and the Beat Goes on…

Pacemakers work by generating an impulse from a power source and transmitting that impulse to the heart muscle. The impulse flows throughout the heart and causes the heart muscle to depolarize. Pacemakers usually consist of three components: the pulse generator, the pacing leads, and the electrodes at the tips of the pacing leads.

Making the Pacer Work

The pulse generator contains the pacemaker’s power source and circuitry. The lithium battery in a permanent or implanted pacemaker is its power source and lasts about 10 years. The circuitry of the pacemaker is a microchip that guides heart pacing.

A temporary pacemaker, which isn’t implanted, is about the size of large cell phone or a telemetry box and is powered by alkaline batteries. These units also contain a microchip and are programmed by a touch pad or dials.

A Stimulus on the Move

An electrical stimulus from the pulse generator moves through wires (referred to as pacing leads or leads) to the electrode tips. The leads for a pacemaker designed to stimulate a single heart chamber are placed in either the atrium or the ventricle. For dual-chamber, or AV, pacing, the leads are placed in both chambers, usually on the right side of the heart.

One Pole or Two

The electrodes—one on a unipolar lead or two on a bipolar lead—send information about electrical impulses in the myocardium back to the pulse generator. The pulse generator senses the heart’s electrical activity and responds according to how it has been programmed.

A unipolar lead system is more sensitive to the heart’s intrinsic electrical activity than is a bipolar system. A bipolar system isn’t as easily affected by electrical activity outside the heart and the generator (e.g., from skeletal muscle contraction or magnetic fields). (See A look at pacing leads.)

Permanent and Temporary Pacemakers

Depending on the patient’s needs, a permanent or a temporary pacemaker can be used to maintain heart rhythm. Pacing lead placement varies according to the patient’s specific needs.

Sensing the Norm

You can also program the pacemaker’s sensing or ability to sense electricity (e.g., P waves and QRS complexes). Sensing is measured and set in millivolts (mV). Most pacemakers are programmed in a demand mode; therefore, only pacing when the heart’s own electrical activity is not sensed. Pacing is inhibited when the heart’s own P waves and QRS complexes are sensed. This may be referred to as demand pacing. So many patients will at times have a paced rhythm, an intrinsic rhythm, or a rhythm with both paced and intrinsic beats at any given time.

Ages and stages

Pacemakers in adult patients Adult patients are more apt to have AV block. Therefore, they usually get a dual-chamber pacemaker. This allows for synchronous pacing and contraction between the atria and ventricles. Cardiac output and exercise tolerance are increased because of increased ventricular filling. Older adults are more prone to permanent atrial fibrillation. Because atrial pacing is not possible during atrial fibrillation, a single-chamber ventricular pacemaker is typical for these patients when they have bradycardia.

Pacemaker Codes

The capabilities of permanent pacemakers may be described by a generic five-letter coding system, although three letters are more commonly used. (See Pacemaker coding system.)

Pacemaker Modes

The mode of a pacemaker indicates its functions. Several different modes may be used during pacing. Here are three of the more commonly used modes and their three-letter abbreviations. (A three-letter code, rather than a five-letter code, is typically used to describe pacemaker function.) Pacemaker rates vary by age (see Pediatric pacemakers) and other patient characteristics.

Ages and stages

Pediatric pacemakers Many young children don’t have AV block. Thus, they may get a single-chamber atrial pacemaker. The pulses per minute are initially set at an appropriate rate for the child’s age. As the child grows, the heart rate can be adjusted to a lower rate.

Read the Records

First, determine the pacemaker’s mode and settings, particularly the rate setting. If your patient had a permanent pacemaker implanted before admission, ask them whether they have a wallet card from the manufacturer that notes which generator and pacing leads were implanted.

If the pacemaker was recently implanted, check the patient’s records for information. Don’t check only the ECG tracing—you might misinterpret it if you don’t know the mode or which pacing leads the patient has.

