Cardiac pacing and pacemakers VI. Analysis of pacemaker malfunction

Pacing for drug-refractory or drug-intolerant hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal-dominant inheritance for which negative inotropes are the most widely used initial therapies. Observational studies and small randomised trials have suggested symptomatic and functional benefits using pacing and several theories have been put forward to explain why. Pacing, although not the primary treatment for HCM, could be beneficial to patients with relative or absolute contraindications to surgery or alcohol ablation. Several randomised controlled trials comparing pacing to other therapeutic modalities have been conducted but no Cochrane-style systematic review has been done.

OBJECTIVES

To assess the effects of pacing in drug-refractory or drug-intolerant hypertrophic cardiomyopathy patients.

SEARCH METHODS

We searched the following on the 14/4/2010: CENTRAL (The Cochrane Library 2010, Issue 1), MEDLINE OVID (from 1950 onwards ), EMBASE OVID (from 1980 onwards ), Web of Science with Conference Proceedings (from 1970 onwards). No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials of either parallel or crossover design that assess the beneficial and harmful effects of pacing for hypertrophic cardiomyopathy were included. When crossover studies were identified, we considered data only from the first phase.

DATA COLLECTION AND ANALYSIS

Data from included studies were extracted onto a pre-formed data extraction paper by two authors independently. Data was then entered into Review Manager 5.1 for analysis. Risk of bias was assessed using the guidance provided in the Cochrane Handbook. For dichotomous data, relative risk was calculated; and for continuous data, the mean differences were calculated. Where appropriate data were available, meta-analysis was performed. Where meta-analysis was not possible, a narrative synthesis was written. A QUROUM flow chart was provided to show the flow of papers.

MAIN RESULTS

Five studies (reported in 10 papers) were identified. However, three of the five studies provided un-usable data. Thus the data from only two studies (reported in seven papers) with 105 participants were included for this review. There was insufficient data to compare results on all-cause mortality, cost effectiveness, exercise capacity, Quality of life and Peak O2 consumption.When comparing active pacing versus placebo pacing on exercise capacity, one study showed that exercise time decreased from (13.1 ± 4.4) minutes to (12.6 ± 4.3) minutes in the placebo group and increased from (12.1 ± 5.6) minutes to (12.9 ± 4.2) minutes in the treatment group (MD 0.30; 95% CI -1.54 to 2.14). Statistically significant data from the same study showed that left ventricular outflow tract obstruction decreased from (71 ± 32) mm Hg to (52 ± 34) mm Hg in the placebo group and from (70 ± 24) mm Hg to (33 ± 27) mm Hg in the active pacing group (MD -19.00; 95% CI -32.29 to -5.71). This study was also able to show that New York Heart Association (NYHA) functional class decreased from (2.5 ± 0.5) to (2.2 ± 0.6) in the inactive pacing group and decreased from (2.6 ± 0.5) to (1.7 ± 0.7) in the placebo group (MD -0.50; 95% CI -0.78 to -0.22).When comparing active pacing versus trancoronary ablation of septal hypertrophy (TASH), data from one study showed that NYHA functional class decreased from (3.2 ± 0.7) to (1.5 ± 0.5) in the TASH group and decreased from (3.0 ± 0.1) to (1.9 ± 0.6) in the pacemaker group. This study also showed that LV wall thickness remained unchanged in the active pacing group compared to reduction from (22 ± 4) mm to (17 ± 3) mm in the TASH group (MD 0.60; 95% CI -5.65 to 6.85) and that LV outflow tract obstruction decreased from (80 ± 35.5) mm Hg in the TASH group to (49.3 ± 37.7) mm Hg in the pacemaker group.

AUTHORS' CONCLUSIONS

Trials published to date lack information on clinically relevant end-points. Existing data is derived from small trials at high risk of bias, which concentrate on physiological measures. Their results are inconclusive. Further large and high quality trials with more appropriate outcomes are warranted.

