Why does the heart rate response to exercise predict adverse cardiac events?

The role of cardiopulmonary exercise testing in risk stratification and prognosis of atrial fibrillation: a scoping review of the literature

BACKGROUND

Cardiopulmonary exercise testing (CPET) is a significant tool for evaluating exercise capacity in healthy individuals and in various pulmonary and cardiovascular conditions, quantifying symptoms and predicting outcomes. Atrial fibrillation (AF) poses a significant burden on patients and health systems; a research marathon is ongoing for discovering the pathophysiologic substrate, natural history, prognostic tools and optimal treatment strategies for AF. Among the plethora of variables measured during CPET, there is a series of parameters of interest concerning AF.

METHODS

We conducted a scoping review aiming to identify significant CPET-related parameters linked to AF, as well as indicate the impact of other cardiac disease-related variables. We searched PubMed from its inception to 12 January 2022 for reports underlining the contribution of CPET in the assessment of patients with AF. Only clinical trials, observational studies and systematic reviews were included, while narrative reviews, expert opinions and other forms of manuscripts were excluded.

RESULTS

In our scoping review, we report a group of heterogeneous, thus noteworthy parameters relevant to the potential contribution of CPET in AF. CPET helps phenotype AF populations, evaluates exercise capacity after cardioversion or catheter ablation, and assesses heart rate response to exercise; peak VO₂ and VE/VCO₂, commonly measured indices during CPET, also serve as prognostic tools in patients with AF and heart failure.

CONCLUSIONS

CPET seems to hold a clinically important predictive value for future cardiovascular events both in patients with pre-existing cardiac conditions and in healthy individuals. CPET variables may play a fundamental role in the prediction of future AF-related events.

Chronotropic Response to Exercise Testing and the Risk of Stroke

Although the chronotropic response to exercise testing, defined as an inadequate heart rate response to incremental exercise to volitional fatigue, is associated with adverse cardiovascular outcomes, it remains unclear whether this response is related to the future risk of cerebrovascular events. We tested the hypothesis that the chronotropic response to exercise is associated with an increased risk of stroke in a general population. This prospective study was based on a population sample of 2,036 men aged 42 to 60 years in the Kuopio Ischemic Heart Disease cohort study. Chronotropic response to exercise was defined as the percentage of chronotropic index ([maximum heart rate - resting heart rate] / [220 - age - resting heart rate] × 100). Incident strokes were obtained from the Finnish national hospital discharge registry. During a median 27-year follow-up, 343 incident stroke (289 ischemic and 66 hemorrhagic) events occurred. Twelve events were diagnosed as both ischemic and hemorrhagic stroke. Comparing the bottom versus top quintile of chronotropic reserve, there was an increased risk of stroke (hazard ratio [HR] 1.73, 95% confidence Interval [CI]: 1.09 to 2.75) and ischemic stroke (HR 1.72, 95% CI, 1.04 to 2.85), but not hemorrhagic stroke (HR 2.23, 95% CI, 0.77 to 6.46) in analyses that adjusted for potential risk factors. These results suggest that an impaired chronotropic response to exercise is independently associated with a higher risk of total and ischemic stroke events in middle-aged men. The role of chronotropic incompetence during exercise testing as a potential prognostic indicator for stroke risk needs further investigation.

Phenotypes of orthostatic blood pressure behaviour and association with visual acuity

BACKGROUND

Manifestations of neurocardiovascular instability (NCVI), including orthostatic hypotension (OH) orthostatic hypertension (OHTN) and impaired blood pressure variability (BPV), have been associated with cardiovascular (CV) events. The eye is highly vascular and we propose an ideal target end organ to investigate pathological implications of NCVI.

OBJECTIVE

To identify and define clinically applicable phenotypes of orthostatic blood pressure (BP) behaviour, analogous to OH, OHTN, and orthostatic BPV and to investigate their relationship to vision.

METHODS

Wave one data from the Irish Longitudinal Study on Ageing (TILDA) were used. Orthostatic BP (OBP) phenotypes were identified and defined from beat-to-beat BP data, measured by digital photoplethysmography during an active stand (AS) lasting 110 s (s). Visual acuity (VA) was assessed using the Early Treatment Diabetic Retinopathy Study (EDTRS) LogMAR chart. The relationship between OBP phenotypes and VA in 4355 adults aged ≥50 years was investigated through multivariate linear regression models.

