Electrocardiographic criteria for vagotonia-validation with pharmacological parasympathetic blockade in healthy subjects

Sudden Cardiac Death Risk Stratification of the Early Repolarization Syndrome: An Updated Review of the Literature

PURPOSE OF REVIEW

Early repolarization syndrome (ERS), once thought to be innocuous, has now been shown to be responsible for ventricular arrythmias and sudden cardiac death occurrence. This review will help the clinician to identify the patients who are most at risk for arrhythmias, so that they can adopt a preventive or secondary treatment approach, either of which is still poorly defined.

RECENT FINDINGS

Patients at high risk are found to be particularly young men, with a personal or family history of syncope or sudden death, who have an inferolateral ER on the electrocardiogram, more elevated J-point, longer J-wave duration and wider J angle, a horizontal or descending ST segment, lower T/R ratio, and small and/or inverted waves. The association with a structural heart disease or another channelopathy potentiates this arrhythmic risk. Taken together, these parameters allow prediction of the malignancy of ER pattern with a certain reliability. Further research is however needed to develop concrete risk stratification algorithms and the therapeutic strategies taken in function of it.

Acute effects of mixed circuit training on hemodynamic and cardiac autonomic control in chronic hemiparetic stroke patients: A randomized controlled crossover trial

Objectives: To investigate whether a single bout of mixed circuit training (MCT) can elicit acute blood pressure (BP) reduction in chronic hemiparetic stroke patients, a phenomenon also known as post-exercise hypotension (PEH).

Methods: Seven participants (58 ± 12 years) performed a non-exercise control session (CTL) and a single bout of MCT on separate days and in a randomized counterbalanced order. The MCT included 10 exercises with 3 sets of 15-repetition maximum per exercise, with each set interspersed with 45 s of walking. Systolic (SBP) and diastolic (DBP) blood pressure, mean arterial pressure (MAP), cardiac output (Q), systemic vascular resistance (SVR), baroreflex sensitivity (BRS), and heart rate variability (HRV) were assessed 10 min before and 40 min after CTL and MCT. BP and HRV were also measured during an ambulatory 24-h recovery period.

Results: Compared to CTL, SBP (∆-22%), DBP (∆-28%), SVR (∆-43%), BRS (∆-63%), and parasympathetic activity (HF; high-frequency component: ∆-63%) were reduced during 40 min post-MCT (p < 0.05), while Q (∆35%), sympathetic activity (LF; low-frequency component: ∆139%) and sympathovagal balance (LF:HF ratio: ∆145%) were higher (p < 0.001). In the first 10 h of ambulatory assessment, SBP (∆-7%), MAP (∆-6%), and HF (∆-26%) remained lowered, and LF (∆11%) and LF:HF ratio (∆13%) remained elevated post-MCT vs. CTL (p < 0.05).

Conclusion: A single bout of MCT elicited prolonged PEH in chronic hemiparetic stroke patients. This occurred concurrently with increased sympathovagal balance and lowered SVR, suggesting vasodilation capacity is a major determinant of PEH in these patients. This clinical trial was registered in the Brazilian Clinical Trials Registry (RBR-5dn5zd), available at https://ensaiosclinicos.gov.br/rg/RBR-5dn5zd.

Clinical Trial Registration:https://ensaiosclinicos.gov.br/rg/RBR-5dn5zd, identifier RBR-5dn5zd

Postexercise hypotension and related hemodynamic responses to cycling under heat stress in untrained men with elevated blood pressure

PURPOSE

To investigate the effect of heat stress on postexercise hypotension.

METHODS

Seven untrained men, aged 21-33 years, performed two cycling bouts at 60% of oxygen uptake reserve expending 300 kcal in environmental temperatures of 21 °C (TEMP) and 35 °C (HOT) in a randomized, counter-balanced order. Physiological responses were monitored for 10-min before and 60-min after each exercise bout, and after a non-exercise control session (CON). Blood pressure (BP) also was measured during the subsequent 21-h recovery period.

