Relationship between dobutamine-induced regional wall motion abnormalities and coronary flow reserve in heart transplant patients without angiographic coronary artery disease

Coronary Microcirculatory Dysfunction and Acute Cellular Rejection After Heart Transplantation

BACKGROUND

Acute cellular rejection is a major determinant of mortality and retransplantation after heart transplantation. We sought to evaluate the prognostic implications of coronary microcirculatory dysfunction assessed by index of microcirculatory resistance (IMR) for the risk of acute cellular rejection after heart transplantation.

METHODS

The present study prospectively enrolled 154 heart transplant recipients who underwent scheduled coronary angiography and invasive coronary physiological assessment 1 month after transplantation. IMR is microcirculatory resistance under maximal hyperemia. By measuring hyperemic mean transit time using 3 injections (4 mL each) of room-temperature saline under maximal hyperemia, IMR was calculated as hyperemic distal coronary pressure×hyperemic mean transit time. The primary end point was biopsy-proven acute cellular rejection of grade ≥2R during 2 years of follow-up after transplantation and was compared by using multivariable Cox proportional hazards regression according to IMR. The incremental prognostic value of IMR, in addition to the model with clinical factors, was evaluated by comparison of C-index, net reclassification index, and integrated discrimination index.

RESULTS

The mean age of recipients was 51.2±13.1 years (81.2% male), and the cumulative incidence of acute cellular rejection was 19.0% at 2 years. Patients with acute cellular rejection had significantly higher IMR values at 1 month than those without acute cellular rejection (23.1±8.6 versus 16.8±11.1, P=0.002). IMR was significantly associated with the risk of acute cellular rejection (per 5-U increase: adjusted hazard ratio, 1.18 [95% CI, 1.04-1.34], P=0.011) and the optimal cutoff value of IMR to predict acute cellular rejection was 15. Patients with IMR≥15 showed significantly higher risk of acute cellular rejection than those with IMR<15 (34.4% versus 3.8%; adjusted hazard ratio, 15.3 [95% CI 3.6-65.7], P<0.001). Addition of IMR to clinical variables showed significantly higher discriminant and reclassification ability for risk of acute cellular rejection (C-index 0.87 versus 0.74, P<0.001; net reclassification index 1.05, P<0.001; integrated discrimination index 0.20, P<0.001).

CONCLUSIONS

Coronary microcirculatory dysfunction assessed by IMR measured early after heart transplantation showed significant association with the risk of acute cellular rejection. In addition to surveillance endomyocardial biopsy, early stratification using IMR could be a clinically useful tool to identify patients at higher risk of future acute cellular rejection after heart transplantation. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02798731.

Cardiac Transplantation in the New Era

The prevalence of heart failure continues to rise due to the aging population and longer survival of people with conditions that lead to heart failure, eg, hypertension, diabetes, and coronary artery disease. Although medical therapy has had an important impact on survival of patients and improving quality of life, heart transplantation remains the definitive therapy for patients that eventually deteriorate. Since the first successful heart transplantation in 1967, significant improvements have been made regarding donor and recipient selection, surgical techniques, and postoperative care. However, the number of potential organ donors has not changed and the growing number of patients in need for transplantation has resulted an increase in waiting list time, and the need for mechanical support. To overcome this issue, the United Network for Organ Sharing implemented an allocation system to prioritize the sickest patients on the list to receive organs. Despite the careful selection of patients, pretransplant immunological screening, and multidrug immunosuppressive regimens, acute and chronic rejections occur and potentially limit graft and patient survival. Treatment for rejection largely depends on the type of rejection, the presence of hemodynamic compromise, and time after transplantation. The limiting factor for long-term graft survival is allograft vasculopathy, an immune-mediated process causing diffuse narrowing of the coronary arteries. Percutaneous coronary intervention and coronary artery bypass surgery are often not an option for this vasculopathy due to the lack of focal lesions, and retransplantation is the only option in appropriate patients.