Look at the 12-Lead ECG

Next, review the patient’s 12-lead ECG. If it isn’t available, examine lead V₁ or MCL₁ on telemetry. If there is only one ventricular lead, it is usually in the right ventricle. Therefore, expect a negatively deflected paced QRS complex in V₁ or MCL₁, just as with a left bundle branch block. An upright QRS complex in V₁ or MCL₁ may mean that the pacing lead is out of position, perhaps even perforating the septum and lodging in the left ventricle, or that there is a properly positioned pacing lead in the coronary sinus vein. When the His bundle is paced, the QRS complex should be narrow.

Scrutinize the Spikes

Then select a monitoring lead that clearly shows the pacemaker spikes. Some monitors have a filter or band width menu that allows adjustment for seeing larger pacemaker spikes. Make sure to use the “paced mode” on the telemetry monitor. If the monitor doesn’t “know” it’s looking at a rhythm that may have pacemaker spikes, it can interpret a pacemaker spike as a QRS complex. Therefore, a pacemaker spike that is not followed by a QRS complex without the “paced mode” on will NOT cause an important alarm.

Mull over the Mode

When looking at the ECG tracing of a patient with a pacemaker, consider the pacemaker mode. Then interpret the paced rhythm. Does it match what you know about the pacemaker?

Unravel the Rhythm

Look for information that tells you which chamber is paced. Is there capture? Is there a P wave or QRS complex after each atrial or ventricular spike? Or do the P waves and QRS complexes stem from intrinsic activity?

Look for information about the pacemaker’s sensing ability. Do you see spikes where you wouldn’t expect them? Like within or too close after a P wave or QRS complex? Remember if the pacemaker is sensing the electricity causing the P waves and QRS complexes, it should withhold a spike. Look at the rate. What’s the pacing rate per minute? Is it appropriate given the pacemaker upper and lower rate setting? Although you can determine the rate quickly by counting the number of complexes in a 6-second ECG strip, a more accurate method is to count the number of small boxes between two complexes and divide this into 1,500.

Troubleshooting Problems

Pacemaker malfunction can lead to arrhythmias and /or loss of AV synchrony. (See When a temporary pacemaker malfunctions) If you see questionable pacemaker activity for a patient with a permanent pacemaker, call the cardiology or cardiac electrophysiology team. There are actions you should take for patients with temporary pacemakers who have questionable pacemaker activity. Pacemaker problems that can lead to low cardiac output, hypotension, syncope, and death include

Mixed signals

When a temporary pacemaker malfunctions Occasionally, pacemakers fail to function properly. When that happens, you need to take immediate action to correct the problem. The strips shown below are examples of problems that can occur with a temporary pacemaker and corrective actions to take in response. Failure to capture Failure to pace Failure to sense intrinsic beats If the patient’s condition has changed, notify the practitioner and ask for new settings. Be prepared to initiate cardiopulmonary resuscitation (CPR) if needed. If pacemaker settings have been altered by the patient or someone else, return them to their correct positions. If the pacemaker has dials, make sure the face of the pacemaker is covered with its plastic shield and remind the patient not to touch the dials. If the heart still doesn’t respond, carefully check all connections. You can also increase the milliampere setting slowly (according to your facility’s policy or the practitioner’s orders), turn the patient from side to side, or change the battery. Keep in mind that the practitioner may order a chest X-ray to determine the position of the pacing lead. If the pacing light is flashing, check the connections to the cable and the patient. The position of the pacing lead in the patient may need to be repositioned (usually under fluoroscopy). If the pulse generator is turned on but the indicators aren’t flashing, change the battery. If that doesn’t help, use a different pulse generator. Decrease the sensitivity by increasing the millivolts. The pacemaker may be inhibiting pacing because of oversensing electrical activity from another heart chamber, muscle, or external source. Make sure a transcutaneous pacemaker, isoproterenol, and atropine are available in case the patient’s heart rate drops. Be prepared to initiate CPR if needed. If the pacemaker is undersensing (it fires but at the wrong times or for the wrong reasons), put the sensitivity control to a smaller number. Change the battery or pulse generator. Remove items in the room that might cause electromechanical interference. Check if the bed is grounded. Unplug each piece of equipment, and then check to see if the interference stops. If the pacemaker still fires on the T wave, turn off the pacemaker (per facility policy or practitioner’s order). Make sure isoproterenol, atropine, and transcutaneous pacemaker are available in case the patient’s heart rate drops, and be prepared to initiate CPR if needed.

