Triple Impedance: - "I sing the body electric"
We are very familiar with the term "electricity", but we do not have an in-depth understanding of its “nature” or its “workings”. However we are all aware that an “electric shock” or a "lightning bolt" can produce a range of effects that range from a minor tingle to a “jolt” to major burns to death. In this post I will discuss three cases of electrical injury that I have been associated with.
My first encounter was about 40 years ago when I was working with a radio locum medical service. I attended a woman in her mid thirties who was distressed after her father died after being electrocuted. She said that her father had been on the roof of his house when he accidentally touched a power line. He apparently was not seriously injured as he was able to climb down unaided from the roof and go into his house. He told his wife about the electrocution and then said “I nearly died”. Shortly afterwards he collapsed and could not be revived.
There is no information on the autopsy findings in Case 1 - this death could be due to an unrelated condition, an (arrhythmogenic) event that was secondary to the increased sympathetic activity following electrocution, or a delayed arrhythmia that was directly linked to the electrocution.
There are several reports of possible delayed arrhythmia after electrocution, but neither of the two most convincing cases had a electrocardiograph (ECG) taken after the electrocution. A 16-year-old female with a past history of palpitations was found dead 10 hours after a 750 volt direct current (DC) shock that produced burns to both hands. A 43-year-old man who had a 3000 volt DC electrical injury collapsed 12 hours later while playing football, and was resuscitated from ventricular fibrillation. On the other hand 24 hours of cardiac monitoring of patients deemed to be at potential risk after high voltage electrical injury has not detected any delayed arrhythmias. The current view is that the risk of a delayed arrhythmia is extremely low in a person with a normal ECG after electric injury.
The second case of electric injury was 20 years ago, and involved a 32 year old electrician who sustained a high voltage injury while working on a construction site. He was thrown backwards by the shock, but did not lose consciousness. There was no history of cardiac disease. On arrival at the Emergency Department (ED) he had burns to his left hand and his right foot. Apart from the skin burns (Figure 1 - Figure 2) the rest of the examination was normal. An ECG taken on arrival is shown in Figure 3.
The pattern suggests injury due to a electrical arc rather than direct contact. The surface of the burns has a white-yellow sheen that is due to the deposit of metal.
The ECG in Case 2 initially shows widened QRS complexes with a left bundle branch block morphology, a ventricular rate of about 68 beats per minute and no visible P waves. This is consistent with an accelerated idioventricular rhythm (AIR). The rhythm strip shows that the accelerated idioventricular rhythm is followed by a short interval of sinus rhythm with an initial rate of about 100 beats per minute (first three sinus beats). The sinus rhythm then slows to a rate of 65 beats per minute, which is slightly slower than the accelerated idioventricular rhythm rate. The shape of the 10th and 11th complexes in the rhythm strip are intermediate between the QRS shape ofthe sinus beats and the QRS shape of the AIR beats, indicating that they are the result of fusion of the sinus beats and the ventricular beats i.e. they are fusion beats.
This patient was treated last year. He is a 40 year old man who sustained a high voltage injury to his left wrist and left forearm while carrying out maintenance on a relay station (Figure 4). Contact with the electric current was brief, there was no loss of consciousness or collapse, and there were no other burns. The patient had severe pain in his left forearm, the second to fifth fingers in the left hand were flexed and he could not straighten the fingers. The radial pulse was palpable and sensation in the hand was intact. The ECG taken on arrival is shown in Figure 5.
There are two depressed area of full thickness skin burn with a grey yellow colour, with a surrounding rim of reddened skin.
Figure 5. Electrocardiograph of Case 3 (R_0046_B) taken in the ED
The ECG in Case 3 is normal. The serum troponin and the serum electrolyte concentrations were normal. The patient was admitted to a non-cardiac monitored bed.
+ A. Impedance
Impedance is the name of an obscure British electronic dance music group that released a popular club remix of the Soft Cell song “Tainted Love” in 1989. Their version has a pulsating and hypnotic beat.