RESULTS

There was a wide fluctuation in the prevalence of OH and OHTN up to 20 s after standing. After 30 s, four distinct OBP phenotypes were identified: in 70 % BP stabilised to within 20/10 mmHg of baseline BP, 4 % had persistent OH, 2 % had persistent OHTN and 25 % had exaggerated orthostatic blood pressure variability BPV. Systolic BPV was associated with worse VA (P = 0.02) as was diastolic BPV (P = 0.03), following adjustment for demographics, health behaviours, self-report eye diseases and diabetes, uncorrected refractive error, objective hypertension and antihypertensives.

CONCLUSIONS

The hypothesis that NCVI may independently modulate CV risk is supported the independent association of exaggerated BPV and worse VA.

Detection of autonomic dysfunction in hemodialysis patients using the exercise treadmill test: the role of the chronotropic index, heart rate recovery, and R-R variability

OBJECTIVE

To evaluate the ability of different parameters of exercise treadmill test to detect autonomic dysfunction in hemodialysis patients.

METHODS

Cross-sectional study involving hemodialysis patients and a control group. Clinical examination, blood sampling, echocardiogram, 24-hour Holter, and exercise treadmill test were performed. A ramp treadmill protocol symptom-limited with active recovery was employed.

RESULTS

Forty-one hemodialysis patients and 41 controls concluded the study. There was significant difference between hemodialysis patients and controls in autonomic function parameters in 24h-Holter and exercise treadmill test. Probability of having autonomic dysfunction in hemodialysis patients compared to controls was 29.7 at the exercise treadmill test and 13.0 in the 24-hour Holter. Chronotropic index, heart rate recovery at the 1st min, and SDNN at exercise were used to develop an autonomic dysfunction score to grade autonomic dysfunction, in which, 83% of hemodialysis patients reached a scoring ≥2 in contrast to 20% of controls. Hemodialysis was independently associated with either altered chronotropic index or autonomic dysfunction scoring ≥2 in every tested model (OR=50.1, P=0.003; and OR=270.9, P=0.002, respectively, model 5).

CONCLUSION

The exercise treadmill test was feasible and useful to diagnose of the autonomic dysfunction in hemodialysis patients. Chronotropic index and autonomic dysfunction scoring ≥2 were the most effective parameters to differentiate between hemodialysis patients and controls suggesting that these variables portrays the best ability to detect autonomic dysfunction in this setting.

Chronotropic incompetence, echocardiographic abnormalities and exercise intolerance in renal transplant recipients

BACKGROUND

Chronotropic incompetence (CI) is an independent predictor of cardiovascular events and overall mortality. The prevalence and significance of CI in renal transplant patient has not been examined.

METHODS

38 non-heart failure renal transplant recipients were recruited for a transthoracic echocardiogram and treadmill stress test using the modified Bruce protocol.

RESULTS

15 patients (39.5%) had CI (defined as failure to reach 85% of the maximum age-predicted heart rate, or <8 0% of predicted heart rate reserve). CI patients had higher left ventricular (LV) mass (216.5 ± 56.1 vs. 183.1 ± 40.0 g, p = 0.04), increased septal wall thickness (11.7 ± 1.4 vs. 10.7 ± 1.1 mm, p = 0.03) and posterior wall thickness (10.9 ± 1.9 vs. 9.5 ± 1.7 mm, p = 0.02). At multivariate analysis, CI was associated with elevated serum creatinine [odds ratio (OR) 1.04, p = 0.03] and increased LV mass (OR 1.03, p = 0.03). CI was associated with shorter exercise duration (3.53 ± 2.20 vs. 8.08 ± 2.34 min, p < 0.01) and lower metabolic equivalents (5.40 ± 2.05 vs. 9.82 ± 2.39, p < 0.01). At multivariate analysis, exercise duration was negatively associated with CI (β = -0.54, p < 0.01).

CONCLUSIONS

CI is present in approximately 40% of asymptomatic renal transplant recipients and is associated with reduced exercise tolerance, left ventricular hypertrophy, and worse allograft function .

Prognostic value of treadmill stress echocardiography at extremes of exercise performance: submaximal <85% maximum predicted heart rate versus high exercise capacity ≥ 10 metabolic equivalents

BACKGROUND

Submaximal stress testing or achieving <85% maximum predicted heart rate (MPHR) may lead to nondiagnostic results and indeterminate outcomes. High exercise capacity (≥ 10 metabolic equivalents, METS) is a predictor of favorable prognosis. The purpose of this study was to evaluate the prognostic value of submaximal or high exercise capacity stress echocardiography.

