Total anomalous pulmonary venous connection in 80 patients: Primary sutureless repair and outcomes.

Introduction: Total anomalous pulmonary venous connection (TAPVC) is a rare but critical cardiac anomaly, in which pulmonary veins are connected to an abnormal location rather than the left atrium. The prognosis can be extremely poor without intervention, with a mortality of 80% during infancy. The purpose of this research is to summarize the outcomes and relevant risk factors of 80 total anomalous pulmonary venous connection (TAPVC) patients who underwent primary TAPVC sutureless repair and discuss the indications and benefits of primary sutureless repair. Methods: This retrospective review included 80 patients with TAPVC who underwent primary sutureless repair at a single institution between January 2015 and December 2020. Patients were subdivided into 4 groups according to Darling's classification. Risk factors that increase the postoperative pulmonary vein flow velocity were explored by Multiple Linear regression. Results: Anatomic TAPVC subtypes included supracardiac 35 (43.8%), cardiac 24 (30%), infracardiac 17 (21.2%), and mixed 4 (5%). Median age at repair was 16.5 days and median weight was 3.5 kg. Preoperative pulmonary venous obstruction (PVO)was presented in 20 (25%) patients. There were 2 early deaths and 1 late death. 2 patients developed postoperative PVO and none required reintervention. Prolonged cardiopulmonary bypass time (CPB) (p = 0.009), preoperative pneumonia (p = 0.022) and gender (p = 0.041) were found to be associated with the increase of postoperative pulmonary vein flow velocity. Discussion: Under the primary sutureless technique, no statistical difference was observed among the 4 subgroups in terms of postoperative pulmonary vein flow velocity (p = 0.589). The primary sutureless technique may eliminate the differences between subtypes while decrease the postoperative PVO rate, which makes it applicable in any subtypes of TAPVC. Following the favorable outcomes in preventing postoperative PVO in all subtypes in this study, we advocate the indications for primary sutureless repair may expand further to all the TAPVC patients.

Impact of early Coronavirus Disease 2019 pandemic on pediatric cardiac surgery in China.

OBJECTIVE: This study aimed to provide an insight into the impact of the early outbreak of the novel Coronavirus Disease 2019 on the care management for patients with congenital heart disease. METHODS: This study respectively enrolled a cohort of surgical patients who underwent surgery in 2018 (group I), 2019 (group II), and 2020 (group III) and a cohort of follow-up patients who had follow-up in 2017 (group A), 2018 (group B), and 2019 (group C) in 13 children hospitals. RESULTS: During the Coronavirus Disease 2019 era, there was a significant decrease in total surgical volume and a change in case mix in terms of an increase in the proportion of emergency operations. Decrease in migration scale index was correlated to the decrease in both surgical volume (r = 0.64, P = .02) and outpatient visit volume (r = 0.61, P = .03). There was a significantly higher proportion of patients who had follow-up through the internet or phone in group C (26.4% vs 9.6% in group B and 8.9% in group A; P < .0001). There was no statistical difference in death or rehospitalization among the 3 follow-up groups (P = .49). There was higher parents' anxiety score (P < .0001) and more use of telemedicine (P = .004) in group C compared with groups A and B. CONCLUSIONS: The Coronavirus Disease 2019 pandemic has resulted in a considerable decrease in total surgical volume and a change of case mix, which seems to be related to the strict traffic ban. Follow-up through the online medical service appears to be an effective alternative to the conventional method.

Impact of miniaturized cardiopulmonary bypass circuits on ultrafiltration during congenital heart surgery.

OBJECTIVE: To investigate whether the miniaturized cardiopulmonary bypass (CPB) system decreased the usage of ultrafiltration (UF), and to explore whether the non-UF with miniaturized CPB strategy could get good clinical results during congenital heart surgery. METHODS: We performed a retrospective analysis of all patients undergoing congenital heart surgery with CPB at Shenzhen Children's Hospital from 1 May 2015 to 30 September 2019. We classified patients to UF with miniaturized CPB group, non-UF with miniaturized CPB group, UF with conventional CPB group and non-UF with conventional CPB group. RESULTS: Of the 2145 patients, 721 (33.6%) were in the conventional CPB group, and 1424 (66.4%) were in the miniaturized CPB group. The UF rate was significantly lower in the miniaturized CPB group compared with that in the conventional CPB group (12.5% vs. 76.8%, p < 0.001). Compared with patients in the other groups, patients in the non-UF with miniaturized CPB group had a shorter postoperative MV time (p < 0.05), and a shorter length of stay in the ICU (p < 0.001) and hospital (p < 0.001). The age of children in the UF with miniaturized CPB group was relatively younger (median: 1.5 months, IQR: 0.3-4.6 months), and the preoperative weight was relatively lower (median: 3.9 kg, IQR: 3.2-5.4 kg). Moreover, this group of children had a relatively longer postoperative MV time and length of stay in the ICU and hospital. CONCLUSION: The miniaturized CPB system could decrease the usage of UF. Good results were achieved in children who did not use UF based on the miniaturized CPB circuit system during congenital heart surgery.

