Coronary and peripheral blood flow changes following biventricular pacing and their relation to heart failure improvement

Reduction in coronary microvascular resistance through cardiac resynchronization and its impact on chronic reverse remodelling of left ventricle in patients with non-ischaemic cardiomyopathy

AIMS

Left bundle branch block (LBBB) induces mechanical dyssynchrony, thereby compromising the coronary circulation in non-ischaemic cardiomyopathy. We sought to examine the effects of cardiac resynchronization therapy (CRT) on coronary flow dynamics and left ventricular (LV) function.

METHODS AND RESULTS

Twenty-two patients with non-ischaemic cardiomyopathy (New York Heart Association class, III or IV; LV ejection fraction, ≤35%; QRS duration, ≥130 ms) were enrolled. One week after implantation of the CRT device, coronary flow velocity and pressure in the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCx) were measured invasively, before and after inducing hyperemia by adenosine triphosphate administration, with two programming modes: sequential atrial and biventricular pacing (BiV) and atrial pacing in patients with LBBB or sequential atrial and right ventricular pacing in patients with complete atrioventricular block (Control). We assessed hyperemic microvascular resistance (HMR, mean distal pressure divided by hyperemic average peak velocity) and the relationship between the change in HMR and mid-term LV reverse remodelling. Hyperemic microvascular resistance was lower during BiV than during Control (LAD: 1.76 ± 0.47 vs. 1.54 ± 0.45, P < 0.001; LCx: 1.92 ± 0.42 vs. 1.73 ± 0.31, P = 0.003). The CRT-induced change in HMR of the LCx correlated with the percentage change in LV ejection fraction (R = -0.598, P = 0.011) and LV end-systolic volume (R = 0.609, P = 0.010) before and 6 months after CRT.

CONCLUSION

Cardiac resynchronization therapy improves coronary flow circulation by reducing microvascular resistance, which might be associated with LV reverse remodelling.

The myocardial ischemia evaluated by real-time contrast echocardiography may predict the response to cardiac resynchronization therapy: a large animal study

Evidence-based criteria for applying cardiac resynchronization therapy (CRT) in patients with ischemic cardiomyopathy are still scarce. The aim of the present study was to evaluate the predictive value of real-time myocardial contrast echocardiography (RT-MCE) in a preclinical canine model of ischemic cardiomyopathy who received CRT. Ischemic cardiomyopathy was produced by ligating the first diagonal branch in 20 beagles. Dogs were subsequently divided into two groups that were either treated with bi-ventricular pacing (CRT group) or left untreated (control group). RT-MCE was performed at baseline, before CRT, and 4 weeks after CRT. Two-dimensional speckle tracking imaging was used to evaluate the standard deviation of circumferential (Cir12SD), radial (R12SD), and longitudinal (L12SD) strains of left ventricular segments at basal as well as middle levels. Four weeks later, the Cir12SD, R12SD, and myocardial blood flow (MBF) of the treated group were significantly improved compared to their non-CRT counterparts. Furthermore, MBF values measured before CRT were significantly higher in responders than in non-responders to bi-ventricular pacing. Meanwhile, no significant differences were observed between the responder and non-responder groups in terms of Cir12SD, R12SD, and L12SD. A high degree of correlation was found between MBF values before CRT and LVEF after CRT. When MBF value>24.9 dB/s was defined as a cut-off point before CRT, the sensitivity and specificity of RT-MCE in predicting the response to CRT were 83.3% and 100%, respectively. Besides, MBF values increased significantly in the CRT group compared with the control group after 4 weeks of pacing (49.8±15.5 dB/s vs. 28.5±4.6 dB/s, p<0.05). Therefore, we considered that myocardial perfusion may be superior to standard metrics of LV synchrony in selecting appropriate candidates for CRT. In addition, CRT can improve myocardial perfusion in addition to cardiac synchrony, especially in the setting of ischemic cardiomyopathy.

