Dual-chamber pacemaker

Amiodarone and carvedilol have been used in combination in 109 patients with severe heart failure and left ventricular ejection fractions of 0.25 (16). They were given amiodarone 1000 mg/week plus carvedilol titrated to a target dose of 50 mg/day. A dual-chamber pacemaker was inserted and programmed in back-up mode at a basal rate of 40. Significantly more patients were in sinus rhythm after 1 year, and in 47 patients who were studied for at least 1 year the resting heart rate fell from 90 to 59. Ventricular extra beats were suppressed from 1 to 0.1/day and the number of bouts of tachycardia over 167 per minute was reduced from 1.2 to 0.3 episodes per patient per 3 months. The left ventricular ejection fraction increased from 0.26 to 0.39 and New York Heart Association Classification improved from 3.2 to 1.8. The probability of sudden death was significantly reduced by amiodarone plus carvedilol compared with 154 patients treated with amiodarone alone and even more so compared with 283 patients who received no treatment at all. However, the study was not randomized, and this vitiates the results. The main adverse effect was s)mptomatic bradycardia, which occurred in seven patients two of those developed atrioventricular block and four had sinoatrial block and/or sinus bradycardia one patient developed slow atrial fibrillation. 

Lithium-ion batteries are compact and lightweight and have high energy density and long lifetimes, which make them useful in pacemakers like the Guidant Pulsar dual-chamber pacemaker pictured here with an eight-year lithium-oxide battery at left. (Leonard Lessin/Photo Researchers, Inc.)... 

If the procedure is to proceed in a smooth and expeditious fashion, careful preoperative planning is essential. The first such decision is whether the patient requires a single-chamber or dual-chamber pacemaker. As a rule, if the patient has intact atrial function, every effort is made to preserve atrial and ventricular relationships. Single-chamber ventricular pacing is usually reserved for the patient with chronic atrial fibrillation or atrial paralysis. A device is selected with acceptable size, longevity, and progranunability. If the heart is chronotropically incompetent, a device that offers some form of rate adaptation... 

Dirix LY, Kersscochot IE, Piemen SH, et al. Implantation of a dual-chambered pacemaker in a patient with persistent left superior vena cava. PACE 1988 11 343. 

Fig. 10.12 (A) Same patient as Fig. 10.11. Pulmonary capillary wedge pressure shows large cannon waves. Scale 0-40mmHg. (B) Same patient after testing with a temporary dual chamber pacemaker with a physiologic AV delay. Note the normal pulmonary capillary wedge pressure. The patient was markedly improved after the implantation of a dual chamber pacemaker with AV delay optimization. (Barold SS. Acquired Atrioventricular Block. In Kusumoto F, Goldschlager N (Eds), Cardiac Pacing for the Clinician, Philadelphia, PA Lippincott, Williams Wilkins, 2001 with permission).

Fig. 12.1 The cumulative risk of developing atrial fibrillation according to the mode of cardiac pacing. Patients with an atrial or dual chamber pacemaker were significantly less likely to develop AF compared to patients receiving a ventricular pacemaker. Reprinted with permission from Kerr CR, Connolly SJ, Abdollah MB et al. Circulation 2004 109 357-62.

Dual chamber pacemakers are more expensive and are also associated with an almost two fold risk of implant-related complications compared to ventricular pacing (2,15). Most of these additional complications are related to the atrial lead (e.g. dislodgement, perforation). Ventricular pacing is more likely to cause pacemaker syndrome particularly in patients with sinus node dysfunction (1,16). For patients with sinus node disease, atrial pacing should be considered for those with intact AV conduction and dual chamber pacemakers should be considered for those with associated AV node conduction abnormalities (17). The dual chamber pacanakers should be programmed to minimize the amount of ventricular pacing. 

Gianfranchi L, Brignole M, Menozzi C, et al. Progression of permanent atrial fibriUation after atrioventricular junction ablation and dual-chamber pacemaker implantation in patients with paroxysmal atrial tachycardias. Am J Cardiol 1998 81 351. ... 

Raj SR, Koshman ML, Sheldon RS Five-year follow-up of patients with dual chamber pacemakers for vasovagal syncope [abstract]. Can J Cardiol 18, xxx (2002). 