Pacemaker Malfunction Due to Subcutaneous Emphysema

The authors describe a case of pacemaker malfunction due to a critical increase of impedance resulting from air entrapment in the pacemaker pocket.

Pacemaker malfunction due to subcutaneous emphysema--a case report

The authors describe a cas of pacemaker malfunction due to a critical increase of impedance resulting from air entrapment in the pacemaker pocket.

Syncope

Syncope is a common admitting diagnosis to intensive care units; however, in half the cases, the etiology goes undiagnosed. The prognosis is adversely affected in patients with a cardiogenic etiology. We discuss the clinical presentation and pathophysiology of cardiovascular causes of syncope (including arrhythmia and conduction disturbances, myocardial disorders, and valvular disorders), vascular causes (obstruction and decreased venous return), peripheral vascular causes (arterial and venous), and noncardiovascular causes (neurological and hematological). A thorough history and physical examination are the best diagnostic tools. In addition, electrocardiograms and 24-hour telemetry monitoring are also useful. Other diagnostic tests should be ordered judiciously, depending on the findings of the initial evaluation. Medical or surgical treatment is directed at the underlying cause.

"Subclinical" pacemaker syndrome: a randomised study of symptom free patients with ventricular demand (VVI) pacemakers upgraded to dual chamber devices

OBJECTIVE

To determine whether symptom free patients with single chamber pacemakers benefit from dual chamber pacing.

DESIGN

A randomised double blind crossover comparison of ventricular demand (VVI), dual chamber demand (DDI), and dual chamber universal (DDD) modes after upgrading from a VVI device.

SETTING

Cardiology outpatient department.

PATIENTS

Sixteen patients aged 41-84 years who were symptom free during VVI mode pacing for three or more years.

INTERVENTION

Pacemaker upgrade during routine generator change.

MAIN OUTCOME MEASURES

Change in subjective (general health perception, symptoms) and objective (clinical assessment, treadmill exercise, and radiological and echocardiographic indices) results between pacing modes before and after upgrading.

RESULTS

75% preferred DDD, 68% found VVI least acceptable with 12% expressing no preference. Perceived general well-being and exercise capacity (p less than 0.01) and treadmill times (p less than 0.05) were improved in DDD mode but VVI and DDI modes were similar. Clinical, echocardiographic, radiological, and electrophysiological indices confirmed the absence of overt pacemaker syndrome, although mitral and tricuspid regurgitation was greatest in VVI mode (p less than 0.01).

CONCLUSIONS

Most patients who were satisfied with long term pacing in VVI mode benefited from upgrading to DDD mode pacing suggesting the existence of "subclinical" pacemaker syndrome in up to 75% of such patients. The DDI mode offered little subjective or objective benefit over VVI mode in this population and should be reserved for patients with paroxysmal atrial arrhythmias. VVI mode pacing should be used only for patients with very intermittent symptomatic bradycardia or atrial fibrillation with a good chronotropic response during exercise.

Benefits of dual chamber pacing in sick sinus syndrome

The effects of DDD (fully automatic) and VVI (ventricular demand) pacing modes on exercise tolerance, symptom diary cards, and Holter monitoring were investigated in a randomised double blind crossover study of 16 patients who had had DDD pacemakers implanted because of frequent syncope. Eight patients presented with sick sinus syndrome and, with one exception, retrograde atrioventricular conduction and eight age and sex matched patients presented with 2:1 or complete atrioventricular block. Maximal symptom limited exercise in those with atrioventricular block was significantly higher after one month of DDD pacing than after VVI pacing. In those with sick sinus syndrome, however, maximal effort tolerance was not significantly different for the two pacing modes. In all but one patient with sick sinus syndrome sinus rhythm developed during exercise in VVI pacing. For both VVI and DDD modes maximal atrial rates were significantly lower in those with sick sinus syndrome. Palpitation and general wellbeing were significantly improved during DDD pacing in the eight patients with sick sinus syndrome. Shortness of breath was improved by DDD pacing in the eight patients with atrioventricular block but not in those with sick sinus syndrome. Holter monitoring showed that sick sinus syndrome patients remained in paced rhythm, either DDD or VVI, for most of the 24 hour period. DDD pacing was better than VVI pacing in sick sinus syndrome with retrograde atrioventricular conduction. Despite their ability to show sinus rhythm and inhibit their pacemakers on exercise patients with sick sinus syndrome are just as likely to have symptomatic benefit from DDD pacing as patients with atrioventricular block.

