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PubMed1989

The choice of index for umbilical artery Doppler waveforms.

Umbilical artery Doppler waveforms acquired from 211 patients were used to investigate the power of different waveform indices in predicting antenatal fetal compromise. Waveform indices were calculated using a BBC microcomputer. The specificity at 100% sensitivity for detection of antenatal fetal compromise was not significantly different for resistance index, pulsatility index, normalised resistance index and normalised pulsatility index, and was approximately 80%. For the indices of resistance time and downslope the specificity was significantly lower. This similarity in the power of a number of indices in the detection of antenatal fetal compromise suggests that standardisation to one of the simpler indices such as resistance index or pulsatility index could be adopted.

Female↗
PubMed1989

Evaluation of ventricular contractility indexes in the dog with left ventricular dysfunction induced by rapid atrial pacing.

Eight dogs were studied by simultaneous invasive hemodynamic and two-dimensional echocardiographic methods to determine whether left ventricular contractility is altered by 2 weeks of rapid atrial pacing. Additionally, this study evaluated the response of three ventricular contractility indexes to both the pacing intervention and acute load alteration. The indexes compared were ejection fraction, peak systolic pressure to end-systolic volume index ratio (SBP/ESVI) and end-systolic wall stress to end-systolic volume index ratio (ESWS/ESVI). After 2 weeks of pacing at 265 +/- 20 min-1 (mean +/- SD), cardiac index and ejection fraction were reduced to 73 +/- 38 ml/kg per min and 22 +/- 6%, respectively, from 161 +/- 22 and 46 +/- 7 before pacing (both p less than 0.001). Concomitantly, SBP/ESVI and ESWS/ESVI were reduced to 34 +/- 10 mm Hg/ml per kg and 54 +/- 19 g/cm2 per ml per kg, respectively, from 84 +/- 29 and 121 +/- 36 before pacing (both p less than 0.005). There were high correlations for the changes in SBP/ESVI and ejection fraction (r = 0.94, p less than 0.001) and ESWS/ESVI and ejection fraction (r = 0.89, p less than 0.003). Acute afterload alteration with phenylephrine depressed ejection fraction but not SBP/ESVI or ESWS/ESVI. Therefore, this study demonstrates 1) that left ventricular contractility is markedly depressed in the dog by 2 weeks of rapid atrial pacing, and 2) that SBP/ESVI and ESWS/ESVI are superior to ejection fraction as ventricular contractility indexes because these ratios accurately measure contractility changes but are influenced less by after-load conditions.

Animals↗
PubMed1992

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes.

OBJECTIVES: The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction. BACKGROUND: Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent. METHODS: Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min). RESULTS: Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups. CONCLUSIONS: Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Cardiac Catheterization↗
PubMed1995

Development and validation of simplified predictive index for major complications in contemporary percutaneous transluminal coronary angioplasty practice. The Registry Committee of the Society for Cardiac Angiography and Interventions.

OBJECTIVES: This study was designed to determine the preprocedural risk factors for major complications (emergent coronary bypass surgery, myocardial infarction or death) of coronary angioplasty and to derive and validate a simplified index that predicts patients' a priori risk of complications. BACKGROUND: Previous studies of risk factors for complications after coronary angioplasty may not be generalizable to current, broad-based angioplasty practice. Furthermore, to our knowledge a clinically useful predictive index has not been derived and independently validated. METHODS: From data collected prospectively for the Registry of the Society for Cardiac Angiography and Interventions for 1992, multivariable logistic regression was used to determine which variables were independently associated with complications in 10,622 first angioplasty procedures. Stepwise regression and receiver operating characteristic curves then were used in this registry to develop a predictive index for complications that was validated using 5,250 first angioplasty procedures in the 1993 registry. RESULTS: Predictors of major complications were multivessel disease, unstable angina, recent myocardial infarction, type C lesion or left main angioplasty, shock, age, geographic region and absence of previous coronary bypass surgery. The derived predictive index consisted of the first six of these variables plus aortic valve disease and classified patients into four risk groups: low (1.3% complications), moderate (2.8%), high (12.7%) and very high (29.7%) risk. This index demonstrated consistent reliability and discriminatory ability when applied to the 1993 data. CONCLUSIONS: Predictors of major complications identified in selected populations also apply currently in broad-based practice. From these variables, a predictive index can stratify patients into risk groups before angioplasty, thus aiding in risk assessment, resource allocation and risk adjustment.

