Euljoon Park

Impedance Cardiography for Atrioventricular Interval Optimization During Permanent Left Ventricular Pacing

TSE, H‐F., et al.: Impedance Cardiography for Atrioventricular Interval Optimization During Permanent Left Ventricular Pacing. Left ventricular (LV) pacing is increasingly used in the management of congestive heart failure. Optimization of the atrioventricular (AV) interval is essential to maximize the hemodynamic benefits of this therapy. Although Doppler echocardiography (echo) is the most widely used method, it is time‐consuming, expensive, and operator‐dependent. We examined the value of an impedance cardiography (IC)‐based method of cardiac output (CO) measurement to optimize the AV interval in 5 men and 1 woman (mean age = 72 ± 11 years) during permanent LV pacing with a 4.8 Fr unipolar coronary sinus pacing lead. Simultaneous measurements of CO by IC and echo were performed at AV intervals of 50, 80, 110, 150, 180, and 225 ms during DDD pacing at 85 beats/min. The optimal AV interval varied between 110 and 180 ms. In 5 of 6 patients (83%), the optimal AV interval by echo and IC was identical. While CO measurements were higher with IC than with echo ( 6.1 ± 0.4 L/min vs 4.7 ± 0.3 L/min, P < 0.05), CO measurements by IC and echo were closely correlated r = 0.67 , P < 0.001). In conclusion, our initial experience suggests that IC is a reliable method of AV interval optimization during LV pacing. IC and echo measurements of CO during LV pacing were closely correlated. (PACE 2003; 26[Pt. II]:189–191)

Thoracic Spinal Cord Stimulation Improves Cardiac Contractile Function and Myocardial Oxygen Consumption in a Porcine Model of Ischemic Heart Failure

Thoracic Spinal Cord Stimulation. Background: Prior experimental studies show that thoracic spinal cord stimulation (SCS) improves left ventricular (LV) ejection fraction (LVEF). The mechanism of this improvement in the LV contractile function after SCS and its effects on the myocardial oxygen consumption remains unknown.

Catheter-based renal sympathetic denervation exerts acute and chronic effects on renal hemodynamics in swine

OBJECTIVES We investigated the acute and chronic effects of catheter-based renal sympathetic denervation (RSD) on renal hemodynamics assessed by average peak velocity (APV), renal blood flow (RBF), renal flow reserve (RFR) and resistive index (RI). BACKGROUND Sympathetic overdrive is accompanied by impaired RBF, whereas there is no data on the effects of transcatheter RSD on renal hemodynamic balance. METHODS Before and post-RSD (acutely and after 1 month), in 9 farm swines we measured APV by a 0.014-inch Doppler flow wire placed in the stem of the renal artery under baseline and hyperemic conditions, induced by intrarenal dopamine (50 μg/kg). RFR was calculated as the ratio of hyperemic to basal peak velocity, and RI was estimated as (peak systolic velocity-end-diastolic velocity)/peak systolic velocity. RSD was achieved via the lumen of the main renal artery with a specifically designed catheter connected to a radiofrequency generator according to prespecified algorithm. RESULTS APV and RBF increased acutely post ablation in all animals, compared to APV and RBF before ablation (61.44 ± 32.6 vs 20.44 ± 6.38 cm/s, p<0.001 and 407.4 ± 335.1 vs 161.1 ± 76.6 ml/min, p=0.003; respectively), whereas RFR and RI were reduced (1.51 ± 0.59 vs 2.85 ± 1.33, p<0.001 and 0.67 ± 0.07 vs 0.74 ± 0.07, p=0.005; respectively). One month post ablation APV and RBF compared to APV and RBF before ablation remained significantly higher whereas RFR and RI remained lower as compared to baseline. CONCLUSIONS Catheter-based RSD exerts acute and chronic effects on renal hemodynamics in a large animal model. If confirmed in humans RBF parameters may be used as direct markers of successful RSD.

