The effect of right ventricular pacing on myocardial oxidative metabolism and efficiency: relation with left ventricular dyssynchrony

MR feature tracking in patients with MRI-conditional pacing systems: The impact of pacing

PURPOSE

To develop feature tracking (FT) software to perform strain analysis on conventional (nontagged) cardiac magnetic resonance imaging (MRI) function images. With the advent of MRI-conditional pacemaker systems, effects of cardiac pacing on myocardial strain can be studied using MR. In this study the impact of pacing on left ventricular (LV) strain was investigated using MR-FT in patients with an MRI-conditional cardiac implantable electronic device (CIED).

MATERIALS AND METHODS

FT was performed on 32 1.5T MR studies (16 patients with an MRI-conditional CIED and 16 control patients with normal scans). Short- and long-axis steady state free precession (SSFP) cines were used for the FT analysis. Strain was assessed using CVI(42) software (Circle Cardiovascular Imaging, Alberta, Canada). In addition, the intra- and interobserver variability was determined using the intraclass correlation coefficient.

RESULTS

Of the 16 patients with an MRI-conditional CIED, five patients were paced during the MRI exam. Despite the occasional presence of susceptibility artifacts induced by the CIED, radial, circumferential, and longitudinal strain parameters could be derived for all patients. Peak radial strain and peak circumferential strain were reduced during pacing when compared to the control group; for radial strain: 20.1 ± 4.7% vs. 33.1 ± 6.9%, P < 0.001, and for circumferential strain -7.5 ± 3.5% vs. -14.9 ± 3.2%, P < 0.05. Peak strain parameters were reproducible on an intra- and interobserver level.

CONCLUSION

MR-FT is feasible in patients with an MRI-conditional CIED and can be used to quantify regional wall motion. J. MAGN. RESON. IMAGING 2016;44:964-971.

Assessment of myocardial metabolic flexibility and work efficiency in human type 2 diabetes using 16-[18F]fluoro-4-thiapalmitate, a novel PET fatty acid tracer

Altered myocardial fuel selection likely underlies cardiac disease risk in diabetes, affecting oxygen demand and myocardial metabolic flexibility. We investigated myocardial fuel selection and metabolic flexibility in human type 2 diabetes mellitus (T2DM), using positron emission tomography to measure rates of myocardial fatty acid oxidation {16-[(18)F]fluoro-4-thia-palmitate (FTP)} and myocardial perfusion and total oxidation ([(11)C]acetate). Participants underwent paired studies under fasting conditions, comparing 3-h insulin + glucose euglycemic clamp conditions (120 mU·m(-2)·min(-1)) to 3-h saline infusion. Lean controls (n = 10) were compared with glycemically controlled volunteers with T2DM (n = 8). Insulin augmented heart rate, blood pressure, and stroke index in both groups (all P < 0.01) and significantly increased myocardial oxygen consumption (P = 0.04) and perfusion (P = 0.01) in both groups. Insulin suppressed available nonesterified fatty acids (P < 0.0001), but fatty acid concentrations were higher in T2DM under both conditions (P < 0.001). Insulin-induced suppression of fatty acid oxidation was seen in both groups (P < 0.0001). However, fatty acid oxidation rates were higher under both conditions in T2DM (P = 0.003). Myocardial work efficiency was lower in T2DM (P = 0.006) and decreased in both groups with the insulin-induced increase in work and shift in fuel utilization (P = 0.01). Augmented fatty acid oxidation is present under baseline and insulin-treated conditions in T2DM, with impaired insulin-induced shifts away from fatty acid oxidation. This is accompanied by reduced work efficiency, possibly due to greater oxygen consumption with fatty acid metabolism. These observations suggest that improved fatty acid suppression, or reductions in myocardial fatty acid uptake and retention, could be therapeutic targets to improve myocardial ischemia tolerance in T2DM.

