d o
t o r e g . c o m
Dr. Mete ALPASLAN
Bedside Cardiac Rhythm and ST Segment Monitoring
Monitors vs ECG machines
Monitors are used to display (and sometimes record) heart's rhythm and the ST segment deviation for a long time. On the other hand, prolonged monitorization of cardiac rhythm and possible ST segment deviation are not the primary objectives of ECG machines.
Arrhythmia detecting algorithms may vary among commercially available monitors.
Most monitors are defibrillator-proof.
For good ECG signal acquisition
The skin is a poor conductor of electricity. Before monitorization, you must prepare the skin for good skin-electrode contact. Skin oils and cutaneous debris must be removed. Clean the skin with soap and water. Do not use ether or pure alcohol. Ether or pure alcohol will dry the skin and increase its resistance.
If hair is present on the skin, shave it before applying the electrodes on the surface.
If you will use snap leadwires, then it will be better if you attach the leadwires to the electrodes first, then apply the electrodes to the patient.
When placing electrodes on the body, choose non-muscular and flat sites to avoid interference by the muscular movement.
Unlike standard 12-lead ECG, the bedside cardiac monitoring limb electrodes are placed on the torso. This reduces muscle artifact due to limb movement and avoids tethering the patient.
The right arm (RA) electrode is placed on the infraclavicular fossa close to the right shoulder.
The left arm (LA) electrode is placed on the infraclavicular fossa close to the left shoulder.
The left leg (LL) electrode is placed below the rib cage on the left side of the abdomen.
This type of electrode placement is the oldest and simplest type of cardiac monitoring, and permits only the monitorization of leads I, II and III.
However, it does not permit ST segment monitorization or differentiation of ventricular tachycardia from supraventricular tachycardia. Alternatively 5- or 10-electrodes may be used for monitoring.
Change electrodes every 24 hours.
The monitor must have proper grounding.
Which lead to choose for monitoring?
Leads with monophasic QRS complexes (either completely positive or completely negative) should be chosen. Leads showing biphasic QRS complexes are not preferred.
To prevent double heart rate counting, leads with tall and narrow QRS complexes but with small P and T waves must be preferred for monitoring.
If asystole developes during monitorization of a patient with tall P waves, the monitor may erroneously count P waves as QRS complexes. This may result in failure to detect the asystole. Therefore choose leads with small P waves.
Monitoring during surgery
To minimize interference from electrosurgery unit, electrocautery, etc. the electrodes should be placed so that the current from the surgical burning area to the return electrode does not go through the measured ECG lead.
Commenting on the ECG data being displayed on the monitor
Some monitors can follow ST segment changes to detect silent ischemia. However this necessitates good ECG signal acquisition to prevent artifacts.
ST segment may show fluctuations due to changes of the body position. Unlike true ischemia, this type of positional ST segment fluctuations are usually accompanied by QRS changes.
Increasing the size of ECG waves on the monitor display does not increase diagnostic capability.
When monitoring patients with atrial fibrillation, abrupt changes may be observed in heart rate. This is normal for an irregularly irregular rhythm in which RR intervals change abruptly.
Since monitors derive instantaneous heart rate from RR interval, it is normal for a monitor to depict abruptly changing heart rates in accordance with the abruptly changing RR intervals. A similar observation may be seen in patients with atrial flutter
and rapidly changing levels of AV block.
Monitoring patients with cardiac pacemakers
When monitoring pacemaker patients,
- PACE PROGRAM must be activated in some commercially available monitors.
- the lead with the largest pacemaker spike must be chosen.
If a pacemaker patient developes asystole, the monitor may count pacemaker spikes as QRS complexes. This may result in failure to detect asystole. Such patients must be kept under close observation.
If a pacemaker patient developes arrhythmias, the rate meter of the monitor may reflect the pacemaker rate. In such patients, do not rely only on the rate meter alarms.
Heart rate double counting may be seen in some pacemaker patients due to separate counting of the pacemaker spike and the following QRS complex.
Pacemaker spike's size and/or shape may vary from patient to patient. Do not use pacemaker spike's size and/or shape for diagnosis.
In some patients with UNIPOLAR pacemakers, repolarization tail may result in double heart rate counting. Leads with prominent repolarization tail should not be chosen for monitoring.
If pacemaker spikes are not detected by the monitor, try alternative electrode placement.
Consistent lead placement is necessary for ST segment monitoring
Some patients neeed monitorization for several days.
During this time, the electrodes may have to be changed (during echocardiography, etc.).
In such patients, electrode locations must be marked with indelible ink.
Replacing the electrodes at the same site will result in reliable ST segment analysis.