Angioplasty, Balloon, Coronary↗
PubMed1989

Improving the sensitivity of the Barthel Index for stroke rehabilitation.

The Barthel Index is considered to be the best of the ADL measurement scales. However, there are some scales that are more sensitive to small changes in functional independence than the Barthel Index. The sensitivity of the Barthel Index can be improved by expanding the number of categories used to record improvement in each ADL function. Suggested changes to the scoring of the Barthel Index, and guidelines for determining the level of independence are presented. These modifications and guidelines were applied in the assessment of 258 first stroke patients referred for inpatient comprehensive rehabilitation in Brisbane, Australia during 1984 calendar year. The modified scoring of the Barthel Index achieved greater sensitivity and improved reliability than the original version, without causing additional difficulty or affecting the implementation time. The internal consistency reliability coefficient for the modified scoring of the Barthel Index was 0.90, compared to 0.87 for the original scoring.

Activities of Daily Living↗
PubMed1992

Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases.

Administrative databases are increasingly used for studying outcomes of medical care. Valid inferences from such data require the ability to account for disease severity and comorbid conditions. We adapted a clinical comorbidity index, designed for use with medical records, for research relying on International Classification of Diseases (ICD-9-CM) diagnosis and procedure codes. The association of this adapted index with health outcomes and resource use was then examined with a sample of Medicare beneficiaries who underwent lumbar spine surgery in 1985 (n = 27,111). The index was associated in the expected direction with postoperative complications, mortality, blood transfusion, discharge to nursing home, length of hospital stay, and hospital charges. These associations were observed whether the index incorporated data from multiple hospitalizations over a year's time, or just from the index surgical admission. They also persisted after controlling for patient age. We conclude that the adapted comorbidity index will be useful in studies of disease outcome and resource use employing administrative databases.

Aged↗
PubMed1994

An index of symptoms for infection with human immunodeficiency virus: reliability and validity.

The objective of this study was to evaluate the reliability and validity of a brief index to measure symptoms in individuals infected with human immunodeficiency virus (HIV). From an ambulatory clinic that specializes in the care of HIV-infected individuals at a university hospital in northeast Ohio, 148 randomly selected outpatients (predominantly homosexual men) with a broad spectrum of HIV disease were enrolled in a prospective, cohort study. In standard interviews, patients rated the frequency of 36 symptoms related to HIV infection on an ordinal scale from zero (never) to three (daily); these interviews were repeated and outcomes determined every 3 months for one year. Clinical data were abstracted from the medical record with a standard chart review. Using specific criteria, 12 symptoms were selected for the HIV Symptom Index: fatigue, fevers, headache, imbalance, paresthesias, memory loss, cough, nausea, diarrhea, sadness, sleep disturbance, and skin problems. The HIV Symptom score (the sum of frequency ratings for the 12 symptoms) ranged from 0 to 31 with a mean of 9.4 (+/- SD 6.6). The test-retest reliability was high (intraclass correlation coefficient = 0.92) as was the internal consistency (Cronbach's alpha = 0.79). The validity of the index was established with three observations. (1) The HIV Symptom Index makes clinical sense and includes a representative spectrum of symptoms of infection. (2) Symptom Index scores were greater in patients with more advanced disease and in patients who were functionally impaired. (3) The Index was responsive to changes in health as the disease progressed.(ABSTRACT TRUNCATED AT 250 WORDS)

AIDS-Related Complex↗
PubMed1996

Searching for an improved clinical comorbidity index for use with ICD-9-CM administrative data.

We studied approaches to comorbidity risk adjustment by comparing two ICD-9-CM adaptations (Deyo, Dartmouth-Manitoba) of the Charlson comorbidity index applied to Massachusetts coronary artery bypass surgery data. We also developed a new comorbidity index by assigning study-specific weights to the original Charlson comorbidity variables. The 2 ICD-9-CM coding adaptations assigned identical Charlson comorbidity scores to 90% of cases, and specific comorbidities were largely found in the same cases (kappa values of 0.72-1.0 for 15 of 16 comorbidities). Meanwhile, the study-specific comorbidity index identified a 10% subset of patients with 15% mortality, whereas the 5% highest-risk patients according to the Charlson index had only 8% mortality (p = 0.01). A model using the new index to predict mortality had better validated performance than a model based on the original Charlson index (c = 0.74 vs. 0.70). Thus, in our population, the ICD-9-CM adaptation used to create the Charlson score mattered little, but using study-specific weights with the Charlson variables substantially improved the power of these data to predict mortality.