RESULTS

Compared to CON, systolic, and diastolic BPs were significantly reduced in HOT (Δ = - 8.3 ± 1.6 and - 9.7 ± 1.4 mmHg, P < 0.01) and TEMP (Δ = - 4.9 ± 2.1 and - 4.5 ± 0.9 mmHg, P < 0.05) during the first 60 min of postexercise recovery. Compared to TEMP, rectal temperature was 0.6 °C higher (P = 0.001), mean skin temperature was 1.8 °C higher (P = 0.013), and plasma volume (PV) was 2.6 percentage points lower (P = 0.005) in HOT. During the subsequent 21-h recovery period systolic BP was 4.2 mmHg lower in HOT compared to CON (P = 0.016) and 2.5 mmHg lower in HOT compared to TEMP (P = 0.039).

CONCLUSION

Exercise in the heat increases the hypotensive effects of exercise for at least 22 h in untrained men with elevated blood pressure. Our findings indicate that augmented core and skin temperatures and decreased PV are the main hemodynamic mechanisms underlying a reduction in BP after exercise performed under heat stress.

Acute Effect of Aerobic and Strength Exercise on Heart Rate Variability and Baroreflex Sensitivity in Men With Autonomic Dysfunction

de Paula, T, Neves, MF, da Silva Itaborahy, A, Monteiro, W, Farinatti, P, and Cunha, FA. Recovery pattern of cardiac autonomic control after aerobic and strength exercises in overweight prehypertensive men. J Strength Cond Res 33(10): 2743-2752, 2019-The extent to which postexercise cardiac autonomic control depends on exercise modality remains unclear, particularly among individuals with autonomic dysfunction (cardiac autonomic dysfunction [CADysf]). This study compared heart rate variability (HRV) and baroreflex sensitivity (BRS) responses to acute aerobic exercise (AE) and strength exercise (SE) in men with CADysf. Twenty men were assigned into control (n = 10: 33.8 ± 3.0 years; 23.7 ± 1.5 kg·m) and CADysf (n = 10: 36.2 ± 9.8 years; 28.4 ± 2.6 kg·m) groups. Cardiac autonomic dysfunction underwent AE, SE, and a nonexercise control day (control session [CTL]) in a randomized, counter-balanced order. Heart rate variability and BRS were assessed in a supine position during 25 minutes of recovery after AE, SE, and CTL. Both HRV indices (p ≤ 0.05; effect size [Cohen's d]: >1.4) and BRS at rest were significantly lower in CADysf than those in controls (p < 0.01; effect size [Cohen's d]: ≥1.36). In CADysf, postexercise increases in heart rate, sympathetic activity (low-frequency [LF] band), and sympathovagal balance (LF:high-frequency [HF] ratio), as well as decreases in R-R interval, parasympathetic activity (HF band), and BRS were observed in AE (p ≤ 0.05; effect size [Cohen's d]: ≥1.31) and SE (p ≤ 0.05; effect size [Cohen's d]: ≥0.79) vs. CTL, but changes were larger after AE than SE (p ≤ 0.05; effect size [Cohen's d]: ≥0.73). In conclusion, both AE and SE elicited postexercise changes in HRV and BRS among CADysf men, primarily reflected by lowered vagal modulation, increased sympathovagal balance, and a delayed BRS recovery pattern. However, those changes seem to be more likely to occur after AE than SE.

Four-second dynamic exercise testing (T4S) for the assessment of cardiac vagal modulation in obese adolescents

BACKGROUND

Reduced vagal activity is often present in obese adolescents. Simple and practical strategies for the assessment of isolate parasympathetic outflow in this population are therefore useful.

OBJECTIVES

To compare the methods derived from heart rate variability (HRV) analysis at rest and 4 s exercise testing (T4S) for the assessment of cardiac parasympathetic modulation in adolescents classified as obese (OB) or with normal weight (NW). Additionally, associations between total and trunk fat versus autonomic modulation determined by the two methods were calculated.