Abe H, Numata T, Hanada H, Kohshi K, Nakashima Y. Successful treatment of severe orthostatic hypotension with cardiac tachypacing in dual chamber pacemakers. Pacing Clin Electrophysiol 23, 137-139 (2000). 

Link MS, Estes NA HI, Griffin JJ, et al. Complications of dual chamber pacemaker implantation in the elderly. Pacemaker Selection in the Elderly (EASE) Investigators. J Interv Card Electrophysiol 1998 2 175-179. 

Reprogram dual-chamber pacemakers to the WI mode of function to avoid having the lithotriptor trigger off the atrial stimulus. 

Figure 18.5 shows pulse generators with three different polarities. In A, a single connector pin identifies the device as unipolar. In B, the two connector pins indicate either a unipolar dual-chamber pacemaker or an older singlechamber pacemaker that accepts a bifurcated bipolar lead. (Although these leads are no longer implanted, some are still in service.) In C, two leads with two pins each represent a bipolar in-Une lead and therefore a dual-chamber bipolar generator. 

The purpose of inspecting the connector block is to determine that the connector and pin are firmly in contact. If the pin of the pacing lead is not firmly in the connector block, intermittent or permanent disruption of the circuit occurs. In Figure 18.6, the chest radiograph demonstrates a dual-chamber pacemaker with a lower pin that is only partially advanced. At presentation, the patient had intermittent failure to capture the ventricle and intermittent failure to deliver a ventricular pacing output. 

Fig. 18.25 Posteroanterior (A) and lateral (B) chest radiographs from a child with a univentricular heart after a septation procedure and implantation of a dual-chamber pacemaker. The ventricular lead has been placed in an epicardial position, and the atrial lead is transvenously positioned. (From Lloyd MA, Hayes DL. Pacemaker and ICD radiography. In Hayes DL, Lloyd MA, Friedman PA, editors. Cardiac pacing and defibriUation a clinical approach. Armonk [NY] Futura Publishing, 2000 485-517. Used with permission of Mayo Foundation for Medical Education and Research.)...

Fig. 18.27 Posteroanterior chest radiograph (A) and close-up view (B) in a patient with a dual-chamber pacemaker and separation of the atrial conductor coil.

The growing availability of AutoCapture capabilities, first introduced in Europe by St. Jude Medical in their Microny family of single-chamber rate-modulated pacemakers has been expanded to the ventricular channel in the Affinity family of dual-chamber pacemakers (50-52). Similar but not identical algorithms have now been introduced by other manufacturers thus reducing the need for periodic capture threshold assessments. However, it does not totally eliminate the need to consider the combined concerns of patient safety and device longevity and periodically assess the event counter diagnostics that accompany this feature. While AutoCapture will protect the patient to... 

Gladstone PJ, Duxbury GB, Berman ND, Arrhythmia diagnosis by electrogram telemetry Involvement of dual chamber pacemaker. Chest 1987 91 115-116. 

A 70-year-old male with ischemic cardiomyopathy (BF 20%) and complete heart block was upgraded from a dual-chamber pacemaker to ICD due to inducible VT (225 b.p.m.). He comes into the office for evaluation after receiving his first shock. The ICD is programmed as a single-zone device, VF > 185 b.p.m. (all 31J shocks), and is not committed. You interrogate the ICD and find the following recorded event. 

A 67-year-old male with a right pectoral dual chamber pacemaker is undergoing implant of a left pectoral ICD due to inducible VT. Prior to induction of VF the pacemaker is programmed DOO with pacing outputs set to 7.5 V. 

The location of the spikes helps to identify the type of pacemaker system in situ. A spike before a P wave denotes atrial pacing, whereas one before the QRS complex identifies ventricular pacing. Spikes before both P waves and QRS complexes can be either dual chamber (atria and ventricle) or Bi-v pacing. As both chambers are synchronized in the Bi-v system only one spike is usually visible. Figures 8.4 and 8.5 show single and dual chamber pacemaker systems. 

Fig. 8.5 Dual chamber pacemaker (spikes before both P and QRS)...

A dual chamber pacemaker (with one lead In the atrium and another in the ventricle) provides versatile programming functions and can sense and pace In both the atrium and ventricle. This type of pacemaker mimics the normal cardiac cycle and maintains atrioventricular (AV) synchrony. It may be used for patients with chronic or intermittent AV block and for those who need atrial pacing or have delayed AV conduction or an increased risk of heart block. 

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