No Need Too Small: New 4 mm & 6 mm COnfidence Flowprobes® for Pediatric Heart Surgery
The size and fragility of very young patients make congenital repairs undoubtedly among the most challenging to perform. Whatever the nature of the defect, the primary goal is to create or restore blood flow to its normal route through the heart and lungs into the systemic circulation so that the patient can grow and thrive. Extended open-chest periods and staged surgeries add to the importance of identifying how much blood is flowing through re-directed pathways. After surgery, waiting for symptomatic confirmation of surgical success is subjective and time-consuming. Identifying single flows, or Qp/Qs flows simultaneously, provides the chance to immediately correct a problem before closing the patient.
Unprecedented Measurement Capability
Our new miniature 4mm and 6mm COnfidence Flowprobes offer unprecedented flow measurement capability during congenital heart defect (CHD) repairs in young children. The four-sensor Flowprobes are customized for vessels with turbulent flows such as the aorta and pulmonary artery. The probe cables are specially oriented to eliminate torsional forces on the vessel. The measurements may either confirm the surgeon’s clinical impressions during the course of the surgery, or they can alert the surgeon to a potential problem at a time when it can be most easily addressed.
For turbulent flow profiles in great arteries and veins, COnfidence Perivascular Flowprobes are engineered for continuous highly accurate volume flow (not velocity) measurements. The Flowprobe’s slim, ergonomic profile creates a minimal footprint in order to fit into tight anatomical sites. Its soft, pliable liner cushions and protects the vessel. It is available in 17 sizes from 4 mm to 36 mm.
Does Measuring Cardiac Parameters in Hemodialysis Patients Have Prognostic Value?
Up to one in four hemodialysis patients will die suddenly. These deaths occur most often during the 12 hours immediately following the hemodialysis session or toward the end of the long 72-hour weekend interval between dialysis sessions.
The causes of sudden deaths in hemodialysis patients are not known. Many patients do not appear to have the typical high-risk factors such as coronary artery disease and heart failure that are associated with sudden death (SCD) in the general population. Their sudden deaths may be related to symptoms associated with chronic kidney disease itself such as vascular calcification, left ventricular hypertrophy, electrolyte/fluid abnormalities, autonomic dysfunction or inflammation.
But until sudden death among hemodialysis patients is better understood, it is crucial to minimize its risk. Assessment and trending of cardiac function with the Transonic HD03 Hemodialysis Monitor is one way to do this. Through a small innocuous injection of saline during the hemodialysis session, cardiac function parameters are measured and calculated. By trending these parameters over time with central hemodynamic profiling, clinicians can better understand the cardiac health of each of their hemodialysis patients and be alerted to a potential cardiac problem in a patient before it produces a fatal result.
Recently, clinicians at the University of Tübingen and the Nephrology Center in Leonberg, Germany, have been studying the prognostic significance of measuring cardiac parameters during the hemodialysis session. They are presenting the results of their prospective cross-sectional study in 185 stable hemodialysis patients at ASN 2016 in Chicago this November.
For their study, cardiac index, access flow, and central blood volume index measurements were collected at the beginning and end of a single HD session using the Transonic HD03 Monitor.
Systemic cardiac index and oxygen delivery index were calculated. A survival analysis was performed after a median follow-up of 606 days.
Thirty-three of the 185 patients (18%) that first participated in the study died during the follow-up period. The patients who died tended to have a lower cardiac index and had significantly reduced systemic cardiac index and oxygen delivery index than did the survivors. Also, drops in cardiac index, systemic cardiac index and oxygen delivery index by the end of the hemodialysis session were significantly higher in the patients who died. On the other hand, there was no difference in access flow, central volume blood index and hemoglobin between survivors and those who died.
The German clinicians concluded that increased mortality was associated with reduced systemic cardiac index and oxygen delivery index at rest, as well as a drop of these parameters by the end of a dialysis session. This groundbreaking study underscores the prognostic relevance of cardiac function for the survival of HD patients and demonstrates the prognostic significance of measuring hemodynamic parameters in HD patients with the HD03 Hemodialysis Monitor.