APPROACH

A cross-sectional study was conducted with 50 adolescents (26 OB and 24 NW, 14.7  ±  1.5 years), comparing autonomic indices provided by HRV and T4S. Body fractioning was determined employing dual-energy x-ray absorptiometry (DXA).

MAIN RESULTS

The cardiac vagal index (CVI) obtained from T4S and standard time- and frequency-domain HRV measures were lower in OB versus NW (P  ⩽  0.05). Correlations between CVI and HRV indices of cardiac vagal modulation were as follows: CVI versus RMSSD (r  =  0.44; P  =  0.003); CVI versus pNN50 (r  =  0.32; P  =  0.04); CVI versus HF (r  =  0.35; P  =  0.02). Associations between body fat, android/gynoid ratio, and percent trunk fat versus CVI were of similar magnitude and direction than versus HRV indices.

SIGNIFICANCE

The T4S proved to be adequate to detect cardiac parasympathetic impairment in obese adolescents. Moreover, vagal modulation assessed by HRV and T4S inversely correlated with visceral adipose tissue. These findings along with the simplicity and safety of the T4S should encourage its use in the assessment of cardiac parasympathetic modulation in obese pediatric populations.

The use of tenoxicam to prevent symptoms of discomfort induced by vagotonia during uterus manipulation in cesarean sections

PURPOSE

Symptoms such as nausea, vomiting, tightness of the chest, bradycardia, and shoulder or abdominal discomfort, caused by vagotonia occurring during uterus manipulation, have concerned healthcare professionals for some time. Patients sometimes report these symptoms when undergoing spinal anesthesia for cesarean sections (CSs). We designed a prospective, double-blind study to investigate the effectiveness of tenoxicam in preventing these symptoms of discomfort.

METHODS

A total of 105 American Society of Anesthesiologists (ASA) class I-II nulliparous pregnant women, who were scheduled for a CS, were enrolled into this prospective, double-blind study. Spinal anesthesia was conducted to reach a peak dermatome level of no more than T3. The 100 patients were randomly divided into 2 groups having completed study course: Group T (N = 50) received a 20 mg dose of tenoxicam in 5 mL of normal saline (NS) immediately after skin incision and Group N (N = 50) only received 5 mL NS. The incidence and severity of the symptoms experienced by the patients were recorded by a nurse anesthetist who was blinded to the injection regimen the patients were receiving. A chi-square test was used for statistical analysis t test and P < .05 was defined as significant.

RESULTS

The incidence and degree of severity of nausea and vomiting were same in both the groups. The incidence and degree of severity of bradycardia, nausea, vomiting, tightness of the chest, shoulder discomfort, and abdominal discomfort were lower in Group T than in Group N.

CONCLUSION

Tenoxicam might theoretically block the parasympathetic vagus pathway and decrease the visceral pain or visceral-specific symptoms, alleviating the symptoms caused by vagotonia. However, the prophylactic effect of tenoxicam in reducing the incidence and severity of nausea and vomiting was not statistically significant. This could be because nausea and vomiting are not solely caused by vagotonia, but also by other mechanisms.

12-lead electrocardiogram features of arrhythmic risk: A focus on early repolarization

The 12-lead electrocardiogram (ECG) is still the most used tool in cardiology clinical practice. Considering its easy accessibility, low cost and the information that it provides, it remains the starting point for diagnosis and prognosis. More specifically, its ability to detect prognostic markers for sudden cardiac death due to arrhythmias by identifying specific patterns that express electrical disturbances of the heart muscle, which may predispose to malignant arrhythmias, is universally recognized. Alterations in the ventricular repolarization process, identifiable on a 12-lead ECG, play a role in the genesis of ventricular arrhythmias in different cardiac diseases. The aim of this paper is to focus the attention on a new marker of arrhythmic risk, the early repolarization pattern in order to highlight the prognostic role of the 12-lead ECG.