Effect of retrograde autologous priming based on miniaturized cardiopulmonary bypass in children undergoing open heart surgery: A STROBE compliant retrospective observational study.

To evaluate the effectiveness of retrograde autologous priming (RAP) based on miniaturized cardiopulmonary bypass (CPB) circuit in children undergoing open heart surgery.We performed a retrospective analysis of all patients (≤15 kg) who underwent open heart surgery with CPB in our center from January 1, 2017, to July 31, 2019. Propensity score matching was used to adjust for significant covariates, and multivariable stratified analysis was used to assess the association of the RAP technique with clinical outcomes.A total of 1111 patients were analyzed. There were 355 (32.0%) children who underwent RAP, and 756 (68.0%) were in the non-RAP group. After propensity score matching, there were a total of 638 patients, with 319 patients in each group. The bloodless priming rate was significantly higher (P = .013), and the ultrafiltration rate was significantly lower (P = .003) in the RAP group than in the non-RAP group. Compared with patients in the non-RAP group, patients in the RAP group had a shorter postoperative mechanical ventilation time (P < .001) and shorter lengths of stay in the intensive care unit (ICU) (P < .001) and the hospital (P < .001). No differences were noted in postoperative hematocrit (P = .920), postoperative 24-hour blood loss (P = .435), and hospital mortality (P = .563). In the stratified analysis, the difference remained statistically significant (P < .05) when the patient weight was >4 kg or the Society of Thoracic Surgeons-European Association for Cardiothoracic Surgery (STAT) category was <3. However, when the patient weight was ≤4 kg or the STAT category was ≥3, there was no significant difference between the 2 groups in terms of bloodless priming, ultrafiltration, postoperative mechanical ventilation time, or length of stay in the ICU or the hospital (P > .05).The RAP technique based on miniaturized CPB system was safe and effective for children who underwent congenital heart surgery. The RAP technique can significantly reduce the priming volume, improve the rate of bloodless priming, and reduce blood product application. It was also associated with a shorter postoperative mechanical ventilation time and shorter lengths of stay in the ICU and the hospital.

The Experience of Early Extubation After Paediatric Congenital Heart Surgery in a Chinese Hospital.

BACKGROUND: Early extubation has become widely adopted in cardiac surgery practices. This study aimed to present experience of early extubation after congenital heart surgery and to explore the factors that affect successful immediate postoperative extubation and early extubation. METHODS: A retrospective analysis was performed of all patients who underwent congenital heart surgery with cardiopulmonary bypass (CPB) at Shenzhen Children's Hospital between 01 May 2015 and 30 September 2019. The demographic and cardiac surgery information were derived from the medical records. Multivariable logistic regression models were used to explore the influence factors for successful immediate postoperative extubation and early extubation. RESULTS: This study consisted of 2,060 patients, 65.0% of whom were extubated in the operating room and 16.1% of whom were extubated early (within 6 hours) in the Intensive Care Unit. The overall rates of reintubation and nasal continuous positive airway pressure were 2.0% and 6.4%, respectively. Preoperative weight (OR, 1.24; 95% CI, 1.20-1.29), preoperative pneumonia (OR, 0.60; 95% CI, 0.44-0.80), CPB type (OR, 1.23; 95% CI, 1.06-1.43), CPB time (OR, 0.98; 95% CI, 0.98-0.99), deep hypothermic circulatory arrest (OR, 0.42; 95% CI, 0.25-0.70), and Society of Thoracic Surgeons-European Association for Cardiothoracic Surgery Congenital Heart Surgery (STAT) categories (OR, 0.54; 95% CI, 0.45-0.65) were included in the immediate postoperative extubation model. In addition to the above six variables, ultrafiltration (OR, 0.63; 95% CI, 0.44-0.89) was also included in the early extubation model. Similar results were found in the immediate postoperative extubation model for non-newborns. The influencing factors for early extubation in the non-newborn population included preoperative weight, preoperative pneumonia, ultrafiltration, CPB time, and STAT categories. CONCLUSIONS: Early extubation for children with congenital heart surgery was successful in this hospital. Patients with early extubation had a lower reintubation rate and nasal continuous positive airway pressure rate, and a shorter length of stay in the ICU and hospital. Early extubation was influenced by age, weight at surgery, preoperative pneumonia, CPB type, CPB time, deep hypothermic circulatory arrest, ultrafiltration, and STAT categories.