Pacemaker follow-up and adequacy of Medicare guidelines

The time of occurrence of cardiac pacemaker problems after implantation was identified to assess the adequacy of published federal guidelines for clinic and transtelephonic follow-up. One hundred eighty-nine pacemaker patients' charts were examined retrospectively to identify pacemaker problems: inadequate sensing, non-capture, battery failure, myoinhibition, muscle stimulation, and inadequate threshold safety margin. Twenty-nine patients (15%) were identified as having pacemaker problems. A total of 41 problems were identified, of which 28 (68%) were corrected by reprogramming. Sixty-one percent of the problems were found during a clinic visit. Problems occurred more frequently during the first year in dual-chamber devices (62%) vs single-chamber devices (35%). During years 1 to 4, when few problems are expected, 30% of all problems of single-chamber devices occurred and 39% of all problems of dual-chamber devices occurred. This is a period of time that Medicare guidelines allow for one clinic visit per year for single- and two visits per year for dual-chamber devices. These data suggest: (1) Many pacemaker problems will be missed with transtelephonic follow-up alone. (2) The majority of problems involving dual-chamber devices occurred in the first year. (3) For both dual- and single-chamber devices, an unexpected significant percentage of problems occurred in 1 to 4 years. (4) Medicare guidelines may be inadequate for follow-up during this time period.

Intermittent pacemaker syndrome: revision of VVI pacemaker to a new cardiac pacing mode for tachy-brady syndrome

A patient with tachy-brady syndrome manifested by paroxysmal atrial fibrillation and symptomatic sinus bradycardia and treated by VVI pacing developed pacemaker syndrome during episodes of ventricular pacing. His cardiac pacemaker was revised to a dual chamber system utilizing the new AV sequential DDI pacing mode which eliminated pacemaker-related tachycardias and totally abolished the pacemaker syndrome symptoms. There have been no further episodes of atrial fibrillation, possibly due to elimination of temporal dispersion of refractory periods during bradycardia. The propensity for atrial fibrillation has also been minimized by excluding competitive atrial stimulation during DVI pacing. The DDI mode provides the clinician increased utility and flexibility in the use of AV sequential pacing therapy.

Hemodynamic findings during sinus rhythm, atrial and AV sequential pacing compared to ventricular pacing in a dog model

The hemodynamic responses of atrial (AP), atrioventricular sequential (AVP) and ventricular pacing (VP) were compared to sinus rhythm (SR) in seventeen anesthetized dogs with intact AV conduction. The atrium and/or ventricle were paced at fixed rates above the control sinus rate. An AV interval shorter than normal conduction was selected to capture the ventricle. The changes of pulmonary capillary wedge pressure (PCWP, mmHg), mean aortic pressure (MAP, mmHg), cardiac output (CO, L/min), systemic vascular resistance (SVR, dynes/s/cm-5), left ventricular stroke work index (SWI) and mean systolic ejection rate (MSER, ml/s) during sinus rhythm, atrial pacing and atrioventricular sequential pacing (expressed in percentages of the individual values during ventricular pacing) were: (Chart: See text) The importance of atrial systole for cardiac performance was clearly demonstrated in dogs with normally compliant hearts. In both atrial and atrioventricular sequential pacing compared to ventricular pacing there was a reduction of pulmonary capillary wedge pressure (PCWP) (p less than 0.01) and systemic vascular resistance (SVR) (p less than 0.01) despite an increase in cardiac output (CO). The lesser mean systolic ejection rate (MSER) found during atrioventricular sequential pacing compared to sinus rhythm and atrial pacing may be explained by the abnormal ventricular depolarization in this pacing mode; nevertheless, the mean systolic ejection rate was still greater than that found during ventricular pacing (p less than 0.05).

