Feasibility of Saphenous Nerve Somatosensory-Evoked Potential Intraoperative Monitoring During Lumbar Spine Surgery: Early Results.

STUDY DESIGN: Retrospective review. OBJECTIVE: Assess the feasibility of saphenous nerve somatosensory evoked potentials (SN-SSEP) monitoring in lumbar spine surgeries. BACKGROUND CONTEXT: SN-SSEPs have been proposed for detecting lumbar plexus and femoral nerve injury during lateral lumbar surgery where tibial nerve (TN) SSEPs alone are insufficient. SN-SSEPs may also be useful in other types of lumbar surgery, as stimulation of SN below the knee derives solely from the L4 root and provides a means of L4 monitoring, whereas TN-SSEPs often do not detect single nerve root injury. The feasibility of routine SN-SSEP monitoring has not been established. METHODS: A total of 563 consecutive cases using both TN-SSEP and SN-SSEP monitoring were included. Anesthesia was at the discretion of the anesthesiologist, using an inhalant in 97.7% of procedures. SN stimulation was performed using 13 mm needle electrodes placed below the knee using 200-400 µsec pulses at 15 to 100 mA. Adjustments to stimulation parameters were made by the neurophysiology technician while obtaining baselines. Data were graded retrospectively for monitorability and cortical response amplitudes were measured by two independent reviewers. RESULTS: Ninety-eight percent of TN-SSEPs and 92.5% of SN-SSEPs were monitorable at baseline, with a mean response amplitude of 1.35 µV for TN-SSEPs and 0.71 µV for SN-SSEPs. A significant difference between the stimulation parameters used to obtain reproducible TN and SN-SSEPs at baseline was observed, with SN-SSEPs requiring greater stimulation intensities. Body mass index is not associated with baseline monitorability. Out of 20 signal changes observed, 11 involved SN, while TN-SSEPs were unaffected. CONCLUSION: With adjustments to stimulation parameters, SN-SSEP monitoring is feasible within a large clinical cohort without modifications to the anesthetic plan. Incorporating SN into standard intraoperative neurophysiological monitoring protocols for lumbar spine procedures may expand the role of SSEP monitoring to include detecting injury to the lumbar plexus. LEVEL OF EVIDENCE: 3.

Frequency of interatrial block in patients with sinus rhythm hospitalized for stroke and comparison to those without interatrial block.

Interatrial block (IAB; P wave > or =110 ms) is a potent correlate of left atrial (LA) enlargement and electromechanical dysfunction and a strong predictor of atrial tachyarrhythmias, in particular, atrial fibrillation. Although these associations increase its risk for embolism, i.e., cardioembolic stroke, such a phenomenon has been inadequately investigated. We investigated 85 general hospital patients who had been admitted to the neurologic unit between January 2003 and December 2004 for embolic stroke. Of those, 66 patients who had electrocardiograms that showed sinus rhythm were evaluated for IAB and categorized as those with IAB and those without (controls). Medical records were then reviewed for common co-morbidities and stroke risk factors, high-resolution carotid artery Doppler ultrasonographic study reports, and 2-dimensional echocardiograms obtained during the current admission for embolic stroke; 40 patients (61%) had IAB. There was a 55% prevalence of LA enlargement (diameter in the parasternal long-axis view > or =40 mm, p <0.001). LA thrombi and/or spontaneous contrast ("smoke") were noted on echocardiograms in 6 patients with IAB (15%) but not in any of the controls (p = 0.038). Five of those 6 patients with such LA thrombi had dilated LA cavities. In conclusion, IAB could be a risk for embolic stroke due to its known sequelae of LA dilation and electromechanical dysfunction that predispose to thrombosis. If prospective studies prove this to be so, the need for anticoagulation use in such patients should be investigated.

Prospective evaluation of atrial tachyarrhythmias in patients with interatrial block.

INTRODUCTION: Interatrial block (P-wave> or =110 ms) is clinically associated with left atrial enlargement and electromechanical dysfunction as well as atrial tachyarrhythmias. We prospectively evaluated the incidence of such arrhythmias, especially atrial fibrillation among patients with interatrial block over the course of 1 year. METHODS: 118 patients (aged 48 to 104 years; female 56.6%) who had been hospitalized between December 15, 2004 and January 14, 2005 were identified and divided into 3 groups based on their respective baseline electrocardiogram (interatrial block=41 patients, sinus non-interatrial block=51 patients and atrial tachyarrhythmia=24 patients). Patients were subsequently followed for 12 months for pertinent cardiovascular events (heart failure, peripheral embolism, transient ischemic attacks and stroke), atrial tachyarrhythmias (atrial fibrillation and atrial flutter) and death as endpoints. RESULTS: 19 patients (17.9%) had atrial fibrillation during the 12-month follow-up (sinus non-interatrial block group=4 [9.1%], interatrial block group=12 [29.3%] and atrial tachyarrhythmia group=3 [14.3%]). Coronary artery disease, hypertension, pre-existing atrial fibrillation history, dilated cardiomyopathy, atrioventricular valvular disease and interatrial block (age- and sex-adjusted hazard ratio=4.2; 95% confidence interval 1.2-14.4; p=0.02) were significantly associated with future events of atrial fibrillation. However, logistic regression analysis indicated that interatrial block was not an independent predictor of future atrial fibrillation whereas only history of pre-existing atrial tachyarrhythmias was (hazard ratio=23.6; 95% confidence interval 4.5-121.7; p=0.0002). CONCLUSION: Interatrial block may be associated with atrial fibrillation but in a 12-month period, does not appear to be an independent predictor of future atrial fibrillation. Continued prospective investigation of such a relationship is certainly warranted given its already known consequences.

Correlation of left atrial size with p-wave duration in interatrial block.

BACKGROUND: Interatrial block (IAB) [P-wave duration > or = 110 ms] is associated with left atrial (LA) enlargement (LAE) and pathophysiologic derangements that result in atrial tachyarrhythmias, LA electromechanical dysfunction, and embolism. However, there has been no study addressing the direct correlation of P-wave duration in IAB and LAE. METHODS: One hundred eighty-one consecutive patients who were admitted to a tertiary care teaching hospital over 5 consecutive days were screened for past transthoracic echocardiogram evaluations and were then matched with ECGs done within 10 days of these echocardiographic investigations. ECGs were evaluated for presence of IAB, and patients were subsequently classified into two groups: control patients and patients with IAB. Patients were also matched for common comorbidities. Mean, SD of age, Pearson correlation coefficient (r), p values, and multivariate and linear regression analyses were analyzed for the investigated variables of LA size, left ventricular hypertrophy (LVH), posterior wall thickness, septal thickness, and P-wave duration. RESULTS: From the sample (n = 66; mean age +/- SD, 71.3 +/- 13.7; female gender, 48.5%), the mean LA size in the control group was 36.7 +/- 4.01 mm and for the group of patients with IAB (n = 38) was 42.2 +/- 7.25 mm (p = 0.004). Linear regression analysis revealed that P-wave duration was significantly correlated with LA size (p = 0.0002, r = 0.606). CONCLUSIONS: Degree of conduction delay in IAB (P-wave duration) is an independent, direct correlate of LAE, and the regression equation (LA size [in millimeters] = 2.47 +/- 0.29 x P-wave duration [in milliseconds]) could be used to estimate LAE.