A strong and steady heartbeat pumping life-sustaining blood to vital organs and tissue — that’s what it’s all about for the patient who has endured the stress and strain of cardiovascular surgery. Nurses keep watch in the critical care unit and progressive care unit (PCU). They assess and reassess a host of variables, such as the patient’s vital signs, circulatory pressures, wound status, and comfort level. They adjust and readjust equipment that helps each patient navigate the high-tech road to recovery.

Many patients require temporary epicardial pacing in the immediate postoperative stage. They may need augmentation of their cardiac output, suppression of dysrhythmias, or conversion of atrial flutter through rapid atrial pacing. Those who develop heart block postoperatively require pacing to maintain normal atrioventricular conduction.^1,2 As an additional benefit, whenever a patient needs an atrial electrocardiogram (ECG) for diagnosis of a dysrhythmia, staff can use the atrial epicardial wires (see Figure 1).³

As a nurse in a cardiovascular CCU or PCU, you may be caring for a patient like Leroy R., a 65-year-old auto mechanic, day one after coronary artery bypass grafting. Leroy is expected to do well, and to ensure this, his surgeon has placed temporary epicardial wires for atrial pacing at a rate of 100 beats per minute (bpm). When the central monitoring station notifies you that Leroy’s heart rate is now 110 bpm but pacemaker spikes are still apparent, you’ll need to recognize that this is a problem and know how to solve it. Any nurse practicing in a cardiovascular critical or transitional care unit is responsible for monitoring patients to ensure the effectiveness of pacemaker therapy and often must initiate this therapy based on standards or protocols.

For most patients having cardiac surgery, epicardial pacing is needed only temporarily to increase heart rate in the immediate postoperative period as a means of enhancing cardiac output until the heart is contracting normally again.² In addition, patients who have undergone valve surgery or congenital heart defect repairs may develop conduction disturbances due to injury or edema of the sinoatrial or atrioventricular node.¹ The American College of Chest Physicians recently published guidelines for the prevention of atrial fibrillation postoperatively; the recommendations indicate that prophylactic atrial pacing to prevent atrial fibrillation after cardiac surgery is safe and that biatrial pacing should be considered, particularly in cardiac surgery patients who are at high risk for developing atrial fibrillation.⁴

Temporary epicardial pacing system

A temporary epicardial pacing system consists of a pulse generator and an epicardial pacing lead or leads. Nurses need to become familiar with the external temporary pulse generator used in their facility. Temporary pulse generators have two main functions — they sense or “see” the heart’s intrinsic rate and deliver an electrical impulse to the heart to cause depolarization of the myocardium when necessary. Depolarization of myocardial cells should result in contraction of the heart muscle.

The epicardial lead is an insulated wire attached to the myocardium during cardiac surgery and used for sensing or pacing the myocardium or both. Usually, atrial wires are attached to the right atrium and placed on the right side of the sternum. Ventricular wires are typically placed on the right ventricle and placed to the left side of the sternum. The surgeon may also place additional wires in subcutaneous tissues. These wires should be labeled as indifferent and can be used only as ground wires.¹

In a bipolar system, two epicardial leads must be in direct contact with the chamber to be paced or sensed, whereas in a unipolar system, only one epicardial lead must be in direct contact. In a unipolar epicardial system, the epicardial lead in contact with the heart chamber to be paced or sensed must be placed in the negative compartment of the cable that goes to the pacemaker generator. Another epicardial lead not in direct contact with the heart chamber to be paced or sensed goes into the positive compartment.¹ If the patient has only one ventricular wire and two atrial wires and needs ventricular pacing, the nurse places the ventricular wire into the negative pole of the pacemaker cable and places one of the atrial wires into the positive pole.² Ventricular pacing can then begin.

Pacemaker codes — letter of the law

A generic five-letter code system developed by the North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group is used to describe pacing modes (see Table 1).⁵ Only the first three letters of this code are used with temporary epicardial pacing. The first letter indicates the chamber paced; the second letter indicates the chamber sensed; and the third letter indicates the response to sensing.

Staff in the surgical suite uses the AOO or asynchronous mode because electrocautery causes the pacemaker generator to inhibit firing — it senses the electrocautery as an intrinsic beat. In the AOO mode, the atria are paced no matter what the patient’s intrinsic heart rate.

With AAI pacing, the synchronous mode, the atria are being paced and sensed, and the pacemaker generator inhibits pacing if it senses that the patient’s intrinsic atrial rate is higher than the generator setting. The generator initiates pacing if it senses that the patient’s intrinsic atrial rate is lower than the setting. This mode is frequently used after cardiac surgery to increase cardiac output and suppress dysrhythmias. Patients who develop atrial fibrillation or atrial flutter with a slow ventricular rate are candidates for the VVI mode or ventricular pacing mode, also called “V-demand” pacing. With VVI pacing, the ventricles are paced and sensed. Patients who develop complete heart block postoperatively require the DVI or dual-chamber pacing mode. In this mode, both chambers are paced, but only the ventricles are sensed. The pacemaker generator inhibits or initiates pacing based on the programmed ventricular rate only. This is also called AV sequential pacing. This type of pacing requires at least one atrial and one ventricular wire and two other wires (indifferent wires).¹

Upbeat language

To care for patients and communicate effectively with colleagues, nurses need to understand the terminology associated with external pacemaker generators and temporary epicardial pacing (see Table 2).

