Electrical Stimulus and Procedure

BasicsBasics

Electrical Waveforms Used With ECT

Sine Wave ECTSine Wave ECT

• Sine wave currents are characterized by a continuous

stream of electricity that flows in alternating directions.

• The number of alterations in direction, or cycles of negative

and positive current flow, is referred to as the frequency of

the stimulus and is measured in hertz (Hz), defined as the

number of cycles per second.

Brief Pulse ECT

• the brief pulse consists of a series of instantaneously rising and falling rectangular pulses of current, with adjacent pulses separated by brief periods of no electrical activity

Brief pulses are characterized by four stimulus parameters:•pulse width•Frequency•Duration•peak current

• The duration of each pulse is referred to as the pulse width, which is measured in milliseconds (ms; thousandths of a second).

• Pulse frequency is defined in terms of pulse pairs per second, although it is common practice to use the same unit of measure, hertz, as used for the sine wave. The actual number of pulses per second is twice the frequency.

• Duration : the length of the entire series of pulses delivered, and is measured in seconds.

• peak current : the maximum intensity of each pulse, measured from the zero baseline, in amperes.

Ultra-Brief Pulse ECT

• “Brief ” pulse has a pulse width of 0.5–2.0 ms, whereas the width of an “Ultra-brief ” pulse is less than 0.5 ms.

Seizure ThresholdSeizure Threshold

• the total amount of electricity necessary to induce a seizure

• Clinical Applications,” is a parameter that is integral to stimulus dosing in clinical practice

• The physiological efficiency of the brief pulse stimulus in activating brain neurons is more optimal than the sine wave because of its rapid rise and fall

Current, Voltage, and Impedance

• current is the number of electrons per second flowing through a circuit.

• In this case, the circuit is made up of the ECT machine, the stimulus cables, the stimulus electrodes, and the patient’s head.

Current, Voltage, and Impedance

• Voltage is the force that drives the flow of electrons during the stimulus.

• It is the push of the system

Current, Voltage, and Impedance

• Impedance is a measure of the obstacle to the current flow.

• It is the level of resistance to be overcome.

current=voltage/resistancewhere current is measured in amperes (A) or milliamperes (mA), voltage is measured

in volts (V), and resistance (impedance) is measured in ohms (Ω).

Mode of Stimulus Delivery

• In addition to the type of waveform used, ECT devices differ in whether they administer the stimulus via a constant current or constant voltage

Total Amount of Electricity Delivered With ECT:

Charge and Energy

• CHARGE= the amount of current in a single pulse x the number of pulses delivered in the series, and is measured in millicoulombs (mC).

• THE AMOUNT OF CURRENT IN A SINGLE PULSE =peak current (in amperes) x pulse width (in milliseconds)

• THE NUMBER OF PULSES = twice the frequency (in hertz) x duration (in seconds).

Clinical Applications

Stimulus Dosing• the purpose of the electrical stimulus in ECT is

to generate an intracerebral current flow sufficient to induce an adequate generalized seizure within the brain.

• The seizure threshold is the minimum amount of stimulus electrical charge that will evoke such a response in a given patient at a given point in time.

• How a series of seizures produces the therapeutic effect of ECT is still unclear, but four important points are generally believed to be true:

1. An induced generalized seizure appears to be necessary for the production of a therapeutic response.

2. Seizures produced by barely suprathreshold stimuli are diminished in efficacy regardless of seizure duration, particularly with unilateral ECT (Sackeim et al. 1987). This effect is probably even more prominent with ultra-brief-pulse stimuli.

3. Seizures produced using markedly suprathreshold levels of stimulus intensity appear to be associated with increased cognitive side effects.

4. The stimulus intensity necessary to produce a therapeutically adequate seizure increases across subsequent treatments within an index ECT course.

Seizure Adequacy

• For many years, an ECT treatment was considered therapeutically adequate if the seizure was generalized and of a certain duration (Abrams 2002; American Psychiatric Association 2001; Ottosson 1960).

• Typical recommended minimal durations have been 20–25 seconds for the motor response and 25 seconds for the ictal electroencephalographic (EEG) response.