Comparison of two cardiopulmonary bypass strategies with a miniaturized tubing system: a propensity score-based analysis.

INTRODUCTION: The existing cardiopulmonary bypass tubing system has already been significantly improved in our hospital by reducing the priming volume; thus, we further employed a new cardiopulmonary bypass strategy in children based on a miniaturized cardiopulmonary bypass circuit. We aimed to compare the effectiveness of new and conventional strategies by analyzing the outcomes after congenital heart surgery. METHODS: We performed a database analysis of all patients undergoing congenital heart surgery with cardiopulmonary bypass at Shenzhen Children's Hospital from 1 May 2015 to 30 June 2017. Propensity score matching was used to adjust for significant covariates, and multivariable regression models and stratified analysis were used to assess the association of cardiopulmonary bypass strategy with outcomes. RESULTS: Of 925 total patients, 55.35% were in the conventional strategy group and 44.65% were in the new strategy group. After propensity score matching, there were 610 patients in total, with 305 patients in each group. In the multivariable regression models, the cardiopulmonary bypass strategy was not significantly associated with successful early extubation (p > 0.05), reintubation (p > 0.05), or nasal continuous positive airway pressure (p > 0.05) rates. The new strategy group had fewer hospital stays (p = 0.04) and intensive care unit stays (p < 0.05) compared with patients who underwent conventional strategy. The difference remained statistically significant (p < 0.05) when The Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery category was <3. CONCLUSION: The implementation of a new cardiopulmonary bypass strategy, with selective ultrafiltration based on a miniaturized cardiopulmonary bypass circuit system, was safe and effective for children who underwent congenital heart surgery in a Chinese hospital. The new cardiopulmonary bypass strategy was associated with fewer hospital and intensive care unit stays.

[A preliminary investigation of relationship between serum apelin level and pulmonary artery pressure in children with congenital heart disease].

OBJECTIVE: To preliminarily investigate the relationship between serum apelin level and pulmonary artery pressure in children with congenital heart disease. METHODS: One hundred and twenty-six children with congenital heart disease undergoing surgical treatment were enrolled as subjects. The serum level of apelin was determined before surgery and at 7 days after surgery. The ratio of pulmonary artery systolic pressure to aortic systolic pressure (Pp/Ps) was calculated before extracorporeal circulation. According to the Pp/Ps value, patients were classified into non-pulmonary arterial hypertension (PAH) group, mild PAH group, moderate PAH group, and severe PAH group. Pulmonary artery mean pressure was estimated by echocardiography at 7 days after surgery. RESULTS: The non-PAH group had the highest serum level of apelin before and after surgery, followed by the mild PAH group, moderate PAH group, and severe PAH group (P<0.05). All groups had significantly increased serum levels of apelin at 7 days after surgery (P<0.05). The serum level of apelin was negatively correlated with pulmonary artery pressure before surgery (r=-0.51, P<0.05) and at 7 days after surgery (r=-0.54, P<0.05). CONCLUSIONS: The decrease in serum apelin level is associated with the development of pulmonary hypertension in children with congenital heart disease. The significance of serum apelin in predicting the development and degree of pulmonary hypertension in children with congenital heart disease deserves further studies.

Comparison of Sutureless and Conventional Techniques to Repair Total Anomalous Pulmonary Venous Connection.

