Cerebral oxygenation and processed EEG response to clamping and shunting during carotid endarterectomy under general anesthesia.

Clamping and shunting during carotid endarterectomy (CEA) surgery causes changes in cerebral blood flow. The purpose of this study was to assess and compare, side by side, the cerebral oxygenation (rSO2) and processed electroencephalogram (EEG) response bilaterally to carotid artery clamping and shunting in patients undergoing CEA under general anesthesia. With institutional approval and written informed consent, patients undergoing CEA under general anesthesia and routine carotid artery shunting were recorded bilaterally, simultaneously and continuously with an rSO2 and processed EEG monitor. The response of the monitors during carotid artery clamping and shunting were assessed and compared between monitors and bilaterally within each monitor. Sixty-nine patients were included in the study. At clamping the surgical-side and contralateral-side rSO2 dropped significantly below the baseline incision value (-17.6 and -9.4% respectively). After shunting, the contralateral-side rSO2 returned to baseline while the surgical-side rSO2 remained significantly below baseline (-9.0%) until the shunt was removed following surgery. At clamping the surgical-side and contralateral-side processed EEG also dropped below baseline (-19.9 and -20.6% respectively). However, following shunt activation, the processed EEG returned bilaterally to baseline. During the course of this research, we found the rSO2 monitor to be clinically more robust (4.4% failure rate) than the processed EEG monitor (20.0% failure rate). There was no correlation between the rSO2 or processed EEG changes that occurred immediately after clamping and the degree of surgical side stenosis measured pre-operatively. Both rSO2 and processed EEG respond to clamping and shunting during CEA. Cerebral oximetry discriminates between the surgical and contralateral side during surgery. The rSO2 monitor is more reliable in the real-world clinical setting. Future studies should focus on developing algorithms based on these monitors that can predict clamping-induced cerebral ischemia during CEA in order to decide whether carotid artery shunting is worth the associated risks. From the practical point of view, the rSO2 monitor may be the better monitor for this purpose.

Medical equipment donations in Haiti: flaws in the donation process.

The magnitude 7.0 earthquake that struck Haiti on 12 January 2010 devastated the capital city of Port-au-Prince and the surrounding area. The area's hospitals suffered major structural damage and material losses. Project HOPE sought to rebuild the medical equipment and clinical engineering capacity of the country. A team of clinical engineers from the United States of America and Haiti conducted an inventory and assessment of medical equipment at seven public hospitals affected by the earthquake. The team found that only 28% of the equipment was working properly and in use for patient care; another 28% was working, but lay idle for technical reasons; 30% was not working, but repairable; and 14% was beyond repair. The proportion of equipment in each condition category was similar regardless of whether the equipment was present prior to the earthquake or was donated afterwards. This assessment points out the flaws that existed in the medical equipment donation process and reemphasizes the importance of the factors, as delineated by the World Health Organization more than a decade ago, that constitute a complete medical equipment donation.

Medical equipment donations in Haiti: flaws in the donation process / Donaciones de equipo médico en Haití: fallas en el proceso de donación

El terremoto de magnitud 7,0 que azotó a Haití el 12 de enero del 2010 devastó la capital, Puerto Príncipe, y sus alrededores. Los hospitales del área afectada sufrieron daños estructurales importantes y pérdidas materiales. El Proyecto Hope procuró reconstruir el equipo médico y la capacidad de ingeniería clínica del país. Un equipo deingenieros clínicos de Estados Unidos y Haití realizó un inventario y una evaluación del equipo médico en siete hospitales públicos afectados por el terremoto. El equipo encontró que solo 28% del equipo estaba funcionando adecuadamente y se usaba para la atención de los pacientes; otro 28% funcionaba pero no se empleaba por razones técnicas; 30% del equipo no funcionaba, pero podía repararse; y 14% no funcionaba y no podía repararse. La proporción de equipo en cada categoría fue similar, independientemente de que el equipo estuviera presente antes del terremoto o se hubiera donado después. Esta evaluación señala las fallas en el proceso de donación de equipo médico y recalca la importancia de los factores que implica una donación completa de equipo médico, ya delineados por la Organización Mundial de la Salud hace más de un decenio.