Estimation of the optimal VV delay by an IEGM-based method in cardiac resynchronization therapy

Determination of the optimal interventricular (VV) delay in cardiac resynchronization therapy currently relies on costly, time‐consuming echocardiographic (ECHO) methods. This study evaluated the performance of a new intracardiac electrogram (IEGM)‐based VV method compared to the aortic velocity time integral (AVTI) method of VV delay optimization. The study included two patient groups. Eleven patients enrolled by a single center in the Rhythm II ICD trial underwent prospective comparisons of the AVTI at the VV interval determined by the IEGM VV method versus the maximum AVTI at the echocardiographically determined optimal VV delay. In 61 patients enrolled in the RHYTHM VV trial, the same testing methods were compared retrospectively. In the prospective study, the maximum AVTI by the ECHO‐based method (24.3 ± 7.9 cm), was closely correlated with maximum AVTI by the IEGM‐based method (23.9 ± 7.9 cm; concordance correlation coefficient = 0.99; 95% confidence, lower limit of 98%. Likewise, in the retrospective analysis, the ECHO‐determined maximum AVTI (22.1 ± 8.2 cm) was similar to that determined by the IEGM‐based method (20.9 ± 8.3 cm; concordance correlation coefficient = 0.98; 95% confidence, lower limit of 97%).

Attenuation of Left Ventricular Adverse Remodeling With Epicardial Patching After Myocardial Infarction

BACKGROUND Previous studies suggested that epicardial patch applied to the infarcted site after acute myocardial infarction (MI) can alleviate left ventricular (LV) remodeling and improve cardiac performance; however, the effects of regional epicardial patch on chronic phase of LV remodeling remain unclear. METHODS AND RESULTS We studied 20 pigs with MI induced by distal embolization and impaired LV ejection fraction (LVEF < 45%) as detected by gadolinium-enhanced cardiac magnetic resonance imaging (MRI). Eight weeks post-MI, all animal underwent open chest procedure for sham surgery (control, n = 12) or patch implantation over the infarcted lateral LV wall (patch group, n = 12). In the patch group, +dP/dt increased and LV end-diastolic pressure decreased at 20 weeks compared with immediately post-MI and at 8 weeks (P < .05), but not in the control group (P > .05). As determined by cardiac MRI, LV end-diastolic and end-systolic volumes increased at 20 weeks compared with 8 weeks in both groups (P < .05). However, the increase in LV end-diastolic volume (+14.1 +/- 1.8% vs. +6.6 +/- 2.1%, P = .015) and LV end-systolic volume (+12.1 +/- 2.4% vs. -4.7 +/- 3.7%, P = .0015) were significantly greater in the control group compared with the patch group. Furthermore, the percentage increase in LVEF (+17.3 +/- 4.9% vs. +4.1 +/- 3.9%, P = .048) from 8 to 20 weeks was significantly greater in the patch group compared with the control group. Histological examination showed that LV wall thickness at the infarct region and adjacent peri-infarct regions were significantly greater in the patch group compared with the control group (P < .05). CONCLUSION Regional application of a simple, passive synthetic epicardial patch increased LV wall thickness at the infarct region, attenuated LV dilation, and improved LVEF and +dP/dt in a large animal model of MI.

Atrial Evoked Response Integral for Automatic Capture Verification in Atrial Pacing

BORIANI, G., et al.: Atrial Evoked Response Integral for Automatic Capture Verification in Atrial Pacing. Beat‐by‐beat Autocapture is currently limited to operation in the ventricle with bipolar leads. The authors investigated the integral of the negative‐going portion of the atrial evoked response integral (AERI) as a potential resource for verification of atrial capture. Intracardiac electrogram signals were collected from 59 patients (ages 67.8 ± 15.1 years) with bipolar, low polarization atrial leads. The signals were collected over a mean period of 6.1 months (minimum 4 days) after lead implantation. St. Jude Medical Affinity pulse generators were used to perform automatic capture threshold tests while the electrogram signals were recorded by a Model 3510 programming device. These signals were transferred to a personal computer in digital form for later analysis. The AERI was calculated at each programmable pacing voltage until capture was lost. The difference between the polarization integral at loss of capture and evoked response integral with successful capture was sufficient to justify enabling the atrial Autocapture feature in 53 of 59 patients in whom bipolar pacing and unipolar sensing was performed. The authors developed a calibration routine to identify automatically those patients in whom atrial Autocapture could be programmed On, based on the polarization integral at loss of capture, the estimated maximum polarization integral, and the AERI. Preliminary analysis indicated that the AERI is a practical resource for beat‐by‐beat atrial capture detection when used with low polarization leads. (PACE 2003; 26[Pt. II]:248–252)