Postexercise hypotension after maximal short-term incremental exercise depends on exercise modality

This study investigated postexercise hypotension (PEH) after maximal cardiopulmonary exercise testing (CPET) performed using different exercise modalities. Twenty healthy men (aged 23 ± 3 years) performed 3 maximal CPETs (cycling, walking, and running), separated by 72 h in a randomized, counter-balanced order. Systolic (SBP) and diastolic blood pressure (DBP), heart rate, cardiac output, systemic vascular resistance (SVR), autonomic function (spontaneous baroreflex sensitivity (BRS) and heart rate variability (HRV)), and energy expenditure (EE) were assessed during a 60-min nonexercise control session and for 60 min immediately after each CPET. Total exercise volume (EE during CPET plus 60 min recovery) was significantly higher in running versus cycling and walking CPETs (P ≤ 0.001). Compared with control, only SBP after running CPET was significantly reduced (Δ = −6 ± 8 mm Hg; P < 0.001). Heart rate and cardiac output were significantly increased (P < 0.001) and SVR significantly decreased (P < 0.001) postexercise. BRS and HRV decreased after all CPETs (P < 0.001), whereas sympatho-vagal balance (low- and high-frequency (LF:HF) ratio) increased significantly after all exercise conditions, especially after running CPET (P < 0.001). Changes in SVR, BRS, sympathetic activity (low-frequency component of HRV), and LF:HF ratio were negatively correlated to variations in SBP (range −0.69 to −0.91; P < 0.001) and DBP (range −0.58 to −0.93; P ≤ 0.002). These findings suggest that exercise mode or the total exercise volume are major determinants of PEH magnitude in healthy men. Because of the running CPET, the PEH was primarily related to a decrease in SVR and to an increase in sympatho-vagal balance, which might be a reflex response to peripheral vasodilatation after exercise.

4-Second Exercise Test: Reference Values for Ages 18-81 Years

Background

Physiological reflexes modulated primarily by the vagus nerve allow the heart to decelerate and accelerate rapidly after a deep inspiration followed by rapid movement of the limbs. This is the physiological and pharmacologically validated basis for the 4-s exercise test (4sET) used to assess the vagal modulation of cardiac chronotropism.

Objective

To present reference data for 4sET in healthy adults.

Methods

After applying strict clinical inclusion/exclusion criteria, 1,605 healthy adults (61% men) aged between 18 and 81 years subjected to 4sET were evaluated between 1994 and 2014. Using 4sET, the cardiac vagal index (CVI) was obtained by calculating the ratio between the duration of two RR intervals in the electrocardiogram: 1) after a 4-s rapid and deep breath and immediately before pedaling and 2) at the end of a rapid and resistance-free 4-s pedaling exercise.

Results

CVI varied inversely with age (r = -0.33, p < 0.01), and the intercepts and slopes of the linear regressions between CVI and age were similar for men and women (p > 0.05). Considering the heteroscedasticity and the asymmetry of the distribution of the CVI values according to age, we chose to express the reference values in percentiles for eight age groups (years): 18–30, 31–40, 41–45, 46–50, 51–55, 56–60, 61–65, and 66+, obtaining progressively lower median CVI values ranging from 1.63 to 1.24.

Conclusion

The availability of CVI percentiles for different age groups should promote the clinical use of 4sET, which is a simple and safe procedure for the evaluation of vagal modulation of cardiac chronotropism.

Early repolarization is associated with atrial and ventricular tachyarrhythmias in patients with acute ST elevation myocardial infarction undergoing primary percutaneous coronary intervention

BACKGROUND

Recent studies found that early repolarization (ER) is significantly more common in survivors of aborted sudden cardiac death. We hypothesized that ER might be more common in patients with ST elevation myocardial infarction (STEMI) who have complications of atrial and ventricular arrhythmias.

METHODS

This study included 266 patients with acute STEMI undergoing primary percutaneous coronary intervention. Twelve-lead electrocardiograms were analyzed for ER, defined as J-point elevation ≥ 0.1 mV and "notching" and "slurring" of the terminal part of the QRS complex in at least 2 lateral or inferior leads. Acute and late atrial and ventricular arrhythmic events were evaluated.

