Deep brain stimulators (DBS) are increasingly prevalent in patients with Parkinson’s disease, dystonia, and other disorders. The DBS devices consist of either (1) a single stimulator implanted on either side of the pectoralis muscle which is capable of stimulating the subthalamic nucleus bilaterally through two separate leads or (2) two stimulating devices, one placed on each side of the chest, stimulating only the ipsilateral side. The DBS leads typically traverse subcutaneously from the subclavicular area to the lateral-posterior neck and then over the occiput to penetrate the skull at variable sites in the parietal area.

Electromagnetic interference from medical and household devices may cause DBS devices to switch ON or OFF. Also, some patients may “experience a momentary increase in their perceived stimulation” described as uncomfortable (Medtronic Physician and Hospital Staff Manual; Soletra® & Kinetra® devices). More importantly, nerve conduction studies pose a theoretical risk of introducing electrical current through the leads, which could be transmitted directly to the brain. The typical stimulation intensity of DBS devices range from 12–50 ìA, which is far below current employed in routine nerve conduction study (personal communication, Medtronics). The course of the DBS leads through the supraclavicular and occipital areas may pose additional risks to Erb’s point and cervical root stimulation. As there currently are no studies assessing the safety of performance of nerve conduction study in patients with DBS devices, the physician should evaluate the risks and benefits of electrodiagnostic testing in each case.
 

 Cardiac pacemakers and implanted cardiac defibrillators (ICDs) are increasingly used in clinical practice, and no evidence exists indicating that performing routine electrodiagnostic studies on patients with these devices poses a safety hazard. However, there are theoretical concerns that electrical impulses of nerve conduction studies could be erroneously sensed by devices and result in unintended inhibition or triggering of output or reprogramming of the device⁵⁴. In general, the closer the stimulation site is to the pacemaker and pacing leads, the greater the chance for inducing a voltage of sufficient amplitude to inhibit the pacemaker. Despite such concerns, no immediate or delayed adverse effects have been reported with routine nerve conduction study.

A single study of 10 patients with pacemakers with bipolar sensing configurations and 5 patients with ICDs found no evidence of cardiac device sensing or malfunctioning with routine nerve conduction study utilizing surface stimulation (including left Erb’s point stimulation in 9 patients).⁵⁴ The authors did not evaluate ICDs placed in the lower abdomen or pacemakers with unipolar sensing mode. Although percutaneous nerve stimulation may be performed in patients with implanted cardiac pacemakers with little risk, 39 complete inhibition of a unipolar pacemaker in conjunction with an interscalene nerve stimulator (utilized for regional anesthesia) was reported.²⁵ A stimulator, therefore, should be used only with extreme caution if it is necessary to stimulate the brachial plexus ipsilateral to a pacemaker or ICD implantation site, particularly if it is unknown if the sensing mechanism is unipolar or bipolar. Caution is advised when performing intramuscular percutaneous stimulation, especially in the upper extremities, as the safety of its performance has not been established. Special care should be given to proper grounding of the patient. Routine consultation with the patient’s cardiologist is not required. In patients with external cardiac pacemakers, the conductive lead, inserted into the heart (usually transvenously) and connected to the external cardiac pacemaker, presents a serious potential hazard of electric injury to the heart.² Nerve conduction studies are not recommended in any patient with an external conductive lead terminating in or near the heart. The nature of recurrent and frequent electrical impulses that may occur with repetitive stimulation or eliciting somatosensory evoked potentials (SSEP) poses a special circumstance. Nerve stimulation in the lower extremities or in distal upper extremities would be unlikely to have untoward effects upon pacemakers or ICDs. Repetitive stimulation for assessing integrity of the neuromuscular junction typically necessitates study of proximal and/or cranial nerve-innervated muscles, which may place the stimulating electrode closer to the cardiac device.

Nonetheless, as there are no data to determine the safety of performing these procedures in patients with pacemakers or ICDs, proximal upper extremity and cranial nerve stimulation sites should be avoided for repetitive and SSEP stimulation. Needle EMG recording does not introduce electrical current into the body and, therefore, poses no risk of interference with implanted cardiac devices.

Excerpt from the AANEM position statement Risks in Electrodiagnostic Medicine.

No known contraindications exist from performing needle EMG and nerve conduction studies on pregnant patients. In addition, no complications from these procedures have been reported in the literature. Evoked response testing, likewise, has not been reported to cause any problems when performed during pregnancy.

Excerpt from the AANEM position statement Risks in Electrodiagnostic Medicine. 

Prosthetic joints may become infected postoperatively due to hematogenous spread of bacteria. Bacteria may enter the circulatory system through infections involving the surgical site or other noncontiguous tissues or following procedures producing bacteremia including dental procedures and gastrointestinal studies. ^4,26,5,61,43 The risk for prosthetic joint infection declines rapidly during the first few postoperative months and continues to decline during the first 2 postoperative years.¹¹ There are no published reports of complications related to needle EMG in patients with prosthetic joints. Based upon current published literature, it is the opinion of the AANEM that there is no contraindication to needle EMG in patients with prosthetic joints when sterile single patient use or properly autoclaved needle electrodes are utilized and infected spaces are not traversed by the needle electrode.

Excerpt from the AANEM position statement Risks in Electrodiagnostic Medicine.