• failure to capture
• failure to pace
• undersensing
• oversensing.

Undersensing

Undersensing is demonstrated by a pacemaker spike when intrinsic cardiac activity is already present. Undersensing causes the pacemaker to fire even if intrinsic electricity is present. Think of it as help being given when none is needed. With undersensing, spikes occur on the ECG where they shouldn’t. Although they may appear in any part of the cardiac cycle, the spikes are especially dangerous with a temporary pacemaker if they fall on the T wave. This can cause “R-on-T,” resulting in VT, ventricular fibrillation, or torsades de pointes. The output of a temporary pacemaker is much higher than that of a permanent pacemaker. Therefore, undersensing with a temporary pacemaker as opposed to a permanent pacemaker can lead to a fatal arrhythmia. With a permanent pacemaker, the unneeded pacing would most likely result in early battery depletion.

The problem can be caused by millivoltage set too high, electrolyte imbalances, disconnection or dislodgment of a lead, improper pacing lead placement, edema or fibrosis at the electrode tip, drug interactions, or a depleted or dead pacemaker battery.

Memory jogger Malfunction of a pacemaker can lead to fatal arrhythmias, hypotension, and syncope. To help you remember common pacemaker problems, think “failure times two, under, over”: failure to capture—spike without a P wave or QRS complex following it failure to pace—no spike on ECG at the rate set under sensing—spike when intrinsic activity already present over sensing—no spike when patient needs it.

How You Intervene

Make sure you’re familiar with different types and modes of pacemakers and how they function. This will save you time and worry during an emergency. When caring for a patient with a pacemaker, follow these guidelines.

What to Teach the Patient and Significant Other (s)

Temporary pacemakers:

• Explain why a pacemaker is needed, how it works, and what they can expect.
• Warn the patient with a temporary pacemaker not to get out of bed without assistance.
• Explain that a transcutaneous pacemaker causes twitching of the pectoral muscles. Reassure that you will be asking the patient if medication is desired for the discomfort.
• Instruct the patient not to manipulate the temporary pacemaker wires or pulse generator; and not to “fiddle” with the implanted generator.

Permanent pacemakers: In addition to explaining need, function, and expectations, give patients with permanent pacemakers the following:

• Teach how to care for the incision. Advise the patient to avoid tight clothing or other direct pressure over the pulse generator. The patient should observe the incision daily and notify the healthcare practitioner of redness or other signs of infection.
• Give the patient the manufacturer’s identification card and tell them to carry it at all times. They should show it to airport or law enforcement personnel as to avoid walking through strong metal detectors used by these staff.
• Inform the patient that they may want to wear a medical identification bracelet indicating that they have an implanted device in case they need medical attention and are unable to speak.
• Emphasize the importance of identifying pacemaker problems via routine remote and in-office checks.
• Explain the signs and symptoms of pacemaker malfunction, how to take a pulse, and what to do if any signs or symptoms exist, including notification of the healthcare practitioner.
• Advise the patient to avoid moving the arm on the side of the pacemaker in an extreme, exaggerated, or repetitive manner for 6 to 8 weeks or per the healthcare provider who cares for the permanent pacemaker.
• Advise the patient to speak to the practitioner who manages the pacemaker before having magnetic resonance imaging, radiation therapy, surgery, or diagnostic studies. The practitioner should also be consulted before use of power-generating equipment, equipment with antennas, or strong magnets.
• Tell the patient to follow normal routines and to increase exercise as tolerated and as allowed by the practitioner.
• Stress the importance of follow-up care and regular check-ups.
• Explain that a remote monitor is frequently used in the patient’s home to alert practitioners of rhythms and device function and to reduce the need for some office visits.

Two Ventricles, Three Leads

Unlike other pacemakers, a biventricular pacemaker usually has three leads rather than one or two: one to pace the right atrium, one to pace the right ventricle, and one to pace the left ventricle. Both ventricles are commonly either paced at the same time or the left ventricle is paced milliseconds before the right ventricle. This causes them to contract about the same time, increasing cardiac output.