RESULTS

The ER pattern was observed in 76 patients (28.6%). Atrial arrhythmia [21/76 (27.6%) vs. 22/190 (11.6%), p=0.001] and ventricular arrhythmia [16/76 (21.1%) vs. 16/190 (8.4%), p=0.004] were more frequently complicated in patients with ER than those without during hospitalization. ER was a significant independent predictor of developing atrial (HR=2.682, 95% CI=1.355-5.310, p=0.005) and ventricular arrhythmia (HR=2.936, 95% CI=1.360-6.335, p=0.006). Three patients with ER and ventricular fibrillation expired during hospitalization [3.9% (3/76) vs. 0% (0/190), p=0.023]. However, the presence of ER did not affect the late recurrence of atrial and ventricular arrhythmia.

CONCLUSIONS

The ER pattern is commonly observed in patients with STEMI and associated with atrial and ventricular tachyarrhythmia during acute setting.

Resting ST amplitude: prognosis and normal values in an ambulatory clinical population

BACKGROUND

There is limited data describing ST segment amplitude in apparently healthy, asymptomatic populations. We analyzed ST amplitude in the standard resting electrocardiogram (ECG) in a large, multiethnic, stable, clinical population.

METHODS

We evaluated computerized ST amplitude measurements from the resting ECGs of 29,281 ambulatory outpatients collected between 1987 and 1999 at the Palo Alto, VA. With the PR interval as the isoelectric line, both elevation criteria (≥0.1 mV, ≥0.15 mV, and ≥0.2 mV) and depression criteria (≤-0.05 mV or ≤-0.1 mV), were applied. Cox-Hazard survival analysis techniques were used to demonstrate in which leads ST amplitude displacement was associated with cardiovascular (CV) death. To create a cohort without ECG patterns clearly associated with disease, we excluded ECGs with inverted T waves, wide QRS, or diagnostic Q waves and coded the remaining "normal" ECGs for ST elevation and depression to determine a normal range.

RESULTS

The only ST amplitudes that were significantly and independently associated with time to CV death when adjusted for age, gender, and ethnicity were ST depression in all of the lateral leads (I, V4 -V6 ). When isolated to the inferior leads, (II and AVF), no ST amplitude criteria were associated with CV death. Among the "normal ECG" subgroup the precordial leads exhibited the greatest median ST amplitudes and the most significant differences between the leads, genders and ethnicities.

CONCLUSIONS

Significant differences in ST amplitude were present in the precordial leads according to gender and ethnicity. This was particularly apparent when amplitude threshold were set for comparisons. Our findings provide the normal range for ST amplitude that when exceeded, should raise clinical concern.

Novel indexes of heterogeneity of ventricular repolarization in subjects with early repolarization pattern

AIM

The presence of early repolarization (ER) in inferior or inferolateral leads has been associated with malignant arrhythmias and increased mortality. Transmural dispersion of repolarization (TDR) has been proposed to underlie arrhythmogenesis in J-wave syndromes. The present study investigated specific electrocardiographic (ECG) markers including Tpeak-Tend interval and (Tpeak-Tend)/QT ratio that reflect TDR in subjects with ER.

METHODS AND RESULTS

The ECGs of 47 healthy individuals (43 males, mean age: 45.7 ± 13.1 years) with an ER pattern in lateral (n = 15) or infero-lateral leads (n = 32) who successfully completed an exercise stress test were analysed at rest, peak workload, and recovery. The ER pattern was defined as slurring or notching of the terminal part of the QRS complex (J-point) ≥ 1 mm, in at least two contiguous leads. Thirty-five age- and sex-matched healthy subjects without ER (28 males, mean age: 48.6 ± 10.2 years) served as comparative controls. Subjects with ER displayed increased Tpeak-Tend interval in lead V(2), Tpeak-Tend dispersion of the precordial leads, and (Tpeak-Tend)/QT ratio in lead V(2) compared with those without ER in all three phases of the exercise test (P < 0.05). In addition, Tpeak-Tend dispersion and the (Tpeak-Tend)/QT ratio in lead V(2) were significantly increased at recovery phase compared with peak exercise only in subjects with ER (P< 0.05). There were no significant differences among the studied ECG parameters regarding the ER location (lateral vs. infero-lateral), the ER type (slurring or notching), or the maximum J-point amplitude (≥ 1.5 vs. <1.5 mm) at baseline ECGs.