Seizure Adequacy

• Because seizures tend to be shorter in elderly patients and also to diminish over the treatment course (Sackeim et al. 1991), some practitioners have used a lower criterion (e.g., <20-second seizure duration late in the treatment course if the patient is older than age 60 years).

• Seizure duration also may be affected by a number of other parameters, including the dose of anesthetic agent and the amount to which the stimulus exceeds the seizure threshold.

Stimulus Intensity

• Evidence suggests that the greater the ECT stimulus intensity is with respect to seizure threshold (i.e., the more suprathreshold the stimulus), the more effective the treatments and the speedier the recovery (Sackeim et al. 1993).

• However, a higher stimulus intensity is directly related to an increase in cognitive side effects. Thus, the logical approach would be to deliver a stimulus that is moderately suprathreshold

• Seizure threshold varies greatly from person to person (up to 40-fold) and also from treatment to treatment, increasing variably over the treatment course (Sackeim et al. 1991).

• Researchers do not yet know how much the stimulus needs to be above seizure threshold to be considered moderate, although for brief pulse bilateral ECT, the estimate is 50%–100% above the individual’s seizure threshold (equivalent to 1.5–2 times seizure threshold), whereas for brief pulse unilateral ECT, estimates run 150%–500% above seizure threshold (i.e., 2.5–6 times seizure threshold).

Stimulus Dosing Strategies

• Two types of methods are generally used to determine electrical stimulus intensity: the dose-titration method and the preselected-dose method (American Psychiatric Association 2001)

Dose Titration

• starting with a stimulus dose at the first treatment that has a moderate (e.g., 50%) chance of inducing a seizure.

• Although beginning at a very low dose would theoretically allow a more precise estimate of seizure threshold for patients with low seizure thresholds, it would also result in excessive numbers of restimulations in patients with higher seizure thresholds.

Electrode Placement

Bilateral and Right Unilateral Electrode Placement• right unilateral electrode placement has also

resulted in decreasing the cognitive side effects (Squire and Slater 1978; Str ِmgren et al. 1976).

• This decrease may be due in part to the relative sparing of nondominant mesial temporal lobe structures by both the stimulus current path and the induced seizure. The most commonly used unilateral placement is the d’Elia placement d’Elia placement (d’Elia 1970)

the following statements appear to be supported by the majority of clinical research and experience:

1. Either technique is generally effective in the treatment of depression. However, some data suggest that specific subgroups, especially patients with mania, may not respond as thoroughly to unilateral treatments (Mukherjee et al. 1994).

2. In some studies, patients reportedly responded faster to bilateral placement, requiring fewer treatments for a course of ECT (Sackeim et al. 2000).

3. Some depressed patients who did not respond to right unilateral placement in ECT experienced significant clinical improvement after they were switched from unilateral to bilateral placement (Abrams et al. 1983)

4. Stimulus intensity just above seizure threshold markedly reduces the efficacy of unilateral ECT. This effect may be present to a lesser degree in bilateral ECT (Sackeim et al. 1993), particularly with ultra-brief-pulse stimuli.

5. Bilateral ECT results in greater acute cognitive side effects than does nondominant unilateral ECT. This difference is most apparent in tests assessing or requiring verbal function (Squire and Slater 1978). Also, although most memory functions appear to be restored in most patients 6 months after ECT, persisting memory complaints are more common in patients who receive bilateral ECT.

• Because of the cognitive advantages of nondominant unilateral electrode placement over bilateral electrode placement, a reasonable approach is to routinely use nondominant unilateral ECT in patients who are more susceptible to profound confusional states. – These patients may include those who are elderly,

who have dementia, or who have developed significant confusion during prior courses of ECT.

• Unilateral ECT is also preferable for individuals who are highly concerned about the effects of ECT on memory functioning.

Bilateral ECT is generally preferable for

patients in whom a rapid response is clinically required (e.g., the actively suicidal patient or the catatonic patient who refuses to eat)

those who have preferentially responded to bilateral ECT in the past

who indicate a preference for this modality