The other day when I was observing my colleague puncturing the inter atrial septum with heavy bore needle during a PTMC procedure the patient was comfortably watching and enjoying the procedure .
Even as multiple wires criss-crossed the left atrium and the balloon hitting the mitral valve repeatedly there was absolutely no pain.
Next day , in an another patient when IAS was punctured it got stained along with pericardium , the patient had severe back pain and procedure was to be stalled temporarily .
What is the lesson learnt ?
The pericardium and the epicardium (same as visceral pericardium ) has rich pain fibers. The above patient who had stain of epicardium had severe pain .
The former patient who had a perfect IAS puncture did not develop pain while the later who had an epicardial track experienced pain.
The same analogy can be seen in patients with myocardial rupture .While sever chest pain is a rule with a free wall tear , it is very rare for patients with ventricular septal rupture to complain sever pain as IVS rupture do not cleave the epicardial layers .It is also uncommon for papillary muscle or chodal rupture to generate significant pain .
What is the difference between epicardium and endocardium in terms of pain fiber innervation ?
Sub- endocardium has less dense nerve supply than sub-epicardium. This is one more reason why isolated sub-endocardial stress less commonly result angina ( Eg Hypertension and sub endocardial strain often silent ) while even minimal irritation or insult of sub-epicardium induce severe pain.
Further , cardiac pain receptors respond differently to type of stimuli .The density of these receptors also vary depending on planes of myocardial tissue .
What are triggers for cardiac pain ?
Any of the following can trigger cardiac pain.The pain receptors in heart are not well developed as that of somatic system.
It is not clear whether the layers of heart has specialized receptors for various sensations.
- Stretch*
- Prick
- Guide wire poke ,
- Needle prick
- Temperature .
- Infection ,
- Inflammation of myocardium , pericardium*
- Pressure injections
- Cardiac ischemia*
* These three factors are responsible for bulk of the cardiac pain . Please note needle prick on the heart is least painful !
How does ischemia generate pain ?
The ischemia of myocytes secrete
Bio chemical
Substance P , prostaglandins, serotonin, adenosine, bradykinin, and other mediators are involved
Neural
Carried by myelinated A-d and unmyelinated C fibers run in the cardiac sympathetic nerves . It is understood ,both the fibers respond to mechanical stretch while Type C fibers also carry chemo signals from bio chemical mediators as well .
Vagus nerve has a major role in carrying afferent signals of pain . It is well known , if pain stimuli is substantial the vaso vagal reflex is activated and bradycardia and hypotension occurs.
How is infarct pain different from Ischemic pain ?
Necrosis of nerve terminal will result in more intense pain and lasts longer .
Clinical examples for stretch induced cardiac pain
- Acute RV/LV dilatation of any cause
- Pulmonary artery/Aortic dilatation
- Pericardial stretch could contribute more in generating this pain
- Mitral valve prolapse (Stretches LV free wall )
Interventional cardiologist should thank god for not innervating the heart extensively . This only allows us to spend hours together inside the patients heart , other wise one would require a general anesthesia for doing a PCI
Does pericardium suffer from ischemia or necrosis ?
Pericardium is not an avascular structure . Pericardium gets its blood supply from twigs of LIMA and phrenic arteries.So there must be some impact of ischemia on pericardium . Since pericardium has rich nerve supply there is every reason to suspect existence of ischemic pericardial pain as well .
But pericardial pain induced by mechanical stretch and inflammation is much more common .While acute pericardial stretch is painful chronic stretch as in slowly accumulating pericardial effusion is a painless event !
Pain relief after CABG
One of the reasons for angina relief post CABG is attributed to the interruption to pericardial nerve supply.
Reference
This 1957 article from circulation still rules cardiac pain literature . http://circ.ahajournals.org/content/16/4/644.full.pdf+html
http://www.annualreviews.org/doi/full/10.1146/annurev.physiol.61.1.143
Dr.S.Venkatesan MD 