CONCLUSIONS

Individuals with ER display an increased TDR that may be related to an increased arrhythmic risk.

Isometric handgrip exercise improves acute neurocardiac regulation

Isometric handgrip (IHG) training (>6 weeks) has been shown to reduce resting arterial blood pressure (ABP) and improve cardiac autonomic modulation. However, the effects of a single bout of IHG on acute neurocardiac regulation remain unknown. The purpose of this study was to examine the effect of IHG exercise on nonlinear heart rate dynamics and cardiac vagal activity. Nonlinear dynamics were assessed by sample entropy, detrended fluctuation analysis (alpha(1)), and correlation dimension techniques. The 4-second exercise test was used to calculate the cardiac vagal index (CVI), an indirect measure of cardiac vagal activity. In a randomized crossover design, 18 older (70 +/- 5 years of age) subjects completed IHG exercise (four 2-min isometric contractions at 30% MVC) and a time-matched control condition. Following a single bout of bilateral IHG, there was a small reduction in systolic blood pressure (125 +/- 2 to 122 +/- 1 mmHg, P < 0.01), in addition to, a significant decrease in alpha(1) (1.42 +/- 0.12 to 1.22 +/- 0.10, P < 0.05), an increase in sample entropy (1.28 +/- 0.03 to 1.40 +/- 0.05, P < 0.001), and an increase in the CVI (1.24 +/- 0.03 to 1.29 +/- 0.03, P < 0.01). These results suggest improvements in acute cardiac autonomic modulation following a single bout of IHG. This may be mechanistically linked to the observed reductions in ABP seen in previous IHG training studies. Alternatively, these acute effects may have clinical applications and require further investigation.

Normal resting electrocardiographic variants in young athletes

With a growing awareness of the tragedy of sudden cardiac arrest (SCA) in young athletes, more extensive pre-participation examinations are being performed prior to competitive sport participation. In addition to a history and physical, young athletes often have a 12-lead resting electrocardiogram (ECG) to better identify heart disease associated with SCA. Complicating this process is that certain "abnormal" resting ECG findings are considered normal variants in healthy children and young adults. The ability to recognize these normal variants is often useful in preventing excessive referral of patients to cardiologists for evaluation of resting ECG's that are benign variations of normal and in making sound decisions regarding appropriate clearance to exercise. This review describes these normal variants.

KEYWORDS

normal variants; early repolarization; athlete's heart.

Water intake accelerates post-exercise cardiac vagal reactivation in humans

Post-exercise cardiac vagal reactivation is well-investigated; however, the effect of water intake during this period has not been well studied. Therefore, our aim was to assess the influence of water intake on the cardiac vagal reactivation after 30 min of a submaximal cycling exercise. Ten healthy subjects (eight men) aged 23-35 years were evaluated. A 3-day testing cycle duration, subjects were randomly chosen to drink either 500 ml (experimental visit) or 50 ml (control visit) of water immediately after the 30-min cycling exercise at a workload representing 80% of a previously measured anaerobic threshold. A cardiac vagal index (CVI) was obtained using the 4-s exercise test measured before and after (10 and 30 min) exercise at each testing day. Data analysis (2 x 3 ANOVA for repeated measures) showed higher cardiac vagal activity at the 30-min post-exercise period when 500 ml of water was ingested. CVI values for the 500 and 50 ml trials were 1.55 +/- 0.04 vs. 1.49 +/- 0.04, P = 0.003 (mean +/- SEM), respectively. Heart rate and blood pressure values were relatively the same. In conclusion, water intake of about 500 ml immediately after 30 min of cycling exercise accelerates post-exercise cardiac vagal reactivation. These results suggest that post-exercise hydration might be beneficial not only for thermoregulation, but also for vagal reactivation.

