28. A 60-year-old man presents to his primary care physician for evaluation of dizziness and increased fatigue. An electrocardiogram is performed as part of his evaluation. The ECG demonstrates complete heart block, with a ventricular rate of 44 beats/min. The patient is referred for implantation of a pace-maker.
Which of the following is NOT an indication for implantation of a cardiac pacemaker?
❏ A. Temporary pacing in the setting of acute myocardial infarction com-plicated by conduction abnormalities and hemodynamic instability
❏ B. Resynchronization in the treatment of heart failure
❏ C. Type I second-degree atrioventricular (AV) block in an asymptomatic athlete
❏ D. Complete AV block
❏ E. Neurocardiogenic syncope with significant bradycardia
Key Concept/Objective: To know the various indications for cardiac pacing
Conduction abnormalities are common in the setting of acute myocardial infarction.
Patients with acute inferior infarction can manifest a variety of abnormalities, including sinoatrial (SA) node dysfunction, first-degree AV block, type I second-degree block, and third-degree block at the level of the AV node. It is uncommon for any of these conduc-tion disturbances to persist after the acute phase of the infarcconduc-tion. These patients often require temporary pacing if they manifest hemodynamic instability. Cardiac resynchro-nization therapy is an exciting new development in the treatment of heart failure.
Complete AV block with bradycardia and the presence of symptoms is an indication for permanent cardiac pacing. Classic neurocardiogenic syncope involves sinus tachycardia followed by bradycardia, vasodilatation, and syncope. Some patients have primarily a vasodepressive (vasodilatation) syndrome, whereas others have a syndrome with a signif-icant cardioinhibitory component (bradycardia). In the setting of bradycardia, cardiac pacemaker implantation is necessary. It is not uncommon for trained athletes to have type I second-degree AV block and be asymptomatic. Pacemaker therapy is not indicated.
(Answer: C—Type I second-degree atrioventricular (AV) block in an asymptomatic athlete)
29. A 67-year-old female patient of yours is admitted to the hospital. She has a permanent pacemaker and sees a cardiologist. In reviewing her chart, you note that her pacemaker program code is VVI, with a lower rate of 60 beats/min.
Which of the following statements regarding this patient's pacemaker program code is false?
❏ A. Both the atria and ventricles are programmed to be paced
❏ B. The sensing lead is in the ventricle
❏ C. When the intrinsic heart rate falls below 60 beats/min, pacing will occur
❏ D. After a paced beat, the pacemaker clock resets and senses the next ven-tricular contraction
❏ E. VVI is also referred to as ventricular demand pacing or ventricular inhibited pacing
Key Concept/Objective: To understand the three-letter code for describing the basic functions of cardiac pacemakers
The three basic functions of a pacemaker—pacing, sensing, and action—are determined by basic pacemaker programming. In 1974, the American Heart Association and the American College of Cardiology proposed a three-letter code for describing the basic func-tions of pacemakers. Under the guidance of the North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG), this code evolved into the five-position code currently in use. The first position denotes the chamber or chambers paced; the second denotes the chamber or chambers sensed; the third denotes the action or actions performed; the fourth denotes rate response; and the fifth denotes multiple site pacing. The simplest mode of pacing is VVI, otherwise known as ventricular demand pacing or ventricular inhibited pacing. The most commonly used mode in dual-chamber pacing is DDD. The most basic timing cycle is the lower rate, which reflects how long the pacemaker will wait after a paced or sensed beat before initiating
pacing. If the pacemaker is set to VVI mode at a lower rate of 60 beats/min, then as long the interval between intrinsic beats is less then 1,000 msec, the pacemaker will reset the lower rate clock with each sensed QRS complex, and pacing will not occur. If, however, the intrinsic heart rate falls below 60 beats/min, the pacemaker’s lower rate clock will time out before an intrinsic beat is sensed, and pacing will occur. After a paced beat, the lower-rate clock is reset and the cycle repeats. (Answer: A—Both the atria and ventricles are programmed to be paced)
30. A 56-year-old woman is admitted for implantation of a permanent pacemaker for management of sick sinus syndrome. The procedure is successful.
Which of the following statements regarding further care of this patient is true?
❏ A. It is standard practice to discharge the patient the day of the procedure if no obvious complications occurred
❏ B. There is no need for telemetric monitoring if admitted
❏ C. A chest radiograph is routinely performed to verify lead position and to evaluate for pneumothorax
❏ D. The rate of adverse events associated with pacemaker implantation is 1%
❏ E. Once the pacemaker has been installed, there is no need for interrogat-ing the device
Key Concept/Objective: To understand the immediate complications associated with pacemaker implantation and appropriate postimplantation care
Overall, transvenous pacemaker implantation is both safe and well tolerated. The risk of major adverse events (e.g., death, myocardial infarction, stroke, and the need for emer-gency thoracotomy) is approximately 0.1%. Other complications sometimes encountered include pneuomothorax, vascular injury, cardiac perforation, tamponade, local bleeding, pocket hematoma, infection, and venous thrombosis. At most institutions, it is standard practice to admit patients for overnight observation after routine pacemaker implanta-tion. Patients are monitored via continuous telemetry. We routinely obtain a portable chest x-ray and a 12-lead ECG immediately after implantation. The day after the proce-dure, the pacemaker is interrogated and the final settings confirmed. Posteroanterior and lateral chest x-rays are obtained both to verify the positioning of the leads and to rule out the possibility of a slowly accumulating pneumothorax. (Answer: C—A chest radiograph is rou-tinely performed to verify lead position and to evaluate for pneumothorax)
31. A 76-year-old man with a permanent pacemaker is admitted to the hospital with a diagnosis of pneu-monia. The patient unfortunately develops respiratory failure and is intubated. A central venous line is placed for administration of antibiotics and pressors. He improves clinically but develops fever. Blood cultures are positive for Staphylococcus aureus. Appropriate antimicrobial therapy is instituted, and the central line is removed. The patient remains febrile with persistently positive cultures.
Which of the following statements regarding pacemaker infection is true?
❏ A. The most common organism causing pacemaker infection is S. aureus
❏ B. Pacemaker infection is easily treated with appropriate antimicrobial therapy
❏ C. Patients with S. aureus bacteremia are not at significant risk for sec-ondary pacemaker infection
❏ D. Infected pacemaker leads can simply be exchanged, as opposed to removing the entire unit
❏ E. Patients with infected pacemaker hardware need to be sent to a refer-ral center with experience in removing these devices
Key Concept/Objective: To understand that pacemaker infection requires special expertise and
that patients should be referred to special centers with experience in device removal and pace-maker infection therapy
Bacterial infections can affect any part of the pacemaker system, and the consequences can be devastating. The most common pathogens are staphylococci, especially S. epidermidis.
Once a pacemaker infection is established, it is difficult to eradicate with antibiotics; thus, infected pacemaker systems usually must be removed in their entirety. Patients with pace-makers in place who acquire S. aureus bacteremia are at significant risk for a secondary device infection. If an infection of an implanted cardiac device is suspected, prompt refer-ral to an experienced center is critical. (Answer: E—Patients with infected pacemaker hardware need to be sent to a referral center with experience in removing these devices)
For more information, see Lowy J, Freedman RA: 1 Cardiovasculaar Medicine: VII Pacemaker Therapy. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds.
WebMD Inc., New York, May 2004