The magnitude 7.0 earthquake that struck Haiti on 12 January 2010 devastated the capital city of Port-au-Prince and the surrounding area. The area’s hospitals suffered major structural damage and material losses. Project HOPE sought to rebuild the medical equipment and clinical engineering capacity of the country. A team of clinical engineers from the United States of America and Haiti conducted an inventory and assessment of medical equipment at seven public hospitals affected by the earthquake. The team found that only 28% of the equipment was working properly and in use for patient care; another 28% was working, but lay idle for technical reasons; 30% was not working, but repairable; and 14% was beyond repair.The proportion of equipment in each condition category was similar regardless of whether the equipment was present prior to the earthquake or was donated afterwards. This assessment points out the flaws that existed in the medical equipment donation process and reemphasizes the importance of the factors, as delineated by the World Health Organization more than a decade ago, that constitute a complete medical equipment donation.

Intraoperative MRI electrical noise and monitor ECG filters affect arrhythmia detection and identification.

Most electrical equipment in the modern operating room (OR) radiates electrical noise (EN) that can interfere with patient monitors. We have described the EN that an intraoperative magnetic resonance imaging (iMRI) system emits and have shown that this high-energy EN diminishes the quality of the ECG waveform during iMRI scans in our neurosurgical OR. We have also shown that the ECG signal filters in our iMRI-compatible patient monitor reduce this interference but, in the process, disturb the true morphology of the displayed waveform. This simulation study evaluates how iMRI-generated EN affects the ability of the anesthetist to detect and identify ECG arrhythmias and whether the patient monitor's ECG signal filters can improve arrhythmia recognition. Using an ECG simulator, we generated Lead II and V5 ECG signal segments that contained either no arrhythmia or one of four common cardiac arrhythmias. We filtered the ECG segments with four filters available on our iMRI-compatible monitor (Veris MR, MEDRAD Inc., Indianola, PA USA). We then digitized the segments and mixed simulated iMRI EN into the resultant tracings. With institutional approval and written informed consent, board-certified anesthesiologists reviewed the tracings, determined if an arrhythmia was present and identified the arrhythmia. We conducted the study anonymously. We reported the data as percent correct arrhythmia detection and correct arrhythmia identification. Thirty-one anesthesiologists completed the study. Overall, the participants correctly detected 79.5% (95% CI: 77.2, 81.7%) of the arrhythmias and correctly identified 62.5% (95% CI: 59.8, 65.3%) of the arrhythmias, regardless of EN presence. Although the proportions among monitor noise filters studied were not significant, the manufacturer-designated MR5 Veris MR filter optimized arrhythmia detection and arrhythmia identification for our participants, regardless if EN was present in the ECG tracings. In the neurosurgical OR, the anesthetist must be able to effectively monitor a patient in the presence of iMRI-generated EN. Depending on the OR design, the patient may be out of the anesthetist's direct view during a scan procedure. The anesthetist must rely on monitored physiologic parameters to assess patient status during this time. He/she should be familiar with his/her monitor's filtering capabilities and routinely adjust the ECG filters to achieve the best compromise between minimized EN effects and maximized displayed ECG signal quality.

Postoperative nausea and vomiting prophylaxis from an economic point of view.