Artifact: The spike on the ECG, which is the pacing stimulus delivered to the myocardium, is called pacing artifact. A P wave follows the pacing artifact when the atria are paced, and a QRS complex follows the pacing artifact when the ventricles are paced. When both chambers are paced, the pacing artifact is visible before both the P wave and QRS complex (see Figure 2). The spike of a unipolar system is larger than that of a bipolar system. Depolarization of the ventricular myocardium is delayed because of the location of the epicardial wires. In this situation, the QRS complex displays a bundle branch pattern with ventricular pacing because the impulse does not originate and travel along the normal conduction pathway.

The physician establishes pacing parameters, which must include the mode of pacing and the number of impulses (heart rate) per minute. The initial settings for output and sensitivity are established at the start of pacemaker therapy, and an assessment of the patient’s response is essential at this time. Assessment parameters include the patient’s hemodynamic status, level of consciousness, quality of peripheral pulses, and oxygenation.

Capture: The term capture indicates depolarization of the myocardium in response to a pacing stimulus. In other words, every spike on the monitoring screen should have a corresponding P wave or QRS complex, depending on the chamber or chambers paced.

Threshold: The minimal amount of voltage (mA) needed to obtain consistent capture is called threshold. Once capture occurs, threshold is determined by decreasing the milliamperes (mA) slowly until one-to-one capture is lost. The mA is then increased gradually until one-to-one capture is restored. To allow for changes over time, the mA should be adjusted two to three times higher than threshold.^6,7 Threshold changes can occur because of metabolic and electrolyte abnormalities, response to medications, changes in integrity or placement of the epicardial wire, or myocardial infarction.

Sensitivity Threshold: The minimum P or R wave amplitude needed for the pacemaker generator to detect or “see” is known as the sensitivity threshold. To determine this value, the nurse gradually increases the sensitivity value (turns the dial to a higher number) until the sense indicator on the pacemaker generator stops flashing. Next, he or she decreases the sensitivity (by turning the dial to a lower number) until the sense indicator starts flashing again. The sensitivity should be adjusted to half the threshold value. For example, if the sensitivity threshold is 4 mV, the sensitivity is set at 2 mV.⁸

Documentation must cover the number and type of wires, mode of pacing, mA, and sensitivity. When therapy starts, the nurse must document the threshold settings and then periodically, depending on the institution’s policy.

Troubleshooting know-how

Despite careful monitoring and fine-tuned settings, problems do occur. For example, the pacemaker generator may not deliver a pacing stimulus, the pacing stimulus may not cause a depolarization, the pacemaker generator may not sense the patient’s intrinsic heart rate, or the generator may sense irrelevant electrical signals that it interprets as the patient’s intrinsic rate.

Undersensing or failure to sense occurs when the pacemaker generator fails to see intrinsic beats. Causes include sensitivity set too high, inappropriate mode selection, loose cable connections, lead displacement, or generator failure.

Measures to correct undersensing include —

• Lowering the sensitivity.
• Checking all connections.
• Changing the batteries in the pacemaker generator.
• Changing the pacemaker generator.⁹

Oversensing occurs when the pacemaker generator senses events unrelated to the patient’s intrinsic rate. Pauses in the ECG tracing show up as the generator senses adventitious signals. Causes include electromagnetic interference (EMI), improperly grounded equipment, tall T waves on the ECG, or sensitivity set too low.

Measures to prevent oversensing include —

• Identifying all sources of EMI and eliminating them.
• Ensuring that all equipment is properly grounded.
• Lowering the sensitivity of the pacemaker generator by increasing the sensitivity number.⁸

Failure to discharge results in the absence of pacing artifact. Causes include loose cable connections, oversensing, electromagnetic interference, battery depletion, generator failure, or problems with the epicardial wires.

If pacing spikes are absent on the ECG monitor, check all connections. If all are secure, try decreasing the sensitivity by dialing up to a higher number. Other nursing interventions include changing the battery or generator, eliminating any source of EMI, and changing the polarity of the epicardial wires.

Pacing artifact on the ECG tracing not followed by the P wave or QRS complex indicates loss of capture. Cause of loss of capture may be due to loose cable connections, increased pacing threshold, displaced or defective pacing electrodes, depleted battery, mA set too low, or metabolic or electrolyte disorder.

