Frequently Asked Questions

ECG Vector Configuration
Left Bundle Branch Block (LBBB)
Atrial Fibrillation
Septic Shock
Exercise
Amputees or Quadriplegics
Electrocautery
Pacemaker Programmers
Minute Ventilation Pacemaker
Automatic Internal Cardiac Defibrillators (AICD)
Automatic External Defibrillator (AED)
Blood Pressure Measurement with BioZ NIBP

ECG Vector Configuration

The ECG vector is user selectable as follows:

Vector	Description
1	Right thorax to left thorax
2	Right neck to left thorax
3	Left neck to left thorax
4	Right thorax to left neck

Back to Top

Left Bundle Branch Block (LBBB)

Question: What is Left Bundle Branch Block and how does it affect ICG technology?

Answer: LBBB is a condition in which the heart does not conduct electrical signals properly through the left branch of the Bundle of His. Depending on the ECG vector, LBBB is manifested in the ECG waveform by marked prolongation of the QRS complex (see Figure 1).

How does LBBB affect ICG?
ICG technology looks at the morphology of the ECG waveform to detect the R wave. The R wave is used to calculate HR, and serves as a marker for identifying the systolic portion of the impedance waveform. Hence, if enough R waves are missed, no numerical data will be displayed.

Figure 1: Left Bundle Branch Block

Back to Top

Atrial Fibrillation

Question: What is Atrial Fibrillation and how does it affect ICG technology?

Answer: Atrial fibrillation is when the normal rhythmical contractions of the cardiac atria are replaced by rapid irregular twitching of the muscular wall, which causes the ventricles to respond irregularly to the dysrhythmic bombardment from the atria¹ .

How does Atrial Fibrillation affect ICG technology?
ICG technology looks at the relationship between the mechanical activity (the ICG waveform) and the electrical activity (the ECG waveform) in order to determine the stroke volume on a beat-by-beat basis. For an ICG beat to be determined valid, certain proprietary acceptance criteria are applied. A-fib is a condition that often causes irregular beat-to-beat electrical and mechanical activity. As such, erratic ventricular filling may or may not occur and thus the ECG and ICG waveforms vary widely from beat-to-beat as well as from patient-to-patient.

Consequently, depending on the degree of A-fib and the specific patient, the ICG technology system may or may not accept an ICG beat as being valid. If enough ICG beats are rejected, the system will not display and/or update the hemodynamic values for that patient.

¹Darovic, G.O. and Franklin, C.M. Handbook of Hemodynamic Monitoring. 1999. W.B. Saunders Company. Philadelphia, PA.

Back to Top

Septic Shock

Question: What is Septic Shock, and how does it affect ICG technology?

Answer: Septic Shock is an infection in the bloodstream, associated with fluid accumulation and hypotension.

How does Septic Shock affect hemodynamics?
Hyperdynamic Phase (Warm shock): Characterized by a normal to high cardiac output and systemic vasodilation (decreased SVR).

Hypodynamic Phase (Cold Shock): Characterized by an inadequate or falling cardiac output, hypotension, and, in some cases, vasoconstriction. Cardiac decompensation and hypotension occur if:

-Preload falls below a critical level.
-Cardiac reserve is limited by pre-existing heart disease.
-Ventricular dysfunction develops secondary to release of myocardial depressant factors and/or the development of myocardial ischemia in patients with pre-existing coronary artery disease².

Hemodynamic Parameter	Hyperdynamic "Warm" Shock	Hypodynamic "Cold" Shock
SVR	ê	ê or ~ or é
CO	é	ê

Key:	é = Increase; ê = Decrease; ~ = Normal or No change

How does Septic Shock affect ICG technology?
Because of fluid accumulation and the fact that fluid is also conductive, sepsis can alter the normal path of the electrical current transmission used to measure the thoracic bioimpedance, which can affect the ability of ICG technology systems to detect pulsatile changes in the delta Z waveform.

Sufficient data has not been acquired to quantify the effect of this condition on the validity of ICG technology data. Under these conditions the clinician should use their judgement when assessing the hemodynamic values.

² Darovic, G.O. and Franklin, C.M. Handbook of Hemodynamic Monitoring. 1999. W.B. Saunders Company. Philadelphia, PA.

Back to Top

Exercise

Question: How does exercise affect ICG technology?

Answer: ICG technology devices are not designed for use during exercise. Heavy respiration and/or motion, such as encountered during exercise, can not be filtered and will affect the impedance signal, thus causing invalid measurements of ICG parameters.

