Types of pacemakers and their complications

Evoked compound action potentials during spinal cord stimulation: effects of posture and pulse width on signal features and neural activation within the spinal cord

Objective.Evoked compound action potential (ECAP) recordings have emerged as a quantitative measure of the neural response during spinal cord stimulation (SCS) to treat pain. However, utilization of ECAP recordings to optimize stimulation efficacy requires an understanding of the factors influencing these recordings and their relationship to the underlying neural activation.Approach.We acquired a library of ECAP recordings from 56 patients over a wide assortment of postures and stimulation parameters, and then processed these signals to quantify several aspects of these recordings (e.g., ECAP threshold (ET), amplitude, latency, growth rate). We compared our experimental findings against a computational model that examined the effect of variable distances between the spinal cord and the SCS electrodes.Main results.Postural shifts strongly influenced the experimental ECAP recordings, with a 65.7% lower ET and 178.5% higher growth rate when supine versus seated. The computational model exhibited similar trends, with a 71.9% lower ET and 231.5% higher growth rate for a 2.0 mm cerebrospinal fluid (CSF) layer (representing a supine posture) versus a 4.4 mm CSF layer (representing a prone posture). Furthermore, the computational model demonstrated that constant ECAP amplitudes may not equate to a constant degree of neural activation.Significance.These results demonstrate large variability across all ECAP metrics and the inability of a constant ECAP amplitude to provide constant neural activation. These results are critical to improve the delivery, efficacy, and robustness of clinical SCS technologies utilizing these ECAP recordings to provide closed-loop stimulation.

Delay of onset of second degree pacemaker block by beta-blockade in patients with P-synchronous pacemakers

Second degree pacemaker block is a safety mechanism of the synchronous pacer at atrial rates above 120-130. The aim of the present study was to determine the work level at which pacemaker block occurred before and after beta-blockade. Seven patients (mean age 53 y.) were submitted to graded, submaximal exercise on a bicycle ergometer without drug and after 0.8 mg pindolol i.v. (6 pats.) or alprenolol orally (1 pat.). Pacemaker block developed at much higher total work after beta-blockade in 3 patients (5800 vs. 1900 kpm. p less than 0.0005), while 4 patients had to stop work due to exhaustion before pacemaker block occurred. Total work increased significantly after beta-blockade (p less than 0.005). Lack of a stable i.v. atrial electrode has delayed the extensive use of the synchronous pacemaker. The design of the generator, however, is not optimal block occurs is too low for a number of patients. beta-Blockade effectively delays the occurrence of pacemaker block and can be of therapeutic value. It is suggested that the P-synchronous pacer should be redesigned with a programmable basic rate (50-70 beats/min) and a programmable upper rate (130-180 beats/min) to ensure that the obvious physiologic advantages of the atrial triggered pacemaker can be maintained both at rest and during physical exercise.

Interference with cardiac pacemaker function

A survey is given of the factors affecting cardiac pacemaker function. Whereas it was earlier considered that external interference was a frequent cause of a pacemaker failure, more recent studies indicate that this is of minor importance. It would appear that failure of pacemaker function due to changes in the QRS-complex, i.e. voltage change, intraventricular conduction defects and frequency changes, intraventricular conduction defects and frequency changes, are more important. A lesser known cause of failure in demand function is the inhibition which arises from skeletal muscle postentials. This appears to be a major problem in some types of pacemaker. Manufacturing defects are unavoidable, and it can still be assumed that electronic component defects may develop in 1 of 1000 pulse generators. Cases with the problem of early run-away pacemaker are still being reported and two such cases are discussed. In one of the patients the run-away phenomenon was intermittent, and was accompanied by a variation in run-away frequency. This possibility should thus always be taken into consideration in a pacemaker patient presenting with snycope. In a patient with a QRS-inhibited pacemaker a double stimulation phenomanen has been observed.

Medical issues and emergencies in the dermatology office

We review the medical issues and emergencies potentially encountered in the practice of general or surgical dermatology. Traditional guidelines have largely consisted of dated extrapolations from the nondermatologic literature concerning procedures that are primarily irrelevant to dermatology. This article outlines a rational approach to organizing an office emergency plan for anaphylaxis, stroke, status epilepticus, myocardial infarction, and hypertensive crisis. We discuss the literature that has influenced current office behavior regarding endocarditis prophylaxis, the use of electrosurgery with pacemakers, arrhythmogenic drug interactions, vasovagal syncope, lidocaine "allergy," and bleeding complications from oral anticoagulants. Recommendations for managing these issues in a dermatologic context are provided.

Electrosurgery and cardiac pacemakers

There are two basic types of cardiac pacemakers: (1) Fixed-rate pacemakers stimulate the heart at a regular rate independent of the intrinsic heart rate. (2) Demand pacemakers sense the heart's spontaneous rhythm. They are more commonly used because they are noncompetitive with the heart. There are two varieties of demand pacemakers: ventricular-inhibited and ventricular-triggered. Their responses to electrical interference are quite different. Potential pacemaker interference is a consideration with high-frequency electrosurgery. The problems with electrosurgical interference have occurred primarily with early pacemaker models. Recent improvements in electrical shielding and filtering systems have made pacemakers very resistant to outside electrical influence. Simple electrodesiccation of small lesions on relatively healthy pacemaker patients poses negligible risks. Caution is advised for marginal patients undergoing extensive electrosurgical procedures. The potential risks are further minimized by proper attention to patient history, monitoring, proper grounding, the avoidance of cutting current, and the use of proper technic.

