Mechanisms of dysrhythmias
- Enhanced automaticity
- Suppressed automaticity
- Re-entry circuit
Re-entry circuit dysrhythmias
Re-Require two pathways, both of which can conduct antegrade and retrograde but in one of which there is transient uni-directional block.
The classical re-entry dysrhythmias are AVNRT (atrioventricular nodal re-entry tachycardia) and those associated with WPW (Wolff-Parkinson-White syndrome).
In many others re-entry may play a role, VT and AF are good examples.
Regular p waves do not equate to sinus rhythm. In sinus rhythm, the P wave vector is directed inferiorly and to the left. Sinus P wave must be negative in aVR, upright in lead I and aVF.
Low atrial rhythm findings
P wave upright in aVR and negative in aVF (in absence of dextrocardia) shows a low atrial (coronary sinus) rhythm. This is generally of no concern.
Usually ventricular ectopics (VE's) that do not generate enough LV pressure to open aortic valve.
VE's are common and in the absence of heart disease unimportant. Atrial ectopics are also common.
The most frequent significant dysrhythmia and one of the most important.
Two lone groups:
- Lone fibrillators; and
- Those with significant cardiac disease
- Irregularly irregular
- No 'a' waves
- Pulse at wrist generally less that rate heart on cardiac auscultation.
Atrial fibrillation and stroke
Approximately 20% of acute stroke due to AF.
Must assess stroke risk in all AF patients.
CHADS2 score: CCF, HT, age>75, diabetes = 1, but previous stroke or TIA=2.
- CHADS2 score of 2 or above: warfarin
- CHADS2 score of 1: either aspirin or warfaring
- CHADS2 score of 0: nothing or aspiring
- Changes to CHADS2 are extra point for age = or >75
- New point for known CVD or PVD
- New point for age 65-74
- New point for female sex (Sc = sex category)
- Maximum points 9
- Much better at stratifying true low risk. Risk of thromboembolism /100 years CHADS2 0 = 1.67 whereas CHA2DS2-VASc 0 = 0.75
- Better also for intermediate risk. CHADS2 1=4.75 but CHA2DS2-VASc 1=2.01
- Reasonably common.
- Patients nearly always have a structural heart disease: atria distension, valvular disease, past operations for congenital heart disease.
- Flutter usually due to re-entrant circuit in RA
- Untreated flutter rate about 300/min
- Ventricular rate usually 150/min
- RX: DCR and then if recurrent: drugs
- RF ablation may cure.
- Multiple types: focal ectopic tachycardia, multifocal atrial tachycardia but the most common is AVNRT.
- AVNRT: slow and fast circuits around AVN
- Usual is down the slow, back up the fast
- Often responsive to vagal stimulation: carotid sinus masage, valsalva.
- One episode and reverted, no RX.
- Repeat episodes: teach valsalva, cure with EP study and RF ablation.
- Generally very concerning but a few benign forms such as RVOT VT
- Most VT due to CAD or cardiomyopathy
- Wide comlpex tachycardia, varying rates up to very fast
- Rx based on haemodynamics: shocked or equivalent then immediate DCR
- More stable: IV amiodarone
- Almost routine now if VT fast and life-threatening
- No other major life-threatening disease e.g. metastatic malignancy
- Proven superior outcome to anti-arrhythmic drugs
- Bypass AVN
- WPW bypass is direct atria to ventricles
- No hold up in AVN so short PR
- Impulse hits myocardium so slow sluggish start to QRS that makes the delta wave. Wide QRS and abnormal QRS vector.
- The great danger is AF.