Which patients are NOT SUITABLE for ST segment monitoring?
Patients with left bundle branch block (LBBB).
Patients with right ventricular pacing (have LBBB morphology).
Patients with atrial fibrillation or atrial flutter (fibrillation or flutter waves deform the ST segment).
Agitated patients with noisy signal due to movement.
References
Circulation 2004;110:2721-2746.
U.S. PATENT: 4934376.
Figure 1. Above is a set of suction cup electrodes for recording of the precordial ECG leads.
These electrodes are not suitable for longer cardiac monitorization.
Figure 2. Above are snap electrodes used for bedside cardiac monitoring.
A hard plastic cover under the electrode protects the underlying gel (left).
Figure 3. The hard plastic cover is removed before applying the snap electrode to the body.
The innermost black circle and the inner white layer encircling it are covered by transparent gel which eases
the conductivity of the electrode. The outer and wider white circle contains the sticky surface.
Figure 4. On the side view, the snap electrode's backside protective plastic cover has a camber.
The reason is to protect the underlying conductive transparent gel.
Otherwise, the underlying gel would be dispelled when touched.
Figure 5. First connect the snap leadwire to the snap electrode, then remove the plastic back cover.
Now the electrode is ready for application on the body.
If you first apply the snap electrode to the patient's body and then try to connect the snap leadwire to the snap electrode, then
the force applied by your hand to connect the snap surfaces will dispell the underlying gel making it ineffective.
This will in turn decrease the signal quality.
Figure 6. The basic cardiac rhythm monitorization is done with 3 electrodes.
The right arm (RA) electrode is placed on the infraclavicular fossa close to the right shoulder.
The left arm (LA) electrode is placed on the infraclavicular fossa close to the left shoulder.
The left leg (LL) electrode is placed below the rib cage on the left side of the abdomen.
Figure 7. Incorrect placement of the electrodes is seen above.
ECG 1. When monitoring, select the leads with
low amplitude P and T waves but with monophasic QRS complexes.
The QRS complexes may be positive (as above) or negative.
ECG 2. When monitoring, select the leads with
low amplitude P and T waves but with monophasic QRS complexes.
The QRS complexes may be positive or negative (as above).
ECG 3. When monitoring, the leads with high amplitude
P and/or T waves are not preferred.
Leads with biphasic QRS complexes as above are not preferred.
ECG 4. When monitoring patients with atrial fibrillation, the heart rate depicted on the monitor may show abrupt changes.
This is normal for an irregularly irregular rhythm like atrial fibrillation.
The long RR intervals will result in slow instantaneous heart rates.
The short RR intervals will result in fast instantaneous heart rates.
The heart rate is calculated by the formula "60000/RR interval (in msec)".
Since the monitor calculates and depicts the instantaneous heart rate in every one or two seconds,
the abruptly changing RR intervals will also change the depicted heart rates.
A similar behaviour may also be observed in atrial flutter with variable AV block.
ECG 5. In some patients with atrial fibrillation, abrupt changes in RR i,ntervals (and therefore in instantaneous heart rates)
are not observed. If the patient with the above ECG was being monitorized, no abrupt changes in heart rate would be observed.
ECG 6. For monitorization, leads with low amplitude P and T waves but with monophasic QRS complexes must be preferred.
The ECG above is from a patient with atrial flutter. The block level does not change frequently.
In this patient, lead I is the most suitable derivation for monitoring.
On the other hand, lead II is not suitable for monitoring since the amplitude of flutter waves are similar to those of the
QRS complexes. Such a similarity may interefere with the measurement of heart rate (ventricular rate)
and ST segment analysis.
Click here for a more detailed ECG
ECG 7. The ECG above is from a 14 years-old male with restictive type cardiomyopathy, awaiting heart transplantation.
The rhythm is atrial flutter and lead I seems to be the best lead for monitorization.
The flutter waves in lead II and especially in lead III have amplitudes similar to those of the QRS complexes.
This may interefere with the measurement of heart rate (ventricular rate) and ST segment analysis.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 8. The ECG above is from a middle-aged man with VVI-type cardiac pacemaker (with unipolar lead).
Some pacemakers with unipolar leads may show repolarization tail. In such patients, leads with
repolarization tail should not be preferred for monitoring.
The ECG above shows pacemaker spike, intersection of the repolarization tail with the QRS complex, QRS complex
and the T wave.
Click here for a more detailed ECG
ECG 9. The above single-channel ECG was recorded during monitorization by the defibrillator.
The rhythm is ventricular bigeminy, but since the defibrillator cannot recognize low-amplitude ventricular beats,
they are not included in heart rate count. Therefore defibrillator prints the heart rate as 47/minute.