Back to Top

Amputees or Quadriplegics

Question: How will an Amputee or Quadriplegic affect ICG technology?

Answer: The standard equation for estimating body surface area is not appropriate for these individuals. Consequently, indexing these parameters may not be valid (over or under-estimation of indexed parameters). Therefore, ICG technology should only be used to get a baseline and for trending on these patients. Enter in patient's height before the amputation occurred.

Back to Top

Electrocautery

Question: How does Electrocautery affect ICG technology?

Answer: ICG technology cannot obtain impedance data during the electrocautery procedure. However, when electrocautery ceases, ICG technology software will recover and provide values.

Back to Top

Ventilators or Chest Tubes

Question: How do Ventilators or Chest Tubes affect ICG technology?

Answer: In most instances ventilators and chest tubes cause no interference with ICG technology. However, in situations where the inflation rate of the ventilator is excessive, it may cause excessive motion of the patient. Heavy respiration and/or motion can not be filtered and will affect the impedance signal, thus causing invalid measurements of ICG parameters.

Back to Top

Pacemaker Programmers

Question: How does a pacemaker programmer affect ICG technology?

Answer: There are two common sources of possible interaction between ICG technology systems and pacemaker or implantable defibrillator systems, Pacemaker Programmer interference and Minute Ventilation Pacemaker interference.

Pacemaker Programmer Interference
Most programmers include internal ECG recording capability, to allow a physician to assess implanted device function without the need for a separate ECG machine or monitor. An important aspect of pacemaker ECG analysis requires that the actual output pulse from the pacemaker (or the pacing part of an implantable defibrillator) be seen clearly on the programmer ECG screen and/or printouts. Many programmers have specialized hardware and software in their ECG circuitry to detect pacemaker output spikes on the skin and then enhances them on the ECG display. ICG technology has similar functions.

Pacemaker spike detectors are sensitive circuits that are designed to pick up very low levels of high frequency stimulation such as a pacemaker output pulse. Some spike detectors however can also pick up the stimulation current from an ICG technology system such as the BioZ. When the erroneous pickup occurs, the ECG on the programmer will show nearly continuous sharp downward spikes at a rate of 30 or more per second.

To test for this form of interference, simply remove the ICG patient cable from the front panel of the system (leaving it connected to the patient). The erroneous spikes should vanish, leaving only the detection of the actual pacemaker.

This spike detection function of the programmer can be turned off. The most common programmer encountered in the field is the Medtronic CareLink. To turn off spike detection on the Medtronic CareLink, it is necessary to exit from the application for the specific pacemaker bringing up the equivalent of the home screen. From the home screen, there is an option for system functions, which allows the function called "artifact detection" to be turned off. The detection defaults to the on position at power-up, and clinic personnel may not be aware that it can be turned off.

Another common programmer is the Guidant 'ZOOM' programmer. The ZOOM has been tested with ICG technology systems, and CardioDynamics has not been able to produce interference between an ICG technology system and the ZOOM. Should interference occur, simply select the "ECG" pulldown menu option and under "Surface ECG" select the "Filter ON" option. This option will change the ECG recording bandwidth to 1-40 Hz, and turn the spike detection off. If the impedance waveform seems to change during pacemaker programming, simply ignore the screen updates on the ICG technology system that occur during this time. Once the interrogation of the pacemaker has ceased, the system will update after the programmed number of data averaging beats has been detected.

Back to Top

Minute Ventilation Pacemaker

Question: How does a Minute Ventilation Pacemaker affect ICG technology?

Answer: MV pacemakers work on a principle similar to ICG, with low amplitude (in the hundreds of micro-amps) constant current pulses sent out at a rate of 20-30 per second between the pacemaker can and the electrodes in the heart. The pacemaker reads the resultant voltage from a different electrode and determines both the rate and tidal volume of respiration. The pacemaker then uses that information to determine the pacing rate of the implanted device.

When the patient is connected to an ICG technology system, the pacemaker reads back a combination of the pacemaker's own stimulation along with the stimulation current of our ICG device. Therefore, the pacemaker can easily get a varying or erroneous reading. In the best case, the pacemaker will reject the readings as noise and have no effect on the pacer rate. In the worst case, the pacemaker will accept the readings and rapidly increase the rate of the pacemaker.

Because of the danger that an unwanted and possibly harmful interaction can exist, the use of ICG technology systems on patients with MV sensor function enabled is not recommended.