Cardiac remodeling in a new pig model of chronic heart failure: Assessment of left ventricular functional, metabolic, and structural changes using PET, CT, and echocardiography

AIMS

Large animal models are needed to study disease mechanisms in heart failure (HF). In the present study we characterized the functional, metabolic, and structural changes of myocardium in a novel pig model of chronic myocardial infarction (MI) by using multimodality imaging and histology.

METHODS AND RESULTS

Male farm pigs underwent a two-step occlusion of the left anterior descending coronary artery with concurrent distal ligation and implantation of a proximal ameroid constrictor (HF group), or sham operation (control group). Three months after the operation, cardiac output and wall stress were measured by echocardiography. Left ventricle (LV) volumes and mass were measured by computed tomography (CT). Myocardial perfusion was evaluated by [(15)O]water and oxygen consumption using [(11)C]acetate positron emission tomography, and the efficiency of myocardial work was calculated. Histological examinations were conducted to detect MI, hypertrophy, and fibrosis. Animals in the HF group had a large anterior MI scar. CT showed larger LV diastolic volume and lower ejection fraction in HF pigs than in controls. Perfusion and oxygen consumption in the remote non-infarcted myocardium were preserved in HF pigs as compared to controls. Global LV work and efficiency were significantly lower in HF than control pigs and was associated with increased wall stress. Histology showed myocyte hypertrophy but not increased interstitial fibrosis in the remote segments in HF pigs.

CONCLUSIONS

The chronic post-infarction model of HF is suitable for studies aimed to evaluate LV remodeling and changes in oxidative metabolism and can be useful for testing new therapies for HF.

The role of biventricular pacing in the prevention and therapy of pacemaker-induced cardiomyopathy

Right ventricular (RV) pacing produces well-known long-term deleterious effects not only on already compromised, but also on the normal left ventricle (LV). The activation pattern mimicks that of left bundle branch block, with delayed activation of the LV free wall, and results in electrical and mechanical dyssynchrony. Long-term mandatory (100%) RV pacing, increases LV dimensions and decreases the ejection fraction. Many of these negative effects of pacing can be overcome by biventricular pacing. In this review, we describe the characteristics of pacemaker-induced cardiomyopathy, its incidence, and the use of cardiac resynchronization therapy (CRT) for its therapy and prevention. The gaps in the current organizational guidelines for using CRT in the treatment of bradycardia are identified, and goals for future research are discussed.

Heart failure in patients with sick sinus syndrome treated with single lead atrial or dual-chamber pacing: no association with pacing mode or right ventricular pacing site

AIMS

Previous studies indicate that ventricular pacing may precipitate heart failure (HF). We investigated occurrence of HF during long-term follow-up among patients with sick sinus syndrome (SSS) randomized to AAIR or DDDR pacing. Furthermore, we investigated effects of percentage of ventricular pacing (%VP) and pacing site in the ventricle.

METHODS AND RESULTS

We analysed data from 1415 patients randomized to AAIR (n = 707) or DDDR pacing (n = 708). Ventricular pacing leads were recorded as located in either an apical or a non-apical position. The %VP and HF hospitalizations were recorded during follow-up. Patients were classified with new HF, if in New York Heart Association (NYHA) functional class IV or if presence of ≥2 of: oedema; dyspnoea; NYHA functional class III. Mean follow-up was 5.4 ± 2.4 years. Heart failure hospitalizations did not differ between groups. In the AAIR group, 170 of the 707 (26%) patients developed HF vs. 169 of the 708 (26%) patients in the DDDR group, hazard rate ratio (HR) 1.00, 95% confidence interval (CI) 0.79-1.22, P = 0.87. In DDDR patients, 146 of the 512 patients (29%) with ventricular leads in an apical position developed HF vs. 28 of the 161 patients (17%) with the leads in a non-apical position, HR 0.67, CI 0.45-1.00, P = 0.05. After adjustments this difference was non-significant. The incidence of HF was not associated with %VP (P = 0.57).

CONCLUSION

In patients with SSS, HF was not associated with pacing mode, %VP, or ventricular lead localization. This suggests that DDDR pacing is safe in patients with SSS without precipitating HF.