When an ECG monitor remains connected during defibrillation, two conditions must be satisfied at the same time. The medical device must not expose the operator, other equipment, or another patient connection to hazardous energy. It must also avoid reducing the defibrillation energy intended for the patient beyond the permitted level.
This is why defibrillation-proof testing is not simply a check that the monitor survives a 5 kV pulse. A device can remain powered and show no visible damage but still fail because it transfers hazardous energy, absorbs too much of the defibrillator discharge, loses stored data, changes operating mode, or does not restore its ECG signal within the required time.
For manufacturers of electrocardiographs, ECG monitors, and multiparameter patient monitors, understanding these separate acceptance requirements is essential before IEC 60601 testing begins.
What Does Defibrillation-Proof Mean in IEC 60601-1?
A defibrillation-proof applied part is an applied part designed to remain safe when the connected patient is subjected to cardiac defibrillation. The applicable general requirements are found in Clause 8.5.5 of IEC 60601-1.
The classification applies to an applied part in its entirety. It should not be assigned informally to one electrode, lead, or connector while excluding the other patient connections that form the same applied part.
Defibrillation-proof classification is also different from Type B, BF, or CF classification. Type B, BF, and CF describe the degree and nature of protection against electric shock. Defibrillation-proof status adds protection against the effects of a defibrillator discharge. The appropriate defibrillation-proof symbol must be used where the classification applies.
Manufacturers that need to establish the underlying classification can refer to Astute Labs’ guide to Type B, BF, and CF applied parts.
Which Medical Devices Require This Evaluation?
The presence of a patient connection does not automatically make an applied part defibrillation-proof. Applicability depends on the intended use, applied-part classification, risk analysis, and relevant particular standard.
Defibrillation protection is commonly relevant to equipment intended to remain connected while a patient may be defibrillated. Examples include diagnostic electrocardiographs, ECG monitoring equipment, and certain multiparameter patient monitors. The exact requirements depend on the device function.
The main ECG particular standards include:
Equipment function | Applicable particular standard |
Electrocardiographs that produce ECG reports for diagnostic purposes | IEC 60601-2-25 |
Electrocardiographic monitoring equipment and relevant ECG telemetry systems | IEC 60601-2-27 |
Ambulatory electrocardiographic systems | IEC 60601-2-47 |
These standards do not have interchangeable scopes. A monitor that displays an ECG waveform is not automatically a diagnostic electrocardiograph. Manufacturers must determine the intended function before establishing the test plan.
IEC 60601-1 Separates the Evaluation into Two Tests
Clause 8.5.5 addresses two distinct questions.
IEC 60601-1 requirement | What the laboratory evaluates |
Clause 8.5.5.1, defibrillation protection | Whether hazardous energy appears elsewhere and whether the equipment returns to basic safety and essential performance |
Clause 8.5.5.2, energy reduction | Whether the connected equipment allows at least 90% of the reference defibrillation energy to reach the specified load |
Passing one requirement does not establish compliance with the other. The equipment may withstand the electrical stress but absorb excessive energy. It may also pass the energy comparison but recover too slowly to provide the required clinical function.
Test One Evaluates Protection and Recovery
The protection test uses a high-voltage circuit representing defibrillator exposure. In the general IEC 60601-1 arrangement, a 32 µF capacitor is charged to 5 kV. The energy stored in the capacitor before discharge is nominally 400 J, although the energy and waveform reaching a specific point depend on the complete test circuit and connected equipment.
During the test, the laboratory evaluates whether hazardous electrical energy appears on locations such as:
- The equipment enclosure
- Signal input or output parts
- Patient connections belonging to another applied part
- Other locations identified by the standard’s test arrangement
The standard uses a defined measurement network and considers a peak voltage exceeding 1 V between its specified measurement points as an indication of hazardous electrical energy. This value should not be interpreted as a general 1 V limit at every point in the medical device. It belongs to the specific Clause 8.5.5 test circuit.
The equipment is then evaluated after the applicable recovery period. It must continue to provide basic safety and essential performance. The required observations should therefore be established before the first pulse is applied.
Common-Mode and Differential-Mode Exposure
Defibrillation energy can stress the patient-input circuit through more than one electrical path.
In the common-mode test, the relevant patient connections of the applied part are connected together and exposed relative to the specified reference. This stresses the isolation between the patient circuit and other parts of the equipment.
In the differential-mode test, the voltage is applied to an individual patient connection while the remaining patient connections of the same applied part are connected as required by the test arrangement. This evaluates the protection between patient connections and through the input network.
For an ECG system with multiple lead wires, this creates a defined lead-by-lead test matrix. Applying one pulse to the patient cable connector does not demonstrate that every required common-mode and differential-mode condition has been covered.
The test is also repeated with the high-voltage polarity reversed where required. ECG particular standards specify additional repetition and lead configuration requirements.
ECG Equipment Must Recover, Not Merely Restart
IEC 60601-1 permits the manufacturer to state a necessary recovery time in the accompanying documents, subject to the applicable safety and essential-performance requirements. ECG particular standards introduce more specific acceptance criteria.
Under the relevant tests in IEC 60601-2-25 and IEC 60601-2-27, the equipment must resume normal operation in its previous operating mode within 5 seconds. It must not lose operator settings or stored data and must continue performing its intended function.
The ECG test arrangement also applies a 10 Hz reference signal. Within 5 seconds after exposure, the recorded signal must be at least 80% of the output observed before the defibrillation pulse under the specified conditions.