METHODS

We evaluated 1781 patients (55 ± 13 years; 59% male) undergoing treadmill stress echocardiography divided into 811 patients with submaximal (<85% MPHR) and 970 patients with high exercise capacity (≥ 10 METS). Resting left ventricular ejection fraction and regional wall motion were assessed. The left ventricle was divided into 16 segments and scored on 5-point scale of wall motion. Abnormal stress echocardiography was defined as stress-induced ischemia (wall-motion score of ≥ 1 grade). Follow-up (3.3 ± 1.5 years) for nonfatal myocardial infarction (MI) (n = 40) and cardiac death (n = 52) were obtained.

RESULTS

By univariate analysis, echocardiographic variables of ejection fraction, peak wall-motion score index (WMSI) and number of new ischemic wall-motion abnormalities were significant predictors of cardiac events. Cumulative survival was significantly worse in patients with abnormal (ischemic) versus normal (nonischemic) stress echocardiography in submaximal (4.4%/year vs. 1.3%/year, P < 0.0001) and high exercise capacity (1.5%/year vs. 0.2%/year, P < 0.0001) studies. Multivariate Cox proportional hazards analysis identified number of new ischemic wall-motion abnormalities as the strongest predictor of cardiac events (P < 0.05) in both groups.

CONCLUSIONS

Despite normal stress echocardiography, the inability to achieve 85% MPHR conferred a higher, intermediate cardiac event rate of 2.9%/year. The ability to achieve 9 minutes (≥ 10 metabolic equivalents, METS) conferred an overall low cardiac event rate of 0.4%/year. However, the absence or presence of ischemia by stress echocardiography was able to further risk stratify patients with either submaximal or high exercise capacity studies.

Long-term outcome of patients with chronotropic incompetence after an acute myocardial infarction

BACKGROUND AND AIM

chronotropic incompetence is risk marker of mortality in various populations, but its value in risk stratification of patients with a recent myocardial infarction (MI) is not known.

METHODS

a consecutive series of 494 patients with a recent MI underwent a symptom-limited bicycle ergometer test and echocardiography before discharge from the hospital. Cardiac death was the primary end-point and sudden cardiac death (SCD) the secondary end-point. Heart rate (HR) response to exercise was evaluated using maximal chronotropic response index (CRI = 100 × (peak HR - resting HR) × (220 - age - resting HR)(-1)).

RESULTS

during 8 years of follow-up, 40 patients (8.1%) experienced cardiac death, of whom 18 died suddenly (3.6%). Abnormal CRI (<39) was the most powerful predictor of the primary end-point with adjusted relative risk (RR) of 5.4 (95% CI 2.9-11.2; P < 0.001) and also a potent risk marker for SCD (adjusted RR 7.3; 95% CI 2.6-20.0; P < 0.001). Adjusted RR of decreased left ventricular ejection fraction (LVEF) (<45%) was 3.4 (95% CI 1.8-6.6; P < 0.001) for cardiac death. In the final predictive model of cardiac death, the removal of CRI decreased c-index from 0.817 to 0.778, whereas c-index was 0.791 after removal of LVEF.

CONCLUSIONS

chronotropic incompetence is a powerful predictor of cardiac mortality among post-MI patients.

A decline in walking distance predicts long-term outcome in patients with known or suspected peripheral artery disease

AIM

To assess the predictive value of a decline in total walking distance and ankle brachial index (ABI) on all-cause mortality and cardiac death in patients with known or suspected peripheral artery disease.

METHODS

Two hundred and sixty-one patients, who performed single-stage treadmill walking test twice to evaluate their peripheral artery disease, were enrolled in an observational study. Patients who underwent surgery during follow-up were excluded. Delta total walking distance and delta resting and exercise ABI consisted of the difference between the first and the second test. All three variables were categorized into two groups: stable/improvement or a decline.

RESULTS

The mean follow-up period was 6 years. At both 5 years and total follow-up, a decline in total walking distance was independent and highly associated with an increased mortality risk and cardiac death [hazard ratio: 2.31 (95% confidence interval 1.35-3.96); hazard ratio: 3.55 (95% confidence interval: 1.53-8.21), respectively]. A decline in resting or exercise ABI after adjustment for delta walking distance was not significantly associated with all-cause mortality or cardiac death.

CONCLUSION

A decline in total walking distance in single-stage treadmill exercise tests is a strong prognostic predictor of all-cause mortality and cardiac death in the short term and long term.

Chronotropic incompetence and autonomic dysfunction in patients without structural heart disease

AIMS

An attenuated heart rate response to exercise, termed chronotropic incompetence (CI), has been reported to be an independent predictor of cardiovascular mortality. We examined the change in autonomic function during exercise testing and correlated the results with CI.

