Wiggles

Mr. Kaminski had never been seriously ill. He had always taken good care of his health. Didn’t smoke, went regularly to the gym, and walked his dog. At the age of 75years he was a very fit man. He had hypertension - with blood pressure values slightly above normal - but was taking medication for it. Checking his pulse regularly during his workout, he had noted that his heart rate had been lower than normal for several months. He collapsed one day after his workout and was brought to the hospital. A complete AV block was diagnosed. Mr. Kaminski received a DDD pacemaker the same day. Further investigations showed no remarkable features. His coronaries were normal. Mr. Kaminski was happy. The problem was solved and he could go back to the gym. However, he was not the same as he had been earlier. His exercise capacity had dropped. It must be the pacemaker, he thought. Reprogramming the pacemaker on several occasions did not solve the problem.
 
Can the echo help to resolve his problem?
Of course I will show you his echo. Can you see what the problem is?
 

Four-chamber view under right ventricular pacing.

 
The problem might not be very obvious to you, but it might help if you saw the contraction pattern when the pacemaker was turned off:

Four-chamber view with the pacemaker turned off.

 
What a difference: the ventricle reveals synchronous contraction now. Go back to the previous four-chamber view and compare the two. The apex wiggles back and forth when the pacemaker is turned on. This form of contraction is known as dyssynchrony. It is caused by activation of the myocardium from the right ventricular apex - the site where the lead had been placed.
 
Can dyssynchrony be measured?
Dyssynchrony can be measured in several ways. A very simple way is to assess the time interval between electrical and mechanical activation (A-EMD) using PW Doppler across the LVOT.
 

 
PW Doppler of LVOT outflow with pacing.

 
Here one measures the time interval between the onset of the QRS complex and the beginning of flow on the Doppler tracing. When electrical activation is long, the time interval increases.The time interval that we measured was 166 ms, which is fairly long (normal <140 ms).
Now compare the Doppler tracing when the pacemaker is turned off:

 

PW Doppler of LVOT flow with the pacemaker turned off.

 
The A-EMD drops to 133 msec. What does this mean? Ejection of blood is delayed under pacing conditions. An indirect sign of inefficient contraction.
 
A more detailed look
There are several other ways to show that all segments of the myocardium do not contract at the same time. One method is derived from speckle tracking echocardiography. This technique enables the investigator to track the deformation of the myocardium. Look at the deformation curves during pacing, and compare them with the curves when the patient has normal conduction.
 

Speckle tracking curves showing the deformation of the
myocardium  on a four-chamber view. All segments do not
contract and relax at the same time.
 

Speckle tracking echocardiography with the pacemaker
turned off. The deformation pattern returns to normal.

 
 
When the ventricle is paced, the curves are all over the place. The lateral wall (red) stretches (positive deflection) while most of the other segments contract (negative deflection). This is exactly what causes the wiggling motion of the heart.
 
So what?
Dyssynchrony does not only occur in RV pacing, but also in the presence of a left bundle branch block. Whatever the cause may be, it leads to inefficient contraction and a drop in cardiac output. Go back and look at Mr. Kaminski's left ventricular function during pacing. It is certainly reduced. Could this be the reason for his drop in exercise capacity? We first need to find out how frequently the ventricle is paced. The pacemaker reading told us that the percentage of paced ventricular beats was 87%, which is fairly high. 
 
What now?
How can we solve Mr. Kaminski's problem? There are two potential solutions: first, we could try to reprogram the pacemaker so that fewer beats are paced. Or, we could switch Mr. Kaminski's DDD pacemaker to a special pacemaker that resynchronizes contraction - a so-called CRT system. By implanting a third lead into the coronary sinus, the left ventricle can be paced from two sides, thus reducing the delay between the septum and the lateral left ventricular wall. This is exactly what we did. Three months later Mr. Kaminski was back for a check-up. With a smiling face, he told us that he was feeling fine.
 

Four-chamber view under CRT pacing.

 
His echo under CRT pacing told us that we had made the correct decision. The wiggles had disappeared.

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