Autocapture enhancements: unipolar and bipolar lead compatibility and bipolar pacing capability on bipolar leads.

BINNER, L., et al.: Autocapture Enhancements: Unipolar and Bipolar Lead Compatibility and Bipolar Pacing Capability on Bipolar Leads. Beat‐by‐beat Autocapture maximizes device longevity by minimizing stimulus amplitude while assuring patient safety. Currently, Autocapture permits use of only bipolar leads. The authors have devised a detection method that operates with unipolar and bipolar leads and covers all pacing and sensing combinations (but bipolar pace and sense simultaneously). This new detection method for unipolar sensing uses the integral of the negative portion of the unipolar evoked response as a robust capture detection feature. When using bipolar leads, the method provides the flexibility of bipolar or unipolar pacing. In this study, unipolar ventricular intracardiac electrograms (EGMs) were recorded in 71 patients, 73.7 ± 9.9 years of age; 9 with high polarization, 62 with low polarization. High polarization had polished platinum or activated carbon electrodes. Low polarization had TiN, platinized platinum, or IrOx electrodes. The intracardiac EGMs were recorded 544 ± 796 days after implant. The pacemakers performed an automatic capture threshold test while the intracardiac EGM signals were recorded in a programmer. These digitized signals were saved for off‐line analysis. The unipolar evoked response was calculated at up to six (depending on capture threshold) pacing voltages and the polarization integral at 4.5 V and at loss of capture. An automatic calibration algorithm determined if the signal‐to‐noise ratio was adequate for Autocapture operation. Autocapture was possible with 60 of 62 of the low polarizations, and with 6 of 9 of the high polarizations. The average values from the data collected were: average unipolar evoked response ‐ 4.1 ± 2.1  mV , average peak negative voltage ‐ 10.0 ± 3.7  mV , average polarization 0.3 ± 0.34 mV, and average signal‐to‐noise ratio (unipolar evoked response/polarization) 38 ± 71. In all cases the algorithm correctly determined the appropriateness of using Autocapture with the electrodes tested and the unipolar evoked response threshold to be used. (PACE 2003; 26[Pt. II]:221–224)

Enhanced rate response algorithm for orthostatic compensation pacing.

Upon orthostatic stress after a period of rest, the heart rate increases rapidly to maintain cardiac output and minimize the fall in arterial pressure. Pacemaker patients are often prone to a deficient response to orthostatic stress. This may cause lightheadedness and, in rare patients with autonomic dysfunction, syncope. To alleviate these undesirable consequences, an enhanced rate response algorithm was developed using an accelerometer. The pacemaker generates two signals from its accelerometer: instantaneous activity level (Act) and long‐term change in activity level (ActVar). Low values of both Act and ActVar indicate a resting state. An increase in Act while ActVar remains low indicates the onset of motion after prolonged rest. Upon detecting this transition, the algorithm increases the pacing rate to a programmable orthostatic compensation rate for a programmable duration. A taped‐on pacemaker with this algorithm was evaluated in three healthy women and two healthy men, 36 ± 8 years of age. Electrocardiogram and ventricular pacing pulses were recorded by a 24‐hour ambulatory system. Each trigger of the orthostatic compensation rate was verified against a >10 beats/min increase in heart rate, a response classified as appropriate. The overall specificity of the algorithm among the five subjects was 78%. The nocturnal specificity (10 pm to 7 am) was 98%, considerably higher than during daytime (72%). In conclusion, a pacing algorithm to alleviate orthostatic stress was developed, which was highly specific during the night hours.