Patients rank postoperative nausea and vomiting (PONV) in the top five most undesirable outcomes of surgery. Thirty percent of all surgical patients experience PONV. We conducted an economic study to determine the financial implications of providing surgical patients with PONV prophylaxis to increase patient satisfaction and minimize postoperative complications. Our main objective was to develop an economic model of PONV prophylaxis. We retrospectively reviewed all surgical cases who received care at our institution from June 2005 to June 2007 in which the surgical patient was billed for treatment of nausea and vomiting while in the hospital. The PONV risk factors for these patients were assessed as well as the revenue stream associated with those patients who returned to the hospital within 5 days with nausea and vomiting as their chief complaint. Of the total number of medical charts reviewed (56,532), 28 (1.57%) of 1783 patients who were billed for PONV while in the hospital returned to the hospital with PONV. The total billable charges for PONV for these returning patients were $83,674; the total reimbursements were $25,816 yielding a 31% reimbursement rate. The total hospital expenses were $24,123 yielding a net hospital profit of $1693 for treating these 28 patients. The average hospital cost and charge per antiemetic drug dose was $0.304 and $3.66, respectively. Using these figures, we determined that our hospital's net profit increases linearly with increased PONV prophylaxis administration. Our economic analysis shows that PONV prophylaxis is economically beneficial for the hospital when weighed against the expenses generated by treating patients returning to the hospital with PONV.

Clinical and economic outcomes of low-field intraoperative MRI-guided tumor resection neurosurgery.

PURPOSE: To compare low-field (0.15 T) intraoperative magnetic resonance imaging (iMRI)-guided tumor resection with both conventional magnetic resonance imaging (cMRI)-guided tumor resection and high-field (1.5 T) iMRI-guided resection from the clinical and economic point of view. MATERIALS AND METHODS: We retrospectively compared 65 iMRI patients with 65 cMRI patients in terms of hospital length of stay, repeat resection rate, repeat resection interval, complication rate, cost to the patient, cost to the hospital, and cost effectiveness. In addition, we compared our low-field results with previously published high-field results. RESULTS: The complication rate was lower for iMRI vs. cMRI in patients presenting for their initial tumor resection (45 vs. 57 complications, P = 0.048). The iMRI repeat resection interval was longer for this cohort (20.1 vs. 6.7 months, P = 0.020). iMRI was more cost-effective than cMRI for patients who had repeat resections ($10,690/RFY vs. $76,874/RFY, P < 0.001). We found no other clinical or economic differences between iMRI- and cMRI-guided tumor resection surgeries. Overall, we did not find the advantages to low-field iMRI that have been reported for high-field iMRI. CONCLUSION: There is no adequate justification for the widespread installation of low-field iMRI in its current development state.

Processed electroencephalogram response of patients undergoing carotid endarterectomy: a pilot study.

BACKGROUND: A risk during carotid endarterectomy (CEA) is cerebral ischemia as a result of clamping of the carotid artery. The Cerebral State Monitor is one of several electroencephalogram monitors that reflects level of consciousness of patients during anesthesia. The monitor reports level of consciousness with the empirical parameter Cerebral State Index (CSI) on a 0-100 scale. In this patient-controlled prospective pilot study, we compared the CSI measured from the surgical and control hemispheres of patients undergoing CEA surgery to determine whether the parameter is affected by presumed changes in cerebral blood flow. METHODS: Fifteen consenting CEA patients entered this institutionally approved study. We connected a separate Cerebral State Monitor to the left and right sides of the patient's head and recorded CSI intraoperatively. We compared the control-side data with the surgical-side data. RESULTS: Clamping caused the surgical-side CSI to drop below the control-side CSI. Shunt activation caused the CSI to rise above the control. The greatest difference between the surgical-side CSI and control-side CSI occurred at the completion of the CEA procedure. These observed trends were not statistically significant in this pilot project. CONCLUSION: Our preliminary results suggest that the CSI, and perhaps other similar indexes, may indicate changes in cerebral blood flow acutely during CEA. Our findings lend promise to a new use for these types of electroencephalogram monitors, which are prevalent in operating rooms today.

Magnetic field threshold for accurate electrocardiography in the MRI environment.