Prognostic Value of Heart Rate Increase at Onset of Exercise Testing

Background— The initial response of heart rate to dynamic exercise has been proposed as having prognostic value in limited studies that have used modalities other than the treadmill. Our aim was to evaluate the prognostic value of early heart rate parameters in patients referred for routine clinical treadmill testing.

Methods and Results— The heart rate rise at the onset of exercise was measured in 1959 patients referred for clinical treadmill testing at the Palo Alto (Calif) Veterans Affairs Medical Center from 1997 to 2004. Multivariable Cox survival analysis was performed for 197 all-cause and 74 cardiovascular deaths that accrued during a mean follow-up of 5.4±2.1 years. Decreased heart rate changes at all initial relative exercise workloads were associated with significantly increased all-cause mortality. The heart rate rise at one-third total exercise capacity, however, was the only early heart rate variable that significantly predicted both all-cause and cardiovascular risk after adjustment for confounders. Failing to reach 1 SD in the heart rate rise at one-third total exercise capacity was associated with a 28% increased all-cause mortality rate (hazard ratio, 0.72; 95% CI, 0.61 to 0.85; P <0.001) and a 35% cardiovascular mortality rate (hazard ratio, 0.65; 95% CI, 0.49 to 0.86; P =0.003). Of all heart rate measurements considered (initial and recovery), the heart rate increase at peak exercise was the most powerful predictor of cardiovascular prognosis after adjustment for potential confounders. The Duke treadmill score, however, was superior to all heart rate measurements in the prediction of cardiovascular mortality.

Conclusions— In the present study population, a rapid initial heart rate rise was associated with improved survival, but the heart rate increase at peak exercise and other conventional measurements such as exercise capacity and the Duke treadmill score were more powerful predictors of prognosis.

Influence of different respiratory maneuvers on exercise-induced cardiac vagal inhibition

Physical exercise inhibits cardiac vagal activity. To study the relationship between heart rate (HR) and respiratory pattern, we applied the 4-s exercise test (4sET) and measured cardiac vagal index (CVI) in 30 healthy subjects who served as their own controls, using the standard plus three additional variations, essentially respiratory, of the original protocol: (a) a maximum inspiratory apnea of 16 s, of which 8 s were in the pre-exercise phase (4sET(insp)); (b) free respiratory pattern (4sET(unc)); and (c) maximum expiratory apnea of 12 s (4sET(exp)). The respective results were expressed by the following CVIs: CVI(insp), CVI(unc) and CVI(exp). CVI was determined in a continuous digital ECG recording through a specific ratio of two RR interval durations. The results [(mean +/- SEM)] for the four different maneuvers were as follows: CVI (1.56 +/- 0.05), CVI(insp) (1.55 +/- 0.05), CVI(unc) (1.63 +/- 0.05) and CVI(exp) (1.37 +/- 0.02). ANOVA-Bonferroni significant differences were only found between CVI(exp) and CVI(insp) (P = 0.009), CVI(unc) (P < 0.001) and CVI (P = 0.003). Dividing our sample in terciles according to CVI values, those with lower CVI, showed an attenuation of biphasic HR response after a 15 s maximum inspiratory apnea. We conclude that cardiac vagal reflex seems to be influencing the biphasic HR response modulation after a 12 s inspiratory apnea as described in the original protocol of 4sET, and this appears to be the option that best discriminates the cardiac vagal reflex, with less variability in the maneuvers when subjects are divided in terciles.

Initial and Final Exercise Heart Rate Transients

STUDY OBJECTIVES

To compare the independent and additive data provided by initial and final heart rate (HR) exercise transients, and to analyze both according to gender, aerobic fitness, clinical status, and medication usage.

DESIGN

Retrospective study.

SETTING

Exercise medicine clinic.

