Myocardial viability and revascularization

Mid wall fibrosis on CMR with late gadolinium enhancement may predict prognosis for LVAD and transplantation risk in patients with newly diagnosed dilated cardiomyopathy-preliminary observations from a high-volume transplant centre

Background

Patients with newly diagnosed dilated cardiomyopathy (DCM) and advanced heart failure have a very high morbidity and mortality with an unpredictable clinical course. We investigated the role of cardiovascular magnetic resonance (CMR) imaging using late gadolinium enhancement (LGE) in this cohort of high‐risk patients. We hypothesized that LGE has high prognostic value in primary DCM patients referred for possible transplantation/left ventricular assist device (LVAD) consideration.

Methods

Over 49 consecutive months, 61 consecutives DCM patients were referred for standard CMR(1.5T, GE) to interrogate the LV pattern, distribution, and extent of LGE (MultiHance, Princeton, NJ). Inclusion criteria for a primary non‐ischaemic DCM and EF <45% were met in 31 patients. DCM patients were categorized into: (i) presence of midwall LV stripe (+Stripe) and (ii) absence of midwall stripe (−Stripe) groups. Primary outcome was defined by the composite of death, need for LV assist device (LVAD), and urgent orthotopic cardiac transplantation (Tx) during a 12‐month follow‐up period. Kaplan–Meier survival analysis was conducted grouping patients by +Stripe and −Stripe.

Results

There were no differences between groups for demographics, blood pressure, labs, baseline LVEF, NYHA class, or invasive haemodynamics. There were 18 patients (58%) with +Stripe. Nine events occurred: seven patients required urgent Tx and/or LVAD implantation and two patients died. The +Stripe categorization strongly predicted the need for LVAD, urgent Tx surgery, and death (log‐rank = 9, P = 0.002). All the events occurred in the +Stripe patients with no MACE experienced in the −Stripe group. The −Stripe group experienced marked signs of improvement in LVEF (P = 0.01) at follow‐up. LVEDD was predictive of need for LVAD/Tx and death by univariate analysis. Otherwise, no common clinical metric such as LVEF, LVEDV, RVEF, RVEDV, or any invasive haemodynamic parameter predicted MACE.

Conclusions

The presence of +Stripe on CMR is strongly predictive of LVAD, transplant need, and death during a 12‐month follow‐up period in DCM patients in this proof of concept study. All −Stripe patients survived without experiencing any events. Incorporating CMR imaging into routine clinical practice may have prognostic value in DCM patients; indicating conservative management in low‐risk patients while expectantly managing high‐risk patients.

Revascularization in heart failure in the post-STICH era

Left ventricular (LV) dysfunction caused by ischemia secondary to coronary artery disease results not only from cardiac myocyte death but also from stunning and hibernation, which are potentially reversible phenomena. Myocardial viability testing is often used in patients with ischemic cardiomyopathy to predict recovery of contractile function after revascularization. Although several observational studies have supported the use of viability testing, the Surgical Treatment for Ischemic Heart failure (STICH) viability substudy challenged its role in clinical decision-making, as viability testing in this study did not predict differential outcomes based on treatment type, and there was a trend toward increased survival in patients with no viability who underwent revascularization. However, the results of the STICH trial have caused controversy because of limitations in study design and implementation. Randomized controlled trials using high-resolution modalities such as positron emission tomography or delayed hyperenhancement cardiac magnetic resonance are needed to determine the incremental benefits that revascularization may afford based on myocardial viability.

CMR in Heart Failure

Heart Failure (HF) is a common syndrome with multiple causes. Cardiovascular magnetic resonance (CMR) is a medical imaging technique with significant advantages, allowing the understanding of aetiology and pathophysiology of HF in the individual patient, permitting specific therapy to be administered and predicting prognosis. This paper discusses the diverse role of CMR in HF.

Use of an intracoronary Doppler guidewire for evaluation of coronary hemodynamics in the porcine model of acute hibernating myocardium during dobutamine stress tests

PURPOSE

To determine the coronary hemodynamic characteristics of acute hibernating myocardium (AHM), evaluate the changes in coronary hemodynamics during dobutamine infusion, and investigate the mechanisms by which dobutamine stress echocardiography (DSE) detects AHM.

METHODS

The porcine model of acute hibernating myocardium was created in 10 animals, all of which underwent DSE with doses of 0-40 μg/kg/min. Myocardial segments abnormality was used as a DSE criterion for evaluating AHM. An intracoronary Doppler guidewire was used to measure the coronary hemodynamics; electrocardiography and systemic hemodynamics were recorded simultaneously. The ischemic regions of myocardium were reperfused, and all variables were recorded. Finally, the animals were euthanized and pathologic changes in the heart tissue were documented.

