Andres Belalcazar

Improved lung edema monitoring with coronary vein pacing leads: a simulation study

This computer simulation study compared the ability of left ventricular coronary vein (LV) pacemaker leads against right ventricular (RV) and right atrial (RA) leads to monitor lung edema using electrical impedance measurements. MRI images were used to construct electrical models of the thorax. Four lead configurations were tested with increases of pulmonary edema, intravascular fluids and heart dilation. The impedance changes observed at end systole with severe lung edema were 8.5%, 11.2%, 12.3% and 26.8% for the RA, RV, RV coil and LV configurations, respectively. Sensitivities in ohms per litre of lung fluid were 19.15, 19.15, 25.07 and 52.11 for the same configurations. The impedance changes for intravascular fluid overload with constant lung status were 1%, 1.3%, 9.2% and 6.4% while the sensitivities were 2, 2, 17 and 11 ohms per litre of intravascular fluid, respectively. Regional analysis of the thoracic sources of impedance revealed a high sensitivity near pacing electrodes and generator, and a low sensitivity to the right lung and all pulmonary vessels. Simulations showed that LV leads have a threefold advantage in sensitivity when monitoring lung edema in comparison to conventional RV leads. To monitor vascular and lung fluids independently, combined impedance configurations may be used. Regional sensitivities must be taken into account for proper clinical interpretation of impedance changes.

Monitoring lung edema using the pacemaker pulse and skin electrodes

Previous clinical studies have shown that impedance measurements using right ventricular (RV) leads can monitor congestion due to heart failure. We previously reported on a three-fold advantage of bipolar left ventricular (LV) leads, which are near the lung, over RV leads in detecting pulmonary edema with impedance. A combined system of internal and external electrodes is now investigated using computer models, for use with conventional cardiac resynchronization (CRT) systems with unipolar LV leads. The system uses the normal LV pacing pulse as current source, and the resultant voltage at two skin electrodes to obtain a lung edema impedance (Z) measurement. Using gated MRIs, thoracic computer models of 3.8 million control volumes were constructed. Changes of Z with edema were simulated with a conventional totally implanted system, as well as with combined implanted-external systems. Right atrial (RA), RV, RV defibrillator coil and LV leads were used. Per cent Z responses to edema were compared. The all implanted responses were RA: 11.8%, RV: 8.6%, RVcoil: 11.3%, LV: 23.8%. The combined system responses were LV-ext: 21.45%, RA-ext: 10.13%, LV-arm leg: 26.08%. The computer models suggest that combined internal-external systems can be as sensitive as the totally implanted ones. Lung edema may be monitored at follow up or home for LV paced patients with only two external electrodes. Using very low impedance configurations optimized by computer can greatly maximize the response, with a cost of poor stability.

Subcutaneous bioimpedance recording: assessment of a method for hemodynamic monitoring by implanted devices.

Background: Diagnostic evaluation of patients with suspected symptomatic arrhythmias is limited by inability to assess the hemodynamic impact of a detected rhythm.

Voluntary cardio-respiratory synchronization

During stereovectorelectrocardiographic (SVEC) measurements, respiration influences the cardiac vector. This cardiac vector is modulated by the change in the heart position due to diaphragm movement, changes in conductivity in thoracic tissues caused by lung inflation, and shifts in the blood volume. For years, the only method to control the respiratory induced variation was for subject or patient to hold his breath, that was until the voluntary cardio-respiratory synchronization (VCRS) technique. The VCRS technique involves instructing a subject to breathe in synchronization with his/her heartbeat by using either a light or sound signal. Triggered by the R wave of the electrocardiogram, the device signals the subject when to inhale and exhale based on a fixed number of heart beats for each phase of the respiratory cycle. With VCRS techniques, respiratory influences of heart rate variability (HRV), which are mostly parasympathetic, can be separated from nonrespiratory effects, in which sympathetic influences may dominate along with very slow changes due to thermo-regulation and other factors. This work shows how VCRS can be used in unique ways to measure HRV and also separate out respiratory influences on other cardiovascular signals.

ASSOCIATION OF ECG R WAVE TO RADIAL PULSE DELAY WITH SUBCLINICAL CARDIOVASCULAR DISEASE AND RISK FACTORS: THE MULTI-ETHNIC STUDY OF ATHEROSCLEROSIS (MESA)

ECG R-wave to Radial Artery Pulse Delay (RRD) is a novel hemodynamic index obtainable from a single tonometric measurement with simultaneous ECG to assess the timing of an electrical marker (ECG R-wave peak) until a corresponding mechanical feature (end diastole at the radial pulse). We studied the

An improved right sided electrical impedance method to monitor pulmonary edema

Currently commercial devices exist that monitor pulmonary edema by measuring the electrical impedance between a lead in the right ventricle (RV) and the device can. Studies have shown up to a 40% false alarm rate with these devices. We have published, using a computer model, about a three fold improvement in lung sensitivity to edema by measuring the impedance between a left ventricle lead in the coronary vein and can, which has been confirmed by others with animal experiments. New research has shown a further improvement with a new lead configuration requiring only right side heart measurements.

RR and R wave to finger pulse interval changes as a function of respiration rate and body position using VCRS

A technique of voluntary cardiorespiratory synchronization (VCRS), where the respiration rate is synchronized at a sub-multiple of the heart rate, was used to investigate the RR wave interval change and R to finger pulse interval change as a function of respiration in 6 subjects. Data were collected with subjects breathing at 4, 8, 12 beats per respiratory cycle in the supine and standing position. Following a tone, the subjects inspired for two, four or six heart beats and expired respectively for two, four, or six beats. The results showed a significant decrease in the RR interval with inspiration and an increase in the R to finger pulse time. This produces an approximate 180 degree phase difference between the pulse time interval change and the RR interval. It is unclear whether R-pulse interval change is due to blood pressure changes, other vasomotor factors or a change in the inotropic state of the heart.