Prognostic role of coronary flow reserve for left ventricular functional improvement after cardiac resynchronization therapy in patients with dilated cardiomyopathy

AIMS

The aim of the study was to assess the value of coronary flow reserve (CFR) for predicting improvement of left ventricular function after cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Study population included 40 patients (mean age 58 ± 9 years) with heart failure (ejection fraction 25, 7 ± 5, 4%) and QRS duration of 158 ± 22 ms, planned for CRT. Before and after CRT implantation, CFR was measured non-invasively during hyperaemia induced with adenosine. Responders were defined by decrease in end-systolic volume ≥15%. Follow-up echocardiography and CFR measurements were obtained after 6 months. At baseline there was no significant difference in left ventricular ejection fraction (LVEF), QRS duration, 6 min walk test distance and coronary flow velocity at rest between responder (n = 26) vs. non-responder group (n = 14, P = ns). Before CRT implantation, responders compared with non-responders, showed a greater increase in coronary flow velocity during hyperaemia, and consequently higher CFR: 2.41 ± 0.60 vs. 1.61 ± 0.45 (P = 0.001). There was significant correlation between CFR before CRT implantation and LVEF after 6 months (r = 0.545, P = 0.001). End-diastolic, end-systolic left ventricular diameter, and CFR before CRT were predictors of LV functional improvement. By multivariate analysis, only CFR before CRT was independent predictor of left ventricular recovery in the follow-up period (P = 0.001).

CONCLUSION

Our results demonstrate that preserved CFR in patients with dilated cardiomyopathy is predictive of left ventricular improvement after CRT implantation.

Effect of cardiac resynchronization therapy on endothelium-dependent vasodilatation in the cutaneous microvasculature

AIMS

Cardiac resynchronization therapy (CRT) improves hemodynamic parameters, exercise capacity, symptoms, functional status, and prognosis among patients with chronic heart failure (CHF). The role of the vascular endothelium in these improvements is largely unknown. In this study, we aimed to investigate whether the endothelium-dependent reactivity of the peripheral microcirculation improves in CHF patients during the first 2 months of CRT.

METHODS

We used local heating and iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) to measure endothelial function and smooth muscle function in the cutaneous microvasculature of 11 CHF patients before and 2 months after CRT.

RESULTS

We found that the perfusion response in the skin to local heating was increased 2 months post-CRT compared with baseline, both in terms of maximum perfusion (baseline: 113 [90-137] vs 2-months post-CRT: 137 [98-175], P=0.037) and area under curve (baseline: 1,601 [935-2,268] vs 2-months CRT: 2,205 [1,654-2,757], P=0.047). Also, the perfusion response to iontophoresis of ACh was improved (Emax: 23.9 [20.6-26.2]vs at 2-months CRT: 31.2 [29.3-33.4], P=0.005). No difference was found between the responses to SNP before and after CRT.

CONCLUSION

These results show that CRT improves endothelium-dependent vasodilatory capacity in the peripheral microcirculation within 2 months of therapy. The improvement in functional capacity that is seen in patients treated with CRT may, therefore, be in part mediated by an improvement of endothelium-dependent vasodilatory capacity.

Trials on the effect of cardiac resynchronization on arterial blood pressure in patients with heart failure