Radiographic pseudofracture of bipolar pacemaker wire

We present a case in which the radiographic appearance of a bipolar pacing lead mimics a wire fracture. Recognition of this normal finding--due to lead construction--will help avoid erroneous diagnosis of wire fracture on chest x-ray films.

The "lead tug" sign for the diagnosis of early and inapparent lead fracture

The cause of pacemaker malfunction in a patient having intermittent pacing failure associated with diminished pacer stimuli was not determined during conventional intraoperative electrical testing. A modest manual pull on the lead, termed the "lead tug" sign, induced an inordinately high lead impedance and established lead fracture as the etiology. The "lead tug" maneuver is proposed as a useful procedure during stimulation studies for the detection of early lead fracture, not apparent from the x-ray film or usual testing protocol.

Pacemaker system failure secondary to air entrapment within the pulse generator pocket. A complication of subclavian venipuncture for lead placement

Air entrapment within the pulse generator pocket may produce pacemaker system malfunction if the anodal contract plate becomes insulated by the accumulation of air. Unipolar pulse generators are predisposed to this complication. We describe a pacemaker-dependent patient who, early after implantation, experienced pacemaker system failure as a complication of subclavian venipuncture. This patient had an unsuspected pneumothorax that progressed to subcutaneous air entrapment within the pulse generator pocket. Management of this previously unreported complication of subclavian venipuncture is rapid, noninvasive and effective. With the growing use of subclavian venipuncture technique for lead placement one should avoid the predisposing factors that can lead to subcutaneous air entrapment.

Hemodynamic and symptomatic consequences of ventricular pacing

After implantation of a ventricular demand pacemaker (VVI), occasional patients continue to have dizziness, syncope, or near syncope ("pacemaker syndrome"). To identify patients in whom VVI pacing may have deleterious effects, we compared cuff blood pressure responses to VVI pacing with blood pressure responses to atrioventricular sequential pacing (DVI) or sinus rhythm in 50 consecutive patients. Patients with intact ventriculoatrial conduction had a much greater decrease in systolic blood pressure with VVI pacing (24 +/- 11 mm Hg) than those with ventriculoatrial dissociation (-4 +/- 15 mm Hg) (P less than 0.005). Patients who were in heart failure had a lesser decrease in blood pressure with VVI pacing than did those without failure (P less than 0.05); 13 of the 14 heart failure patients lacked ventriculoatrial conduction. Ten patients had symptomatic dizziness after VVI pacing; the incidence of symptoms was higher in patients with ventriculoatrial conduction (9 of 23) than in those without ventriculoatrial conduction (1 of 27) (P less than 0.003). We conclude that the presence of intact ventriculoatrial conduction appears to be a crucial determinant of the hemodynamic response to VVI pacing, and its presence may identify patients who are at risk for "pacemaker syndrome."

Pacemaker-induced hypotension

We report a case of hypotension and decreased cardiac output resulting from artificial ventricular pacemaker rhythm. Hemodynamic deterioration was associated with loss of normal time relationships between atrial and ventricular contraction and paradoxical fall in systemic vascular resistance despite a low output state. The therapeutic implications of this unusual response are discussed.

The malfunctioning pacemaker system. Part I

The success of an implanted cardiac pacemaker is dependent upon the establishment of a harmonious relationship between the artificial pacemaker and the human receiver. Failure of a pacemaker system may arise from an electronic or mechanical defect within the pacemaker, a physiologic problem, or from a poor relationship between the normal function of both. Such malfunctions may necessitate the repair, replacement, or repositioning of a pacemaker component or removal of a source of external interference. True pacemaker malfunctions must be clearly distinguished from pseudo-malfunctions, where there is no pacemaker system defect. These situations may, variously, require the repair of faulty testing equipment, reassessment of falsely interpreted test data, or treatment of the patient for an unrelated disorder. This paper outlines a system for investigating patients with suspected pacemaker malfunction. For simplicity, only malfunctions associated with the ventricular inhibited pacing system will be discussed.