Although the electrocardiogram is known to be nondiagnostic within the bore of any high-field magnet due to the magnetohydrodynamic effect, there are an increasing number of applications that require accurate electrocardiogram monitoring of a patient inside the MRI room but outside of the magnet bore. Magnetohydrodynamic effects on the ST segment of the electrocardiogram waveform were investigated in six subjects at magnetic field strengths ranging from 6.4 mT to 652 mT at the aortic midarch, and the electrocardiogram was found to be accurate at magnetic fields below 70 mT. This corresponds to a distance of 160 cm from the isocenter and 80 cm from the bore entrance for the 1.5-T MRI system used in this study. These results can be translated to any MRI system, with knowledge of the fringe field. Accurate electrocardiogram monitoring is feasible in close proximity to the MRI magnet, such as during and after pharmacologic or exercise stress, or interventional or surgical procedures performed in the MRI room.

SNAP II versus BIS VISTA monitor comparison during general anesthesia.

INTRODUCTION: Effectively monitoring the level of consciousness during general anesthesia is clinically beneficial to both the patient and the physician. An electroencephalogram (EEG)-based level-of-consciousness monitor can help minimize intraoperative awareness as well as the effects of over-sedation. In this study, we compared the SNAP II (Stryker Instruments, Kalamazoo, MI USA) and BIS VISTA (Aspect Medical Systems, Newton, MA USA) monitors' primary metrics (SI and BIS, respectively) in terms of correlation, agreement and responsiveness to return to preoperative baseline in surgical cases involving general anesthesia. METHODS: With institutional approval and written informed consent, 33 patients received general anesthesia with isoflurane while undergoing abdominal surgery. We attached both the SNAP II and BIS VISTA electrodes to each patient. We collected data from each monitor simultaneously and continuously, beginning just prior to induction and ending after extubation. Each monitor's level-of-consciousness index is a unit less metric that ranges from 0 to 100, with 100 indicating full consciousness. We performed a Bland-Altman and parameter difference analyses on the data. We calculated the time it took for each monitor to return to preoperative baseline level following cessation of anesthesia. We established an equivalence between the two indices over their entire range for our particular clinical scenario. RESULT: The indices were correlated (r = 0.736, P < 0.0001, N = 3,706 data point pairs). There was an overall difference between the two indices (median = 16.0, 25th/75th%ile = 10.0/21.1) with BIS lower than SI. A 40-60 BIS range (the typical target range during general anesthesia) was approximately equivalent to a 54-74 SI range. In all 33 subjects, SI reached baseline before BIS at the end of the case (median = 3.3 min, 25th/75th%ile = 1.6 min/8.2 min versus median = 8.9 min, 25th/75th = 3.7 min/14.5 min, P = 0.0200), even though both metrics were equal at the beginning of the case. DISCUSSION: Although the SI and BIS both can assess a patient's level of consciousness and are correlated, they are not in agreement with each other numerically and therefore are not interchangeable. It is difficult to assess each monitor's true responsiveness to acute changes in consciousness level from our study design. The differences between the metrics we observed in this study are most likely due to differences in signal processing methodologies, EEG frequencies employed and signal filtering utilized in the monitors.

A comparative study of dexmedetomidine with midazolam and midazolam alone for sedation during elective awake fiberoptic intubation.

STUDY OBJECTIVE: To evaluate the efficacy of dexmedetomidine with midazolam (DEX-MDZ) versus midazolam only (MDZ) for sedation during awake fiberoptic intubation (AFOI). DESIGN: Randomized, double-blinded study. SETTING: Academic medical center. SUBJECTS: 55 ASA physical status I, II, III, and IV patients, aged 18-85 years, scheduled for non-emergency surgery with AFOI. INTERVENTIONS: All patients received intravenous (IV) glycopyrrolate 0.2 mg premedication, oxygen by nasal cannula, and topical local anesthetics to the airway. MDZ subjects received IV midazolam 0.05 mg/kg with additional doses to achieve a Ramsay Sedation Scale (RSS) score of >or= 2. DEX-MDZ patients received midazolam 0.02 mg/kg followed by dexmedetomidine one microg/kg, then an infusion of dexmedetomidine 0.1 microg/kg/hr and titrated to 0.7 microg/kg/hr to achieve RSS>or=2. MEASUREMENTS: Observers' Assessment of Alertness/Sedation (OAA/S) and RSS were evaluated. The anesthesiologist rated AFOI ease of placement. Two observers rated patients' comfort and reaction to placement at three time points: preoxygenation, at introduction of the fiberoptic laryngoscope, and at introduction of the endotracheal tube (ET) before surgery. Following surgery, patients were asked if they recalled the AFOI and also to rate their satisfaction with the intubation. RESULTS: DEX-MDZ patients were significantly calmer and more cooperative during AFOI and had fewer adverse reactions to AFOI than did the MDZ patients. They also were more satisfied with the AFOI (P < 0.001) than were the midazolam-only patients. There were no significant hemodynamic differences between the two subject groups. CONCLUSIONS: Dexmedetomidine in combination with low doses of midazolam is more effective than midazolam alone for sedation in AFOI.

