Luigi Padeletti, Maria Cristina
Porciani, Antonio Michelucci, Andrea Colella, Silvio Vena, Pietro Ticci, Massimo Zoppi,
Gian Franco Gensini.
Istituto di Clinica Medica Generale e Cardiologia, Universita degli Studi di Firenze,
Florence, Italy
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Atrial fibrillation (AF) is the most common cardiac
arrhythmia with a prevalence from 0.2% to 9% in different age groups between general
population1. AF causes an haemodynamic disadvantage due
to the loss of atrial contraction to ventricular filling, and is associated with a high
embolic risk. This risk is increased by the presence of various clinical conditions such
as hypertension, congestive heart failure, previous embolic episodes, diabetes, and ECG
findings like increased size of the left atrium and reduced ejection fraction. All this
needs a continous anticoagulant or thrombotic drug therapy, with frequent lab testing and
increased haemorrhagic risk. During AF the relative risk for stroke ranges from four- to
sixfold in a medium average case and as much as seventeenfold in selected categories of
patients. Summarizing, the risks related to this tachyarrhythmia fall into three groups:
1. associated with the underlying cardiac disease;
2. as a consequence of AF;
3. due to the inappropriate pharmacological treatment of the condition.
Compared with control groups matched by age and disease, patients experiencing AF show
a twofold increase in cardiovascular mortality.
Conversion to normal sinus rhythm is related to the duration of AF, atrial size,
underlying heart disease. In placebo controlled trials the pharmacological conversion rate
to sinus rhythm is greater than 75% when AF lasts less than 48 hours. This high successful
rate falls to 10-20% when the arrhythmia is present for longer periods2.
Electrical defibrillation was the first and most important non-pharmacological
approach in the management of AF. The reported success rate for external cardioversion
(EXTC) ranges from 61 to 90%3. This technique requires
general anaesthesia or heavy sedation. In addition, there is a potential risk of
myocardial necrosis, ventricular tachyarrhythmias or thromboemolisms4.
Embolic events have been reported in 0.6-7% of patients who underwent this procedure. This
is due to arterial embolisms, caused by the dislogment of a preformed thrombus from the
left atrium when sinus rhythm is restored and the effective atrial contraction is
reestablished5. As a consequence of this, anticoagulant
drug therapy must be continued for 1 to 3 months after an efficacious cardioversion. The
efforts in research to find a more efficacious "low energy" cardioversion of AF,
have been finalized to obtain: a) the possibility of an implantable atrial defibrillator
in patients suffering from recurrent AF and b) the elective cardioversion for all the
patients in which EXTC has been inefficacious. Research on this subject has introduced the
following experimental steps regarding low energy AF cardioversion: 1) the insertion of a
single electrode in the right atrium together with an external lead; 2) the adoption of
biatrial electrodes combining a right atrium electrode with a left atrium one positioned
in the coronary sinus or in the right ventricle or descending pulmonary artery; 3) the
introduction of defibrillation electrodes larger surface area; 4) the application of
biphasic waveforms to atrial defibrillation6. Since
1993, various studies demonstrate that endocavitary atrial cardioversion (ENDC) is not
only feasible, but has much more success than external cardioversion (95-98%)7.
In 88% of patients refractory to external cardioversion, normal sinus rhythm is
restored with ENDC with less than 12J (safe limit value for combined right atrium-coronary
sinus electrode positioning)7. Normal sinus rhythm can
be restored in 100% of patients with ENDC using a configuration without maximum energy
limits8. ENDC is more efficacious than EXTC (95-98% vs
61-90%), and no general anaesthesia is required. The mechanical function of the atrium
recovers much before (< 1 week vs 3-4 weeks), and in case of energies lower than 10J
has been reported a disappearance of the atrial stunning within 24 hours from the
cardioversion9. The usage of lower energies limits
atrial stunning, with a prominent reduction of post cardioversion embolic risk, therefore
anticoagulant drug therapy could be interrupted much earlier.