Aged↗
PubMed1995

Multichannel detection of magnetic compound action fields with stimulation of the index and little fingers.

Magnetic compound action fields (CAFs) over the right arm were measured from 63 sensor positions with two 7-channel SQUID gradiometer systems following electrical stimulation of the index and little fingers as well as the ring finger separately. The wave forms of the CAFs were primarily biphasic, corresponding to the depolarization and repolarization currents of the stimulated nerves. Maximum amplitudes of the CAFs were 60-140 fT for the index finger stimulation and 40-90 fT for the little finger stimulation. The field mapping of the CAFs revealed a propagating quadrupolar pattern with different distributions for the index and little fingers. The results agree with the anatomical location of the median and ulnar nerves for the index and little finger stimulation respectively. The isofield maps, due to ring finger stimulation, showed complex patterns as a result of simultaneous activation of the median and ulnar nerves. By comparing the amplitudes of the maxima of the CAFs due to index finger stimulation with those after median nerve stimulation at the wrist, the numerical ratios of the constituent digital nerve fibers for the index finger within the median nerve at the wrist were estimated. The ratios of 0.14-0.41 (mean 0.27), determined with measurement of the CAFs, are fairly consistent with those calculated from the reported histological data.

Adult↗
PubMed1992

Development and evaluation of an index to predict early postmenopausal bone loss.

An index to predict individual postmenopausal bone loss is presented. The index is developed by means of data from a 10-year prospective Norwegian study in which bone mass of the distal forearm was measured annually in 73 women. All the women were 47 years old and premenopausal at inclusion. Independent risk factors for postmenopausal bone loss were identified by applying multivariate regression analysis on anthropometric, biochemical, nutritional, and life-style variables measured at menopause. The analysis identified low body weight, reduced renal phosphate reabsorption, and smoking as significant independent risk factors, and by means of these three factors a predictive index for postmenopausal bone loss was developed. This index was validated by using data from a 10-year longitudinal Dutch study, in which bone mass of the proximal radius was measured annually in 86 women, aged between 49 and 57 years and perimenopausal at inclusion. We defined women with the highest index score as "high-risk persons." According to this definition approximately 25% of the perimenopausal women were classified as high-risk persons, and the estimated sensitivity/specificity/positive predictive power were 36%, 89%, and 74%, respectively, when used to select women with a postmenopausal bone loss above average. We conclude that the index may be helpful in identifying healthy perimenopausal women in whom bone mass measurements should be considered.

Female↗
PubMed2006

Surgical site infection in patients submitted to digestive surgery: risk prediction and the NNIS risk index.

BACKGROUND: Some problems have been reported with the power of the National Nosocomial Infection Surveillance (NNIS) risk index to predict the risk of surgical site infections (SSI) for specific procedures. OBJECTIVES: To develop an alternative risk prediction index for SSI and to compare the performance with the NNIS index. METHODS: A prospective cohort study was carried out with all (609) patients submitted to digestive tract surgery in 2 general teaching hospitals in the city of São Paulo, Brazil, from August 2001 through March 2002. RESULTS: The final incidence rate of SSI was 24.5%; 149 cases of SSI were identified: 33 (22.1%) during hospitalization and 116 (77.9%) after discharge. Logistic multivariate analysis was used for construction of the model. Obesity, surgery risk, adjusted duration, and video laparoscopic surgery were statistically significant (P < .05) for all previous procedures. The performance of the NNIS model in this study showed a low predictive capacity for the occurrence of SSI as determined by the receiver operating characteristic (ROC) curve (0.627; 95% CI: 0.575-0.678) compared with the alternative model developed with this population (0.732; 95% CI: 0.685-0.779). CONCLUSION: The presence of obesity, adjusted duration, and surgery risk significantly increased the risk for SSI. The NNIS risk index was not significant for SSI in the sample studied, and laparoscopic access was associated with a significant reduction in the risk for SSI. Although the NNIS index is a well-known and simple index, other models depicting variables related to SSI with a better sensitivity and specificity can be developed. Additional studies are required to confirm our results.

