophylaxis:

• Bradycardia-induced ventricular tachyarrhythmias (e.g., torsades de pointes)
• Increased risk of advanced atrioventricular block (e.g., acute myocardial infarction, infective endocarditis, surgery in patients with underlying conduction defects)

• Overdrive pacing for termination of tachyarrhythmias:

• Supraventricular tachycardia
• Ventricular tachycardia

• Improving hemodynamic function:

• Sequential atrioventricular pacing

Contraindications

• Specific advance directives (e.g., do not attempt resuscitation for cases of pulseless electrical activity)
• Asymptomatic bradycardia
• Severe hypothermia (risk of ventricular fibrillation)

Equipment

• Pacing catheter with pulse generator
• Transcutaneous electrodes with pacing unit (integrated with current cardioverter-defibrillators)

image Anatomy

The heart is located behind the sternum. Its base is at the level of the third intercostal space immediately to the right of the sternum, and its apex is at the level of the fifth intercostal space inferior and usually just medial to the nipple. Transcutaneous pacing can be performed by delivering electric impulses through the chest cavity to “capture” and drive the electrical activity of the heart. Electrodes can be placed on the anterior chest wall, with one electrode below the right clavicle lateral to the sternum and the other electrode below the breast tissue along the midaxillary line. Electrodes can also be placed in an anteroposterior configuration with the anterior electrode placed over the precordium and the posterior electrode at the right infrascapular location. For transvenous pacing, the pacing catheter can be advanced through the brachial (antecubital), femoral, internal jugular (preferable right), subclavian (preferable left), or the right subclavian via supraclavicular access (experienced practitioner).

image Procedure

Transvenous Temporary Pacing

• Admit the patient to an appropriately equipped hospital area with capability for monitoring cardiac rhythm, oxygenation, and vital signs, along with airway management and cardiopulmonary resuscitation.
• Obtain a 12-lead electrocardiogram (ECG).
• Attach monitor leads to the patient, and ensure proper display of the patient’s rhythm.
• Perform procedure under fluoroscopy if available and time permits; otherwise use the ECG and rhythm to guide placement.
• Establish vascular access under local anesthesia and full sterility, advancing a proper-size introducer sheath.
• Select pacing catheter contingent on approach. Catheters for use under fluoroscopy are semirigid (usually made of woven polyester) to facilitate steering into position. Catheters designed for blind placement have a balloon at the tip to be floated into position. Transvenous pacing can also be accomplished using multipurpose pulmonary artery catheters built with up to five electrodes for right atrial and right ventricular pacing.
• Blind placement using a balloon-tipped catheter can be guided by the ECG. A V1 lead of a conventional ECG is connected to the distal pole (cathode) of the pacing catheter and used to monitor a unipolar intracavitary electrogram. The catheter is floated, seeking display of a right ventricular intracavitary electrogram point at which the balloon can be deflated and the catheter advanced a few centimeters to position its tip in the right ventricular apex. Endocardial contact is confirmed by development of an “injury” current characterized by prominent ST-segment elevation. The pacing electrode is connected to the pulse generator and used in unipolar or bipolar configuration. In emergency situations when pacing is immediately required, the pacing lead may be advanced with the pulse generator on, set to its maximum output, and in the asynchronous mode at a rate of 70 to 100 ppm.
• A defibrillator should be available during insertion and afterward, because life-threatening ventricular tachyarrhythmias may develop, especially if the pacing lead moves within the ventricular cavity.
• Leave a sterile sleeve around the catheter (available with most introducer kits) to facilitate subsequent repositioning if required.
• Obtain an anteroposterior and lateral chest x-ray to verify proper placement and exclude complications.
• Set pacing options as follows:

