The
Circulator Boot unlike other pneumatic devices primarily used on the
legs for arterial, venous and lymphatic conditions is cardiosynchronous
and triggered by the EKG. It identifies large and rapid electrical
changes as being the QRS complex, which occurs during electrical
systole. The actual contraction of the left ventricle, mechanical
systole, follows immediately thereafter:
In
the above example, the QRS is electrically positive (+, upright or
depicted as "qRs") but can be biphasic (+/- or depicted as "RS") or
electrically negative (-, inverted and
pointing downward or depicted as "S") depending on the position of the
EKG electrodes and the orientation of the heart within the chest
cavity. For the Circulator Boot Heart Monitor to detect a strong
distinct signal, the white electrode should be placed where the QRS is
positive and the black electrode where it is negative. The green
electrode is a ground and can be placed anywhere, but commonly between
the white and black electrodes. Just like a flashlight, no signal is
obtained if the electrical input has two positives or two negatives;
one needs to contact both the positive and negative poles of the
battery. Body-build alters the position of the heart and its electrical
orientation. Abdominal obesity elevates the diaphragm and pushes the
left ventricle towards the left axilla. Conversely, the heart hangs
vertically in the tall thin person orientating the left ventricle more
toward the pelvis.
Electrical Position Orientation of QRS Complex
(and body build)
avR or right arm avL or left arm avF or legs
Vertical (thin)
-
- +
Intermediate -
+/- +/-
Horizontal (obese)
-
+ -
In
practice, one may guess in most cases where a good signal might be
obtained by noting the body-build of the patient. For example, a large
woman with large breasts may be spared possible discomfort by placing
the white electrode on the left shoulder and the black on the right
shoulder.
The
chest electrodes normally become progressively more positive from V1 to
V6 as they change position from overlying the relatively thin muscle of
the right ventricle to overlying the more powerful left ventricle:
-
V1: right 4th intercostal space (T-waves usually inverted or negative)
-
V2: left 4th intercostal space (T-waves commonly neutral)
-
V1 and V2 are oriented over the right side of the heart and are mostly negative.
-
V3: halfway between V2 and V4
-
V4: left 5th intercostal space, mid-clavicular line
-
V3 and V4 are the middle leads located in the midline of the heart.
-
V5: horizontal to V4, anterior axillary line (T-waves upright and positive)
-
V6: horizontal to V5, mid-axillary line (T-waves upright and positive but less so than in V5)
-
V5 and V6 are oriented over the left side of the heart and are mostly positive.
Problems
may arise in patients with a history of myocardial infarction causing
electrical holes in their hearts. Again, T-wave abnormalities may
accompany ischemia and /or electrolyte abnormalities. Thus, placement
of the black electrode on the right shoulder or V1 may detect strong
negative T-wave
which coupled with an occasional narrow high T-wave in V5 or V6 may
trick the Heart Monitor to interpret the presence of another QRS
complex. In the latter situation, the QRS light on the monitor would
blink twice for each heartbeat and leg compressions would not be
optimally timed. Heart rhythm disturbances will trigger similar
disturbances in the rhythm of the boot compressions, palpable pulses,
ausculted heart sounds and the blinking of the monitor QRS LED. Whereas
interference due to static commonly causes the monitor QRS LED to
flicker, rhythm disturbances (atrial fibrillation and premature beats)
are associated with distinct quick blinks. Patients
with rapid atrial fibrillation are best treated after every other
heartbeat (the 2:1 setting) to smooth out their irregularity.
FOR
MOST PATIENTS, PLACEMENT OF THE BLACK ELECTRODE BETWEEN V1 AND V2 AND
THE WHITE ELECTRODE AT V5 WILL PROVIDE A STRONG DISTINCT QRS SIGNAL. IT
IS TO BE APPRECIATED THAT AS THE BOOT OPERATES, THE PLASTIC BAGS MAY
RUB AGAINST DRY SKIN OR PIECES OF CLOTHING AND GENERATE HIGH VOLTAGE
STATIC ELECTRICITY THAT MAY INTERFERE WITH THE DETECTION OF THE QRS;
THE GROUNDING BRACELET IS IMPORTANT HERE. A CLUE TO THIS PROBLEM IS THE
OBSERVATION OF A STRONG DISTINCT BLINK THAT DISAPPEARS SHORTLY AFTER
THE LEG COMPRESSIONS BEGIN. AGAIN, IT IS TO BE APPRECIATED THAT THE QRS LED MAY FLICKER IF THE ELECTRODES ARE MAKING POOR CONTACT DUE TO DRY SKIN OR SKIN THAT HAS BEEN LUBRICATED WITH CREAMS OR OINTMENTS. CONTACT IS ALWAYS IMPROVED IF THE SKIN IS RUBBED CLEAN WITH AN ELECTROLYTE SOLUTION SUCH AS SALINE OR SEA SOAKS.
In a small number of patients, an electrocardiogram with multiple extra leads is needed to find optimal electrode positions.