If the MV sensor is turned on, it can be easily turned off with the programmer. There is usually a sub-menu for sensor functions, which control the selection of one or both of the activity of MV sensors and the various sensitivity and timing settings of the sensor functions. Simply program the MV sensor to "off" if it was previously turned on. Hemodynamic monitoring can now be completed.

When finished monitoring, turn the MV sensor back on. In most cases, the patient must be kept still for 3-10 minutes after the MV sensor is re-enabled to recalibrate itself. After the recalibration, the patient can be sent home.

It is a good practice when doing CardioDynamic's requested re-programming of a pacemaker, to make a parameter printout before the re-programming and one just after to verify that the settings are the same. Since the interference problem does not always happen, some clinics may not choose to change the setting due to the recalibration time required. That choice can be left to the nurse as long as the disclosure of the possible interaction is advised.

Back to Top

Automatic Internal Cardiac Defibrillators (AICD)

Question: What is an Automatic Internal Cardiac Defibrillator and how does it affect ICG technology?

Answer: Internal Cardiac Defibrillators are specialized devices designed to directly treat a cardiac tachydysrhythmia. If a patient has a ventricular ICD and the device senses a ventricular rate that exceeds the programmed cut-off rate of the ICD, the device performs cardioversion/defibrillation. Alternatively, the device, if so programmed, may attempt to pace rapidly for a number of pulses, usually around 10, to attempt pace-termination of the ventricular tachycardia. Newer ICD devices are a combination of pacer and ICD³.

How does an Automatic Internal Cardiac Defibrillator affect ICG technology?
There have been no reported interactions between AICDs and ICG technology devices.

³ Weinberger, B.M. Pacemaker and Automatic Internal Cardiac Defibrillator. (7/25/2001). Available: http://www.emedicine.com/emerg/topic805.htm

Back to Top

Automatic External Defibrillator (AED)

Question: What is an Automatic External Defibrillator (AED), and how does it affect ICG technology?

Answer: AEDs are external devices that can be used by minimally trained laypersons in emergency situations. They not only administer an electrical shock, but also read the heart rhythm patterns of the patient. This significantly reduces the amount of training needed for their effective use and allows people with minimal training to perform defibrillation in emergency situations with little risk of additional injury to the patient. AEDs are used in ambulances and fire rescue vehicles, as well as places that are cut off from traditional emergency assistance, such as airplanes, stadiums, casinos, shopping malls and golf courses⁴.

How does an AED affect ICG technology?
There have been no reported interactions between AEDs and ICG technology devices.

⁴ AED (Automatic External Defibrillator, Automatic External Cardioverter). 2001. Available: http://www.heartcenteronline.com

Back to Top

Blood Pressure Measurement with BioZ NIBP

Question: Why are the systolic and diastolic BP values obtained by the oscillometric (BioZ NIBP) method different from those obtained by the auscultatory (manual) method?

Answer: When the BioZ NIBP method is the source for determining BP, the Oscillometric method is used. This method measures the pressure pulse within the cuff in incremental steps and has a maximum value of approximately 1 mmHg, which occurs at the MAP. A sophisticated algorithm is then applied to plot the Oscillometric Envelope of pulse pressure measurements vs. cuff pressure measurements. This oscillometric envelope is used to determine the MAP, SBP and DBP values.

The shape of an actual patient Oscillometric Envelope varies from measurement-to-measurement and from individual-to-individual. Therefore, it is quite possible to have different systolic and diastolic pressures for the same measured MAP, as well as different MAPs for the same systolic and diastolic pressures.

When using the auscultatory method, the systolic and diastolic pressures are measured and the MAP is traditionally calculated by using the formula: MAP = DBP + (SBP-DBP)/3. This is not the formula used by the BioZ. The formula for calculating MAP in the BioZ when SBP and DBP values are entered MANUALLY is as follows:

If [(SBP-DBP)/DBP] < 0.5 Then KP = 0.333
If [(SBP-DBP)/DBP] > 1.0 Then KP = 0.25

KP = 0.333 -{[(SBP-DBP)/DBP) - 0.5]/6}
MAP = DBP + [KP (SBP-DBP)]

For Example:

If a BP = 150/65 is entered manually into the BioZ the calculated MAP would be:

(150-65)/65 = 1.31, therefore, KP = 0.25 and MAP = 65 + [0.25(150-65)] = 86.25

In the example above, the simple equation of MAP = DBP + (SBP-DBP)/3, the MAP would equal 93.33 instead of 86.25

In summary, Manual entry of systolic and diastolic pressures results in a calculated MAP. Automatic BP by the BioZ NIBP results in a measured MAP and calculated systolic and diastolic pressures.

Back to Top