+ B. Electrical Impedance
According to the Encyclopaedia Britannica "Electrical impedance is a measure of the total opposition that a circuit or a part of a circuit presents to electric current. Impedance includes both resistance and reactance. The resistance component arises from collisions of the current-carrying charged particles with the internal structure of the conductor. The reactance component is an additional opposition to the movement of electric charge that arises from the changing magnetic and electric fields in circuits carrying alternating current. Impedance reduces to resistance in circuits carrying steady direct current.
+ C. I Sing the Body Electric
"I Sing the Body Electric!" is a 1969 collection of short stories by the American science fiction writer Ray Bradbury. The book takes its name from the title of one of the short stories, which in turn took used the title of a poem by Walt Whitman published in his 1855 collection Leaves of Grass. The short story is about a family with three children whose mother dies. The father decides to buy an electric grandmother to help around the house and serve as a nanny for the children.
+ D. Incidence of Electrical injury
- Approximately 1500 people were hospitalised in Australia as a result of an electrical injury during the two year period 2002–03 to 2003–04. This equates to an age-adjusted rate of 3.78 cases per 100,000 population for the period. There were 77 cases in which lightning was associated with the injury.
- There were 162 deaths due to electrical injury in a four year period between 2001 and 2004. Only 7 of these deaths were associated with lightning.
- Approximately 1000 people die of exposure to electricity annually in the United States
- There are about 1000 deaths per year worldwide due to lightning
+ E. Applied Physics of Electrical Injury
Electricity is the flow of electrons
Amperage is the term used for the rate of flow of electrons: 1 ampere of current = 6.242 x 1015 electrons passing a given point in 1 second.
Electrons move (flow) from a region of higher potential/concentration to a region of lower potential/concentration This potential difference, expressed in voltage (V), represents the force driving the electrons. Household voltage is approximately 120 V (US) and 220-240 V in Australia/Asia.
Ohm’s Law expresses the relationship between current (I), voltage (V) and resistance (or impedance) (R) as I = V/R i.e. current is directly proportional to voltage and inversely proportional to resistance.
Current may be direct or alternating. In alternating current (AC) the direction of electron flow changes rapidly in a cyclic fashion; for example, standard household current is an alternating current that flows at 60 cycles per second. Direct current (DC) flows constantly in one direction across the potential. Examples of direct current include batteries, automobile electrical systems, high-tension power lines, and lightning.
The heat produced [by the current] is proportional to the resistance and the square of the current (Joule’s Law) (Figure 6).
+ F. Factors that Determine the Damage Due to Electricity
The primary determinants of damage/injury are:
The point of contact: For industrial shocks the points of contact are usually on the upper limbs, hands and wrists, whereas for lightning they are mostly on the head, neck and shoulders. Injury may also occur indirectly through ground current or current “splashing” from a object that is hit by lightning
The amount of current: For a 1-second contact time, a current of 1 milliampere (mA) is the threshold of perception, a current of 10-15 mA causes pain and muscular contraction and a current of 50-100 mA can cause respiratory paralysis and ventricular fibrillation
Type of current - alternating vs direct: Alternating current is 4 to 5 times as dangerous as an equal voltage of direct current
Voltage: High voltage electrical injuries (HVEI) are defined as those where the voltage is 1000 V or greater. Household electricity has a voltage of 110 to 230 V, high-tension power lines have voltages greater than 100, 000 V and lightning strikes are can produce 10 million V.
Resistance: Tissues with a higher resistance to electricity are skin, bone, and fat. Other tissues such as muscle, nerves and blood vessels have a low resistance and conduct electricity readily. Skin resistance [to electricity] is mainly in the stratum corneum [of the skin]. The resistance of dry skin is greater than moist or wet skin. Dry skin may have extensive superficial tissue damage but little conduction to deeper structures.