Adolescent↗
PubMed2005

Relation of systemic ventricular function quantified by myocardial performance index (Tei) to cardiopulmonary exercise capacity in adults after Mustard procedure for transposition of the great arteries.

After Mustard repair for transposition of the great arteries, the right ventricle serves as a chronically overloaded systemic ventricle (SV). Thus, during long-term follow-up, dysfunction of the right ventricle with consecutive heart failure (HF) is not unusual. Early signs and symptoms of HF are depressed parameters of right ventricular (RV) function at rest and exercise intolerance. It was hypothesized that the measurement of RV function parameters, N-terminal pro-brain natriuretic peptide (NT-pro-BNP), and peak oxygen uptake (VO2max) during exercise testing were suitable for the early detection of subclinical HF. In 33 asymptomatic adolescents and adults who had undergone Mustard repair, RV function was analyzed by the myocardial performance index (Tei index). NT-pro-BNP and VO2max were also determined. The corresponding data from 52 patients operated on for left-to-right shunt defects without residual lesions served as reference data. In patients who underwent the Mustard procedure, the Tei index and NT-pro-BNP were elevated (mean Tei index of the SV 0.63 +/- 0.17 vs 0.34 +/- 0.05, p <0.002; mean NT-pro-BNP 240 +/- 230 vs 57 +/- 39 pg/ml, p <0.0001), and VO2max was reduced (27 +/- 6 vs 32 +/- 6 ml x kg(-1) x min(-1), p <0.002). A good correlation was found between the Tei index and VO2max (r = -0.83, p <0.0001). In conclusion, RV function is depressed in most patients with Mustard repair. Ventricular dysfunction in such asymptomatic or minimally symptomatic patients can be detected by measurement of the Tei index, NT-pro-BNP, and VO2max. These parameters are simple and reliable screening methods to stratify patients with impaired cardiac dysfunction before they become symptomatic.

Adolescent↗
PubMed2005

Feasibility study of the retrospective use of the Adult Comorbidity Evaluation index (ACE-27) in patients with cancer of the head and neck who had radiotherapy.

The Adult Comorbidity Evaluation index (ACE-27) is a relatively new measure of comorbidity and the aim of this study was to assess the feasibility of retrospective examination of casenotes to estimate this index in patients who were given radiotherapy for head and neck cancer. We examined the casenotes of 157 of 168 consecutive patients diagnosed with an index primary tumour of the head and neck at the Clatterbridge Centre of Oncology in 1992 and 1993. Three comorbidity measures, the ACE-27, Charlson comorbidity index (CL) and Washington University Head Neck Cancer Index (WUHNCI) were calculated. In the grading of the ACE-27, 5 patients (3%) were grade 3, 21 (13%) were grade 2, 57 (36%) were grade 1 and 74 (47%) were grade zero. There was a trend in survival by ACE-27 grading with little difference between mild and moderate severity (p=0.08). There were no significant correlations between survival and either the Charlson index (p=0.80) or the WUHNCI (p=0.68). There were no significant correlations of any of the indices or of clinico-demographic factors with recurrence rates.

Adult↗
PubMed2005

The Tei index for evaluation of fetal myocardial performance in sick fetuses.

OBJECTIVE: The Tei index is a useful, new, noninvasive Doppler index of combined systolic and diastolic function calculated by isovolumic relaxation time plus isovolumic contraction time divided by ejection time. Sick fetuses were evaluated with the Tei index. METHODS: The study group underwent two-dimensional/Doppler echocardiographic measurement of their Tei index and included 10 monochorionic diamniotic (MD) twin pairs with non-twin to twin transfusion syndrome (TTTS), 4 twin pairs with TTTS, 12 fetuses with intrauterine growth retardation (IUGR), 14 fetuses of diabetic mothers, 3 hydrops fetalis fetuses, 8 fetuses of mothers treated with a tocolytic agent, and 40 normal fetuses (control group). RESULTS: The Tei indices in the following groups were significantly higher than the control: recipient fetuses in TTTS, large for gestational age (LGA) fetuses of diabetic mothers, and fetuses with hydrops fetalis. CONCLUSION: The Tei index may be a useful tool for the assessment of fetal cardiac status in a variety of sick fetuses. Recipient fetuses in TTTS, LGA fetuses of diabetic mothers, and hydrops fetalis fetuses may have abnormal myocardial performance. The Tei index readily provides early detection of diminished myocardial function, particularly ventricular dysfunction.