Atrial activation time and pattern of linear triple-site vs. single-site atrial pacing after cardioversion in patients with atrial fibrillation.

AIMS Multisite atrial pacing has been suggested to be effective in suppressing atrial fibrillation (AF), however, the effect of linear triple-site atrial pacing (LTSP) in humans has not been evaluated. We compared the effects of LTSP to single-site atrial pacing (SSP) on the atrial activation and wavefront propagation pattern in patients with persistent AF. METHODS AND RESULTS In 10 patients with persistent AF, the effects of LTSP and SSP were evaluated by left atrial (LA) endocardial non-contact multielectrode array mapping and multipolar catheters. LTSP and SSP were delivered from the high right atrium (HRA), the distal coronary sinus (CS), and within the LA at the site showing maximal overlay of low-voltage zones during sinus rhythm and pacing at HRA and CS. Atrial activation time and pattern, P wave duration, and the prevention of AF induced by burst pacing were assessed with these pacing interventions. Compared with SSP, LTSP at the HRA, CS, and LA shortened atrial activation times (183 +/- 24 vs. 174 +/- 24 ms, 186 +/- 29 vs. 166 +/- 28 ms, and 171 +/- 40 vs. 163 +/- 39 ms; P < 0.05, respectively). P wave duration was shorter with LTSP than SSP at all three sites (141.7 +/- 35.1 vs. 146.9 +/- 38.5 ms, 138.1 +/- 34.6 vs. 145.7 +/- 33.7 ms, and 142.7 +/- 33.4 vs. 151.3 +/- 35.1 ms; P < 0.05, respectively). LTSP initially depolarized a larger area than SSP, and produced more uniform and planar wavefront propagation. LTSP prevented the burst-induction of AF during LA pacing in 3 of 10 patients, while SSP was never successful. CONCLUSION In patients with persistent AF, LTSP provided more rapid and uniform activation of the atria compared with SSP, which was associated with prevention of burst-induction of AF in some patients. Further study is required to determine whether LTSP can modify the substrate of chronic AF, leading to frank AF suppression.

Blood pressure response to transition from supine to standing posture using an orthostatic response algorithm.

Upon standing from a supine position, the normal response is an increase in heart rate to maintain blood pressure (BP). In patients with chronotropic incompetence, heart rate may not increase upon standing, and they may experience orthostatic hypotension (OH). We evaluated a new orthostatic response (OSR) pacing algorithm that uses an accelerometer signal to detect sudden activity following prolonged rest to trigger a 2 minutes increase in pacing rate to 94 bpm. Ten recipients of DDDR pacemakers which contain the OSR compensation algorithm (mean age = 77 ± 9 years, 8 women) with sick sinus syndrome (n = 6) or atrioventricular block (n = 4) were studied. In all patients BP was measured before and 0.5, 1, 1.5, 2, and 3 minutes after standing at their programmed base rate. A 20 mmHg fall in systolic BP upon standing was observed in five patients (OH patients), while the other five were considered non‐OH patients. The measurements were repeated with the OSR algorithm turned on. Mean BP was defined as 1/3 systolic BP + 2/3 diastolic BP. Baseline heart rate was significantly slower in OH patients (62 ± 2 bpm) than non‐OH patients (71 ± 7 bpm, P < 0.05). In OH patients mean BP increased significantly upon standing (P < 0.05 for all comparisons) with the algorithm ON instead of decreasing with the algorithm OFF, at 1 minute (+3.4 vs −10.3 mmHg), 1.5 minutes (+7.0 vs −4.9 mmHg), 2 minutes (+1.6 vs −6.7 mmHg), and 3 minutes (+2.5 vs −8.5 mmHg). These preliminary results suggest that the OSR algorithm maintains BP upon standing in patients with OH.