Actual indications to ENDC may be summarized as follows:
- patients in whom EXTC has been inefficacious;
- patients in whom EXFC has a high probability to be inefficacious: (left atrium size
> 50 mm; recent AF; body mass index > 25 kg/mq; high transthoracic impedance due to
obesity or pulmonary emphysema);
- patients in whom general anaesthesia represents a contraindication;
- patients in whom a long period of atrial stunning is expected (long duration AF;
both atria dilatation; heart failure);
- patients with unvoluntary induced AF during electrophysiologic study, in whom the
normal sinus rhythm could be restored without general anaesthesia and drug therapy;
- patients refractory to EXTC or to drug therapy that may remain in normal sinus
rhythm for a long period after ENDC or in whom an atrial defibrillator is implanted to
treat recurrences of AF;
- primary care patients following open heart surgery, with recurrent AF which needs
repetitive cardioversions10.
We report on 62 patients (pts), who underwent low-energy internal cardioversion. Their
mean age was 65 ± 11.3 years, 47 of them were male and 15 were females. The mean body
mass index was 25.4 ± 3.9, the left atrium transverse diameter ranged from 55 to 35 mm
with a mean of 43.9 ± 4.6 mm. In the patients submitted to internal cardioversion the
mean energy necessary to restore the sinus rhythm was 5.82 ± 2.5 joules and the mean
impedance of 76.2 ± 15.8 ohms. The procedure has been ineffective in 10% of patients. In
the first 50 cases a Bard USCI 6F decapolar electrocatheter was positioned in the high
right atrium free wall as a cathode and a second USCI 6F decapolar electrocatheter was
inserted into coronary sinus. A 6F USCI tripolar or tetrapolar catheter was placed in the
right ventricular apex to provide R wave sinchronization and to deliver backup ventricular
demand pacing. The defibrillator used was a Telectronics 4510 Implant Support Device. The
positioning of the decapolar catheter into the coronary sinus was helped by the previous
introduction of a left coronary artery 7F Bard USCI Amplatz Catheter into the coronary
sinus ostium. Once positioned, the decapolar catheter was inserted into the lumen of the
Amplatz catheter and correctly positioned in the distal coronary sinus. In the last 12 pts
a Medtronic Transvene system was adopted. With this technique, two different catheters are
used. The first, with a 5 cm coil is positioned in the right ventricle, the second, with
an 8 cm coil is placed in the superior vena cava. Adopting this procedure, positioning of
catheters in cardiac chambers is safe, fast and easy. Coronary sinus catheterization is
not necessary, avoiding: a) subclavian vein puncture with the consequential typical
bleeding problems in patients receiving oral anticoagulant drug therapy; b) coronary sinus
catheterization by Amplatz catheter. All this leads to time saving and cost-containment
benefits.
Electrical cardioversion of paroxysmal atrial fibrillation in a small percentage of
patients induces pain and discomfort accompanied by anxious reactions. These patients have
therefore to be treated with intravenous diazepam. The reason of this is not yet clear. It
has been recently shown a direct correlation between intensity of delivered energy and
pain11. We think that other determinants may cause
symptoms induced by intracardiac electrical discharges. The matter is rather controversial
as other studies failed to find out a correlation between delivered energy and symptoms12.
A key for understanding possible causes of symptoms derives from a research carried
out by our group: 20 consecutive patients before undergoing cardioversion were observed by
a rheumatologist in a double-blind research. It was shown that the 4 symptomatic patients
for pain and discomfort induced by electrical cardioversion had tender point scores much
higher than the non-symptomatic group. The scores were evaluated following the American
College of Rheumatology criteria for fibromyalgia13. It
is of interest that the highest scores of those proposed by the criteria were found at the
level of the second rib (bilateral, second costo-chondral junctions, just lateral to the
junctions on upper surfaces) within the area where the patients referred pain and
discomfort.
In conclusion, ENDC is an efficacious and safe technique, and our current experience
indicates that the right atrium-right ventricle coil-lead configuration has low atrial
defibrillation thresholds. Further investigation however, is necessary to optimize the
variables (lead size and location, shock waveform and duration, etc) involved in this
procedure14.
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Atrial fibrillation – transvenous internal
cardioversion
low energy atrial defibrillation, endocavitary atrial cardioversion, external
cardioversion, indications, atrial defibrillation threshold, right atrium-right ventricle
coil-lead configuration, pain torelability OA
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