Coronary microvasculopathy in heart transplantation: Consequences and therapeutic implications

Despite the progress made in the prevention and treatment of rejection of the transplanted heart, cardiac allograft vasculopathy (CAV) remains the main cause of death in late survival transplanted patients. CAV consists of a progressive diffuse intimal hyperplasia and the proliferation of vascular smooth muscle cells, ending in wall thickening of epicardial vessels, intramyocardial arteries (50-20 μm), arterioles (20-10 μm), and capillaries (< 10 μm). The etiology of CAV remains unclear; both immunologic and non-immunologic mechanisms contribute to endothelial damage with a sustained inflammatory response. The immunological factors involved are Human Leukocyte Antigen compatibility between donor and recipient, alloreactive T cells and the humoral immune system. The non-immunological factors are older donor age, ischemia-reperfusion time, hyperlipidemia and CMV infections. Diagnostic techniques that are able to assess microvascular function are lacking. Intravascular ultrasound and fractional flow reserve, when performed during coronary angiography, are able to detect epicardial coronary artery disease but are not sensitive enough to assess microvascular changes. Some authors have proposed an index of microcirculatory resistance during maximal hyperemia, which is calculated by dividing pressure by flow (distal pressure multiplied by the hyperemic mean transit time). Non-invasive methods to assess coronary physiology are stress echocardiography, coronary flow reserve by transthoracic Doppler echocardiography, single photon emission computed tomography, and perfusion cardiac magnetic resonance. In this review, we intend to analyze the mechanisms, consequences and therapeutic implications of microvascular dysfunction, including an extended citation of relevant literature data.

Cardiac allograft vasculopathy: advances in diagnosis

Cardiac allograft vasculopathy (CAV), characterized by diffuse intimal thickening and luminal narrowing in the arteries of the allograft, is the leading cause of morbidity and mortality in cardiac transplant recipients. Many transplant centers perform routine annual surveillance coronary angiography. However, angiography can underdiagnose or miss CAV due to its diffuse nature. Intravascular ultrasound (IVUS) is more sensitive than angiography. IVUS provides not only accurate information on lumen size, but also quantification of intimal thickening, vessel wall morphology, and composition. IVUS has evolved as a valuable adjunct to angiography and the optimal diagnostic tool for early detection. Noninvasive testing such as dobutamine stress echocardiography and nuclear stress test have shown considerable accuracy in diagnosing significant CAV. Computed tomographic imaging and cardiac magnetic resonance imaging are promising new modalities but require further study. This article reviews the diagnostic methods that are currently available.

Coronary flow reserve by transthoracic echocardiography predicts epicardial intimal thickening in cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV) is the leading cause of morbidity and mortality in heart transplantation (HT). We sought to investigate the role of coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) in CAV diagnosis. CAV was defined as maximal intimal thickness (MIT) assessed by intravascular ultrasound (IVUS) > or =0.5 mm. CFR was assessed in the left anterior descending coronary artery in 22 HT recipients at 6 +/- 4 years post-HT. CAV was diagnosed in 10 patients (group A), 12 had normal coronaries (group B). The mean MIT was 0.7 +/- 0.1 mm (range 0.03-1.8). MIT was higher in group A (1.16 +/- 0.3 mm vs. 0.34 +/- 0.07 mm, p < 0.0001). CFR was 3.1 +/- 0.8 in all patients and lower in group A (2.5 +/- 0.6 vs. 3.7 +/- 0.3, p < 0.0001). CFR was inversely related with MIT (r =-0.774, p < 0.0001). A cut point of < or =2.9, identified as optimal by receiver operating characteristics analysis was 100% specific and 80% sensitive (PPV = 100%, NPV = 89%, Accuracy = 91%). CFR assessment by CE-TTE is a novel noninvasive diagnostic tool in the detection of CAV defined as MIT > or =0.5 mm. CFR by CE-TTE may reduce the need for routine IVUS in HT.

Diagnosis of graft coronary artery disease

PURPOSE OF REVIEW

Graft coronary artery disease is the leading cardiac cause of death in patients who have undergone cardiac transplantation. Due to denervation, classic symptoms of angina are not reliable. Many transplant centers have a protocol of routine annual surveillance cardiac angiography because treatment options are limited, especially with advanced disease. Angiography is an assessment of the arterial lumen, however, and can miss nonfocal disease. This paper reviews invasive and noninvasive diagnostic tools for graft coronary artery disease. Intravascular ultrasound is the most sensitive, but the cost and lack of widespread expertise make it unpopular. Noninvasive techniques have been studied. An ideal test would be sufficiently sensitive to detect disease and allow for prognostic information. Dobutamine echocardiography is the most sensitive noninvasive test but can have a high false-positive rate. It is also not universally available. Exercise nuclear imaging is specific and can be used as a confirmatory test in patients with positive dobutamine echocardiograms.

RECENT FINDINGS

Computed tomographic imaging and cardiac magnetic resonance imaging are exciting new modalities but require further study.

SUMMARY

There is no test sensitive and specific enough yet that can be confidently used to replace coronary angiography.