Current pathway: Current is concentrated at its entrance to the body, then diverges centrally, and finally converges before exiting. A horizontal (hand-hand) pathway is more likely to involve the heart than a vertical (hand-foot) pathway. Low-voltage current generally follows the path of least resistance (i.e, nerves, blood vessels), while high-voltage current takes a more direct path between entrance and ground. Some of the current from a lightning strike passes over the surface of the body (‘external flashover’)
Duration of contact
+ G. Pathophysiology of Electrical Injury to the Heart
Electrical injury to the heart can cause:
Loss of normal cardiac impulse formation due to ventricular fibrillation or asystole. Ventricular fibrillation is more common with low-voltage alternating current, whereas asystole is more frequent with electric shocks from direct current or high-voltage alternating current.
Abnormal impulse formation (causing ectopic beats or tachycardias) or abnormal impulse conduction or both
Myocyte damage due to thermal injury or electroporation. Electroporation is a technique in which an electrical field is applied m to cells to increase the permeability of their cell membrane. Electrical injury may increase the number of pores in cell membranes or increase their size.
Myocardial necrosis and fibrosis: Nuclear medicine studies have demonstrated anterior, septal, inferior and apical defects after electrocution. Focal necrosis has been found in sub-endomyocardial biopsy specimens from patients after electrical injury. A post-mortem study in four person who died after electrocution found widespread focal necrosis throughout the myocardium, including the specialized tissue of the sinus and atrioventricular nodes, in all the hearts. Cells in the His bundle and bundle branches were less affected. A survivor of high voltage electrical injury who developed progressive cardiac failure that eventually required cardiac transplantation. The patient's heart showed bi-ventricular disease with diffuse interstitial fibrosis of the subepicardial layer.
Coronary artery abnormalities: Contraction band necrosis of smooth muscle cells in the tunica media of the coronary arteries. Coronary artery spasm is a postulated mechanism because coronary angiography is nearly always normal in electrocuted patients with ST- T changes on their ECG identical to those seen in acute myocardial infarction. Coronary artery endothelial dysfunction, with impaired dilation to acetylcholine, was found in the coronary microvascular and conduit arteries after 20 J shocks to the exposed heart of dogs.
+ H. Effects of Medical Electrical Shocks on the Heart
- The administration of electrical stimuli is accompanied by temporary asystole.
- ECT produces a significant and transient decrease in left-ventricular systolic and diastolic function.
External direct current (DC) shocks for electrical cardioversion of atrial and ventricular arrhythmias:
- Serum troponin is not increased after cardioversion for atrial fibrillation or atrial flutter in persons with normal or reduced ejection fraction
- Transient and brief ST elevation may be seen after cardioversion
- There is a case report of ECG changes of widespread ST-segment elevation (mimicking acute myocardial infarction) lasting at least 1 hour after DC cardioversion for ventricular defibrillation due to Brugada syndrome
+ I. Effects of Electric Injury on the Heart
Many publications are case reports or retrospective studies that are biased towards unusual presentations or high voltage electrical injuries, thus making it difficult to have a overview of the most common presentations.
High Voltage Energy Injury (HVEI) vsLow Voltage Energy Injury (LVEI)
HVEI - Voltage ≥ 1000 V:
- Can cause ventricular fibrillation *
- More likely to cause asystole than LVEI *
- Greater risk of electricity induced apnoea *
- Possibility of lengthy muscle paralysis *
- High incidence of skin burns and muscle damage
- More likely to produce echocardiographic abnormalities (focal or global hypokinesis; reduced ejection fraction) that usually resolves completely
*Immediately after electric injury
Low Voltage Energy Injury (LVEI) < 1000 V:
- This is the type of electrocution seen in most EDs
- More likely to cause ventricular fibrillation than asystole *
- Many patients do not have any burn injury
- ECG abnormalities may be seen in up to one third of patients, but these are either non-specific or mostly resolve within 6 hours or less
*Immediately after electric injury
Features Common to HVEI and LVEI
- The risk of malignant dysrhythmias, such as ventricular fibrillation or ventricular tachycardia, is greatest at the time of injury.
- The great majority of deaths from electrocution (98 percent) occur at the scene
- By the time of presentation to the emergency department the risk of a malignant dysrhythmia isvery low.
- The role of troponin (or CK MB) measurement in electrical injury is not clear. The clinical significance of an elevated serum troponin level is uncertain. Baseline and 12 hour troponin measurement may be carried out if high risk features are present.
