Increased coronary artery blood flow with aortomyoplasty in chronic heart failure

In vivo evaluation of the improved MCMS-0102 pacemaker with a rapid pacing mode for induction of experimental heart failure in animals

The MCMS-0102 cardiac pacemaker for rapid ventricular pacing to induce heart failure in animals has been improved in terms of miniaturization and performance. To determine the performance of the new MCMS-0102, six devices were implanted in beagle dogs, and two of these devices were reimplanted for continued pacing in a total of eight beagle dogs. The hearts were paced at 260 beats per minute for 4 weeks (P group: n = 8). The hemodynamic status of the P group was examined and compared with nonpaced dogs (NP group: n = 8). The neurohumoral status of the P group was evaluated before and after rapid pacing. Stable operation of the six devices during rapid pacing was confirmed using the telemetry system. Postmortem examinations revealed features similar to clinical heart failure characterized by massive ascites, pleural effusion, cardiomegaly, and liver congestion in all the paced dogs. Cardiac output was 1.1 +/- 0.2 l/min in the NP group and 0.5 +/- 0.1 l/min in the P group (P < 0.0001). The left atrial pressure and the central venous pressure of the P group and the NP group were 23 +/- 6 versus 6 +/- 2 mmHg (P < 0.0001) and 10 +/- 3 versus 4 +/- 3 mmHg (P < 0.001), respectively. In the paced dogs, plasma renin activity increased from 0.5 +/- 0.4 to 8.5 +/- 7.4 ng/ml/h (P < 0.05) and atrial natriuretic peptide levels increased from 69 +/- 41 to 229 +/- 72 pg/ml (P < 0.001). The improved MCMS-0102 was successfully implanted in beagle dogs and it succeeded in inducing the congestive heart failure model.

Extra-Ascending Aortic Versus Intra-Descending Aortic Balloon Counterpulsation—Effect on Coronary Artery Blood Flow

BACKGROUND

Diastolic counterpulsation has been used to provide circulatory augmentation for chronic heart failure or for short-term cardiac support. Recently an extra-aortic balloon (EAB) counterpulsation device has been proposed.

AIM

To compare the circulatory effects of counterpulsation using the EAB or an intra-aortic balloon (IAB) in the acute pig model.

METHODS

In six anaesthetized great white pigs (paced at 100 bpm), ECG, arterial and central venous pressures, flow in the coronary circulation and descending thoracic aorta were measured. Baseline data was collected, then with the EAB or an IAB fitted using 1:1 and 1:2 counterpulsation modes. Baseline data was compared to EAB and IAB data in 1:1 mode. Assisted beat data compared to unassisted beat data was also analysed in 1:2 mode.

RESULTS

Both devices augmented peak diastolic arterial pressure, and decreased afterload. EAB counterpulsation increased diastolic coronary flow in both the 1:1 mode by 69% (p < 0.05) and in the 1:2 mode by 63% (assisted versus unassisted beat, p < 0.05). The IAB significantly increased diastolic coronary flow only in the 1:2 mode by 28% (p < 0.01). Both devices augmented total coronary flow and some augmentation of aortic flow was observed.

CONCLUSION

The circulatory effect of the EAB and IAB counterpulsation were comparable. This suggests the EAB could be used as a non-blood contacting heart assist device in patients suffering moderate-severe heart failure.

Aortomyoplasty: hemodynamics and comparison to the intraaortic balloon pump

BACKGROUND

Aortomyoplasty (AMP), a procedure in which the latissimus dorsi muscle (LDM) is wrapped around the aorta and stimulated during diastole, is a potential method of chronic counterpulsation. Counterpulsation by the intraaortic balloon pump (IABP) is a proven treatment for ischemic coronary syndrome and heart failure but cannot be used chronically. This study examined the long-term potential of a unique AMP configuration and compared its performance to the IABP.

MATERIALS AND METHODS

AMP was done using a wringer configuration (AMP-W) in nine dogs. Six and 12 months later, acute hemodynamic augmentation was evaluated by measuring differences in mean diastolic aortic pressure (mDAP), peak left ventricular pressure (pLVP), and the endocardial viability ratio (EVR) between stimulated and unstimulated beats.

RESULTS

The diastolic augmentation obtained by AMP-W at 6 months and by AMP-W and IABP at 12 months was statistically significant. Additionally, the enhancements in EVR (16.1 +/- 4.3%), mDAP (8.6 +/- 2.5%), and pLVP (-1.8 +/- 1.0%) at 6 months were similar to those in EVR (19.1 +/- 5.2%), mDAP (13.1 +/- 3.6%), and pLVP (-0.8 +/- 1.3%) at 12 months. Most importantly, the augmentation obtained by AMP-W at 12 months was similar to that of the IABP: EVR (17.1 +/- 5.9%), mDAP (13.4 +/- 6.7%), and pLVP (-1.5 +/- 0.8%).

CONCLUSIONS

AMP-W is a safe, robust procedure, capable of providing counterpulsation equivalent to the IABP, 12 months following surgery. The potential for AMP-W to offer chronic counterpulsation and to benefit the ischemic heart should be investigated further.

Circulatory benefits of diastolic counterpulsation in an ischemic heart failure model after aortomyoplasty

OBJECTIVE

Aortomyoplasty is an experimental surgical procedure in which the latissimus dorsi muscle is wrapped around the thoracic aorta and stimulated to contract during diastole, providing diastolic counterpulsation. We hypothesized that aortomyoplasty could improve cardiac function in a chronic ischemic heart failure model, similar to the improvement seen with the intra-aortic balloon pump.

METHODS

Six dogs (25-30 kg) successfully underwent aortomyoplasty followed by serial coronary microembolization. Ejection fraction decreased from 63.5% to 36.5%. Two weeks after the final microembolization, the muscle was conditioned for 4 months to achieve fatigue resistance. One year after aortomyoplasty, hemodynamic studies during 1 hour of aortomyoplasty and 1 hour of intra-aortic balloon counterpulsation determined mean diastolic aortic pressure, peak left ventricular pressure, and endocardial viability ratio for assisted and unassisted beats. Cardiac output, stroke volume, and parameters of cardiac function were also measured.

RESULTS

Endocardial viability ratio increased by 23.8% +/- 7.9% (P =.001) with aortomyoplasty counterpulsation and by 22.7% +/- 12.9% (P =.021) with the intra-aortic balloon pump. Both aortomyoplasty and the intra-aortic balloon pump significantly increased mean diastolic aortic pressure and reduced peak left ventricular pressure. Improvements in cardiac function with aortomyoplasty and the intra-aortic balloon pump were similar. Cardiac output increased from 2.61 +/- 0.88 to 3.07 +/- 1.06 L/min (P =.006), and index of afterload decreased from 5.4 +/- 1.4 to 4.8 +/- 1.4 mm Hg/mL (P =.02) during 1 hour of aortomyoplasty counterpulsation.

CONCLUSION

One year after the procedure, aortomyoplasty counterpulsation provided diastolic augmentation and improved cardiac performance similar to the improvement provided by the intra-aortic balloon pump in a chronic ischemic heart failure model. Aortomyoplasty has the potential to benefit patients with ischemic heart disease refractory to current therapies.