Surgical repair of total anomalous pulmonary venous connection (TAPVC) is challenging. This study aimed to compare the outcomes of the sutureless and conventional techniques for primary repair. From October 2007 to December 2013, 179 consecutive patients underwent repair of TAPVC (sutureless, n = 81; conventional, n = 98). Propensity score matching was used to submit 140 patients to stratified analysis by the presence or absence of preoperative pulmonary venous obstruction (pre-PVO). Surgeons׳ performance differences were assessed with multilevel mixture survival analysis. Freedom from death and postoperative PVO (post-PVO) were evaluated with Kaplan-Meier curves. Risk factors for death and post-PVO were explored using Cox proportional hazard model. Surgeons׳ multilevel effects did not exist in this study. Following matching, Kaplan-Meier curves showed that for patients with pre-PVO (totally 38 cases), rates of freedom from death and post-PVO at 1 year were 80.0% (59.8%-100.0%) in the sutureless group, which was significantly better than that in the conventional group (38.3% [15.2%-61.4%], P = 0.02). For patients without pre-PVO (totally 102 cases), rates of freedom from death and post-PVO at 1 year were 96.1% [95% CI: 90.8%-100.0%] and 86.7% [76.5%-96.9%] in the sutureless and conventional groups, respectively (P = 0.15). Conventional technique was a risk factor for death (hazard ratio = 4.14, 95% CI: 1.29-13.28) and post-PVO (hazard ratio = 5.56, 95% CI: 1.18-26.27) adjusting for type of TAPVC, pre-PVO, and other confounders. In conclusions, the sutureless strategy for primary repair of TAPVC is safe and effective. For patients with pre-PVO, this strategy may associate with decreased mortality and post-PVO with statistical significance.

[Anomalous origin of the left coronary artery from the pulmonary artery in infants: clinical features and the perioperative treatment strategies].

OBJECTIVE: To investigate the clinical features and individualized treatment strategies for infants with anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA). METHOD: Data of 25 less than 1-year-old infants with ALCAPA who presented at Guangdong Cardiovascular Institute between 2006 and 2013 were retrospectively reviewed. The patients' cardiac function was evaluated with echocardiography during follow-up. RESULT: Most patients presented with symptoms of heart failure, such as tachypnea, diaphoresis, poor feeding, failure to thrive etc. Electrocardiogram showed abnormal q wave in 23 patients and ST-T segment change in 16 patients.Echocardiography showed dilated left ventricle in 25 patients, endocardial hyperplasia in 5 patients, dilated right coronary artery and extensive collateralization between the right and left coronary artery systems in 11 patients. The left ventricular ejection fraction (LVEF) was (45.5±13.9)% (25%-77%). The left ventricular fractional shortening (LVFS) was (22.0±7.3)% (12%-38%). Twenty one patients underwent cardiovascular CT scan. Left coronary artery originated from left posterior sinus in 9 patients, from right posterior sinus in 1 patient, from lower main pulmonary artery in 5 patients, from the bifurcation of main pulmonary artery in 1 patient.Five patients showed ambiguous left coronary artery origination.Sixteen patients were misdiagnosed in other primary or secondary hospitals in 17 patients who were transferred to our tertiary hospital, only 1 case who underwent angiography was diagnosed correctly. Two patients were misdiagnosed in 8 patients first-presented in our hospital. Their diagnoses were corrected after reexamining with echocardiography and cardiovascular CT scan. The preoperative therapies included using inotropic agents, diuretics and vasodilators according to cardiac function. Two patients underwent left coronary artery orifice ligation. Twenty three patients underwent reimplantation of left coronary artery to reconstruct dual coronary system. Patients of NYHA IV with moderate mitral regurgitation (MR) and NYHA III with severe MR underwent mitral annuloplasty. If LVEF was less than 30% after weaning from cardiopulmonary bypass, blood pressure could not be maintained with medication, or lactates increased progressively, extracorporeal membrane oxygenation (ECMO) was demanded. Two patients showed low cardiac output syndrome immediately after surgical procedures, died from refractory ventricular fibrillation even with ECMO.In survived 23 patients during the early stage after surgeries, duration of ventilation was 7-500 hours, 11 of them were supported with ventilator for less than 60 hours. The mean length of hospital stay was (23.4±13.9) d (8-65 d). The follow-up duration ranged from 1-91 months (median 28.5 months). One case was lost to follow up. The patient died from infection 3 months after discharge. The cardiac functions of the remaining 22 patients were improved. The size of left ventricle of 14 patients recovered to normal. LVEF increased to the normal level in 20 cases. No patient underwent redo procedure. CONCLUSION: The accurate diagnosis can be made based on history, electrocardiogram, echocardiography and other imaging diagnostic tools.Individualized treatment strategy is helpful for seriously sick infants. Aggressive ECMO support can increase surviving rate for patients with postoperative low cardiac output syndrome.

