Diastolic Augmentation w/ Brian Cress
- foamfrat
- 4 days ago
- 3 min read
Updated: 2 days ago
The intra-aortic balloon pump (IABP) remains a commonly utilized mechanical circulatory support device in the management of cardiogenic shock. Despite the emergence of more advanced support modalities, the IABP continues to serve a critical role in optimizing coronary perfusion and reducing left ventricular (LV) workload.
In this episode, Brian Cress and I discuss the underlying physiology of diastolic augmentation and strategies for maximizing therapeutic benefit during patient transport and critical care management.
Coronary Perfusion and the Importance of Diastole
Coronary arteries are predominantly perfused during diastole. This is largely due to the elevated intra-myocardial pressure during systole, which compresses the coronary vasculature and impedes flow. As the myocardium relaxes in diastole, vascular resistance decreases, allowing for coronary perfusion to occur more effectively.
Two key parameters influence this process:
Aortic diastolic pressure: Higher values facilitate greater coronary perfusion pressure.
Left ventricular end-diastolic pressure (LVEDP): Lower values reduce retrograde resistance and enable improved forward flow into the coronary circulation.
Mechanism of the Intra-Aortic Balloon Pump
The IABP functions by inflating and deflating a balloon catheter within the descending thoracic aorta in synchrony with the cardiac cycle:
Inflation occurs immediately following aortic valve closure (at the dicrotic notch), which increases diastolic pressure and enhances coronary perfusion.
Deflation occurs just before the onset of systole, reducing aortic pressure and consequently decreasing afterload. This assists in LV ejection and reduces myocardial oxygen demand.
This process, known as counterpulsation, provides targeted hemodynamic support without increasing systemic vascular resistance.
Interpreting IABP Waveforms
The IABP console displays two critical pressure metrics during diastole:
Parameter | Definition |
Augmented Diastolic Pressure | Peak aortic pressure achieved during balloon inflation in diastole |
Assisted End-Diastolic Pressure | Aortic pressure just prior to balloon deflation and onset of systole |
For example, a patient with a native blood pressure of 114/56 mmHg may present the following IABP readings:
Augmented Diastolic Pressure: 141 mmHg
Assisted End-Diastolic Pressure: 49 mmHg
The goal is to improve coronary perfusion while minimizing LV afterload. Elevated augmentation (e.g., >160 mmHg) may indicate excessive inflation volume or unnecessary concomitant vasopressor support. Adjustments to IABP augmentation settings or pharmacologic therapy may be warranted.
Time-Dependent Considerations
Perfusion is not determined solely by pressure amplitude but also by the duration of the diastolic interval. As heart rate increases, diastolic time shortens, decreasing overall coronary perfusion despite adequate pressure. This relationship is often called the diastolic time pressure index (DTPI).
Rate control may be beneficial in certain scenarios; however, reversible causes of tachycardia (e.g., pain, agitation, inadequate sedation) should be addressed first before pharmacologic intervention.
Assessing Clinical Response
Because invasive hemodynamic monitoring (e.g., pulmonary artery catheterization) is not always feasible in transport settings, providers must rely on surrogate measures to evaluate IABP efficacy:
Echocardiography: Improvements in LV wall motion or mitral valve leaflet excursion (e.g., E-point septal separation) may indicate enhanced LV unloading.
Arterial waveform trends: An increase in mean arterial pressure (MAP) or reduction in vasopressor requirements can signify improved end-organ perfusion.
Heart rate trends: A spontaneous decline in compensatory tachycardia may reflect improved cardiac output and reduced sympathetic drive.
In the event of a fiber-optic failure, a transducer can be connected to the balloon pump arterial port. However, this should only be performed by personnel familiar with flushing and priming the sheath to avoid thrombotic or air embolic complications. Proximal monitoring (i.e., at the balloon tip) offers better timing accuracy than more distal sites.
Clinicians should regularly assess augmented and assisted pressures, heart rate, and evidence of LV unloading to ensure therapeutic targets are met. With proper integration, the IABP can significantly enhance myocardial oxygen delivery during periods of critical dysfunction.
