‘Size and Flow Matter’ – Memoir of an AV fistula

Blog Post, NSMC 2019

My name is Fistulus Magnus. I came to this world a decade ago, by the hands of a very skilled surgeon, who anastomosed my host’s brachial artery to his cephalic vein. My host’s name is Mr. Hohf. I take a lot of pride in having served Mr. Hohf diligently over the years. He unfortunately suffers from end-stage kidney disease (ESKD) that resulted from diabetes and is currently undergoing in-center hemodialysis three times a week.

You must be wondering where I got my name. Well, it was bestowed upon me by the other fistulas at the dialysis unit. While some never quite served their hosts with the appropriate blood flow on dialysis, others were just not mature enough for the job (no pun intended). I, on the other hand, was raging through every single dialysis session without issues. All the other fistulas looked up to me. My size spoke for itself. I was the Arnold Schwarzenegger of all fistulas. Big, tortuous, pulsatile and most importantly, easy to poke. Dialysis nurses loved me, but Mr. Hohf, not so much. He would constantly try to keep me away from prying eyes under his long sleeves but I took no offence. Deep down under, I knew I was the reason he was still alive. After all, as the good nephrologist always says, ‘Your fistula is your lifeline’. I carried on and did my duty.

Example of a dilated and tortuous AV fistula.
https://bjaed.org/article/S2058-5349(17)30161-0/pdf

I was worried for Mr. Hohf though. He has required recurrent hospital admissions for ‘volume overload’ and ‘hypoxic respiratory failure’ over the past year (No, I did not go to medical school, but years of being around medical people teaches you medical terms). We were now at our fourth admission in eight months. His most recent echocardiogram showed grade 2 diastolic dysfunction, pulmonary hypertension with peak pulmonary artery (PA) pressure of 60 mmHg, dilated inferior vena cava and a high cardiac output of about 8 L/min. Although, his dialysis treatments were optimized to ensure euvolemia, but his respiratory status remained tenuous. A left heart catheterization showed non obstructive coronary artery disease, with high left ventricular end diastolic pressure of 22 mmHg. CT scan chest with pulmonary embolism (PE) protocol was negative. Infections were ruled out. He had no chronic obstructive pulmonary disease (COPD) or asthma. It was presumed that Mr. Hohf was non-compliant with dietary restrictions and his dialysis unit miscalculated his dry weight. The heart failure was attributed to non-ischemic cardiomyopathy. While in the hospital, his dialysis sessions were complicated by  intra-dialytic hypotension and development of cramps. Discharge to home then ensued. Shortly after, we were back with the same issues, despite adhering to fluid and salt restriction and outpatient dialysis.

‘I have good exercise capacity but I just cannot handle this fistula’

One fine morning during our fifth admission, a team of nephrologists laid eyes on me. Mr. Hohf was on high flow oxygen therapy, with accessory muscles working as hard as they could. The medical team was paying attention to me and I was keen to show them my excellent skills on dialysis. One of the nephrologists reached out to my anastomotic site and occluded the blood flow to the point of augmenting the pulse at my inflow. The other physician measured Mr. Hohf’s blood pressure and pulse, while I was being compressed against the shaft of the humerus. They noticed a 20 mmHg increase in blood pressure and drop in heart rate by  20 beats per minute. “The Nicoladoni Brenham sign!” one of them exclaimed, with a glow in his eyes reminiscent of kids on Easter.

The next day, a duplex study was done that revealed a flow of almost 4L/min through my outflow tract. This was more than 30% of Mr. Hohf’s cardiac output! ‘Duh! I wouldn’t expect anything less. I am Fistulus Magnus after all’, I told myself. Unfortunately, reality started to unfold. We were taken for a repeat echocardiogram where the same maneuver was performed followed by measurement of the cardiac output. Indeed there was a 30% drop in cardiac output on occlusion of my anastomotic site. I was ‘hemodynamically significant’ they said. I was the cause of Mr. Hohf’s recurrent admissions and pulmonary hypertension. I was the reason why Mr. Hohf’s heart was failing.

The hemodynamic changes following AV fistula creation. Sometimes, blood flow increases to undesirable limits. https://journal.chestnet.org/article/S0012-3692(17)32290-0/pdf

All these years, I fulfilled my duties believing strongly that I was doing the best for my host; growing bigger and bigger and allowing higher blood flows. It turns out I was shunting too much blood back to the heart and the myocytes were having a hard time coping with the workload. I was like a dam with flood gates wide open, resulting in a downstream reservoir that could barely cope with the gigantic rush of water. Owing to my size, tortuosity and blood flow, I was causing more harm than good. A diagnosis of ‘high output cardiac failure due to arteriovenous (AV) fistula’ was assigned to us.

So what next? The nephrologists recommended that I undergo banding to reduce my size and blood flow. It was a reality check, but I warded off all apprehension and proceeded with the procedure.

The surgery was performed successfully and we were both sent home. I felt very frail and flimsy, but dialysis seemed to run well regardless. Most importantly, Mr. Hohf had not had an admission in over six months and he had a better control over his breathing and volume status. A follow up echocardiogram showed that his pulmonary hypertension had improved with peak PA pressure of 40 mmHg and cardiac output of 5.0 L/min.

In the end I realized that things worked out for the best, and  saved Mr. Hohf many hospital admissions, mental stress and procedures. My colleagues at dialysis tell me this is a rare condition, but it may very well be more common than we think.  Physicians should keep a higher index of suspicion for conditions like this. There is a newbie across the hallway who is sizing up to be like my previous self. I will make sure to give him a well informed word of advice: ‘Size…and flow matter.’

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