Cardiomyopathies↗
PubMed2005

Charlson comorbidity index as a predictor of long-term outcome after surgery for nonsmall cell lung cancer.

OBJECTIVE: To evaluate the impact of the Charlson comorbidity index on long-term survival in nonsmall cell lung cancer surgery and determine whether this index is a better predictor of long-term survival than individual comorbid conditions. METHODS: From January 1989 to December 2001, 433 (340 men, 93 women) consecutive curative resections for nonsmall cell lung cancer were performed. Each patient was preoperatively assessed according to the Charlson comorbidity index. Survival curves were estimated by the Kaplan-Meier method. Risk factors for overall and disease free survival were determined by univariate and multivariate Cox regression analysis. RESULTS: The patients ranged in age from 37 to 82 years, with a mean age of 65 years. Hospital mortality was 3.7%. Five-year overall and disease free survival was 45 and 43%, respectively. Among patients with Charlson comorbidity grade 0, 5-year overall survival was 52%, among patients with Charlson comorbidity grade 1-2 it was 48%, and among patients with Charlson comorbidity grade > or =3 it was 28%. Univariate analysis showed that male gender, age, congestive heart failure, chronic pulmonary disease, Charlson comorbidity index, clinical stage, pathological stage, and type of resection were significantly associated with an impaired survival. Multivariate analysis showed that age (relative risk, 1.02; 95% confidence interval, 1.01-1.03), Charlson comorbidity grade 1-2 (relative risk, 1.4; 95% confidence interval, 1.0-1.8), Charlson comorbidity grade > or =3 (relative risk, 2.2; 95% confidence interval, 1.5-3.1), bilobectomy (relative risk, 1.7; 95% confidence interval, 1.2-2.5), pneumonectomy (relative risk, 1.5; 95% confidence interval, 1.1-2.0), pathological stage IB (relative risk, 1.5; 95% confidence interval, 1.1-2.2), IIB (relative risk, 1.9; 95% confidence interval, 1.2-3.0), IIIA (relative risk, 1.9; 95% confidence interval, 1.1-3.1), IIIB (relative risk, 2.8; 95% confidence interval, 1.2-6.8), and IV (relative risk, 12.4; 95% confidence interval, 3.2-48.2), were associated with an impaired survival. CONCLUSIONS: The Charlson comorbidity index is a better predictor of survival than individual comorbid conditions in nonsmall cell lung cancer surgery. We recommend the use of a validated comorbidity index in the selection of patients for NSCLC surgery.

Adult↗
PubMed2006

Evaluation of the myocardial performance index for early detection of mitoxantrone-induced cardiotoxicity in patients with multiple sclerosis.