Coronary flow reserve by contrast-enhanced echocardiography: a new noninvasive diagnostic tool for cardiac allograft vasculopathy

Noninvasive tests have proven unsatisfactory in cardiac allograft vasculopathy (CAV) diagnosis. We assessed coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) in heart transplantation (HT). CFR was assessed in the left anterior descending coronary artery in 73 HT recipients (59 male, aged 50+/-12 years at HT), at 8+/-4.5 years post-HT. CFR measurements were taken blindly from coronary angiographies. CFR cut points were the standard value of <or=2 and those defined by receiver operating characteristics (ROC) curve analysis. CFR was lower in patients with CAV (2.3+/-0.7 vs. 3.2+/-0.5, p<0.0001). The <or=2 cut point was 100% specific and 38% sensitive. The <or=2.7 cut point, optimal by ROC analysis, was 87% specific and 82% sensitive. Accuracy rose from 71% with the standard<or=2 cut point to 85% with the optimal cut point of <or=2.7. CFR by CE-TTE may offer promise as a novel, easily repeatable and accurate noninvasive tool in CAV detection. However, further longitudinal studies in larger patient cohorts are warranted before widespread adoption can be advocated.

Alteration of the left ventricular contractile reserve in heart transplant patients: a dobutamine stress strain rate imaging study

BACKGROUND

Strain rate imaging (SRI), a recently developed Doppler-derived process, allows quantification of myocardial systolic function. We investigate whether SRI quantifies the contractile reserve during dobutamine stress tests in heart transplant patients (HT), when compared with normal individuals.

METHODS

An incremental dobutamine test (5 to 40 microg/kg per minute) was performed in 10 HT and 15 control subjects, all of whom displayed normal coronary angiography. Gray-scale and color myocardial Doppler data were acquired in standard B-mode views at baseline, low-dose, peak, and recovery. Longitudinal SR was processed from the myocardial velocities for each segment. The changes in maximal systolic SR were used to quantify myocardial contractile reserve.

RESULTS

Dobutamine infusion failed to induce clinical symptoms or electrocardiographic (ECG) changes in either group. Visually determined wall motion score was considered normal in all segments for each stage of the dobutamine stress. Heart rate was augmented similarly in both groups during dobutamine infusion. In controls, systolic SR increased gradually with incremental dobutamine dose and returned to baseline values upon recovery. Conversely, in HT patients, the increase in systolic SR was blunted at peak dobutamine, at which point it was significantly different vs controls.

CONCLUSIONS

Quantitative assessment of myocardial function using SRI during dobutamine stress revealed an impaired contractile reserve in HT patients with normal coronary angiography. These subtle changes in regional myocardial function could not be identified using visual wall motion scoring. Additional studies are necessary to evaluate whether SR imaging detection of contractile reserve impairment will improve clinical efficiency or event prediction in this population.

Simultaneous assessment of fractional and coronary flow reserves in cardiac transplant recipients: Physiologic Investigation for Transplant Arteriopathy (PITA Study)

BACKGROUND

The utility of measuring fractional flow reserve (FFR) to assess cardiac transplant arteriopathy has not been evaluated. Measuring coronary flow reserve (CFR) as well as FFR could add information about the microcirculation, but until recently, this has required two coronary wires. We evaluated a new method for simultaneously measuring FFR and CFR with a single wire to investigate transplant arteriopathy.

METHODS AND RESULTS

In 53 cases of asymptomatic cardiac transplant recipients without angiographically significant coronary disease, FFR and thermodilution-derived CFR (CFRthermo) were measured simultaneously with the same coronary pressure wire in the left anterior descending artery and compared with volumetric intravascular ultrasound (IVUS) imaging. The average FFR was 0.88+/-0.07; in 75% of cases, the FFR was less than the normal threshold of 0.94; and in 15% of cases, the FFR was < or =0.80, the upper boundary of the gray zone of the ischemic threshold. There was a significant inverse correlation between FFR and IVUS-derived measures of plaque burden, including percent plaque volume (r=0.55, P<0.0001). The average CFRthermo was 2.5+/-1.2; in 47% of cases, CFRthermo was < or =2.0. In 14%, the FFR was normal (> or =0.94) and the CFR was abnormal (<2.0), suggesting predominant microcirculatory dysfunction.

CONCLUSIONS

FFR correlates with IVUS findings and is abnormal in a significant proportion of asymptomatic cardiac transplant patients with normal angiograms. Simultaneous measurement of CFR with the same pressure wire, with the use of a novel coronary thermodilution technique, is feasible and adds information to the physiological evaluation of these patients.