Regional myocardial perfusion during chronic biventricular pacing and after acute change of the pacing mode in patients with congestive heart failure and bundle branch block treated with an atrioventricular sequential biventricular pacemaker

Positron Emission Tomography in Heart Failure: From Pathophysiology to Clinical Application

Imaging modalities are increasingly being used to evaluate the underlying pathophysiology of heart failure. Positron emission tomography (PET) is a non-invasive imaging technique that uses radioactive tracers to visualize and measure biological processes in vivo. PET imaging of the heart uses different radiopharmaceuticals to provide information on myocardial metabolism, perfusion, inflammation, fibrosis, and sympathetic nervous system activity, which are all important contributors to the development and progression of heart failure. This narrative review provides an overview of the use of PET imaging in heart failure, highlighting the different PET tracers and modalities, and discussing fields of present and future clinical application.

Effect of cardiac resynchronization therapy on septal perfusion and septal thickening: Association with left ventricular function, reverse remodelling and dyssynchrony

BACKGROUND

We evaluated the effect of cardiac resynchronization therapy (CRT) on septal perfusion and thickening at 6 months post implantation assessed on Tc99m-MIBI Gated myocardial perfusion SPECT (GMPS).We also studied the association of change in septal perfusion and thickening with primary outcome defined as at least one [improvement in ≥1NYHA class, left ventricular ejection fraction (LVEF) by ≥ 5%, reduction of end-systolic volume (ESV) by ≥ 15%, and improvement ≥ 5 points in Minnesota living with heart failure questionnaire (MLHFQ)].

METHOD

One hundred and five patients underwent clinical and GMPS evaluation before and at 6 months post CRT.

RESULT

Post CRT there was significant improvement in mean normalized septal perfusion uptake and in septal thickening (P value = 0.001, both). There was no significant relation between improvement in septal perfusion and primary outcome. However, improvement in septal thickening was statistically significant with favorable primary outcome (P = 0.001).There was no significant correlation between improvement of septal perfusion and improvement in LVEF, reduction in End diastolic volume (EDV), ESV, and Left ventricular Dyssynchrony (LVD). But, there was significant correlation between improvement of septal thickening and these parameters.

CONCLUSION

Improvement in septal thickening was associated with reverse remodeling, improvement in LVEF, and reduction of LVD.

Effects of Epicardial and Endocardial Cardiac Resynchronization Therapy on Coronary Flow: Insights From Wave Intensity Analysis

Background

The increase in global coronary flow seen with conventional biventricular pacing is mediated by an increase in the dominant backward expansion wave (BEW). Little is known about the determinants of flow in the left‐sided epicardial coronary arteries beyond this or the effect of endocardial pacing stimulation on coronary physiology.

Methods and Results

Eleven patients with a chronically implanted biventricular pacemaker underwent an acute hemodynamic and electrophysiological study. Five of 11 patients also took part in a left ventricular endocardial pacing protocol at the same time. Conventional biventricular pacing, delivered epicardially from the coronary sinus, resulted in a 9% increase in flow (average peak velocity) in the left anterior descending artery (LAD), mediated by a 13% increase in the area under the BEW (P=0.004). Endocardial pacing resulted in a 27% increase in LAD flow, mediated by a 112% increase in the area under the forward compression wave (FCW) and a 43% increase in the area under the BEW (P=0.048 and P=0.036, respectively). There were no significant changes in circumflex parameters. Conventional biventricular pacing resulted in homogenization of timing of coronary flow compared with baseline (mean difference in time to peak in the LAD versus circumflex artery: FCW 39 ms [baseline] versus 3 ms [conventional biventricular pacing], P=0.008; BEW 47 ms [baseline] versus 8 ms [conventional biventricular pacing], P=0.004).

Conclusions

Epicardial and endocardial pacing result in increased coronary flow in the left anterior descending artery and homogenization of the timing of waves that determine flow in the LAD and the circumflex artery. The increase in both the FCW and the BEW with endocardial pacing may be the result of a more physiological activation pattern than that of epicardial pacing, which resulted in an increase of only the BEW.