This requirement can expose a failure that visual inspection misses. The display may switch back on quickly while the analogue front end remains saturated, the waveform stays outside the visible range, or the signal-processing chain takes too long to restore a usable trace.
Test Two Evaluates Defibrillator Energy Reduction
Input-protection components are expected to control the high-voltage stress reaching sensitive electronics. However, a protection network that diverts excessive energy can interfere with the clinical purpose of the defibrillator.
Clause 8.5.5.2 therefore compares the energy delivered to a 100 Ω load under two conditions:
- E1: Energy delivered with the medical equipment connected
- E2: Energy delivered with the medical equipment disconnected
To comply, E1 must be at least 90% of E2. In practical terms, the connected equipment must not reduce the energy delivered to the test load by more than the permitted amount.
The energy-reduction evaluation uses its own specified test arrangement. Relevant ECG particular standards modify parts of that arrangement, so it should not be assumed that the same circuit used for the protection test can be reused without modification.
The test is conducted with the applicable patient connections and manufacturer-recommended accessories. The laboratory measures energy rather than judging the result only from peak voltage. Capacitance, inductance, resistance, switching behaviour, cable characteristics, and the protection network all influence the waveform and delivered energy.
Why Physical Survival Does Not Establish Compliance
No visible damage is only one observation. A device may still be non-compliant if any of the following occurs:
- Hazardous energy appears on the enclosure or another connection
- The device resets into a different operating mode
- Operator settings or stored data are lost
- The ECG trace does not recover within the required time
- Signal amplitude remains below the required recovery level
- The protection circuit reduces delivered defibrillation energy excessively
- Basic safety or essential performance is compromised after exposure
Manufacturers should therefore define measurable post-pulse acceptance criteria. Statements such as “device remains functional” are usually too broad to support a repeatable test.
Design Details That Commonly Affect the Result
Patient-Input Protection Network
Gas discharge devices, transient suppressors, resistors, capacitors, diodes, and other protection components must be selected as a coordinated network. A component may withstand the voltage but produce excessive clamping, leakage, recovery delay, or energy diversion when assessed as part of the complete circuit.
Analogue Front-End Recovery
The input amplifier can remain saturated after the main pulse has ended. Protection design must consider how rapidly the complete acquisition path returns to its specified operating range, not only whether the semiconductor components avoid permanent damage.
PCB Spacing and Isolation
Defibrillation stress must be considered in the physical layout of the patient circuit. IEC 60601-1 specifies that creepage distances and air clearances associated with defibrillation-proof applied parts must not be less than 4 mm where Clause 8.9.1.15 applies.
The requirement should be evaluated across the actual isolation path, including component terminals, PCB traces, connectors, shielding, mounting hardware, and nearby conductive parts.
Multiple Applied Parts
Multiparameter monitors can include ECG, temperature, invasive pressure, SpO2, or other patient connections. The defibrillation test must consider whether energy entering one applied part can appear at another applied part or accessible connection.
Firmware and Operating-State Recovery
The defibrillation event can trigger resets, watchdog actions, alarm interruptions, filter changes, blank displays, or corrupted data. Firmware behaviour must therefore be included in essential-performance verification after the pulse.
Patient Cables and Accessories Are Part of the Test Configuration
The test should use the patient cables, lead wires, electrodes, transducers, and accessories specified by the manufacturer and required by the applicable standard.
These accessories can change resistance, capacitance, isolation, and protection behaviour. Replacing a patient cable after testing may affect the stress reaching the equipment, the energy delivered to the load, or the recovery characteristics of the ECG channel.
Manufacturers should identify each approved accessory by model, construction, and intended lead configuration. Where several options are marketed, the test plan should justify which configurations represent the relevant worst cases.
Information Manufacturers Should Prepare Before Testing
Efficient test planning begins with a clear definition of the applied part and its patient connections. The submission package should identify:
- Applicable general and particular standards
- Type B, BF, or CF classification
- Defibrillation-proof classification and marking
- Complete patient-connection map
- Manufacturer-specified patient cables and accessories
- Isolation and patient-input circuit diagrams
- Protection components and their safety functions
- Intended operating mode during defibrillation
- Declared recovery time and recovery behaviour
- Essential-performance acceptance criteria
- Expected handling of alarms, settings, and stored data
- Risk controls associated with defibrillator exposure
The risk-management file should address hazardous energy transfer, reduced therapeutic energy, delayed waveform recovery, loss of monitoring, misleading information, loss of alarms, and changes to stored data or operating settings.
Manufacturers can also review Astute Labs’ guidance on ECG machine testing under IEC 60601-2-25 when preparing a diagnostic electrocardiograph.
Defibrillation-Proof Applied Parts Testing at Astute Labs
Astute Labs supports manufacturers with Medical Device Testing for IEC 60601-1 and applicable medical equipment requirements. Defibrillation-related evaluation begins by confirming the product function, applied-part classification, patient connections, accessories, test configurations, and essential-performance criteria.
This preparation helps prevent incomplete test matrices and unclear recovery decisions. It can also identify design concerns involving patient-input protection, isolation spacing, accessory selection, energy diversion, and post-pulse performance before they cause repeated formal testing.
For Indian manufacturers, a clearly defined test configuration and traceable report can support the technical evidence required for the relevant regulatory pathway. The applicable standard edition, laboratory scope, and submission requirements should be confirmed for the device and intended market.
Astute Labs works with medical device manufacturers to evaluate defibrillation-proof applied parts, document test results, and address test findings within the wider IEC 60601 compliance programme. Contact us