Different Ventricles, Different Timing

Under normal conditions, the right and left ventricles contract simultaneously to pump blood to the lungs and body, respectively. However, in heart failure, the damaged ventricles can’t pump as forcefully and the amount of blood ejected with each contraction is reduced. If the ventricular conduction pathways are also damaged, electrical impulses reach the ventricles at different times, producing asynchronous contractions. This condition, called intraventricular conduction defect, further reduces the amount of blood that the heart pumps, worsening the patient’s symptoms.

An Important Tip

Unlike traditional lead placement, the pacing lead for the left ventricle is placed into a branch of a cardiac vein via the coronary sinus. This vein lies on the exterior of the left ventricle. The left ventricle is paced through the wall of the vein. Because this pacing lead isn’t anchored in place, lead displacement may be more likely to occur. (See Biventricular lead placement.)

Improves Symptoms and Quality of Life

Biventricular pacing produces an improvement in the patient’s symptoms and activity tolerance. Moreover, biventricular pacing improves left ventricular remodeling and diastolic function and reduces sympathetic stimulation. As a result, in many patients, the progression of heart failure is slowed and quality of life is improved.

Sympathetic Response

To compensate for reduced cardiac output, the sympathetic nervous system releases neurohormones, such as aldosterone, norepinephrine, and vasopressin, to boost the amount of blood ejected with each contraction. The resultant tachycardia and vasoconstriction increase the heart’s demand for oxygen, reduce diastolic filling time, promote sodium and water retention, and increase the pressure that the heart must pump against. The effect on the patient is a worsening of symptoms. Resynchronization therapy can reduce symptoms of heart failure, decrease hospitalizations and morbidity, and improve quality of life.

Who’s a Cand idate?

Not all patients with heart failure benefit from biventricular pacing. Cand idates should have both systolic heart failure and intraventricular conduction delay along with these characteristics:

• symptomatic heart failure despite maximal medical therapy
• moderate to severe heart failure (New York Heart Association class III or IV)
• QRS complex greater than 0.13 second
• left ventricular ejection fraction (EF) of 35% or less.

Many patients who meet criteria for biventricular pacing also meet criteria for a defibrillator. Therefore, patients having defibrillators with biventricular pacing (biventricular implantable cardioverter-defibrillator [ICD]) is very common.

Caring for the Patient

Provide the same basic care for the patient with a biventricular pacemaker that you would for a patient with a stand ard permanent pacemaker. Specific care includes these guidelines:

• Before the procedure, ask the patient if he/she has an allergy to iodine or shellfish because contrast medium is used to visualize the coronary sinus and veins. Notify the practitioner if an allergy exists.
• Because of the position of the left ventricular lead, watch for stimulation of the diaphragm and left chest wall. Ask patients if they feel any thumping in or on their chest. Notify the practitioner if this occurs because the left ventricular pacing lead output or configuration may need to be reprogrammed or the left ventricular lead may need repositioning.
• Observe the ECG for pacemaker spikes. Although both ventricles are paced, usually only one ventricular pacemaker spike is seen.
• Note the presence of positive R waves in lead V₁, and negative R waves in leads I and aVL. Notify the practitioner if this isn’t the case or if the R-wave direction changes at any time.

What to Teach the Patient

Provide the same basic teaching that you would for the patient receiving a permanent pacemaker. Additionally, when a patient gets a biventricular pacemaker, be sure to cover these points:

• Explain to the patient and their family why a biventricular pacemaker is needed, how it works, and what they can expect. Include that it can take 6 months for a patient to notice heart failure symptom improvement and that heart failure medications are still necessary.
• Tell the patient and their family that it’s sometimes difficult to place the left ventricular lead and that the procedure can take 4 hours or more.
• Stress the importance of calling the practitioner immediately if the patient develops chest pain, shortness of breath, swelling of the hand s or feet, or a weight gain of 3 lb (1.4 kg) in 24 hours or 5 lb (2.3 kg) in 72 hours.