Click here for a more detailed ECG
Monitors vs ECG machines
Monitors are used to display (and sometimes record) heart's rhythm and the ST segment deviation for a long time. On the other hand, prolonged monitorization of cardiac rhythm and possible ST segment deviation are not the primary objectives of ECG machines.
Arrhythmia detecting algorithms may vary among commercially available monitors.
Most monitors are defibrillator-proof.
For good ECG signal acquisition
The skin is a poor conductor of electricity. Before monitorization, you must prepare the skin for good skin-electrode contact. Skin oils and cutaneous debris must be removed. Clean the skin with soap and water. Do not use ether or pure alcohol. Ether or pure alcohol will dry the skin and increase its resistance.
If hair is present on the skin, shave it before applying the electrodes on the surface.
If you will use snap leadwires, then it will be better if you attach the leadwires to the electrodes first, then apply the electrodes to the patient.
When placing electrodes on the body, choose non-muscular and flat sites to avoid interference by the muscular movement.
Unlike standard 12-lead ECG, the bedside cardiac monitoring limb electrodes are placed on the torso. This reduces muscle artifact due to limb movement and avoids tethering the patient.
The right arm (RA) electrode is placed on the infraclavicular fossa close to the right shoulder.
The left arm (LA) electrode is placed on the infraclavicular fossa close to the left shoulder.
The left leg (LL) electrode is placed below the rib cage on the left side of the abdomen.
This type of electrode placement is the oldest and simplest type of cardiac monitoring, and permits only the monitorization of leads I, II and III.
However, it does not permit ST segment monitorization or differentiation of ventricular tachycardia from supraventricular tachycardia. Alternatively 5- or 10-electrodes may be used for monitoring.
Change electrodes every 24 hours.
The monitor must have proper grounding.
Which lead to choose for monitoring?
Leads with monophasic QRS complexes (either completely positive or completely negative) should be chosen. Leads showing biphasic QRS complexes are not preferred.
To prevent double heart rate counting, leads with tall and narrow QRS complexes but with small P and T waves must be preferred for monitoring.
If asystole developes during monitorization of a patient with tall P waves, the monitor may erroneously count P waves as QRS complexes. This may result in failure to detect the asystole. Therefore choose leads with small P waves.
Monitoring during surgery
To minimize interference from electrosurgery unit, electrocautery, etc. the electrodes should be placed so that the current from the surgical burning area to the return electrode does not go through the measured ECG lead.
Commenting on the ECG data being displayed on the monitor
Some monitors can follow ST segment changes to detect silent ischemia. However this necessitates good ECG signal acquisition to prevent artifacts.
ST segment may show fluctuations due to changes of the body position. Unlike true ischemia, this type of positional ST segment fluctuations are usually accompanied by QRS changes.
Increasing the size of ECG waves on the monitor display does not increase diagnostic capability.
When monitoring patients with atrial fibrillation, abrupt changes may be observed in heart rate. This is normal for an irregularly irregular rhythm in which RR intervals change abruptly.
Since monitors derive instantaneous heart rate from RR interval, it is normal for a monitor to depict abruptly changing heart rates in accordance with the abruptly changing RR intervals. A similar observation may be seen in patients with atrial flutter
and rapidly changing levels of AV block.
Monitoring patients with cardiac pacemakers
When monitoring pacemaker patients,
- PACE PROGRAM must be activated in some commercially available monitors.
- the lead with the largest pacemaker spike must be chosen.
If a pacemaker patient developes asystole, the monitor may count pacemaker spikes as QRS complexes. This may result in failure to detect asystole. Such patients must be kept under close observation.
If a pacemaker patient developes arrhythmias, the rate meter of the monitor may reflect the pacemaker rate. In such patients, do not rely only on the rate meter alarms.
Heart rate double counting may be seen in some pacemaker patients due to separate counting of the pacemaker spike and the following QRS complex.
Pacemaker spike's size and/or shape may vary from patient to patient. Do not use pacemaker spike's size and/or shape for diagnosis.
In some patients with UNIPOLAR pacemakers, repolarization tail may result in double heart rate counting. Leads with prominent repolarization tail should not be chosen for monitoring.
If pacemaker spikes are not detected by the monitor, try alternative electrode placement.
Consistent lead placement is necessary for ST segment monitoring
Some patients neeed monitorization for several days.
During this time, the electrodes may have to be changed (during echocardiography, etc.).
In such patients, electrode locations must be marked with indelible ink.
Replacing the electrodes at the same site will result in reliable ST segment analysis.
Which patients are NOT SUITABLE for ST segment monitoring?