AIMS: Multiple sclerosis is the most common cause of neurological disability in young adults. Mitoxantrone is a synthetic anthracenedione, recently approved for the treatment of worsening multiple sclerosis, which is known to induce cardiotoxicity. This study was designed to evaluate the early alterations in left ventricular function in patients with multiple sclerosis receiving mitoxantrone, by the use of the myocardial performance index, a new parameter of global (systolic and diastolic) ventricular function. METHODS AND RESULTS: The study included 29 Caucasian patients with multiple sclerosis (mean age 41.8+/-9.3 years, 12 males and 17 females) treated with mitoxantrone (mean cumulative dose 30.8+/-18.2 mg/m(2)) who were compared with 28 healthy subjects (mean age 37.8+/-11.8 years, 13 males and 15 females). Both groups underwent a complete two-dimensional and Doppler echocardiography including assessment of the mitral inflow and left ventricular outflow patterns for estimation of the Doppler-derived myocardial performance index. This parameter is defined as the sum of isovolumic contraction time and isovolumic relaxation time, divided by ventricular ejection time. No differences were observed in blood pressure, heart rate, left ventricular diameters, mass and ejection fraction in multiple sclerosis patients compared to the controls. The mitral flow pattern showed a significant decrease of E wave calculated as peak velocity (E(pv)) (63.3+/-13.4 vs. 77.2+/-17.2, P<0.002) and time velocity integral (E(tvi)) (8.8+/-1.9 vs. 10.3+/-2.4, P<0.02), with a significant decrease of E(pv)/A(pv) ratio and a non-significant decrease of E(tvi)/A(tvi) ratio in the patients. In addition, E-wave deceleration time was significantly increased in multiple sclerosis patients compared to controls (178.2+/-30.2 vs. 137.9+/-14.7, P<0.0001). The mean value of myocardial performance index was 0.55+/-0.1 in patients compared to 0.37+/-0.06 in the controls (P<0.0001). A significant correlation between the given cumulative dose of mitoxantrone and myocardial performance index (r=0.67, P<0.001) and E-wave deceleration time (r=0.45, P<0.001) respectively were demonstrated. CONCLUSION: The myocardial performance index represents a parameter of combined systolic and diastolic myocardial performance strongly correlated with the given cumulative dose of mitoxantrone. The myocardial performance index may be an adjunctive parameter to conventional echocardiography for detecting sub-clinical cardiotoxicity of mitoxantrone in the clinical management of the multiple sclerosis patients.

Adult↗
PubMed2006

An extended index to quantify normality of gait in children.

Clinical gait analysis aims to quantify and assess the mechanics of walking and identify deviations from 'normal' movement patterns. To facilitate the use of clinical equipment, protocols are required to process data and produce a few meaningful summary measurements which can, in turn, be used to flag gait abnormalities. Earlier work produced a one-dimensional index of gait, calculated from sagittal hip, knee and ankle rotation angle patterns. The objective of this study was to extend the original index, incorporating kinematic and kinetic data from multiple planes, while allowing for correlations between component measures. A one-dimensional index of normal gait was developed, based on normative gait data (N=45 children, aged 3-13 years). The new one-dimensional index was calculated using correlation patterns between seven component indices, each of which has diagnostic interpretation. The effectiveness of the new index was tested using immature normative data (N=14) and hypotonic data (N=10). Approximately 85% of immature normative children and 100% of hypotonic children were classified as either unusual or extreme by the one-dimensional index. These data reduction protocols improve objective gait analyses in the clinical setting.

Adolescent↗
PubMed2006

Unified rate-dependent atrioventricular nodal function: consistent recovery and fatigue properties revealed with S1S2S3 protocols and different recovery indexes.

BACKGROUND: Rate-dependent nodal properties are commonly assessed with premature protocols performed at different basic rates. Because characteristics of responses differ with recovery time index, the true nature of nodal rate-dependent properties is elusive. OBJECTIVES: The purpose of this study was to reveal consistent nodal rate-dependent properties regardless of selected recovery index. METHODS: With S(1)S(2)S(3) protocols, we independently varied basic and pretest cycle lengths and thereby distinguished cumulative from noncumulative effects of rate on nodal conduction time in rabbit heart preparations. Nodal responses to 30 basic and pretest cycle length combinations (five with identical basic and pretest cycles as in standard protocols) were analyzed using both atrial (AA) and His-atrial (HA) intervals as recovery index. RESULTS: AA and HA curves had an identical shape for any of 30 steady-state conditions. When assessed with constant pretest cycle lengths, cumulative effects (fatigue) of shortened basic cycle lengths were also independent of recovery index. Shortening of pretest cycle length at fixed basic rates led to apparent inhibitory and facilitatory effects when assessed with AA and HA curves, respectively. These effects vanished when a single long cycle was inserted after the pretest cycle. In all responses including those obtained with standard protocols, combined effects of basic and pretest cycle lengths set nodal conduction time. CONCLUSION: S(1)S(2)S(3) protocols reveal consistent nodal recovery and fatigue properties regardless of recovery index used. Changes in nodal function curves arising from the use of different recovery indexes mainly depend on pretest effects. This study provides a new approach to a unified interpretation of nodal recovery and fatigue properties.

Analysis of Variance↗