Anesthesia for brain tumor resection using intraoperative magnetic resonance imaging (iMRI) with the Polestar N-20 system: experience and challenges.

The Polestar N-20 Scanner (Medtronic Navigation, Louisville, CO) is an intraoperative magnetic resonance image (iMRI) guidance system designed for neurosurgery. Sixty-five patients underwent craniotomy for tumor resection using the iMRI during the period from April 2005 to December 2006. Anesthesiologists used an iMRI-compatible patient monitoring system (Veris MR, MEDRAD, Indianola, PA), anesthesia machine (Aestiva/5 MRI, Datex-Ohmeda, Madison, WI), and infusion pumps (Continuum; MEDRAD). Average setup time for each case (from intubation to incision) was one hour, 33 minutes and showed learning improvement over the 21-month period. The challenges facing the anesthesiologists in these cases included the need to use longer intravenous (IV) catheters and gas delivery and sampling lines, which increased dead space. Electrocardiographic signals became contaminated with electrical noise during iMRI scan procedures, which made it difficult to distinguish rhythm changes. None of our iMRI patients underwent a repeat resection, whereas the repeat resection rate for conventional tumor resection is reported to be as high as 30%. The use of a small, low-field iMRI system provided adequate imaging for resection of lesions without the need of repeat resections in the weeks following the initial procedure, and did not significantly alter the anesthetic procedure. A team effort between the anesthesiologists, surgeons, nurses, and MRI technicians is paramount for the practical and efficient use of these iMRI systems.

Myocardial electrical activity does not affect myocardial electrical impedance measurements.

OBJECTIVE: Myocardial electrical impedance (MEI) has shown to be an effective indicator of myocardial ischemia. We have previously developed a novel monitor for measuring MEI in near-real time. The object of this study was to test whether drug-induced changes in the frequency of the periodic myocardial electrical activity, as measured by the heart rate (HR), affect MEI measurements made with our monitor. METHODS: Thirty dogs were randomly assigned to one of three study groups (placebo, isoproterenol or esmolol) and then anesthetized with sodium thiamylal, intubated, ventilated, given isoflurane, and had venous, arterial, and pulmonary artery catheters placed. Median sternotomy was performed to facilitate myocardial exposure and to allow the left anterior descending (LAD) coronary artery to be isolated. Following baseline measurements, saline (control), isoproterenol or esmolol was administered and the LAD coronary artery was occluded in a timed sequence in order to study the effects of heart rate changes and demonstrate induced myocardial ischemia on MEI. RESULTS: Isoproterenol raised the HR and esmolol lowered the HR without affecting our MEI measurements. Myocardial electrical impedance increased during LAD coronary artery occlusion in all groups, as previously shown. CONCLUSION: These results demonstrate that our MEI monitor is unaffected by the frequency of the periodic myocardial electrical activity that generates the HR.

Electrical noise in the intraoperative magnetic resonance imaging setting.