Two-dimensional echocardiographic recognition of a pacing catheter perforation of the interventricular septum

A case of a pacing catheter perforation of the interventricular septum is presented here. The entire catheter length was visualized by two-dimensional real-time echocardiography utilizing the subcostal approach; the catheter was seen entering the left ventricle through the high interventricular septum.

Analysis of pacemaker malfunction and complications of temporary pacing in the coronary care unit

The medical records of 100 patients who received 113 temporary transvenous pacemakers were reviewed to determine the incidence of complications and malfunction. Malfunction, defined as failure to capture or sense, or both, occurred in 42 (37 percent) of 113 temporary pacemakers. The initial malfunction occurred within 24 hours in 21 (50 percent) and within 48 hours in 36 (86 percent) of the 42 pacemakers. Although the incidence of malfunction was not significantly different for brachial and femoral venous pacing catheters, 7 (37 percent) of 19 brachial venous pacemakers required repositioning or replacement compared with 8 (9 percent) of 91 femoral venous catheters (p = 0.005). Thirty-seven complications occurred in 23 (20 percent) of 113 episodes of pacing; ventricular tachycardia during catheter insertion, fever and phlebitis were the most common complications. No complication resulted in death. The incidence of complications and perforation was greater for brachial than for femoral venous pacemakers (p less than 0.05). Sepsis, local infection and pulmonary embolus occurred only with femoral venous pacemakers. Sepsis, phlebitis and pulmonary embolus were more common with temporary pacemakers in place for 7 hours or longer (p = 0.04). Recognition to the problems peculiar to each pacing catheter site and shortening the duration of pacing should help minimize problems with temporary pacing.

Dislodgment of pacemaker electrode simulating focal motor seizure

The unusual finding of dislocation of the electrode of a pacemaker in a patient caused repetitive twitching of the right leg. Initial confusion with focal motor seizure resulted in the administration of antiepileptic medication. Malposition of the electrode was confirmed by appropriate roentgenographic studies, and subsequent repositioning terminated the episode.

Clinical experience with a new transvenous atrial lead

Although systems using atrial pacemakers offer potential clinical advantages for many patients now receiving ventricular devices, atrial systems have been used in less than 1% of the implantations of permanent pacemakers. The unavailability of clinically successful, easily positioned atrial leads is regarded as the most significant factor in the underutilization of atrial pacing systems. A permanent transvenous atrial lead has been developed and has performed well in 16 months of evaluation in 28 patients. Acute thresholds for voltage at a pulse width of 1 msec ranged from 0.40 v to 2.0 v (average, 1.1 v). Acute peak-to-peak amplitudes of the atrial electrogram were notably high, ranging from 2.5 mv to 7.5 mv (average, 5.1 mv) as measured oscilloscopically. Intermittent failure of sensing occurred in three patients during the period immediately after implantations. Spontaneous dislodgment of the lead from the right atrial appendage occurred in two patients. Atrial sensing and pacing functions remained intact in the first case, and no revision was performed. The lead was repositioned in the second patient and has remained in good position. No complications relating to the lead have been noted in the remaining patients.

Pacemaker-induced endocardial friction rub

Two patients had a typical sounding cardiac friction rub after placement of a temporary transvenous pacemaker. Absence of myocardial perforation was documented in one patient during thoracotomy for placement of an epicardial electrode and in the other with an electrogram recorded from the pacemaker as it was being withdrawn. The rubs disappeared during pacemaker removal. These cases are believed to represent endocardial friction rubs resulting from contact of the pacing wire with the endocardium.

Carotid sinus syndrome: new surgical considerations

1. Direct surgical denervation of the carotid sinus would appear to offer the best long-term results for carotid sinus syncope. 2. Carotid sinus denervation should be done under temporary cardiac pacing for safety and for completeness of denervation. 3. Arteriography is indicated to eliminate those cases of cerebral vascular insufficiency that might mimic carotid sinus syndrome. Credit must be given to Dr. R. Hughes, Clearfield, Pa., who recognized this diagnosis and referred the patient for therapy.

Demand pacemaker arrhythmias caused by intermittent incomplete electrode fracture. Diagnosis with testing magnet

This report describes how the testing magnet was used to diagnose intermittent and incomplete electrode fracture in two patients with an implanted demand pacemaker. During fixed-rate pacing the interval between two consecutive pacemaker spikes intermittently doubled in length, suggesting that the pulse generator was continuing to fire on time into a transiently disrupted circuit. Attenuated pacemaker spikes occurring at the anticipated time of pacemaker discharge also provided a diagnostic clue. Ventricular electrograms from the defective electrodes registered small false signals.