What It is

An ICD consists of a programmable pulse generator, a shocking lead, and one or more pacing leads. The pulse generator is a small battery-powered computer that monitors the heart’s electrical signals and delivers electrical therapy when it identifies an abnormal rhythm. The leads are insulated wires that carry the heart’s signal to the pulse generator and deliver the electrical energy from the pulse generator to the heart.

What to Teach the Patient

• Explain to the patient and their family why an ICD is needed, how it works, potential complications, and what they can expect. Make sure they also understand ICD terminology.
• Discuss signs and symptoms to report to the practitioner immediately.
• Explain actions patient should take if they receive a shock with and without symptoms or get multiple shocks. For example, call their cardiologist when they receive a shock and call 911 if they feel ill after a shock or get sequential shocks.
• Educate family members in emergency techniques (such as dialing 911 and performing CPR) in case the device fails to restore circulation.
• Advise patients to speak with their physician before operating a transport vehicle (e.g., car, bus, plane).

Who’s a Cand idate?

Radiofrequency ablation is commonly used in treating patients with atrial tachycardia, atrial fibrillation, atrial flutter, AV nodal reentry tachycardia (AVNRT), inappropriate sinus tachycardia, bypass tracts like Wolff–Parkinson–White (WPW) syndrome, VT, and frequent premature ventricular contractions.

Understand ing the Procedure

The patient first undergoes an electrophysiology study to identify and map the specific areas of the heart that cause or support the arrhythmia. The ablation catheters are inserted into a vein, usually the femoral vein, and advanced into the heart where short bursts of radiofrequency waves destroy small targeted areas of heart tissue. The destroyed tissue can no longer conduct electrical impulses. Other types of energy may also be used, such as microwave, sonar, or cryo (freezing).

How You Intervene

When caring for a patient after radiofrequency ablation, follow these guidelines:

• Provide continuous cardiac monitoring, assessing for arrhythmias and ischemic changes.
• Place the patient on bed rest as ordered and keep the affected extremity straight. For example, when a figure-of-eight suture is used, patients usually remain flat for 4 hours after the suture is placed. Maintain the head of the bed between 15 and 30 degrees.
• Assess the patient’s vital signs every 15 minutes for the first hour, then every 30 minutes for 4 hours, unless the patient’s condition warrants more frequent checking.
• Assess peripheral pulses distal to the catheter insertion site as well as the color, sensation, temperature, and capillary refill of the affected extremity.
• Check the catheter insertion site for pain, bleeding, bruit, and hematoma formation.
• Medicate for pericardial discomfort.
• Monitor the patient for complications, such as hemorrhage, retroperitoneal bleed, access site hematoma or pseudoaneurysm, stroke, perforation of the heart, cardiac tamponade, phrenic or vagus nerve damage, pericarditis, atrial–esophageal fistula, pulmonic vein stenosis, heart failure, thrombosis, arrhythmias, and sudden death.

What to Teach the Patient

When a patient undergoes radiofrequency ablation, be sure to cover these points:

• Discuss with the patient and their family why radiofrequency ablation is needed, how it works, and what they can expect.
• Warn the patient and their family that the procedure can be lengthy: an average of 6 hours.
• Explain that the patient may be hospitalized for 24 hours to monitor their heart rhythm and monitor and /or remove intravascular and potential pericardial fluid.
• Advise the patient to continue prescribed medication exactly as directed, especially anticoagulation for stroke prevention. Postdischarge calls to patients can confirm this.
• Have the patient (1) return demonstrate taking their pulse, (2) describe what an irregular, fast, or slow pulse feels like, (3) state actions to take with an abnormal pulse.
• Advise the patient to call the team who performed the ablation with any signs or symptoms of complications, such as shortness of breath or edema caused by fluid overload. An extremely rare but often fatal complication of atrial fibrillation ablation is an atrial–esophageal fistula that can cause hemoptysis, fever, malaise, or dysphagia.
• Explain rationale for temporary limitations per the cardiology team, such as in driving, upper endoscopy, or vigorous activity.
• Provide implanted device teaching if the patient had a pacemaker or ICD inserted. (For more information about pacemaker teaching, see What to teach the patient, page 205.)