BACKGROUND: Intraoperative magnetic resonance imaging (iMRI) is a tool now commonly used in neurosurgery. Safe and reliable patient care in this (or any other) operating room setting depends on an environment, where electrical noise (EN) does not interfere with the operation of the electronic monitoring or imaging equipment. In this investigation, we evaluated the EN generated by the iMRI system and the anesthesia patient monitor used at this institution that impacts the performance of these two devices. METHODS: We measured the EN generated by our iMRI-compatible anesthesia patient monitor as detected by the EN analysis algorithm in our iMRI system. We measured the EN generated by our iMRI system during scanning as detected in the electrocardiogram (ECG) waveform of our patient monitor. We analyzed the effects on EN reduction and signal quality of the ECG noise filters provided in our iMRI-compatible anesthesia patient monitor. RESULTS: Our patient monitor generated EN that was detectable by the iMRI EN analysis algorithm; however, this interference was within the iMRI manufacturer's acceptable limits for an iMRI scan (<10% more than background system-level noise). In the clinical case analyzed, the iMRI generated a narrow-band low-frequency (20 Hz) relatively high-energy EN that interfered with the ECG signal of our patient monitor during an iMRI scan. This EN was correlated with the acoustic noise from the iMRI system during the scan and was associated with the radio frequency (RF) and magnetic gradient pulsations of the iMRI system. The integrity of the ECG waveform was nearly entirely lost during a scan. The filters of the ECG monitor diminished but did not entirely eliminate this 20 Hz interference. We found that the filters alter the morphology of the ECG signal, which may make it difficult to identify clinically relevant ECG changes. CONCLUSION: The EN generated by our anesthesia patient monitor is within acceptable limits for the iMRI system. The iMRI generates EN which renders the ECG unreadable in the most commonly used filter mode. The monitor's filters diminish this noise but also alter the morphology of the ECG waveform. The anesthesiologist must be cognizant of these technical compromises and recognize that adjusting the ECG filters on the monitor is required to obtain a useful ECG signal for patient monitoring during the iMRI scan but that the diagnostic value of the ECG will be reduced.

Electrotonic remodeling following myocardial infarction in dogs susceptible and resistant to sudden cardiac death.

Passive electrical remodeling following myocardial infarction (MI) is well established. These changes can alter electrotonic loading and trigger the remodeling of repolarization currents, a potential mechanism for ventricular fibrillation (VF). However, little is known about the role of passive electrical markers as tools to identify VF susceptibility post-MI. This study investigated electrotonic remodeling in the post-MI ventricle, as measured by myocardial electrical impedance (MEI), in animals prone to and resistant to VF. MI was induced in dogs by a two-stage left anterior descending (LAD) coronary artery ligation. Before infarction, MEI electrodes were placed in remote (left circumflex, LCX) and infarcted (LAD) myocardium. MEI was measured in awake animals 1, 2, 7, and 21 days post-MI. Subsequently, VF susceptibility was tested by a 2-min LCX occlusion during exercise; 12 animals developed VF (susceptible, S) and 12 did not (resistant, R). The healing infarct had lower MEI than the normal myocardium. This difference was stable by day 2 post-MI (287 +/- 32 Omega vs. 425 +/- 62 Omega, P < 0.05). Significant differences were observed between resistant and susceptible animals 7 days post-MI; susceptible dogs had a wider electrotonic gradient between remote and infarcted myocardium (R: 89 +/- 60 Omega vs. S: 180 +/- 37 Omega). This difference increased over time in susceptible animals (252 +/- 53 Omega at 21 days) due to post-MI impedance changes on the remote myocardium. These data suggest that early electrotonic changes post-MI could be used to assess later arrhythmia susceptibility. In addition, passive-electrical changes could be a mechanism driving active-electrical remodeling post-MI, thereby facilitating the induction of arrhythmias.

Vacuum-assisted apical suction devices induce passive electrical changes consistent with myocardial ischemia during off-pump coronary artery bypass graft surgery.