Measures to troubleshoot loss of capture include —

• Checking all connections from the epicardial wires to the pacemaker generator.
• Trying a change of polarity of the epicardial wires if all connections are secure.
• Increasing the mA if the change in polarity doesn’t work.
• Correcting any metabolic or electrolyte abnormalities.¹⁰

Leroy, the patient described earlier, needed a nurse with troubleshooting skills. His pacemaker generator was not sensing his intrinsic atrial rate. His nurse discovered that the pacemaker generator was set in the AOO mode. After connecting Leroy to a bedside monitor, she determined that his sensitivity threshold was 1 mV; she programmed the sensitivity at 0.5 mV. After this step, his pacemaker generator was able to “see” his intrinsic atrial rate. She also noted on the bedside monitor that the pacemaker generator stopped firing because his intrinsic atrial rate was higher than the rate programmed on the pulse generator. If his heart rate fell below 100 bpm, the pacemaker generator would begin firing again.

Nursing care — vigilant and skillful

Nurses play a vital role in the care of patients undergoing temporary epicardial pacing as they assess pacemaker function, monitor for complications, prevent microshock, and educate patients and family members.

Continuous ECG monitoring is a must for all patients with temporary epicardial pacing. It provides a tool for ongoing assessment of the pacemaker’s function and thus ensures rapid response if pacemaker failure occurs.

Other nursing interventions include —^3,6

• Setting cardiac monitor alarms just below and above the prescribed pacing heart rate so that failure to sense and/or capture is recognized immediately. Many cardiac and telemetry monitoring systems require programming for “pacemaker in use” when epicardial pacing is initiated.
• Running and analyzing a rhythm strip at the beginning of each shift and with any changes in heart rate or rhythm or in patient condition.
• Conducting a thorough physical assessment of the patient’s response to this therapy on initiation at least every four hours. Monitor vital signs, peripheral pulses, oxygenation, level of consciousness, skin temperature, and color. Check the security of all lead connections and the external pacemaker generator at every assessment. This is especially important for ambulatory patients.
• Protecting pacemaker controls from manipulation by the patient.
• Keeping spare batteries and pacemaker generators available at all times.
• Labeling the pulse generator with the date and time of each battery change.
• Reviewing the manufacturer’s instructions for each generator for more specific information about battery life.

Complications are rare with temporary epicardial pacing, but may include infection or dysrhythmias. Infection can occur at the epicardial wire sites. At each assessment, examine the sites for redness, edema, and drainage. Monitor the patient for systemic signs of infection, such as fever, chills, and malaise. Perform site care according to the hospital’s policy.

Dysrhythmias can occur when the pacemaker is not sensing appropriately. A pacing stimulus that falls on the refractory or vulnerable period can produce atrial fibrillation or a lethal ventricular dysrhythmia depending on which chamber or chambers are paced. Safety precautions are vital with epicardial pacing since the wires provide a direct route to the myocardium. A microshock, an electrical current that passes through the body to the myocardium, can cause an atrial or ventricular dysrhythmia. Sources of microshock are stray electrical current, electricity, and ungrounded equipment.

To prevent a microshock, wear gloves when handling the wires, ground all electrical devices, eliminate carpeting from patient care areas, and insulate epicardial wires. When epicardial pacing wires are not it use, they must be insulated. However, no studies are available on the best materials or techniques. Methods of insulation described in the literature include placing the wires in a nonlatex glove, needle cover, dry syringe barrel, or dry glass phlebotomy tube, plastic caps provided by the manufacturer, or tape or gauze over the pins.¹¹ Follow the individual hospital’s policy on insulating epicardial wires.

Before the patient leaves the hospital, the physician or advanced practice nurse removes the epicardial pacing wires at the bedside. After removal, the patient must be monitored for signs and symptoms of cardiac tamponade and is usually restricted to bed rest for a period of time that may vary in each hospital. If blood or fluid collects in the pericardial sac, the build-up will compress the heart and interfere with normal contraction and cardiac output. Signs and symptoms of tamponade include jugular venous distention, muffled heart sounds, hypotension, tachycardia, anxiety, decreased peripheral pulses, dyspnea, decreased oxygen saturation, and pulsus paradoxus. Patients who develop cardiac tamponade may require emergent pericardiocentesis at the bedside or an emergent surgical procedure to drain the pericardial sac and control the bleeding.

The thought of cardiovascular surgery alone often terrifies even the most stoic of patients and families. Add the sight of epicardial wires to the postoperative bedside and they may become even more frightened. Nurses are the translators, the ones who reassure, comfort, teach, and explain. Explanations should be simple and include the reason for the therapy, care of the wires and generator, electrical safety precautions, and instructions on the importance of not touching the wires or manipulating generator controls.

Patients often regain some sense of control through understanding and participating in their care. They need to know when to notify the nurse — a loose wire might be one example. Reassurance that temporary epicardial pacing supports a smooth recovery and is usually just that — temporary — can go a long way in helping the patient and family cope and move forward.