PATIENTS

A total of 544 subjects (363 men) with a mean (+/- SD) age of 50 +/- 14 years (age range, 10 to 91 years), including asymptomatic and coronary artery disease patients.

MEASUREMENTS AND RESULTS

HR transients were obtained from the following two exercise protocols: 4-s exercise test (4sET) followed by a maximal cardiopulmonary cycling exercise test (CPET). The initial HR transient was represented by the cardiac vagal index (CVI), which was obtained by the 4sET, and the final transient (ie, HR recovery [HRR]) was determined by the following equation: CPET maximal HR - the 1-min postexercise HR. Transients were modestly related (r = 0.22; p < 0.001) when adjusted for age, aerobic fitness, clinical status, and negative chronotropic action drug usage. The transients were unrelated to gender (vs CVI, p = 0.10; vs HRR, p = 0.15). Subjects with a measured maximum oxygen uptake (VO2max) exceeding 100% of the predicted maximal aerobic power showed higher CVIs than those in less aerobically fit subjects (VO2max < 50% subgroup, p = 0.009; VO2max < 75% subgroup, p = 0.034). Both transient results differed for asymptomatic and cardiac subjects (CVI, 1.32 +/- 0.02 vs 1.42 +/- 0.02, respectively [p = 0.001]; HRR, 33 +/- 1 beats/min (bpm) vs 37 +/- 1 bpm, respectively [p = 0.009]).

CONCLUSIONS

The initial and final HR transients were modestly related, suggesting a potentially complementary clinical role for both measurements in the assessment of autonomic function in patients with coronary artery disease. Although both HR transients tended to behave similarly under the influence of several variables, the initial HR transient, measured during 4sET, was more likely to discriminate distinct subgroups compared with the final HR transient.

Fidedignidade intra e interdias do teste de exercício de quatro segundos

O teste de exercício de quatro segundos (T4s) é validado farmacologicamente para a avaliação da função vagal cardíaca e consiste em pedalar, o mais rápido possível, um cicloergômetro sem carga do quarto ao oitavo segundo de uma apnéia inspiratória máxima de 12 segundos. Um índice vagal cardíaco (IVC) adimensional é obtido pelo quociente entre a duração dos ciclos cardíacos (intervalos RR no eletrocardiograma) imediatamente antes e o mais curto do exercício. Objetivou-se determinar a fidedignidade inter e intradia do T4s e a necessidade de realizar duas tentativas, conforme descrito no protocolo original. No estudo 1, analisou-se prospectivamente a fidedignidade interdias dos resultados de 15 indivíduos assintomáticos (28 ± 6 anos) submetidos ao T4s por cinco dias seguidos, sendo realizadas duas tentativas a cada dia. Para determinar a fidedignidade intradia do IVC, foram realizadas, randomicamente em um dos dias, nove tentativas consecutivas do T4s. No estudo 2, calculou-se, retrospectivamente, a fidedignidade intradia do IVC de 1.699 indivíduos (47 ± 17 anos) em duas tentativas. O IVC apresentou elevada fidedignidade intradia e interdias (r i = 0,92; IC 95% = 0,84 a 0,97 e r i = 0,77; IC 95% = 0,49 a 0,92, respectivamente) no estudo 1, assim como, no estudo 2 (r i = 0,89; IC 95% = 0,88 a 0,90). Apesar da elevada fidedignidade, havia mínimas diferenças entre as médias (média ± EPM = 1,32 ± 0,01 vs. 1,37 ± 0,01; p < 0,001), sendo que em apenas 15% dos casos essa diferença foi maior do que 0,20, não representando, assim, maior relevância clínica. Verificou-se, ainda, que, em 65% das observações, a segunda tentativa foi considerada a melhor e que a realização de apenas uma induziria a erros de interpretação clínica em 27% dos dados. Em síntese, este estudo demonstrou a elevada fidedignidade do IVC avaliado pelo T4s, além de justificar a necessidade de realizar duas tentativas consecutivas em seu protocolo.