farnsworth
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I am not too sure about the pathophysiology, but a PAC can elicit arrhythmia upon traversing through the right ventricle. The incidence of a RBBB is seen in significant amount of patients (approx 5%), especially in patients w/ stenosis of the right coronary artery (RCA). If a complete LBBB was present and you provoke an additional block of the right bundle branch -> total AV block and you need a pacer!
Indications for PAC in patients:
- measurement of hemodynamics (cardiac output/index, left ventricular stroke work (index), right ventricular stroke work (index), pulmonary vascular resistance, systemic vascular resistance)
- optimize volume therapy (right ventricular preload by CVP measurement, left ventricular preload by PAOP measurement)
- optimize therapy w/ inotropes and/or vasopressors (SVR, CO etc)
- monitoring of pulmonary arterial pressure
- measurement of mixed venous saturation (on determination of arterial oxygen saturation together w/ mixed and pulmonary capillary saturation you can calculate the intrapulmonary shunt fraction (often refered to as 'venous admixture') w/ the Bergren formula)
- as the CVP tracing can point to tricuspid valve insufficiency, the PAP tracing can point to mitral valve insufficiency (to determine the extent of valve insufficiencies you still need TTE, or better: TEE).
So the indications in patients w/ acute MI: mainly hemodynamic monitoring and filling pressures, optimizing inotropic/vasopressor therapy.
No study could demonstrate a positive effect of the PAC on the outcome of patients, but no study could prove that insertion of PAC worsens the outcome. Some studies showed, that in quite a number of patients a PAC was inserted because of 'hemodynamic instability', but the therapy was not guided according to the values -> red cap syndrome (the PAC has a port which has to be connected to a monitor. This port is protected w/ a red cap, but you have to remove the red cap in order to connect the PAC to the monitor. So if the red cap is still in place, you can be sure, that nobody used the catheter for hemodynamic monitoring).
One has to be careful in the interpretation of PAC pressure measurements, especially regarding volume status: pressure does not always reflect volume! In a patient w/ a diastolic left ventricular dysfunction, small volume swings can produce enormous differences in PAOP values. In that case transpulmonary dye dilution techniques (for measuring global enddiastolic volume, intrathoracic blood volume, and extravascular lung water) and echocardiography are more useful. For continous cardiac monitoring pulse contour analyses has some advantage, but may not be accurate in patients w/ AFib.
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| farnsworth
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Pacing (just a summary):
- transvenous pacer: insertion of a pacer usually through a 5F sheath into a central vein, pretty much like a PAC (with a balloon at the tip). If the pacer reaches the right atrium you might see a spike on the ECG tracing, followed by a P wave (may be inverted) and a narrow QRS complex. If this happens, deflate the balloon, reduce the output to prevent myocardial/endocardial damage. If not atrial response can be elicited, advance the pacer into the right ventricle, until you see a response in the ECG tracing (wide QRS complex). Atrial pacing is favored, because atrial contraction contributes to 15-20% of the cardiac output (better ventricular filling).
- sequential temporary pacer: you need pacer wires in the atrium and in the ventricle. This is usually the case of open heart surgery: pacer electrodes are placed on the myocardium of the ventricle and the atrium. This allows sequential (atrial pacing followed by pacing of the ventricles). The wires are connected to a pacer (outside the body!) which is capable of sequential pacing (I would call these pacers the 'Mercedes of temporary pacing': you can adjust the atrial and the ventricular outlet power separately, the AV delay. They work in DDD, VVI, AAI, AAO, VVO mode etc...) In theory you can use to transvenous temporary pacers for sequential pacing, but I don't know if this is routinely done (if you can speak of routine temporary pacing....)
- sequential permanent pacer: same principle as temporary sequential pacing. The pacer wires are usually inserted through the cephalic vein into the right atrium and ventricle, pacer implanted. You can program different pacing modalities (usually: DDD(R)).
Maybe a cardiologist is following this thread and can correct me, if I was wrong.
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| docnikki
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thanks farnsworth..that was amazing!!
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