Determinants of the development of mitral regurgitation in pacing-induced heart failure

Evaluation of Left Ventricular Diastolic Dysfunction with Early Systolic Dysfunction Using Two-Dimensional Speckle Tracking Echocardiography in Canine Heart Failure Model

BACKGROUND

This study evaluated the role of two-dimensional speckle tracking echocardiography (2DSTE) for predicting left ventricular (LV) diastolic dysfunction in pacing-induced canine heart failure.

METHODS

Pacing systems were implanted in 8 adult mongrel dogs, and continuous rapid right ventricular pacing (RVP, 240 beats/min) was maintained for 2 weeks. The obtained measurements from 2DSTE included global strain rate during early diastole (SRe) and during late diastole (SRa) in the longitudinal (L-SRe, L-SRa), circumferential (C-SRe, C-SRa), and radial directions (R-SRe, R-SRa). Changes in heart morphology were observed by light microscopy and transmission electron microscopy at 2 weeks.

RESULTS

The onset of LV diastolic dysfunction with early systolic dysfunction occurred 3 days after RVP initiation. Most of the strain rate imaging indices were altered at 1 or 3 days after RVP onset and continued to worsen until heart failure developed. Light and transmission electron microscopy showed myocardial vacuolar degeneration and mitochondrial swelling in the left ventricular at 2 weeks after RVP onset. Pearson's correlation analysis revealed that parameters of conventional echocardiography and 2DSTE showed moderate correlation with LV pressure parameters, including E/Esep' (r = 0.58, P < 0.01), L-SRe (r = -0.58, P < 0.01), E/L-SRe (r = 0.65, P < 0.01), and R-SRe (r = 0.53, P < 0.01). ROC curves analysis showed that these indices of conventional echocardiography and strain rate imaging could effectively predict LV diastolic dysfunction (area under the curve: E/Esep' 0.78; L-SRe 0.84; E/L-SRe 0.80; R-SRe 0.80).

CONCLUSION

2DSTE was a sensitive and accurate technique that could be used for predicting LV diastolic dysfunction in canine heart failure model.

Hemodynamics and myocardial blood flow patterns after placement of a cardiac passive restraint device in a model of dilated cardiomyopathy

BACKGROUND

The present study examined a cardiac passive restraint device which applies epicardial pressure (HeartNet Implant; Paracor Medical, Inc, Sunnyvale, Calif) in a clinically relevant model of dilated cardiomyopathy to determine effects on hemodynamic and myocardial blood flow patterns.

METHODS

Dilated cardiomyopatht was established in 10 pigs (3 weeks of atrial pacing, 240 beats/min). Hemodynamic parameters and regional left ventricular blood flow were measured under baseline conditions and after acute placement of the HeartNet Implant. Measurements were repeated after adenosine infusion, allowing maximal coronary vasodilation and coronary flow reserve to be determined.

RESULTS

Left ventricular dilation and systolic dysfunction occurred relative to baseline as measured by echocardiography. Left ventricular end-diastolic dimension increased and left ventricular fractional shortening decreased (3.8 ± 0.1 vs 6.1 ± 0.2 cm and 31.6% ± 0.5% vs 16.2% ± 2.1%, both P < .05, respectively), consistent with the dilated cardiomyopathy phenotype. The HeartNet Implant was successfully deployed without arrhythmias and a computed median mid-left ventricular epicardial pressure of 1.4 mm Hg was applied by the HeartNet Implant throughout the cardiac cycle. Acute HeartNet placement did not adversely affect steady state hemodynamics. With the HeartNet Implant in place, coronary reserve was significantly blunted.

CONCLUSIONS

In a large animal model of dilated cardiomyopathy, the cardiac passive restraint device did not appear to adversely affect basal resting myocardial blood flow. However, after acute HeartNet Implant placement, left ventricular maximal coronary reserve was blunted. These unique results suggest that cardiac passive restraint devices that apply epicardial transmural pressure can alter myocardial blood flow patterns in a model of dilated cardiomyopathy. Whether this blunting of coronary reserve holds clinical relevance with chronic passive restraint device placement remains unestablished.

Different Effects of Propranolol, Phenylephrine, and Saline Volume Loading on Catecholamine-Induced Left Ventricular Outflow Tract Obstruction in Acute Coronary Syndrome

Hemodynamic deterioration due to left ventricular outflow tract (LVOT) obstruction can occur during catecholamine infusion in patients with acute coronary syndrome (ACS). The purpose of the present study was to compare the utility of propranolol, phenylephrine infusion, and rapid saline loading for reversal of dobutamine-induced LVOT obstruction in a canine model of ACS. ACS was induced via left anterior descending artery ligation in 21 open-chest anesthetized dogs, and LVOT obstruction, defined as an LVOT gradient > 30 mmHg, was induced by dobutamine infusion (20 to 40 microg/kg/min). Subsequently, the effects of propranolol infusion (0.7 to 1.0 microg/kg/min, n = 8), phenylephrine infusion (10 to 200 microg/kg/min, n = 7), and saline loading (200 to 400 mL/hr, n = 6) were assessed by serial hemodynamic measurements. All interventions produced significant and comparable improvements in the LVOT pressure gradient (propranolol: 60 +/- 16 to 15 +/- 12; phenylephrine: 68 +/- 15 to 12 +/- 10; saline loading: 58 +/- 18 to 22 +/- 10 mmHg; P < 0.001 for baseline versus postintervention; P = NS for comparison between interventions). Phenylephrine produced the greatest elevation in aortic pressure (propranolol: +15 +/- 13; phenylephrine: +51 +/- 36; saline loading: +15 +/- 15 mmHg; P < 0.05), while saline loading produced the greatest increase in cardiac output (propranolol: +0.05 +/- 0.12; phenylephrine: +0.28 +/- 0.37; saline loading: +0.73 +/- 0.48 L/min; P < 0.05). Propranolol was the only intervention that produced a significant decrease in diastolic pulmonary artery pressure (16 +/- 5 to 11 +/- 3 mmHg, P < 0.05). Propranolol, phenylephrine infusion, and saline volume loading were similarly effective in reversing dobutamine-induced LVOT obstruction in this canine model of ACS. However, each intervention produced different hemodynamic effects with potentially different clinical indications.