Cardiac resynchronization therapy (CRT) increases cardiac performance in patients with heart failure, but its effect on arterial pressure is not well established. To determine the effect of CRT on systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure (PP) a systematic review using standard nomenclatures for CRT was done in Scopus (MEDLINE and Embase), Cochrane Controlled Trials Register, National Institutes of Health http://www.ClinicalTrials.gov database, and bibliography of select meta-analyses for studies evaluating CRT in patients with dilated cardiomyopathy. Two independent investigators extracted the articles based on predefined criteria. The primary outcome was difference in arterial pressure parameters from baseline to after CRT in nonrandomized cohort trials. This was then validated by comparing the change in arterial pressure between CRT and medical therapy groups in randomized controlled trials. A random-effects model was used for analyses. Analyses of 15 nonrandomized studies showed that CRT resulted in an increase (from baseline) in SBP by 4.4 mm Hg (95% confidence interval [CI] 0.8 to 8.0, p = 0.02), no change in DBP (p = 0.21), and an increase in PP by 2.8 mm Hg (95% CI 1.0 to 4.6, p = 0.003). Results from the 3 randomized controlled trials were concordant with an increase in SBP by 3.9 mm Hg (95% CI 1.1 to 6.8, p = 0.007), no effect on DBP (p = 0.40), and an increase in PP by 4.3 mm Hg (95% CI 4.1 to 4.5, p <0.001) compared to medical therapy. In conclusion, CRT is associated with a modest increase in SBP and PP in patients with heart failure.

Usefulness of NT-pro BNP monitoring to identify echocardiographic responders following cardiac resynchronization therapy

Background

Cardiac resynchronization therapy (CRT) improves left ventricular (LV) volumes, mitral regurgitation (MR) severity and symptoms of patients with heart failure (HF). However, ≥ 30% of patients have no significant clinical or echocardiographic improvement following CRT. Reverse remodeling after CRT correlates with improved clinical outcomes. We hypothesized that in NT-pro BNP monitoring is accurate to identify responders following CRT.

Methods

42 consecutive patients (mean age 66 ± 12 years, male 68%) with HF undergoing CRT were prospectively enrolled. Responders at follow-up were defined by echocardiography (decrease in LV end systolic volume ≥ 15%). Echocardiography and NT-pro BNP measurement were performed at baseline and repeated 3 to 6 month after CRT.

Results

There was no significant difference between responders (n = 29, 69%) and non-responders (n = 13, 31%) regarding baseline NT-pro BNP level. Responders had significantly higher decrease in NT-pro BNP levels during follow-up than non-responders (absolute: -1428 ± 1333 pg.ml^-1 vs. -61 ± 959 pg.ml^-1, p = 0.002; relative: -45 ± 28% vs. 2 ± 28%, p < 0.0001). A decrease of ≥ 15% in NT-pro BNP 3–6 months after CRT identifies echocardiographic responders with a sensitivity of 90% and a specificity of 77%.

Conclusion

NT-pro BNP monitoring can accurately identify echocardiographic responders after CRT.

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.

Improvement in cardiac adrenergic function post biventricular pacing for heart failure

AIMS

We investigated whether biventricular (BiV) pacing favourably affects cardiac sympathetic activity in heart failure (HF).

METHODS AND RESULTS

In 10 HF patients treated with BiV pacing, we assessed cardiac sympathetic activity by metaiodobenzylguanidine ((123)I-MIBG) imaging. Patients were randomized in a double-blinded crossover fashion, for two weeks of either inactivation of BiV pacing or BiV pacing, with crossover to the alternate group for a further two weeks. After randomization blocks, cardiac (123)I-MIBG imaging and a 6 min walk test were performed. BiV pacing was associated with significant improvements in cardiac (123)I-MIBG uptake reflected by increases in early (BiV 1.71 +/- 0.09 vs. non-BiV 1.63 +/- 0.06, P = 0.03) and late (at 4 h) heart to mediastinal ratio of uptake (BiV 1.54 +/- 0.08 vs. non-BiV 1.45 +/- 0.06, P = 0.03). Additionally, pulmonary (123)I-MIBG uptake, measured as lung to mediastinal ratio, significantly improved (P = 0.009). Six-minute walk and systolic blood pressure tended to improve with BiV vs. non-BiV pacing (P = 0.09).

CONCLUSION

In patients with stable HF, BiV pacing is associated with long-term improvements in cardiac sympathetic nerve activity, as reflected by improvements in cardiac (123)I-MIBG uptake. This is a potential mechanism for morbidity and mortality benefits observed in larger studies.