Surgical outcome of isolated total anomalous pulmonary venous connection in adults: a 14-year experience.

AIM OF THE STUDY: To investigate the surgical result of adult total anomalous pulmonary venous connection (TAPVC). METHODS: From March 1997 to March 2011, 12 adult cases of isolated TAPVC, with an average age of 24.9 ± 6.7 years (from 18 to 41 years), underwent surgical repair in our department. All patients suffered from right-sided volume overload with clinical manifestations varying from mild cyanosis to severe heart failure. RESULTS: According to Darling's classification, eight cases were classified as supracardiac type, four as cardiac type. Unobstructed connections were established between the left atrium and the pulmonary common vein in all patients with external cardiac approach in four supracardiac cases, and internal cardiac approach in four cardiac and three supracardiac cases, and Warden technique in one supracardiac patient. Concomitant operations included De Vega's tricuspid annuloplasty in six patients, patent arteriosus ductus closure in two. All patients survived the operation, and postoperative follow-up was 100% complete with a period ranging from 10 months to 14 years. NYHA grade decreased from 2.33 ± 0.49 to 1.08 ± 0.29 (p < 0.01). Three patients had postoperative tricuspid insufficiency. Five patients had cardiac arrhythmia, among two symptomatic cases; one controlled with medication, another received a successful radiofrequency ablation for incision-related atrial flutter. CONCLUSIONS: Surgical correction of isolated adult TAPVC can be carried out safely with acceptable long-term outcome. Postoperative tricuspid insufficiency and cardiac arrhythmias may have a negative long-term impact, which should be evaluated preoperatively and managed individually during surgery.

[Effects of different arterial oxygen partial pressures on serum protein S100ß and neuron specific enolase during cardiopulmonary bypass in infants with cyanotic congenital heart disease].

OBJECTIVE: A prospective study was conducted to probe into the relationship between arterial oxygen partial pressure (PaO2) and brain injury during cardiopulmonary bypass (CPB) in infants with cyanotic congenital heart disease (CHD). METHOD: Enrolled in the study were 45 cyanotic infants, who were less than three years old and underwent corrective cardiac surgery from August 1(st), 2010 to January 31(st), 2011 at Guangdong General Hospital. All the infants had a pulse oxygen saturation (SpO2) lower than 85% and were randomly allocated into three groups by a specific computer program. In controlled group 1 (G1 group), PaO2 levels were controlled at 80 - 120 mm Hg (1 mm Hg = 0.133 kPa) during CPB; in controlled group 2 (G2 group), PaO2 levels at 120 - 200 mm Hg during CPB; while in uncontrolled group (G3 group), PaO2 levels were at 200 - 400 mm Hg during CPB. Blood samples were collected just before starting CPB, at the end of CPB, and at 3 h, 5 h, and 24 h after CPB (T1, T2, T3, T4, T5) for the determination of serum concentrations of protein S100ß, neuron specific enolase (NSE), and adrenomedullin (ADM) by ELISA. RESULT: Protein S100ß rose significantly after starting CPB. In group G3, it reached a peak of (699 ± 139) ng/L by the end of CPB, significantly higher than those in groups G1 and G2 [(528 ± 163) ng/L and (585 ± 155) ng/L], and was positively correlated with PaO2 levels (r = 0.526, P < 0.01). NSE levels of group G1 were continuously rising after starting CPB and reached significantly high levels at 3 h or 5 h after CPB [(12.2 ± 3.4) µg/L and (12.3 ± 3.7) µg/L], while those of group G2 rose significantly during CPB [(10.9 ± 4.8) µg/L] and even higher at 3 h or 5 h after CPB [(12.6 ± 5.1) µg/L and (13.2 ± 5.4) µg/L]. NSE levels of group G3 rose significantly during CPB and maintained at a high level [(12.2 ± 5.7) µg/L] afterwards. There was no significant difference in serum ADM concentrations among different time points in each group and among these three groups. All the infants were discharged from the hospital without any obvious nervous symptom and sign. CONCLUSION: High PaO2 during CPB in infants with CHD might cause an increase of serum protein S100ß and NSE, indicating that brain injury might become worse with a higher PaO2 and might be positively correlated with PaO2 during CPB.