+ J. Summary of Cardiac Effects After Electrocution
Changes in First 24 hours
Changes in P wave morphology
Right bundle branch block
Transient Brugada pattern in V1-V3
Non-specific ST depression or T wave inversion
ST-T elevation that resembles the changes seen in ST elevation myocardial infarction (coronary arteries are normal on angiography)
Prolonged QT interval
Atrial ectopic beats⁄Ventricular ectopic beats
Atrial fibrillation (usually paroxysmal)
Junctional rhythms (can last for 24 hours)
Bradycardia: Transient marked bradycardia, usually due to first degree heart block. Wenckebach heart block and complete heart block can occur, but usually resolve spontaneously
Intermediate: Days or weeks
- ST-T changes similar to those seen in acute myocardial infarction become less marked or resolve
- Sinus tachycardia and hypertension (can last for some weeks)
- Intraventricular conduction block can persist for up to two weeks
- Bradycardia with impaired chronotropic response to exercise
Focal or global hypokinesis (usually resolves)
Reduced ejection fraction (usually resolves)
Takotsubo-shaped hypokinesis of the left ventricle (following lightning strike)
Long term: Months or years
Persistent left ventricular dysfunction (very rare)
Progressive left ventricular failure (extremely rare)
+ K. Who Needs Cardiac Monitoring After Electrical Injury
The following are some recommendations from the recent literature.
The criteria proposed for ECG monitoring included loss of consciousness or documented arrhythmias in the field, and ECG abnormalities on admission.
Comment: The implication is that the presence of burns or muscle damage is not an indication for monitoring. Case 3 had clinical evidence of full thickness burns to his forearm and muscle injury, but no evidence of compartment syndrome. He was admitted to a non monitored bed
Routine cardiac monitoring is not required after household voltage electrical injury if the patient is asymptomatic and has nomral initial electrocardiography.
Comment: What if the patient has a small skin burn? I think patients with a small skin burn should have 4 - 6 hours of cardiac monitoring in the ED. If there are no abnormalities the patient can be discharged.
Asymptomatic patients with transthoracic current and/or tetany and a normal initial ECG do not require cardiac monitoring after an electrical injury with voltage < 1000 V and no loss of consciousness.
Comment: This supersedes earlier guidelines that recommended cardiac monitoring if the electrocution was associated with repetitive muscle spasms (tetany) or if the burn injury pattern (hand-hand) meant that the current had passed through the thorax. Loss of consciousness after electrical injury remains a indicator for cardiac monitoring, but the evidence for this approach is debatable.
Electrocution is a relatively uncommon presentation to the ED. Most of the tissue damage occurs at the time of electrical injury. For practical purposes all lethal cardiac rhythms occur at the time of electrocution, although respiratory depression and prolonged muscle paralysis after lightning can cause secondary damage because of anoxia. About one in three persons who come to the ED after electrocution will have some change in their ECG tracing or their rhythm, but these changes are usually minor or reversible or both. The management of persons with significant ECG changes or rhythm abnormalities is supportive.
James TN, Riddick L, Embry JH. Cardiac abnormalities demonstrated postmortem in four cases of accidental electrocution and their potential significance relative to nonfatal electrical injuries of the heart. Am Heart J. 1990; 120:143–157
Soar J, Perkins GD, Abbas G et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation. 2010; 81:1400–1433
To NT, Haquin G, de Montpreville V, et al. Extensive myocardial fibrosis after high-voltage electric shock demonstrated by delayed-enhancement cardiac magnetic resonance imaging. Circulation. 2015; 131:e366-e368
Cemin R, Rauhe W, Marini M et al. Serum troponin I level after external electrical direct current synchronized cardioversion in patients with normal or reduced ejection fraction: no evidence of myocytes injury. Clin. Cardiol. 2005; 28:467–470
Shan P, Lin J, Xu W, Huang W. ST-segment elevation after direct current shock mimicking acute myocardial infarction: a case report and review of the literature. Am J Emerg Med. 2014; 32:1438.e1-3. doi: 10.1016/j.ajem.2014.04.005.