ELECTRICALLY SENSITIVE PATIENTS

23,28,55,58

EDX Studies in the Critical Care Unit

The critically ill patient is at particular risk for electrical injury because certain protective factors may not be operative.² Two important defenses against electric injury are frequently lost in these patients. First, the high skin resistance provided by dry, intact skin is often breached by intravenous and intra-arterial catheters with leakage and spills around the catheter site. With lowered resistance, current applied in these areas will be conducted more efficiently to the rest of the body, including the heart.^42,35,32,24

The second important protection against electric injury is the large volume of soft tissue which surrounds the heart (i.e., the trunk) and dilutes any electric current applied to the body, protecting the heart from direct electric current application. In the critically ill patient, intracardiac catheters are now commonplace. Such catheters bypass this large electric sink and provide small, otherwise harmless currents, potentially lethal, direct access to the immediate vicinity of the heart(microshock).² Most manufacturers make intracardiac devices electrically isolated so that they will not conduct electricity. The same attention, however, must be given to these catheters as to other percutaneous catheters; for example, stimulation in the immediate vicinity of the catheter should be avoided and should never be done in the presence of fluid spills or leakage.

Two common sources of current which might affect the hospitalized patient are leakage current from attached electric equipment and applied current from stimulators that are a part of electrodiagnostic machines. Stimulator complications can be avoided by refraining from stimulating next to areas with percutaneous catheters and especially avoiding areas where there is fluid leakage. “Leakage current” is current that leaks to the instrument chassis and then can be delivered to the connected patient if improper grounding conditions exist. The maximum current allowed to leak from the case or from patient connections is 10μA.^{59,9,8,7,6,37} The electrodiagnostic physician is responsible for ensuring the machine in use meets these minimum specifications. Providing proper patient grounding is necessary to protect patients from electric injury. The third ground wire is required on all electric equipment for patient use because it provides a harmless route for any chassis leakage current. The current flows directly to the ground, instead of to the patient. Testing of the third ground wire integrity and outlet grounds should be performed at regular intervals.⁵⁵ Special safety considerations arise when patients are connected to multiple machines. Defects in outlet grounds or ground faults may occur in individual outlets. Thus, if a person is connected to equipment supplied from different outlets, one with a functional ground and the other nonfunctional, leakage current may flow from the machine connected to the nonfunctional outlet round, through the patient into the functional outlet ground wire of lower voltage. Thus, it is  recommended that the patient be disconnected from all nonessential electric equipment. The remaining equipment should be plugged into the same outlet or, at least, outlets in the same vicinity which are likely to share a common ground. When using electrodiagnostic equipment, it is recommended that the ground be placed between the stimulator and the recording electrodes, as well as keeping ground and needle electrodes in close proximity. This practice helps ensure that any leakage current or applied current will return to ground and not spread to the rest of the body. If proper attention is given to equipment leakage current, grounding, and location and type of percutaneous catheters, electrodiagnostic testing of the electrically sensitive patient can be performed without risk.

Electrodiagnostic laboratories should have in place a power outage and surge rotection policy. In an effort to assist laboratories in meeting this standard, the AANEM has developed model policies: Model Power Outage Protection Policy.(http://www.aanem.org/accreditation/ModelPoweroutageSurgeProtectionPolicy.cfm)

Bleeding and hematoma are potential risks of needle EMG in patients with or without disorders of hemostasis. There is limited data regarding the incidence of clinically significant bleeding complications from needle EMG and additional risks in patients who are receiving antiplatelet or anticoagulant therapy or who suffer from thrombocytopenia or clotting factor deficiencies. Additionally, the use of subcutaneous partially fractionated heparin (e.g. Lovenox®) is becoming more commonplace. The degree of anticoagulation is not readily measurable, which may also result in increased risk of hemorrhagic complications. Some practitioners utilize vapocoolant spray to improve hemostasis, although there are no studies assessing the utility of this technique. Likewise, no data indicates that various needle parameters (e.g. gauge, monopolar vs. concentric, etc.) present different risks for bleeding complications. In a retrospective, uncontrolled study of patients who were not receiving anticoagulants, 14 asymptomatic paraspinal muscle hematomas were identified by MRI in 5 of 45 muscles. In a survey of 47 electrodiagnostic laboratories with ACGME-approved fellowships, 3 laboratories reported a single instance of serious bleeding complications (requiring intervention) occurring in anticoagulated patients.³¹ One laboratory reported two instances of serious bleeding complications. In the only prospective study, subclinical hematomas were visualized by ultrasonography in 3 of 209 muscles. There was no statistical difference in hematoma rates in subjects taking anti-platelet or anticoagulant therapy compared to control subjects. ⁴⁰ There are few published case reports of bleeding complications following needle EMG. These include a 64-year-old man anticoagulated with coumadin (prothrombin time = 28s [control = 12.4s], partial thromboplastin time = 68 [26]). He developed subcutaneous bleeding following needle EMG examination with a drop in hematocrit from 43 to 29%, resulting in angina and requiring blood transfusion.¹³ There are two cases of hematoma and compartment syndrome affecting the calf²⁷ (73-year-old man with recent aspirin usage) and forearm60 (34-year-old woman with no bleeding risks). There is an additional report of calf hematoma and pseudoaneurysm in an 81-year-old woman with an INR = 2.5. ⁵³ The risks and benefits of needle EMG examination should be considered in patients with known disorders of hemostasis, and needle EMG should be performed with added caution. Each case should be considered individually with regard to the potential benefits of the study relative to the risks of intramuscular hemorrhage or other bleeding. If the decision is made to perform needle EMG in such a patient, it is advisable to first examine small, superficial muscles to watch for bleeding problems. Prolonged pressure over the needle site will usually produce hemostasis.