Mitral Valve Repair without Cardiopulmonary Bypass or Atriotomy Using the Coapsys Device: Device Design and Implantation Procedure in Canine Functional Mitral Regurgitation Model

BACKGROUND

Myocor developed a unique system, the Coapsys annuloplasty system, to treat functional mitral regurgitation (MR) without cardiopulmonary bypass (CPB). This study was conducted to test the feasibility of the Coapsys implantation procedure in a canine functional MR model.

METHODS

Functional MR with heart failure was induced in 9 dogs by rapid ventricular pacing (230 beats/min for 30 +/- 4 days). The Coapsys device, which consists of anterior and posterior epicardial pads connected by a subvalvular chord, was then surgically implanted. Under epicardial echocardiographic guidance, we placed the Coapsys device across the left ventricular chamber using the delivery instrument and needle assembly. We sized the Coapsys device by drawing the posterior leaflet and annulus toward the anterior leaflet with the sizing instrument. Final device size was selected when MR was minimized or eliminated as assessed by 2-dimensional color Doppler echocardiography.

RESULTS

In all cases, we successfully implanted the Coapsys device without CPB or atriotomy. MR was reduced an average of 2 grades. No adverse events, such as hemodynamic compromise or structural valve damage, were noted.

CONCLUSION

Coapsys device implantation was feasible and safe on a beating canine heart. All accessory tools used for device implantation were found useful.

Optimal Mitral Annular and Subvalvular Shape Change Created by the Coapsys Device to Treat Functional Mitral Regurgitation

We have reported that the Myocor Coapsys (Myocor, Inc, Maple Grove, MN) device treated functional mitral regurgitation (MR) by reducing mitral annular dimension and repositioning papillary muscles. This study was conducted to evaluate the optimal Coapsys device sizing level. The Coapsys device was implanted in seven dogs after induction of MR by rapid ventricular pacing. The device consists of anterior and posterior pads connected by a subvalvular cord. The device was tightened in 5% increments of the left ventricular epicardial to epicardial dimension up to 40%. Hemodynamic and echocardiographic measurements were repeated at each tightening level. The Coapsys significantly reduced or eliminated functional MR, and the reduction was maximized at the 30% tightening level or lower in all cases. Although the left ventricular end diastolic volume decreased significantly, forward stroke volume was maintained until the 35% tightening level. The forward ejection fraction significantly increased from 33 +/- 24% at baseline to 62 +/- 42% at 40% tightening level. Mean aortic pressure decreased slightly but significantly. The Coapsys device can be applied over a broad range of tightening levels with significant reduction in MR without negative physiologic impact. This feature makes the device usable [corrected] in a variety of clinical settings.

The Coapsys device to treat functional mitral regurgitation: in vivo long-term canine study

OBJECTIVE

We evaluated the capability of the Myocor Coapsys device (Myocor, Inc, Maple Grove, Minn) to reduce functional mitral regurgitation in a canine model of dilated cardiomyopathy.

METHODS

Functional mitral regurgitation with heart failure was induced in 7 dogs by rapid ventricular pacing. The Coapsys device, which consists of anterior and posterior epicardial pads connected by a subvalvular chord, was then implanted. Heart failure was maintained by continued pacing for 8 weeks. Hemodynamic and echocardiographic measurements were performed at pre- and postsizing and after 8 weeks. The Coapsys subvalvular chord was cut to verify that maintenance of valve competency was due to the device.

RESULTS

All implants were performed off-pump without atriotomy. Mitral regurgitation was reduced in all animals; mean mitral regurgitation grade was reduced from 2.9 +/- 0.7 to 0.7 +/- 0.8 (P =.00005) and was maintained at 0.8 +/- 0.8 after 8 weeks, without hemodynamic compromise or structural damage to the mitral valve. Mitral regurgitation returned to 3.6 +/- 0.8 (P =.102 versus presizing) after cutting the Coapsys subvalvular chord.

CONCLUSION

The Coapsys device consistently and chronically reduced functional mitral regurgitation. This device is in clinical trials in the United States.

Off-pump mitral valve repair using the Coapsys device: a pilot study in a pacing-induced mitral regurgitation model

PURPOSE

The purpose of this study was to evaluate the ability of the Myocor Coapsys device to restore leaflet apposition and valve competency off-pump in a canine model of functional mitral regurgitation (MR).

DESCRIPTION

The Coapsys device was surgically implanted in 10 dogs after MR induction by rapid ventricular pacing. The Coapsys consists of anterior and posterior epicardial pads connected by a subvalvular chord. The annular head of the posterior pad was positioned at the annular level to draw the posterior leaflet and annulus toward the anterior leaflet. Final device size was selected when MR was minimized or eliminated as assessed by color flow Doppler echocardiography.

EVALUATION

All implants were placed off-pump without atriotomy, and mean MR grade was reduced from 2.9 +/- 0.7 to 0.6 +/- 0.7 (p < 0.001) acutely. No hemodynamic compromise was noted.

CONCLUSIONS

The Coapsys device consistently and significantly reduced or eliminated functional MR acutely. Further study will be required to assess the chronic stability of the repair in this animal model.