OBJECTIVE: Off-pump coronary artery bypass graft surgery is common therapy to completely revascularize diseased hearts. In order to graft posterior arteries in this procedure, the heart must be lifted from the chest cavity and manipulated to expose the surgical field using an apical suction device. This suction device may cause unwanted myocardial ischemia. METHODS: In this observational study, we measured myocardial electrical impedance, a parameter that responds to myocardial ischemia, as well as ST-segment changes during off-pump coronary artery bypass graft surgery in 12 patients with two-vessel coronary artery disease undergoing revascularisation of the left anterior descending and the posterior descending coronary arteries. During the posterior descending artery revascularisation phase of the procedure the apical suction device was oriented over the electrodes used to measure myocardial electrical impedance, thus allowing us the opportunity to assess myocardial ischemia in this region of the heart. RESULTS: In these 12 patients, myocardial electrical impedance progressively increased under the suction device during posterior coronary artery revascularisation, suggesting that myocardial ischemia developed in this region of the myocardium. ST-segment changes were negligible while the heart was vertically displaced (and the suction device attached), but increased immediately when the heart was returned to the neutral anatomical position. CONCLUSION: Our data suggest that the apical suction device may cause ischemia while the heart is vertically displaced and electrically disconnected from the body. Under these conditions, ST-segment changes may not detect myocardial ischemia. Myocardial electrical impedance has the potential to reliably detect intraoperative myocardial ischemia under these circumstances.

Early time course of myocardial electrical impedance during acute coronary artery occlusion in pigs, dogs, and humans.

Changes in myocardial electrical impedance (MEI) and physiological end points have been correlated during acute ischemia. However, the importance of MEI's early time course is not clear. This study evaluates such significance, by comparing the temporal behavior of MEI during acute total occlusion of the left anterior descending coronary artery in anesthetized humans, dogs, and pigs. Here, interspecies differences in three MEI parameters (baseline, time to plateau onset, and plateau value normalized by baseline) were evaluated using Kruskal-Wallis ANOVA and post hoc tests (P < 0.05). Noteworthy differences in the MEI time to plateau onset were observed: In dogs, MEI ischemic plateau was reached after 46.3 min (SD 12.9) min of occlusion, a significantly longer period compared with that of pigs and humans [4.7 (SD 1.2) and 4.1 min (SD 1.9), respectively]. However, no differences could be observed between both animal species regarding the normalized MEI ischemic plateau value (15.3% (SD 4.7) in pigs, vs. 19.6% (SD 2.6) in dogs). For all studied MEI parameters, only swine values resembled those of humans. The severity of myocardial supply ischemia, resulting from coronary artery occlusion, is known to be dependent on collateral flow. Thus, because dogs possess a well-developed collateral system (unlike humans or pigs), they have shown superior resistance to occlusion of a coronary artery. Here, the early MEI time course after left anterior descending coronary artery occlusion, represented by the time required to reach ischemic plateau, was proven to reflect such interspecies differences.

Myocardial electrical impedance responds to ischemia and reperfusion in humans.

Myocardial electrical impedance (MEI) is correlated to ischemia and reperfusion of the heart muscle. The entire body of work with MEI to this point has been carried out in animal subjects in vivo and excised tissue samples. In this study, we measured MEI clinically for the first time in human patients who were undergoing off-pump coronary artery bypass (OPCAB) surgery. MEI was measured with a monitor designed in this laboratory and approved by the FDA for use on human subjects. Our patient population (n = 18) had a 70%-100% stenosis of the diseased coronary artery targeted for bypass. We measured MEI continuously during surgery and at 3, 6, 24, and 72 h postoperatively from two temporary pacing electrodes attached to the heart muscle. Absolute baseline impedance ranged from 173 to 729 ohms. MEI increased with occlusion of the diseased artery prior to bypass. The percent increase from baseline was inversely correlated to the percent stenosis of the diseased artery. MEI decreased below baseline immediately on reperfusion following bypass in all patients and continued decreasing over the measurement period. MEI is a reliable clinical indicator of ischemia and reperfusion in humans and may indicate the effectiveness of coronary artery surgery. The parameter may have monitoring and diagnostic value in heart disease in humans.