Subcutaneous implantable cardioverter-defibrillator

• Subcutaneous system that defibrillates VT and ventricular fibrillation
• Main advantage is avoidance of vascular access and associated complications
• Patients must meet selection criteria prior to implant: ECG morphology and no need for bradycardia pacing, antitachycardia pacing or resynchronization therapy

That’s a wrap!

Nonpharmacologic treatments review Pacemaker A device that electrically stimulates the myocardium to depolarize Atrial and Ventricular Stimulation Atrial only: spike followed by a P wave and the patient’s intrinsic QRS complex and T wave Ventricular only: patient’s intrinsic atrial rhythm, then a spike followed by a QRS complex and T wave Atrial and ventricular: first spike followed by a P wave, then a second spike, followed by QRS complex Pacemaker Codes First letter identifies the heart chambers being paced. Second letter signifies the heart chamber sensed by the pacemaker. Third letter refers to the pacemaker’s response to the intrinsic electrical activity of the heart. Fourth letter refers to the pacemaker’s rate modulation. Fifth letter refers to the pacemaker’s location or absence of multisite pacing. Pacemaker Modes AAI = single-chamber pacemaker; paces and senses the atria VVI = single-chamber pacemaker; paces and senses the ventricle(s) DDD = dual-chamber pacemaker; paces when the atria or ventricles don’t respond on its own; paces the atria when the atrial rate falls below the lower set rate; senses and paces both atria and ventricles Evaluating Pacemakers Determine the pacemaker’s mode and settings. Review the patient’s 12-lead ECG. Select a monitoring lead that clearly shows the pacemaker spikes. Adjust the ECG monitor filter or band width if necessary and if possible. Select Paced Mode to prevent missed alarms for noncapture. Interpret the paced rhythm. Look for information that tells which chamber is paced and about the pacemaker’s sensing ability. Troubleshooting Pacemakers Failure to capture: indicated by a spike without a complex Failure to pace: no spike Undersensing: spikes where they don’t belong Oversensing: no spike when the patient actually needs it Leadless Pacemaker Paces the right ventricle only Indicated for some patients with high-grade AV block or SND with atrial fibrillation; and when implant of an atrial lead would be difficult or unnecessary. Biventricular Pacemaker Pacemaker usually has three leads: one to pace the right atrium, one to pace the right ventricle, and one to pace the left ventricle. Both ventricles contract in synchrony, increasing cardiac output. Cand idates For treatment of patients with: class III and IV heart failure, with both systolic failure and ventricular dyssynchrony symptomatic heart failure despite maximal medical therapy QRS complex greater than 0.13 second left ventricular EF of 35% or less Benefits of Biventricular Pacing Improves symptoms, activity tolerance, and quality of life Reverses left ventricular remodeling and diastolic function, and reduces sympathetic stimulation His Bundle Pacing The right ventricular lead is placed in the right atrium next to the His–Purkinje network. This allows for depolarization of both ventricles via a normal conduction pathway, resulting in more physiologic conduction. Paced QRS complexes on ECG should be narrow. Radiofrequency Ablation Invasive procedure that uses radiofrequency energy to destroy heart tissue or conduction pathway responsible for arrhythmia Useful for atrial tachycardia, atrial fibrillation, and flutter; VT; premature ventricular contractions; AVNRT; inappropriate sinus tachycardia; and WPW syndrome Types of Ablation Reentrant: e.g., atrial fibrillation ablation (also known as pulmonary vein isolation), VT ablation, accessory pathway ablation Focal: e.g., His bundle ablation (with pacemaker insertion), atrial tachycardia ablation, sinus node modification Implantable Cardioverter-Defibrillator Implanted device that monitors for bradycardia, VT, and ventricular fibrillation Provides pacing for bradycardia, and pacing and shocks to break arrhythmias Types of Therapy Antitachycardia pacing: bursts of pacing to interrupt VT Cardioversion: shock synchronized to the R wave to terminate VT Defibrillation: asynchronized shock to terminate ventricular fibrillation Bradycardia pacing: pacing when the heart rate is below the rate set Programming Information Type and model Status of tachyarrhythmia therapy (on or off) Recorded arrhythmias Therapies to be delivered