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Pre-Operative Intra-Aortic Balloon
Counterpulsation in Stable Patients with
Left Main Coronary Disease
November 2001
The use of intra-aortic balloon counterpulsation (IABC) to reduce left ventricular afterload and myocardial oxygen consumption is clearly indicated in patients with refractory myocardial ischemia or acute myocardial infarction complicated by cardiogenic shock.1–4 However, the ability of IABC to increase diastolic antegrade coronary blood flow through critically stenosed coronary arteries is not well substantiated.1,2,5–8 Therefore, the role of “prophylactic” IABC in hemodynamically stable patients with severe coronary artery disease undergoing surgical revascularization remains controversial.3,9–14 The purpose of this study was to evaluate the effect on mortality of prophylactic, pre-operative IABC in stable patients with severe left main coronary disease undergoing coronary artery bypass graft surgery (CABG).
METHODS
Data from all patients undergoing CABG or IABC at the Hahnemann University Hospital are prospectively collected in dedicated databases. We performed a post-hoc analysis on all patients entered into these databases from 1993 to 1999, who had undergone CABG for left main coronary artery stenosis >= 50%, without any pre-operative hemodynamic compromise or ongoing ischemia. The Institutional Review Board at Hahnemann University Hospital approved this protocol. Patients with congestive heart failure, cardiogenic shock, ongoing angina, previous CABG, and those requiring valve replacement were excluded. A total of 457 patients were identified retrospectively and divided into two groups. Group 1 comprised 287 patients whose primary cardiologists/cardiac surgeons chose not to deploy IABC. Group 2 comprised 170 patients who received prophylactic, pre-operative IABC. Pre-operative IABC was deployed before transfer to the operating room, usually the day before CABG. The clinical outcomes assessed were peri-operative 30-day mortality, cardiopulmonary bypass time, and post-operative length of stay.
Intra-operative transesophageal echocardiography was performed in 7 patients with IABC, using a Hewlett-Packard HP Sonos 1,500 system with a 3.7–5.0 MHz transesophageal transducer. The pulsed Doppler sample volume was positioned within the lumen of the distal left main beyond the stenosis or in the left circumflex artery.15–19 Measurements of the peak diastolic flow velocity and velocity-time integral of augmented and non-augmented beats were obtained during 1:3 assist ratio.
Subsequent to the analysis of the Hahnemann patient cohort, we compared the no IABC Group 1 Hahnemann patients to a larger group of 342 patients with left main disease and bypass surgery (having similar demographic characteristics) derived from the Benchmark IABC Registry.20 The Registry is an ongoing, large-scale, prospective registry established in January 1997 to track the use of IABC with more than 10,000 patients entered from over 100 hospitals.
Definitions. Peripheral vascular disease was identified in the databases if the patient experienced claudication, had a revascularization procedure, or aortic aneurysm surgery. Previous myocardial infarction was identified by a history of hospital admission with an “abnormal” enzyme pattern, or an abnormal electrocardiogram with pathological Q-waves.
Statistical analysis. Demographic data are expressed as means ± standard deviation (SD). Comparisons between Hahnemann Group 1 no IABC vs. Hahnemann Group 2 IABC, and Hahnemann Group 1 vs. Benchmark IABC Registry patients were performed using the difference of sample proportions. In addition, the Chi-square test, with Yates correction (when necessary), was applied. A probability value (p) of Present study. The goals of the present study were to assess the clinical outcome and changes in coronary flow in normotensive, clinically stable patients with ejection fractions above 20% in whom IABC was deployed as a prophylactic device prior to coronary bypass surgery. We focused on patients with left main disease because of the recent shift in clinical practice in many hospitals to deploy IABC in such patients.14,21 We observed strong trends toward a mortality advantage in patients with IABC. In the internal Hahnemann comparison, peripheral vascular disease was the principle determinant of survival. Nevertheless, patients with or without PVD experienced lower mortality rates if they received IABC. A large number of our peri-operative deaths, however, were the due to CVA. We did not systematically image the ascending aorta and arch or the carotid arteries. A recent analysis by Allie et al.24 in 20 patients with left ventricular ejection fractions less than 30%, significant left main obstruction, and severe internal carotid disease, who were treated with prophylactic IABC prior to sequential carotid and coronary surgery, demonstrated no deaths or strokes. IABC has also been shown to augment cerebral flow.25 To broaden the perspective beyond a single-center experience, we compared the Hahnemann no IABC group to patients from the Benchmark IABC Registry with similar coronary anatomy and clinical indications proceeding to CABG with prophylactic IABC. Again, IABC appeared beneficial, but the benefit was confined to the larger patients with a body mass index above 26.4 kg/m2.
Balloon counterpulsation augments proximal coronary blood flow in non-obstructed arteries, especially in those patients with a systolic pressure less than 90 mmHg.2,7 The effect on distal coronary flow beyond obstructive stenoses, as assessed by the super-selective intracoronary flow velocity 0.018´´ Doppler guidewire (Flowire, Rancho Cordova, California), however, has been felt to be minimal.8 Our subset of 7 stable normotensive patients consistently demonstrated a significant augmentation in coronary blood flow beyond their severe left main stenoses.
Study limitations. The present study was a post-hoc analysis of prospectively gathered data, and not a randomized study. The decision regarding deployment of IABC was left up to the cardiologist/cardiac surgeon team.
CONCLUSION
In patients who are stable, normotensive, and have reasonable or normal ventricular function, we observed a trend favoring survival with IABC. Using transesophageal echo-Doppler analysis of coronary blood flow, the present study also demonstrated that IABC augmented distal coronary flow beyond severe left main stenoses even in normotensive patients. While unadjusted mortality rates appear lower with prophylactic IABC, confounding variables such as PVD mandate a larger, prospective, randomized clinical trial in order to clarify the role of IABC in hemodynamically stable patients with left main disease.26
Acknowledgment. The Datascope Corporation, Cardiac Assist Division provided financial support for the statistical analysis.
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