Current concepts relating coronary flow, myocardial perfusion and metabolism in left bundle branch block and cardiac resynchronisation therapy

Cardiac resynchronisation therapy (CRT) improves mortality and symptoms in heart failure patients with electromechanically dyssynchronous ventricles. There is a 50% non-response rate and reproducible biomarkers to predict non-response have not been forthcoming. Therefore, there has been increasing interest in the pathophysiological effects of dyssynchrony particularly focusing on coronary flow, myocardial perfusion and metabolism. Studies suggest that dyssynchronous electrical activation effects coronary flow throughout the coronary vasculature from the epicardial arteries to the microvascular bed and that these changes can be corrected by CRT. The effect of both electrical and mechanical dyssynchrony on myocardial perfusion is unclear with some studies suggesting there is a reduction in septal perfusion whilst others propose that there is an increase in lateral perfusion. Better understanding of these effects offers the possibility for better prediction of non-response. CRT appears to improve homogeneity in myocardial perfusion where heterogeneity is described in the initial substrate. Novel approaches to the identification of non-responders via metabolic phenotyping both invasively and non-invasively have been encouraging. There remains a need for further research to clarify the interaction of coronary flow with perfusion and metabolism in patients who undergo CRT.

Role of cardiac MRI and nuclear imaging in cardiac resynchronization therapy

Cardiac resynchronization has emerged as a highly effective therapy for heart failure. However, up to 40% of patients do not benefit from this treatment. In this Review, we discuss the potential role of MRI and nuclear molecular imaging in providing additional insights into the response to cardiac resynchronization therapy. Variables with potential prognostic and therapeutic values include the evaluation of cardiac dyssynchrony, scar, cardiac sympathetic function, myocardial blood flow, myocardial glucose and oxidative metabolism. Other molecular targets to characterize apoptosis, fatty acid metabolism, angiogenesis and angiotensin-converting enzyme activity will also be described. The potential use of these techniques in identifying and measuring responses to cardiac resynchronization therapy and future areas of research will be explored.

Effects of cardiac resynchronization therapy on coronary blood flow: evaluation by transthoracic Doppler echocardiography

BACKGROUND

Relatively limited and conflicting data are available on the effects of cardiac resynchronization therapy (CRT) on coronary blood flow (CBF).

AIMS

To investigate changes in the left anterior descending coronary artery (LAD) flow under different CRT pacing modes by means of transthoracic Doppler echocardiography (TTE).

METHODS

Twenty-two responders to CRT (67+/-11 years) with idiopathic dilated cardiomyopathy underwent TTE assessment of LAD flow and Tissue Velocity Imaging during 4 programming modes: intrinsic conduction (IC), right ventricular pacing (RV), simultaneous biventricular pacing (BVP), BVP with left ventricular (LV) pre-activation.

RESULTS

Mean coronary flow velocity (CFV) was increased by simultaneous BVP (p=0.0063 vs. IC) and BVP with LV pre-activation (p<0.0001 vs. IC; p=0.027 vs. simultaneous BVP). Peak CFV and LAD flow velocity/time integral were highest during BVP with LV pre-activation. A reduction in septal-to-lateral delay and an increase in peak systolic velocity in the basal septum were observed during simultaneous BVP and BVP with LV pre-activation.

CONCLUSIONS

In CRT responders with idiopathic dilated cardiomyopathy, an increase in LAD flow, assessed by TTE, was observed during simultaneous BVP and BVP with LV pre-activation. This was associated with an improvement in regional myocardial contraction and a decrease in intraventricular dyssynchrony.

Volume overload modulates effects of cardiac resynchronization therapy independently of myocardial reperfusion: results of the RESYNC study

OBJECTIVES

Cardiac resynchronization therapy (CRT) may induce significant changes in regional wall motion and perfusion. However, the link between these variables in patients with heart failure has not been investigated.

METHODS

Thirty-six patients with idiopathic (n = 22) or ischemic (n = 14) cardiomyopathy (mean age 70 +/- 8 years, 24 male) were studied by echocardiography and gated single-photon emission computed tomography (SPECT) before and within 2 months after CRT.

RESULTS

New York Heart Association class improved in all but four patients. The perfusion analysis indicated that, in all but three patients, there was a significant improvement of tracer uptake. Baseline end-diastolic volume index obtained by gated SPECT modulated increase of ejection fraction (P < 0.001), reduction of end-systolic volume index (P < 0.01) and improvement of motion (P < 0.001), as well as of left ventricular wall thickening (P < 0.002). Finally, despite CRT inducing significant reperfusion independently of volume overload (P < 0.05), extension of perfusion defect correlated with global improvement in the follow-up (P < 0.05).