Long-term follow-up after pacemaker implantation in sick sinus syndrome

In 74 symptomatic patients suffering from sick sinus syndrome, survival after pacemaker implantation and additional drug therapy was determined. The 5-year survival was poor (47.2%). Evidence of other cardiac disease (present in 44.6%) influenced the prognosis unfavorably, especially in combination with continuing symptoms. As yet the phase of SSS in which chronic cardiac pacing is required, should be considered as a critical stage.

The value of redundancy in chronic bipolar pacemaker electrode systems

Bipolar pacing systems, because of the presence of two intracardiac electrodes, provide lead redundancy. This allows conversion of bipolar to unipolar pacing or the reversal of lead polarity. During a 3-year period, this redundancy was utilized in 34 (13.7%) of 248 patients with chronic bipolar lead systems during follow-up pacemaker surgery. Of the 34 patients, elective pulse generator change was the most frequent indication for surgery (23 patients) and in this group redundancy was used most often to select the lead configuration with the highest R-wave amplitude and lowest stimulation threshold, or to solve the problem of weld defects of the connector pins or frayed insulation. The remaining 11 patients underwent surgery for pacemaker system malfunction and in this group redundancy was used to avoid the need for lead repositioning or placement of a new catheter system. Lead redundancy in those patients in whom bipolar pacing has been selected provides flexibility at the time of additional pacemaker surgery, and its use may obviate the need for a change in catheter system when stimulation thresholds are excessive, wire fraction is irreparable, or bipolar sensing signals are inadequate.

Inhibition/filter characteristics and input impedances of QRS-inhibited demand pacemakers determined by in vitro studies

There is still no standardized test procedure established for demand pacemakers. Much work has been done to reduce demand failures, but more knowledge is needed to arrive at better results. This study was initiated by in vivo observations of pacemaker malfunctions and unwanted pacemaker effects, the objective being to arrive at a better match between spontaneous cardiac activity and the pacemaker system. The study describes inhibition characteristics and input impedances in some modern temporary as well as permanent QRS-inhibited pulse generators, based on in vitro experiments with various signal waveforms. The different pulse generators tested showed a wide variety of inhibition characteristics. The interrelationship between signal amplitude and maximum derivative required to obtain pacemaker inhibition is pointed out. A better approach to describe the inhibition characteristics of demand pacemakers seems to be the introduction of the time integral (voltseconds) instead of the maximum derivative of a signal (Fig. 3). It is shown that this method nearly removed the discrepancies in inhibition characteristics between different pulse waveforms used. The input impedances were also widely dispersed and were in some instances of a magnitude so low that it would lead to marked reduction of the electrogram amplitude in case the electrode/tissue interface impedance was high. The characteristics of temporary pulse generators were in several respects different from those of the permanent ones. The results obtained with a temporary unit during a test procedure are therefore not the same as for a permanent pacemaker system.

Intracardiac electrocardiography during permanent pacemaker implantation: predictors of cardiac perforation

Intracardiac electrograms from 50 successive patients undergoing permanent pacemaker implantation have been analyzed. There were 29 male and 21 female patients aged 14 to 93 years (mean age 68.4 years). The electrograms were obtained using methods that simulated the wave form that would be detected by unipolar cardiac pacemakers. Three types of electrographic patterns were identified: qR pattern with a q/R ratio of less than 1 (type I): QR pattern with a Q/R ratio between 1 and 4.4 (type II); and Qr pattern with a Q/r ratio between 12 and 15 (type III). A type I pattern was seen in 29 patients (58 percent), type II in 18 (36 percent) and type III in 3 patients (6 percent). The duration of the follow-up period ranged from 3 weeks to 20 months (mean 9.7 months); three patients were lost to follow-up study. There were four deaths apparently unrelated to the pacemaker. Recognizable problems (either pacing or sensing failure) occurred in one patient (6 percent) with a type II pattern, in two patients (66.7 percent) with a type III pattern and in no patient with a type I pattern. On the basis of these data it is suggested that at the time of pacemaker implantation, intracardiac electrograms with a type I pattern indicating good pacing thresholds and sensing should be sought. If type II wave forms occur with good pacing thresholds and sensing then the electrode could probably be left in position. The incidence of a type III pattern is rare; when it does occur it is greatly suggestive of myocardial perforation. When this pattern is seen, the pacemaker catheter must be repositioned.