Palliative arterial switch for transposition of the great arteries, ventricular septal defect, and pulmonary vascular obstructive disease: midterm outcomes.

OBJECTIVE: Our objective was to evaluate the early and midterm outcomes of palliative arterial switch operation in which a ventricular septal defect was not closed or repaired with a fenestrated patch in patients with transposition of the great arteries, ventricular septal defect, and severe pulmonary vascular obstructive disease. METHODS: Between March 2000 and September 2009, the palliative arterial switch operation was performed in 21 patients with a mean age of 3.7 years (range, 0.5-15). Mean preoperative values for systolic pulmonary arterial pressure and systemic arterial oxygen saturation were 91 mm Hg and 69%, respectively. Eighty-one percent of the patients were in New York Heart Association functional class III or IV preoperatively. RESULTS: Early mortality was 14.3%. Mean follow-up was 4.0 years (maximum 9.5 years). Regression of pulmonary arterial pressure occurred in 8 patients (44% of the early survivors). Three of the 8 fenestrations were closed interventionally. Mean postoperative systemic arterial oxygen saturation increased significantly to 93% (P < .001). One late death occurred 3 months after surgery. All the long-term survivors (n = 17) were in New York Heart Association functional class I or II (P < .001). CONCLUSIONS: The palliative arterial switch operation significantly improved the quality of life and possibly life expectancy in patients with transposition of the great arteries, ventricular septal defect, and severe pulmonary vascular obstructive disease. Postoperative pulmonary vascular resistance might be reversible in some patients. Closing the ventricular septal defect with a fenestrated patch, which can be easily closed nonsurgically later on, might contribute to a safer postoperative recovery.

Metamaterial with simultaneously negative bulk modulus and mass density.

We report a metamaterial which simultaneously possesses a negative bulk modulus and mass density. This metamaterial is a zinc blende structure consisting of one fcc array of bubble-contained-water spheres (BWSs) and another relatively shifted fcc array of rubber-coated-gold spheres (RGSs) in epoxy matrix. The negative bulk modulus and mass density are simultaneously derived from the coexistent monopolar resonances from the embedded BWSs and dipolar resonances from the embedded RGSs. The Poisson ratio of the metamaterial also turns negative near the resonance frequency.

[The delay time of pediatric LVAD of ECG-triggering mode].

Electrocardiac signal is one of the most important signals which is used to trigger ventricular assist device (VAD), and the delay time of VAD assistance is very important to get a satisfied result. Proper delay will give VAD relatively enough time to assist, avoiding left heart failure caused by the collision of the heart and VAD during systolic phase. This becomes much more important when the left atrium drainage is insufficient. The aim of our study is to set up an equation to calculate the delay time by RR interval. We try to set up an equation about RR and R-Ao like: R-Ao = A x (RR)n + B(A and B are constant). RR represents the RR interval and R-Ao represents the duration of the period between the peak point of QRS and the point of aortic valve closing; First, calculate RR according to weighting average method, and then, calculate the anticipant R-Ao according to the before-mentioned equation. After adjustment, R-Ao will be used as assistance delay time. R-R interval was measured in 457 selected pediatric patients who were undergiong left heart catheterization and who did not have arrhythmias. From the ECG recording during catheterization, R-R interval was measured while R-Ao was obtained from aortic pressure wave chart; Plot graphs with R-Ao as dependent variable and (RR)n as independent variable; find out correlating model and calculate the arguments A and B of R-Ao = A x (RR)n + B. The results showed that the relation between (RR)1/3 and R-Ao is the most significant, the relation coefficient is 0.733, the regress coefficient is -0.182 (P < 0.001) and the interception is 1.070. This means that R-Ao = (-0.182) (RR) 1/3 + 1.070. The likelyhood degrees of different sections differ markedly. When heart rate is less than 120 beats per min. The relation argument is about 0.733 while 0.45 when heart rate is more than 120 beats per min, Therefore, we can use the equation R-Ao = (-0.182) (RR)1/3 + 1.070 to calculate R-Ao when heart rate is less than 120 beats per min.