Patients with left bundle branch block (LBBB).
Patients with right ventricular pacing (have LBBB morphology).
Patients with atrial fibrillation or atrial flutter (fibrillation or flutter waves deform the ST segment).
Agitated patients with noisy signal due to movement.
References
Circulation 2004;110:2721-2746.
U.S. PATENT: 4934376.
Figure 1. Above is a set of suction cup electrodes for recording of the precordial ECG leads.
These electrodes are not suitable for longer cardiac monitorization.
Figure 2. Above are snap electrodes used for bedside cardiac monitoring.
A hard plastic cover under the electrode protects the underlying gel (left).
Figure 3. The hard plastic cover is removed before applying the snap electrode to the body.
The innermost black circle and the inner white layer encircling it are covered by transparent gel which eases
the conductivity of the electrode. The outer and wider white circle contains the sticky surface.
Figure 4. On the side view, the snap electrode's backside protective plastic cover has a camber.
The reason is to protect the underlying conductive transparent gel.
Otherwise, the underlying gel would be dispelled when touched.
Figure 5. First connect the snap leadwire to the snap electrode, then remove the plastic back cover.
Now the electrode is ready for application on the body.
If you first apply the snap electrode to the patient's body and then try to connect the snap leadwire to the snap electrode, then
the force applied by your hand to connect the snap surfaces will dispell the underlying gel making it ineffective.
This will in turn decrease the signal quality.
Figure 6. The basic cardiac rhythm monitorization is done with 3 electrodes.
The right arm (RA) electrode is placed on the infraclavicular fossa close to the right shoulder.
The left arm (LA) electrode is placed on the infraclavicular fossa close to the left shoulder.
The left leg (LL) electrode is placed below the rib cage on the left side of the abdomen.
Figure 7. Incorrect placement of the electrodes is seen above.
ECG 1. When monitoring, select the leads with
low amplitude P and T waves but with monophasic QRS complexes.
The QRS complexes may be positive (as above) or negative.
ECG 2. When monitoring, select the leads with
low amplitude P and T waves but with monophasic QRS complexes.
The QRS complexes may be positive or negative (as above).
ECG 3. When monitoring, the leads with high amplitude
P and/or T waves are not preferred.
Leads with biphasic QRS complexes as above are not preferred.
ECG 4. When monitoring patients with atrial fibrillation, the heart rate depicted on the monitor may show abrupt changes.
This is normal for an irregularly irregular rhythm like atrial fibrillation.
The long RR intervals will result in slow instantaneous heart rates.
The short RR intervals will result in fast instantaneous heart rates.
The heart rate is calculated by the formula "60000/RR interval (in msec)".
Since the monitor calculates and depicts the instantaneous heart rate in every one or two seconds,
the abruptly changing RR intervals will also change the depicted heart rates.
A similar behaviour may also be observed in atrial flutter with variable AV block.
ECG 5. In some patients with atrial fibrillation, abrupt changes in RR i,ntervals (and therefore in instantaneous heart rates)
are not observed. If the patient with the above ECG was being monitorized, no abrupt changes in heart rate would be observed.
ECG 6. For monitorization, leads with low amplitude P and T waves but with monophasic QRS complexes must be preferred.
The ECG above is from a patient with atrial flutter. The block level does not change frequently.
In this patient, lead I is the most suitable derivation for monitoring.
On the other hand, lead II is not suitable for monitoring since the amplitude of flutter waves are similar to those of the
QRS complexes. Such a similarity may interefere with the measurement of heart rate (ventricular rate)
and ST segment analysis.
Click here for a more detailed ECG
ECG 7. The ECG above is from a 14 years-old male with restictive type cardiomyopathy, awaiting heart transplantation.
The rhythm is atrial flutter and lead I seems to be the best lead for monitorization.
The flutter waves in lead II and especially in lead III have amplitudes similar to those of the QRS complexes.
This may interefere with the measurement of heart rate (ventricular rate) and ST segment analysis.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 8. The ECG above is from a middle-aged man with VVI-type cardiac pacemaker (with unipolar lead).
Some pacemakers with unipolar leads may show repolarization tail. In such patients, leads with
repolarization tail should not be preferred for monitoring.
The ECG above shows pacemaker spike, intersection of the repolarization tail with the QRS complex, QRS complex
and the T wave.
Click here for a more detailed ECG
ECG 9. The above single-channel ECG was recorded during monitorization by the defibrillator.
The rhythm is ventricular bigeminy, but since the defibrillator cannot recognize low-amplitude ventricular beats,
they are not included in heart rate count. Therefore defibrillator prints the heart rate as 47/minute.
Click here for a more detailed ECG