RESULTS

There was no myocardium necrosis. There were 55 myocardial segments with abnormal DSE responses after stenosis, among which 41 segments were judged as AHM because of a biphasic response. Average peak velocity (APV) and coronary flow velocity reserve were improved during DSE. Coronary and systemic hemodynamics were increased during dobutamine infusion. There were significant differences for APV at all evaluated doses and for heart rate blood pressure product at higher doses. The difference between APV resting values and the values for peak dosage (ΔAPV) correlated with the amount of AHM during DSE. Coronary volume blood flow and coronary flow velocity reserve decreased after stenosis.

CONCLUSIONS

ΔAPV may reflect the number of hibernating segments. The relative imbalance between blood supply and oxygen consumption in regional myocardium may be one of the mechanisms by which DSE detects AHM.

Dual manganese-enhanced and delayed gadolinium-enhanced MRI detects myocardial border zone injury in a pig ischemia-reperfusion model

BACKGROUND

Gadolinium (Gd)-based delayed-enhancement MRI (DEMRI) identifies nonviable myocardium but is nonspecific and may overestimate nonviable territory. Manganese (Mn(2+))-enhanced MRI (MEMRI) denotes specific Mn(2+) uptake into viable cardiomyocytes. We performed a dual-contrast myocardial assessment in a porcine ischemia-reperfusion (IR) model to test the hypothesis that combined DEMRI and MEMRI identifies viable infarct border zone (BZ) myocardium in vivo.

METHODS AND RESULTS

Sixty-minute left anterior descending coronary artery IR injury was induced in 13 adult swine. Twenty-one days post-IR, 3-T cardiac MRI was performed. MEMRI was obtained after injection of 0.7 mL/kg Mn(2+) contrast agent. DEMRI was then acquired after injection of 0.2 mmol/kg Gd. Left ventricular (LV) mass, infarct, and function were analyzed. Subtraction of MEMRI defect from DEMRI signal identified injured BZ myocardium. Explanted hearts were analyzed by 2,3,5-triphenyltetrazolium chloride stain and tissue electron microscopy to compare infarct, BZ, and remote myocardium. Average LV ejection fraction was reduced (30±7%). MEMRI and DEMRI infarct volumes correlated with 2,3,5-triphenyltetrazolium chloride stain analysis (MEMRI, r=0.78; DEMRI, r=0.75; P<0.004). MEMRI infarct volume percentage was significantly lower than that of DEMRI (14±4% versus 23±4%; P<0.05). BZ MEMRI signal-to-noise ratio (SNR) was intermediate to remote and core infarct SNR (7.5±2.8 versus 13.2±3.4 and 2.9±1.6; P<0.0001), and DEMRI BZ SNR tended to be intermediate to remote and core infarct SNR (8.4±5.4 versus 3.3±0.6 and 14.3±6.6; P>0.05). Tissue electron microscopy analysis exhibited preserved cell structure in BZ cardiomyocytes despite transmural DEMRI enhancement.

CONCLUSIONS

The dual-contrast MEMRI-DEMRI detects BZ viability within DEMRI infarct zones. This approach may identify injured, at-risk myocardium in ischemic cardiomyopathy.

Anterior wall viability and low ejection fraction predict functional improvement after CABG

BACKGROUND

Absence of myocardial hyperenhancement on cardiac magnetic resonance imaging (CMR) predicts functional improvement after coronary artery bypass graft surgery (CABG). However, not all patients with absence of hyperenhancement improve their left ventricular ejection fraction (LVEF) after CABG. We sought to identify other characteristics associated with improvement in LVEF after CABG.

METHODS

Preoperative CMR was obtained in 95 patients who underwent CABG from 2003 to 2007 at The Ohio State University Medical Center. Follow-up LVEF was assessed by echocardiogram between 3 wk and 2 y postoperatively (mean: 7±0.5 mo). Improvement in LVEF was defined as a postoperative increase in LVEF≥10%. CMR and clinical factors were analyzed for predictors of functional improvement.

RESULTS

Mean age was 61±1 y with 79 males. LVEF improved from 28%±2% preoperatively, to 38%±2% postoperatively (P<0.0001). Forty-three patients improved their LVEF. Patients who improved their LVEF had a lower preoperative LVEF (P=0.0001) and higher anterior wall viability (P=0.03). Preoperative LVEF (odds ratio 0.89, 95% CI 0.83-0.95, P=0.001) and left ventricular end systolic volume index (odds ratio 0.97, 95% CI 0.95-0.99, P=0.015) were predictors of improvement in LVEF by multivariable logistic regression analysis.

CONCLUSIONS

Recruitment of viable non functioning myocardium of the anterior wall is responsible for the improvement in ejection fraction. Low LVEF, non-remodeled left ventricle, and anterior wall viability predict improvement in ejection fraction after CABG. These criteria may help clinicians select patients who would benefit from surgical revascularization.