The interdependence between electrogram, total electrode impedance and pacemaker input impedance necessary to obtain adequate functioning of demand pacemakers

Electrogram maximum derivatives (DMAX, SMAX) and electrogram amplitudes (AMAX, UMAX) (Figure 2), were studied in 71 cases during permanent pacemaker treatment. During the acute phase, (at first implantation), 29 patients were studied, and during the chronic phase, (at pulse generator replacement), 42 patients were studied. Of these patients, 27 (acute phase) and 36 (chronic phase) were studied for tissue impedance (RT) and interface impedance (Faraday resistance RF and Helmholtz capacity CH). DMAX and SMAX changed from 3.47 +/- 0.33 V/s (mean +/- SEM) to 2.46 +/- 0.23 V/s and 1.93 +/- 0.20 V/s to 1.32 +/- 0.12 V/s; p < 0.02; p < 0.01. AMAX and UMAX remained nearly unchanged from acute to chronic phase. A paired comparison in 13 patients showed almost identical results. Electrograms recorded in patients with bundle branch block showed no statistical difference in DMAX, SMAX, AMAX, and UMAX compared with electrograms recorded in patients with QRS-complexes of normal duration. No correlation was found between rise in myocardial threshold and fall in DMAX and SMAX from acute to chronic phase; p > 0.8, p > 0.5. Patients with coronary heart disease were found to have significantly higher AMAX than patients classified as having rhythm disturbances of primary cause; p < 0.01. Extremely low values of amplitudes and maximum derivatives were found in some patients with myocardial infarctions and cardiomyopathies. No difference existed in DMAX, SMAX, AMAX, and UMAX recorded from electrodes with a 8 mm2 area compared with a 12 mm2 area (p > 0.5). RT was statistically significantly higher on the smaller compared with the larger surface electrodes (p > 0.005). There was a slight but not statistically significant fall in RT from acute to chronic phase (p > 0.2). RF ranged from 2.0-94.6 kohms. There was no statistically significant differences between the 8 mm2 compared with the 12 mm2 electrodes (p > 0.2). CH varied between 0.7 and 37.0 microfarads, with significantly lower values for the smallest electrodes (p < 0.05). In patients with electrograms of borderline amplitudes and maximum derivatives for being sensed, the low CH found with the small tip electrodes, will gave a higher risk of demand failure if the input impedance in the sensing circuit of a demand pacemaker is too low.

Unusual artifacts in electrocardiographic monitoring

Three unusual artifacts noted during Holter and telemetry monitoring, not previously described, are presented. Recognition of the artifacts prevented misinterpretation and wrong treatment. The clues to the identification of the artifacts and the need for avoiding wrong interpretation and inappropriate treatment are discussed. The cause of the telemetry artifact is discussed.

Gas pocket causing pacemaker malfunction

Pacemaker malfunction was attributed to the increase in impedance to current flow caused by a pocket of air separating the anodal contact plate of a unipolar generator from the overlying skin. Lack of capture was noted 20 hours after implantation. The malfunction was permanently corrected by bedside aspiration of the gas with a sterile syringe.

Intraoperative pacemaker electrical testing

To determine the clinical value of intraoperative pacemaker system electrical testing, the results of 200 consecutive pacemaker procedures (95 ventricular and 6 atrial primary implantations, 88 generator replacements, and 11 system revisions) were reviewed. The rationale and technique of testing maneuvers are described, including the use of a compact pacing system analyzer wrapped and used on the sterile operating field.