• Determine pacing threshold, and set pacing output. For this purpose, set pacemaker rate to exceed the spontaneous heart rate by 10 to 20 beats/min and the output to a level expected to capture 100% of the beats (i.e., 6 mA). Capture is verified on the ECG by identifying the presence of a spike (pulse) followed by a wide QRS complex. The output is reduced gradually until beats are no longer captured and increased again to identify the minimal level at which 100% of the beats are paced; this is the threshold output. This threshold level should be less than 1 mA for ventricular pacing and less than 2 mA for atrial pacing, in the unipolar and the bipolar configurations; otherwise, the lead must be repositioned. The output is set at about three times the threshold level for reliable capture.
• Set sensitivity (range 0.5-20 mV), allowing the native R wave to inhibit the pacemaker impulse when the generator is set in synchronous mode. The output is first set to its minimal level (e.g., 0.1 mA) and the pacing rate to a value below the spontaneous heart rate. Starting from maximal sensitivity (the lowest value, i.e., 0.5 mV), gradually decrease the sensitivity (increasing its value) until the unit stops sensing the R wave. For reliable inhibition, the sensitivity is set at about three times the sensitivity threshold (e.g., if the threshold is 3 mV, the level is set at 1 mV).
• The pacing rate for bradyarrhythmias is set according to physiologic needs, usually between 60 and 75 beats/min. Higher rates (800 beats/min) are available for override pacing of ventricular or supraventricular tachyarrhythmias.
• Sequential atrioventricular pacing requires placement of an additional lead or use of multipurpose pulmonary artery catheters along with a dual-chamber pulse generator. The individual chamber specifications for dual-chamber generators are similar, with the option of setting the AV pacing interval between 20 and 300 msec.

Transcutaneous Temporary Pacing

• Transcutaneous pacing is noninvasive and can be used in emergency settings with ease and minimal delay while preparing for more definitive therapy, or it can be used prophylactically.
• Pacing is limited to the ventricles (with minimal capability for atrial pacing); capture is not always attained, and tolerability may be poor.
• Place electrodes on the anterior chest wall or in an anteroposterior configuration as described under Anatomy. Place negative electrode (cathode) anteriorly, close to the heart (typically over the palpable cardiac impulse or centered on a V3 lead) to minimize the capture threshold. Place positive electrode (anode) over the right upper region of the chest or the posterior chest wall between the bony spine and the inferior border of either the left or right scapula.
• Determine pacing threshold as for transvenous pacing (described earlier), bearing in mind that the pacing threshold is much higher (20 to 140 mA), particularly in patients with emphysema, pericardial effusion, and in patients undergoing positive pressure ventilation. The pacing output is set 5 to 10 mA above the threshold. Pulse generators are designed to deliver high current levels (200 mA) with longer pulse duration (20 to 40 msec) to facilitate capture and minimize patient discomfort.
• Ensure that capture occurs by demonstrating coincident pulse generation; do not rely on the ECG capturing artifacts from skeletal muscle activity.

image After Procedure

Postprocedure Care

• Obtain an ECG.
• Assess hemodynamic status.
• Monitor native and paced rhythms.
• Establish etiology, and institute definitive treatment.

Complications

• Pacemaker malfunction, defined as failure to sense, failure to capture, or both
• Ventricular dysrhythmias at the time of insertion
• Myocardial perforation with risk of cardiac tamponade
• Diaphragmatic stimulation
• Complications related to the vascular access (e.g., phlebitis, pneumothorax, arterial puncture, brachial plexus injury, pulmonary embolism, sepsis)

image Outcomes and Evidence

• Effective in pacing a desired heart rate
• Transvenous pacing more effective than transcutaneous pacing (lower capture rate)
• Lack of effectiveness for treatment of cardiac arrest due to asystole or pulseless electrical activity
• Temporary measure pending resolution of the rhythm abnormality or permanent definitive pacemaker placement

Suggested Reading

Jafri SM, Kruse JA. Temporary transvenous cardiac pacing. Crit Care Clin. 1992;8:713-725.

Sherbino J, Verbeek PR, MacDonald RD, Sawadsky BV, McDonald AC, Morrison LJ. Prehospital transcutaneous cardiac pacing for symptomatic bradycardia or bradyasystolic cardiac arrest: a systematic review. Resuscitation. 2006;70:193-200.

Gibson T. A practical guide to external cardiac pacing. Nurs Stand. 2008;22:45-48.

Maddali MM. Cardiac pacing in left bundle branch/bifascicular block patients. Ann Card Anaesth. 2010;13:7-15.

Neumar RW, Otto CW, Link MS, Kronick SL, Shuster M, Callaway CW, et al. Part 8: adult advanced cardiovascular life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122:S729-67.

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