CONCLUSIONS

Volume overload may identify responders to resynchronization therapy. CRT induced a significant 'reperfusion' both in ischemic and idiopathic cardiomyopathies, even if this is not sufficient to improve left ventricular function in patients with more severe volume overload. Finally, simultaneous evaluation of volume overload and perfusion defects may result useful in identifying CRT responders.

Cardiac Resynchronization Therapy

Encouraged by the clinical success of cardiac resynchronization therapy (CRT), the implantation rate has increased exponentially, although several limitations and unresolved issues of CRT have been identified. This review concerns issues that are encountered during implantation of CRT devices, including the role of electroanatomical mapping, whether CRT implantation should be accompanied by simultaneous atrioventricular nodal ablation in patients with atrial fibrillation, procedural complications, and when to consider surgical left ventricular lead positioning. Furthermore, (echocardiographic) CRT optimization and assessment of CRT benefits after implantation are highlighted. Also, controversial issues such as the potential value of CRT in patients with mild heart failure or narrow QRS complex are addressed. Finally, open questions concerning when to combine CRT with implantable cardioverter-defibrillator therapy and the cost-effectiveness of CRT are discussed.

Effect of cardiac resynchronization therapy on global and regional oxygen consumption and myocardial blood flow in patients with non-ischaemic and ischaemic cardiomyopathy

AIMS

We studied the effects of cardiac resynchronization therapy (CRT) on global and regional myocardial oxygen consumption (MVO2) and myocardial blood flow (MBF) in non-ischaemic (NICM) and ischaemic dilated cardiomyopathy (ICM).

METHODS AND RESULTS

Thirty-one NICM and 11 ICM patients, all of them acute responders, were investigated. MVO2 and MBF were obtained by 11C-acetate PET before and after 4 months of CRT. In NICM global MVO2 and MBF did not change during CRT, while the rate pressure product (RPP) normalized MVO2 increased (P=0.03). Before CRT regional MVO2 and MBF were highest in the lateral wall and lowest in the septum. Under therapy, MVO2 and MBF decreased in the lateral wall (P=0.045) and increased in the septum (P=0.045) resulting in a more uniform distribution. In ICM, global MVO2, MBF, and RPP did not change under CRT. Regional MVO2 and MBF showed no significant changes but a similar tendency in the lateral and septal wall to that in NICM.

CONCLUSION

CRT induces changes of MVO2 and MBF on a regional level with a more uniform distribution between the myocardial walls and improved ventricular efficiency in NICM. Based on the investigated parameters, CRT appears to be more effective in NICM than in ICM.

Effects of Cardiac Resynchronization Therapy on Myocardial Perfusion Reserve

Background— Cardiac resynchronization therapy (CRT) is a relatively new treatment strategy for patients with heart failure and mechanical asynchrony. Reported effects of CRT on regional myocardial blood flow (MBF) are conflicting, and effects on hyperemic MBF are scarce. The aim of the present study was to assess serial changes of MBF and MBF reserve in patients receiving a biventricular pacemaker.

Methods and Results— Fourteen patients with heart failure (NYHA class III or IV; left ventricular ejection fraction <35%), QRS width >120 ms, and sinus rhythm were studied (mean age, 58±10 years; 8 men). MBF and hyperemic MBF were measured at baseline, 3 months after biventricular pacing (CRT on), and after cessation of pacing (CRT off) with PET and H 2 15 O. CRT had no significant effect on resting MBF (baseline versus CRT on versus CRT off: 0.82±0.25 versus 0.69±0.24 versus 0.74±0.24 mL · min −1 · mL −1 ; P =NS). Hyperemic MBF increased during CRT (1.91±1.03 versus 2.66±1.66 versus 1.92±1.06 mL · min −1 · mL −1 ; P =0.01 by MANOVA), as did MBF reserve (2.25±1.00 versus 3.76±2.38 versus 2.49±0.94 mL · min −1 · mL −1 ; P =0.023). CRT (reversibly) resulted in a more homogeneous distribution of regional resting MBF as demonstrated by the septal-to-lateral ratio. The decrease in the ratio of left ventricular end-diastolic volume to left ventricular mass, as a reflection of wall stress, was related to the increase in hyperemic MBF ( r =0.53, P <0.05). Left ventricular ejection fraction increased from 25±7% to 37±9% ( P <0.01).

Conclusions— Resting MBF is unaltered by CRT despite an increase in left ventricular function. However, the distribution pattern of resting MBF becomes more homogeneous. Hyperemic MBF and consequently MBF reserve are enhanced by CRT.