Artunc F, Friedrich B, Heyne N, Haag S, “Prognostic significance of hemodynamic parameters in hemodialysis patients,” JASN Abstracts 2016; 27: 571A Abstract # FR PO883 (Transonic Reference # HD11003A)
How Arteriovenous Fistulas Impact Cardiovascular Hemodynamics
The philosophy at Miulli General Hospital, Acquaviva delle Fonti, Italy, is “Patient first, not fistula first, but avoid a catheter if at all possible.” To this end, Carlo Basile and colleagues from the Division of Nephrology, have studied the influence of an arteriovenous (AV) fistula on the load of the left ventricle in hemodialysis patients.1
Eighty-six hemodialysis patients with an AV access were enrolled in the cross-sectional study. Of the 86, 56 had a lower arm fistula and 30 had an upper arm fistula. Vascular access flow (Qa) and cardiac output (CO) were measured in each patient with the Transonic HD02 Hemodialysis Monitor. Mean arterial pressure (MAP) was also measured.
From these measurements, total peripheral vascular resistance (TPVR) was calculated as MAP/CO. Resistance of the arteriovenous fistula (AR) and systemic vascular resistance (SVR) were connected in parallel and were calculated as AR = MAP/Qa and SVR = MAP/(CO – Qa).
Left ventricular load (LLV) was calculated on the principle of a simple physical model where LLV (watt) was equal to TPVR*CO2.2
The researchers found that access flow, cardiac output, and left ventricular load increased significantly in upper arm fistulas compared with lower arm fistulas. On the other hand, total peripheral vascular resistance, access resistance and systemic vascular resistance decreased significantly in upper arm AVFs compared with lower arm AVFs.
Moreover, they discovered that the correlation between fistula flow and left ventricular load was not linear, but that LLVAVF calculated as % of LLV rose with increasing fistula flow according to a quadratic polynomial regression model, but only in lower arm AVFs. On the other hand, no statistically significant relationship was found between the left ventricular load and access flow in upper arm AVFs.
1Basile C, Vernaglione L, Casucci F, Libutti P, Lisi P, Rossi L, Vigo V, Lomonte C. “The impact of haemodialysis arteriovenous fistula on haemodynamic parameters of the cardiovascular system,” Clin Kidney J. 2016 Oct;9(5):729-34. (Transonic Reference # HD11001A)
2Válek at al."Arteriovenous Fistula, Blood Flow, Cardiac Output, and Left Ventricle Load in Hemodialysis Patients" ASAIO J. 2010 May-Jun;56(3):200-3 (Transoinc Reference # HD7951A)
European System for Cardiac Operation Risk Evaluation (EuroSCORE) II
In the U.S., most cardiac surgery programs subscribe to the Society of Thoracic Surgeons (STS), and utilize their data-collection worksheets. STS also provides a scoring system to predict operative mortality. However, now an increasing number of surgeons, here and abroad, are also using the European System for Cardiac Operative Risk Evaluation (EuroSCORE).
Having the ability to predict a patient’s short and long-term survival based on specific patient factors is beneficial to the surgeon and the patient. For the surgeon, it can assist with surgical procedural decision-making, such as whether to perform a CABG on or off-pump. For the patient, it gives insight as to the actual risk of dying during or shortly after any given cardiac surgery.
The original EuroSCORE, presented in 1998, was based on over 20,000 patients, and has proven to be very accurate. The more complicated EuroSCORE II, adopted in 2011, has refined the age factor, and provides additional accuracy when considering complicated co-morbidities.
While statistical analysis can be very useful, every patient still provides a unique picture that can’t be predicted precisely. Still, the EuroSCORE II model provides results in the 80% accuracy range at 0-days and 31 days, and dropping into the mid 70% range at 1 and 5-year outcomes. This is impressive, considering the complexity of conditions in many cardiac patients.
MRI-Safe Flowprobe Used in Pig Hyperoxia Study
Little is known about the impact of hyperoxia on the ischemic heart. Although oxygen is frequently administered and is generally expected to be beneficial, current guidelines limit its use after return of spontaneous circulation after cardiac arrest.