METHODS AND RESULTS

Exercise testing using a bicycle ergometer was performed in 172 patients who had no evidence of cardiac disease. Chronotropic incompetence was defined as the failure to achieve 85% of the age-predicted maximum heart rate, heart rate reserve <80%, or chronotropic response index <0.80. We analysed the relationship between CI and the change in two components of heart rate variability during exercise testing: high-frequency (HF) component (0.15-0.40 Hz) as an index of vagal modulation and the ratio of low-frequency (LF) component (0.04-0.15 Hz) to HF component as an index of sympathovagal balance. Heart rate variability indexes before exercise were similar in patients with and without CI. Percentage changes after exercise in the ratio of LF to HF component were higher in patients with CI than in those without CI (84 +/- 15 vs. 41 +/- 16%, P < 0.05), whereas percentage changes in an HF component were similar in the two groups.

CONCLUSION

Our data suggested that CI in patients without structural heart disease was mainly caused by a pathophysiological condition in which sympathetic activation was not well translated into heart rate increase. Further study is needed to determine the post-synaptic sensitivity of the beta-adrenergic receptor pathway in relation to CI.

Prognostic value of myocardial perfusion SPECT images in combination with the maximal heart rate at exercise testing in Japanese patients with suspected ischemic heart disease: a sub-analysis of J-ACCESS

OBJECTIVES

We assessed whether a combination of summed stress scores (SSS) using exercise myocardial perfusion SPECT (Ex-SPECT) and maximal heart rate accurately predicts cardiac events through a sub-analysis of J-ACCESS (Japanese Assessment of Cardiac Events and Survival Study by Quantitative Gated SPECT) which was conducted to evaluate the prognosis of Japanese patients with suspected ischemic heart disease.

METHODS

In J-ACCESS, 2,373 patients with suspected coronary artery disease not receiving beta-blocker treatment underwent Ex-SPECT. These patients were categorized into the following four groups: Group A [achieved target heart rate (THR) and SSS < 4: n = 631], B (did not achieve THR and SSS < 4: n = 612), C (achieved THR and SSS >or= 4: n = 570), and D (did not achieve THR and SSS >or= 4: n = 560). We evaluated the incidence rate of cardiac events including cardiac death, myocardial infarction, and heart failure requiring hospital admission during a 3-year period.

RESULTS

In Group A, B, C, and D, 9 of 631 (1.4%), 15 of 612 (2.4%), 23 of 570 (4.0%) and 30 of 560 (5.4%) patients experienced cardiac events, respectively. Although the hazard ratio of the SSS >or= 4 was 2.45 (p < 0.001) and that of the attained THR was 0.69 (p = 0.10) in the multiple Cox regression analysis, Kaplan-Meier curves showed that the cardiac events rate was lower in the order of A, B, C, and D (p < 0.001).

CONCLUSION

The combination of SSS using Ex-SPECT and the maximal heart rate is a useful predictor of cardiac events in patients with suspected coronary artery disease.

Usefulness of chronotropic incompetence in response to exercise as a predictor of myocardial infarction in middle-aged men without cardiovascular disease

An attenuated heart rate (HR) response to exercise, or chronotropic incompetence, has been shown to predict adverse cardiac events in subjects without known cardiovascular disease (CVD). The aim of the present study was to investigate whether chronotropic incompetence independently predicts acute myocardial infarction (AMI) in middle-aged men. In addition to previously established chronotropic incompetence variables, we focused on a new chronotropic incompetence variable, the HR increase from 40% to 100% of maximal work capacity (HR40-100), as a predictor of AMI. The subjects were a representative sample of 1,176 middle-aged men who did not have CVD and did not use HR-lowering medication at baseline. The association of chronotropic incompetence variables with the risk of AMI was examined by Cox regression models including numerous known risk factors for AMI. During an average follow-up of 11.0 years, there were 106 AMIs (9.0%). In Cox multivariable model, the risk of AMI increased by 33% for each SD decrement of 13 beats/min in HR40-100 (95% confidence interval [CI] 9 to 64). When considered concurrently, HR40-100 was the only chronotropic incompetence variable that improved the predictive value of the model containing other risk factors for AMI. Men with a low HR40-100 (<46 beats/min) and a heightened increase in systolic blood pressure (SBP) (>67 mm Hg) were at particularly high risk, with a 3.1-times higher incidence of AMI than those with a normal HR40-100 and SBP increase (95% CI 1.7 to 5.7). In conclusion, a low HR40-100 predicted AMI in men without previous CVD independent of other exercise test or clinical variables.