Canadian and Swiss researchers sought to investigate the effect of hyperoxia on myocardial oxygenation and myocardial function parameters in animals with significant stenoses of the left anterior descending (LAD). coronary artery They also investigated the effects of PaCO2 changes on myocardial oxygenation during hyperoxia in this model.
For their study, a left-sided thoracotomy was performed and a MR-safe perivascular Flowprobe was applied to the proximal LAD in 22 healthy Yorkshire-Landrace pigs.
Eleven pigs served as controls. In the other eleven pigs a perivascular hydraulic occluder was mounted around the LAD distal to the Flowprobes. All animals received a bolus of 5000 U heparin intravenously. PaO2 was increased to >300 mmHg.
Three animals had to be excluded from each group of pigs (control and experimental) for various reasons, resulting in eight animals in each group. The study found:
- There was no significant difference in baseline LAD flow between the control and stenosed animals.
- LAD flow decreased in all animals after PaO2 was increased to >300 mmHg.
- Hyperoxia resulted in a significant decrease of myocardial signal intensity in oxygenation- sensitive cardiovascular magnetic resonance images of the midapical segments of the LAD territory in the eight stenosed pigs. This was accompanied by a decrease in circumferential strain in the same segments.
- Ejection fraction, cardiac output, and oxygen extraction ratio also declined in these animals.
- Changing PaCO2 levels did not have a significant effect on any of the parameters.
- However, hypercapnia did not seem to seem significantly attenuate the hyperoxia-induced changes.
From their study, the researchers concluded that ventilation-induced hyperoxia may decrease myocardial oxygenation and lead to ischemia in myocardium subject to severe coronary artery stenosis and accompanied by ventricular dysfunction.
Guensch DP, Fischer K, Shie N, Lebel J, Friedrich MG, “Hyperoxia Exacerbates Myocardial Ischemia in the Presence of Acute Coronary Artery Stenosis in Swine,” Circ Cardiovasc Interv. 2015 Oct;8(10): (Transonic Reference # 10690A)
Transonic True Flow Is Distinguishing Feature of aVAD™
An August MD+DI article entitled “ReliantHeart’s aVAD™ Gets CE Mark” by contributor Marie Thibault announces that medtech company ReliantHeart has won European approval for its newest device. One of the “novel features” that distinguishes the aVAD™ from other LVADs on the market is its incorporation of True Flow diagnostics. Rather than deriving a calculated blood flow, ReliantHeart utilizes Transonic’s ultrasonic probes to provide patients and clinicians with real-time flow at the pump’s outflow graft.
Thibault writes, “These added capabilities may allow clinicians to detect potential patient problems earlier.” According to ReliantHeart’s website, such problems include dehydration and atrial fibrillation, the early patterns of which can be detected by True Flow measurements and True Flow amplitudes. These flow readings will be reported via the aVAD’s™ 24/7 remote monitoring system.
ReliantHeart CEO Roger Ford emphasizes the need to “set the alarms properly so that the thresholds for low flow or high power provide an advance warning of something that could be a bad outcome.”
The aVAD™ is modeled off of ReliantHeart’s last LVAD, the HeartAssist5®. “We’ve made this really powerful new pump but the blood path is exactly the same,” says Ford. This similarity in design enabled the aVAD™ to receive a CE Mark without a trial.
The article also details the aVAD’s™ projected entry into the US market. ReliantHeart expects the aVAD™ to enter an FDA IDE trial in the first quarter of 2017, contingent on successful FDA animal trials. These animal studies include testing of a removable cable that significantly decreases risk of driveline infection, a feature that the CE Marked aVAD™ does not currently include, but one ReliantHeart wishes to incorporate into the European model soon.
However, at the heart of the aVAD™ is still Transonic’s ultrasonic flow probe technology. Ford asserts that “the first thing [physicians] need to do is trust the flow.” He simply and effectively concludes, “It will improve patient outcomes.”